Nuclear Physics News International
Volume 25, Issue 3 July–September 2015
FEATURING: RIKEN • Neutron-Antineutron Oscillations at ESS • HIgS • SUBARU
10619127(2015)25(3)
Physics Magazines
Editor: Editor: Editors: Hannu Mutka, ILL Gabriele-‐Elisabeth Körner, NuPECC Ronald Frahm, Univ. of Wuppertal
Michael C. Martin, ALS Motohiro Suzuki, SPring-‐8
You can learn more about the physics magazines published by Taylor & Francis, as well view as current and past al editori topics and sign up for : alerts at
www.tandfonline.com
Please contact Maureen Williams [email protected] ( ) for advertising opportunities.
Nuclear Physics News Volume 25/No. 3
Nuclear Physics News is published on behalf of the Nuclear Physics European Collaboration Committee (NuPECC), an Expert Committee of the European Science Foundation, with colleagues from Europe, America, and Asia.
Editor: Gabriele-Elisabeth Körner Editorial Board Maria José Garcia Borge, Madrid (Chair) Eugenio Nappi, Bari Rick Casten, Yale Klaus Peters, Darmstadt and EPS/NPB Jens Dilling, Vancouver Hermann Rothard, Caen Ari Jokinen, Jyväskylä Hideyuki Sakai, Tokyo Yu-Gang Ma, Shanghai James Symons, Berkeley Douglas MacGregor, Glasgow and EPS/NPB
Editorial Office:Physikdepartment, E12, Technische Universitat München, 85748 Garching, Germany, Tel: +49 89 2891 2293, +49 172 89 15011, Fax: +49 89 2891 2298, E-mail: [email protected]
Correspondents (from countries not covered by the Editorial Board and NuPECC) Argentina: O. Civitaresse, La Plata; Australia: A. W. Thomas, Adelaide; Brasil: M. Hussein, São Paulo; India: D. K. Avasthi, New Delhi; Israel: N. Auerbach, Tel Aviv; Mexico: E. Padilla-Rodal, Mexico DF; Russia: Yu. Novikov, St. Petersburg; Serbia: S. Jokic, Belgrade; South Africa: S. Mullins, Cape Town.
Nuclear Physics News ISSN 1061-9127
Advertising Manager Subscriptions Maureen M. Williams Nuclear Physics News is supplied free of charge to PO Box 449 nuclear physicists from contributing countries upon Point Pleasant, PA 18950, USA request. In addition, the following subscriptions Tel: +1 623 544 1698 are available: E-mail: [email protected] Volume 25 (2015), 4 issues Circulation and Subscriptions Personal: $132 USD, £80 GBP, €109 Euro Taylor & Francis Group, LLC Institution: $1,109 USD, £669 GBP, €885 Euro 530 Walnut Street Suite 850 Philadelphia, PA 19106, USA Tel: +1 215 625 8900 Fax: +1 215 207 0050
Copyright © 2015 Taylor & Francis Group, LLC. Reproduction without permission is prohibited. All rights reserved. The opinions expressed in NPN are not necessarily those of the editors or publishers. The views expressed here do not represent the views and policies of NuPECC except where explicitly identified.
Vol. 25, No. 3, 2015, Nuclear Physics News 1 Nuclear Physics Volume 25/No. 3 News
Contents Editorial ENSAR, a Nuclear Science Project for European Research Area by Ketel Turzó, Marek Lewitowicz, and Muhsin N. Harakeh...... 3 Laboratory Portrait A Dream Come True: Our 80-Plus-Year History with Nine Cyclotrons at RIKEN by Hideto En’yo...... 5 Feature Article A New Experiment to Search for Neutron–Antineutron Oscillations at the European Spallation Source by Camille Theroine...... 13 Facilities and Methods Nuclear Physics Research at the High Intensity Gamma-Ray Source (HIgS) by Henry R. Weller, M. W. Ahmed, and Y. K. Wu...... 19 The g-Ray Beam-Line at NewSUBARU by Hiroaki Utsunomiya, Satoshi Hashimoto, and Shuji Miyamoto...... 25 Meeting Reports 11th International Spring Seminar on Nuclear Physics—Shell Model and Nuclear Structure: Achievements of the Past Two Decades by Angela Gargano...... 30 15th International Conference on Nuclear Structure: NS2014 by Greg Hackman and Iris Dillmann...... 32 News and Views Extreme Light Infrastructure–Nuclear Physics (ELI–NP) by Victor Zamfir...... 34 IUPAP Young Scientist Prize in Nuclear Physics by Alinka Lépine-Szily...... 39 Calendar...... 40
Cover Illustration: RIKEN Nishina Center, RIBF Building—see article on page 5.
2 Nuclear Physics News, Vol. 25, No. 3, 2015 editorial
ENSAR, a Nuclear Science Project for European Research Area
During the period from September munity, using as main criterion • Numerous workshops, schools 2010 to December 2014, the European scientific and technical promise, and town meetings were orga- project European Nuclear Science combined with a rather rapid ap- nized on essential topics for the and Applications Research (ENSAR) plicability; and last but not least, community such as physics with coordinated research activities of the • to stimulate multidisciplinary and high-intensity stable beams– Nuclear Physics community perform- application-oriented research. ECOS, EURISOL techniques ing research in three major subfields: and methods, nuclear astrophys- Nuclear Structure, Nuclear Astrophys- To pursue its objectives ENSAR ics, gamma detectors and appli- ics, and Nuclear Applications. comprised 20 work packages: 6 Net- cations of nuclear science. Such ENSAR has been an “integrated working Activities (NAs) including events are especially important activity” funded for 8 M€ by the Eu- that of the management of the project, for young researchers. ropean Commission within the Sev- FISCO; 7 Joint Research Activities It is also interesting to note some enth Framework Programme (FP7), (JRAs); and 7 Transnational Access significant figures connected with EN- meaning a project offering support for Activities (TNAs). Among all suc- SAR during its running period: networking activities, joint research cessful results that came out of EN- activities and transnational access SAR, we may distinguish some main • Around 40 persons were hired to major infrastructures in Europe. features: specifically for ENSAR activi- Therefore, it has profited the commu- ties. • ENSAR core aim was to provide nity at large, much beyond the thirty • About 1800 users were sup- access to seven of the comple- official beneficiary institutions that ac- ported during their experiments mentary world-class large-scale tively participated in this project. at ENSAR infrastructures, which facilities: GANIL (F), GSI (D), ENSAR’s top-priority objectives corresponds to more than 34,000 joint LNL-LNS (I), JYFL (FI), were: hours of beam delivered. KVI (NL), CERN-ISOLDE • More than 200 articles were • to ensure that the European com- (CH) and ALTO (F). These fa- published in high-impact peer- munities of Nuclear Structure, cilities have provided stable and reviewed journals. Nuclear Astrophysics and Ap- radioactive ion beams of excel- • About 100 scientific events, for plications of Nuclear Science lent qualities ranging in ener- scientists or civil society, were concentrate on the most essen- gies from tens of keV/u to a few organized by the ENSAR partici- tial Joint Research Activities, GeV/u for European scientists to pating institutions to present and for further improvements and perform their research projects. discuss Nuclear Physics and its extensions of the infrastructure • A large part of the ENSAR proj- applications. facilities; ect was dedicated to R&D in • to focus on activities that are in order to improve functionality With all these successes, ENSAR general relevant to more than one of and access to the European fulfilled completely the foreseen de- facility; research infrastructures: impor- liverables promised in its application • to benefit from the R&D poten- tant progress has been achieved to the European Commission. But tial of the European University on ECR sources, actinide targets, such a project is much more than a groups, often in leading posi- ion-beam production, detectors, contract with the European Com- tions; simulations, instrumentation for mission. It has provided important • to promote the most needed rare nuclear processes and theo- and essential support to the Nuclear R&D, as identified by the com- retical models. Physics community, especially at a
The views expressed here do not represent the views and policies of NuPECC except where explicitly identified.
Vol. 25, No. 3, 2015, Nuclear Physics News 3 editorial
time of tight financial budgets. For in- many activities and large offer of ser- stance, ENSAR was by far the main vices. funding for scientists from European The support for the nuclear science countries with financial difficulties to research infrastructures and for their perform experiments at the ENSAR users’ communities with benefit to Eu- research infrastructures from 2010 to ropean society at large will continue 2014. ENSAR was also of great help in the coming four years through the to young researchers who could join recently EU-funded ENSAR2 project. experiments and/or propose their own, thus gaining in knowledge and expe- Marek Lewitowicz rience. Some researchers from other GANIL Caen fields, such as biology and medicine, could perform experiments with ion beams for the first time, thanks to EN- SAR support. We can conclude that ENSAR was a very important project for nuclear science and its applications in the European Research Area, through its Ketel Turzó GANIL Caen
Muhsin N. Harakeh KVI-CART Groningen
OPEN ACCESS
Authors may now choose to publish their articles aylor with T & Francis Open
Select. For more information and available licenses, please visit:
http://journalauthors.tandf.co.uk/preparation/OpenAccess.asp
4 Nuclear Physics News, Vol. 25, No. 3, 2015 laboratory portrait
A Dream Come True: Our 80-Plus-Year History with Nine Cyclotrons at RIKEN
Introduction: History of tory. In 1931, Dr. Yoshio Nishina be- In 1937, Nishina built the first Japa- Cyclotrons in RIKEN came a Chief Scientist of RIKEN. Our nese cyclotron based on the extensive At RIKEN, there is a long and research center was named after him knowledge learned from Ernest Law- unique tradition: whenever a new cy- since he is indeed the father of nuclear rence. Nishina’s second cyclotron, clotron is completed, a memorial photo physics in Japan. He was, at the same one of the world’s largest accelerators is taken with everybody involved with time, a theorist, an experimentalist, an at the time shown in Figure 1a, was the construction project on top of it. accelerator-builder, and a promoter of completed in 1944. This cyclotron Figures 1a–d show a part of our his- nuclear application. fated for a tragic end was destroyed
(a) (b)
(c) (d) Figure 1. (a) The RIKEN Cyclotron #2, completed in 1944, presently at the bottom of Tokyo Bay. Yoshio Nishina is at the center. (b) The RIKEN Cycloton #4, completed in 1966, presently exhibited as the monument in the RIKEN Wako Campus. Hiroo Kum- agai is at the center. (c) The RIKEN cyclotron #5, in operation since 1986. Hiromichi Kamitsubo is at the center. (d) The RIKEN cyclotron #9 (SRC: Superconducting Ring Cyclotron) in operation since December 2006. Yasushige Yano is at the center.
Vol. 25, No. 3, 2015, Nuclear Physics News 5 laboratory portrait
RIBF Accelerator Complex The schematic view of RIBF is shown in Figure 2. A typical accelera- tor operation uses the four cyclotrons, RRC (5th), fRC (7th), IRC (8th), and SRC (9th) in cascade, with one of the linear accelerators (RILAC1 or RI- LAC2) as the injector. The RIKEN Ring Cyclotron (RRC) can accept ions either from RILAC1, RILAC2, or the AVF cyclotron (6th). While RILAC2 is specially designed to accelerate only heavy nuclei larger than xenon and AVF only light nuclei, RILAC1 is versatile. In principle, we can oper- ate three experiments simultaneously Figure 2. Bird’s eye view of the RIKEN RI Beam Factory. Two linear accelera- by using RILAC1 for super-heavy- tors (RILAC and RILAC2) and fi ve cyclotrons (AVF, RRC, fRC, IRC and SRC) element search, RILAC2 with four are shown with the experimental facilities. cyclotrons in cascade to deliver 345 MeV/u uranium to BigRIPS, and the and abandoned into Tokyo Bay by the est intensity, recording 40 pnA in AVF cyclotron to deliver 5 MeV/u U.S. Army, just after World War II. In April 2015. With the use of this pow- light ions to the CNS Radio Isotope 1952, RIKEN’s third cyclotron was erful beam, many experiments are be- beam (CRIB) facility. rebuilt from the fi rst one. The fourth ing performed by diverse groups of Figure 3 shows our records of cyclotron, the fi rst heavy-ion cyclo- researchers from all over the world beam intensities with the bullets and tron in Japan (Figure 1b) was built who are producing many new data that the outlook with the dashed line. For in 1966, as a symbol of the rebirth of were just a dream only several years lighter ions, we have almost reached Japanese nuclear science. These four ago. The impossible dream of Yoshio our design goal of 1,000 pnA. This cyclotrons are history. Nishina has fi nally come true. corresponds to 6.2 kW of beam power Today, the RIKEN RIBF delivers the world’s strongest heavy-ion beam using 5 cyclotrons from the 5th to the 9th. The 5th (Figure 1c) and 6th were built in the 1980s. By using them as an injector, we completed the 7th, 8th, and 9th cyclotrons in 2006. Today, the heart and soul of the Nishina Center is the 9th cyclotron (Figure 1d), Super Conducting RING Cyclotron (SRC), which operates with Big-RIPS, the super conducting RI separator. These accelerators are located 23 m under- ground of the RIBF building. You can see from the number of people in Fig- ure 1d how big SRC is. Weighing 8,300 tons in total, it is as heavy as the Eiffel Tower. Figure 3. The history of beam intensity improvements. For light and medium The RIKEN Radioactive Isotope nuclei, we have almost reached the facility’s radiological limit of 1,000 pnA. For Beam Factory (RIBF) delivers the heavy nuclei such as Xe or U, the design goal is 100 pnA. Achieved beam intensi- uranium-beam with the world’s high- ties are shown with bullets and the prospects with the dashed line.
6 Nuclear Physics News, Vol. 25, No. 3, 2015 laboratory portrait
in the case of oxygen. For heavier nu- intensities as a typical performance RIBF Experimental Facility clei like uranium, we faced many dif- measure of the facilities. In reality, BigRIPS (RIKEN Projectile ficulties to crank up the intensity. For there are many more details to be con- Fragment Separator) example, in order to ensure stable op- sidered for the comparison, but a very The beam from SRC goes into the eration, we had to develop a gas-filled rough comparison to the present RIBF RI separator BigRIPS. The BigRIPS charge stripper to replace the origi- shows that the upcoming projectile- separator is composed of fourteen nally planned disk-type charge strip- fragmentation facility (PF) will be superconducting triplet quadrupoles per. In addition, we had to modify fRC able to deliver RIs by a factor of ten with large apertures (±40 mr hori- to accept lower charge states, such to hundred times more, the new ISOL zontally and ±50 mr vertically) and as 65+. facilities by thousand times more, and six room-temperature dipoles with The present beam performances in the next 20 or more years, the Super a bending angle of 30 degrees. The can be found in Ref. [1]. We have ac- ISOLs by 10,000 times more. 48 70 maximum magnetic rigidity of the Bi- celerated Ca with 415 pnA and Zn With the facilities under construc- gRIPS separator is as large as 9.5 Tm with 100 pnA. For uranium, we have tion expected to become operational and 8.8 Tm in the first and the second achieved 40 pnA, and 342 pnA for around 2020, the worldwide research 78 stage, respectively. The total length of Kr. Our goal for the uranium beam is capability to promote RI science will the BigRIPS separator is 78.2 m. As 100 pnA, which we expect to reach in be dramatically improved by then. of the summer 2014, 120 new isotopes 2015–2016. Presently, the beam avail- We at RIKEN must upgrade our fa- and 43 new isomers were discovered ability for users exceeds 90%. cility in the next five to ten years to with BigRIPS. Although many of Although the RIKEN RIBF is remain competitive. To go beyond them are yet to be published, available the world’s leading RI beam facil- 100 pnA of uranium beam, our plan is intensities of these isotopes are known ity, new facilities are currently being to change fRC to a super conducting so users can plan their experiments. constructed around the world ready cyclotron and to build a superconduct- Up to now, 308 isotopes have been to become strong competitions or ing LINAC. The expected increase in delivered to 78 different experiments. may even surpass the performance of beam intensity is almost 100 times, Figure 4 shows the bird-eye view of RIBF. Table 1 summarizes the world- reaching five to ten thousands particle 138 BigRIPS and its discovery record. wide situation, with a list of Sn nano amps. RI beams purified in BigRIPS go to either of the three beam-lines, that Table 1. RIKEN RIBF is compared with projectile-fragmentation (PF) facili- is, Zero Degree Spectrometer line, ties and ISOL facilities under construction (Super ISOLs are still in the plan- SAMURAI multi-particle spectrom- ning stage). Expected intensities of 138Sn are listed below. These values are very eter line, or SHARAQ high resolution rough estimates calculated by the author; readers should refer to the latest sta- line, as shown in Figure 2. tus reports of these facilities. Zero Degree Spectrometer Facility Power Fission/s or Category country Beam (kW) beam current Type 138Sn/sec At the end of the Zero Degree PF Running RIBF U + 86 4 100pnA SC cyclotron 3*106 Spectrometer, the Euroball, known Japan 345 MeV as the RISING detector at GSI, is PF Coming FRIB U + 76 ~ +80 USA 200MeV 400 8300 pnA SC Linac 108 ~ 109 now being operated by the EURICA RISP U + 77 ~ +81 (Euro-Riken Cluster Array) collabora- 8 9 Korea 200 MeV 400 8000 pnA SC Linac 10 ~ 10 tion [2]. A hundred days of beam time FAIR U + 28 Germany 1500 MeV 10 50 pnA Synchrotron 107 ~ 108 were approved by the RIBF Program ISOL Coming ARIEL e 50 MeV 10 mA SC Linac Advisory Committee (PAC), 80% of Canada p 500 MeV 1 mA ~100 1*1014 Cyclotron 2*109 HIE-ISOLDE which have been executed in the so- CERN p 1 GeV 2 mA 2 4*1012 SC Linac 2*108 called EURICA campaign. Figure 5 SPIRAL2 d 40 MeV shows the nuclei measured with EU- France 5 mA 200 1*1014 Cyclotron 2*109 SPES p 40 MeV RICA at RIBF. Published results are Italy 0.2 mA 8 1*1013 Cyclotron 3*108 updated in their home page [2]. The Super ISOL Future EURISOL p 1 GeV EU 5000 mA 4 MW 1*1015 SC Linac 4*1011 powerfulness of EURICA at RIBF can CARIF be seen in the reference [3], where the China Reactor 6 MW 2*1015 — 5*1010 β-decay half-lives of 110 neutron-rich
Vol. 25, No. 3, 2015, Nuclear Physics News 7 laboratory portrait
isotopes of the elements from 37Rb to the DALI-2, NaI gamma ray detector, form invariant mass spectroscopy and 50Sn were measured. The new data combined together with the MINOS missing mass spectroscopy). The en- have direct implications for r-process setup. MINOS is a Saclay-made thick tire program can be seen in their col- calculations and reinforce the notion liquid hydrogen target combined with laboration page [5]. that the second (A ≈ 130) and the rare- a state-of-the-art recoil tracker. Inter- Figure 8 shows some examples of earth-element (A ≈ 160) abundance action points are measured with MI- exclusive coulomb breakup of a bor- peaks may result from the freeze-out NOS and a precise Doppler correction romean halo nucleus 22C. Using the of an (n,γ) ↔ (γ,n) equilibrium. can be performed to the de-excited 48C primary beam, they have done Another important discovery is the gamma rays. The SEASTAR col- the measurements with 10 pps of 22C one highlighted by the “Nature” article laboration had the fi rst run and 68Fe beam. Similar measurements were describing that the neutron number 34 excited peaks were newly observed also performed for 26O. For both 21C is a new magic number in Ca isotopes together with many other new peaks and 26O, new excited states were [4], which was confi rmed by the mea- for a variety of nuclei (Figure 7). found [6]. surement of the 2+ states of 54Ca as Another major interest for the shown in Figure 6. To perform further SAMURAI (Superconducting SAMURAI spectrometer is “Equa- systematic measurements of 2+ states Analyzer for MUlti-particle from tion of State.” When we talk about the in the region of the r-process path, RAdio Isotope Beam) nuclear phase diagram, it is usually we have started the SEASTAR proj- Just next to the Zero Degree Spec- done two dimensionally; temperature ect (Shell Evolution and Search for trometer, the SAMURAI spectrom- and density. Another important axis is Two-plus energies At RIBF). Unlike eter is in operation. SAMURAI is isospin asymmetry δ, which must be other experiments, a single SEASTAR characterized by its magnet with the very asymmetric in a neutron star. One proposal covers a variety of nuclei bending power of 7 Tm. The special of the possible approaches toward the in many regions of the nuclear chart, feature of this gigantic spectrometer large δ region is to use neutron-rich and was approved by PAC within the is to perform kinematically complete ion beams. The SπRIT collaboration new framework called “Proposal for measurements by detecting multiple has introduced a large Time Projec- Scientifi c Program.” SEASTAR uses particles in coincidence (i.e., to per- tion Chamber in SAMURAI as shown
Figure 4. The RIKEN RI Beam Separator BigRIPS (left) and the nuclear chart with RI beam delivery at RIBF (above). Up to now, RI beams at RIK- EN RIBF have been produced by in-fl ight fi ssion of 238U or projectile frag- mentation of 14N, 18O, 48Ca, 70Zn, and 124Xe. New isotope searches have been performed whenever we signifi cantly increased the beam intensity. As of summer 2014, 120 new isotopes and 43 new isomers were discovered. We have determined production cross sections of 877 deferent RIs (blue squares) for users to plan their experiments.
8 Nuclear Physics News, Vol. 25, No. 3, 2015 laboratory portrait
Figure 5. The EURICA collaboration at RIKEN RIBF and the nuclei measured in the EURICA campaign. in Figure 9, aiming to reach δ = 0.25 reactions. One of the highlights of the kick the RI into the closed orbit. The (say 25% more neutrons than protons) experiments using SHARAQ is a tetra ring can accept RIs with the momen- by colliding two Sn isotopes (132Sn on neutron search with double-charge- tum acceptance of 0.5% and the iso- 124Sn). The EOS should change drasti- exchange 4He (8He, 8Be)4n reaction. chronicity at the level of 10–6. This cally even with this δ. The results will soon be available, enables us to provide mass measure- so stay tuned for the update in the ments for r-process nuclei with very SHARAQ (Spectroscopy with High- homepage [7]. low production rate (~1/day) and short resolution Analyzer and Radio Active Using the SHARAQ spectrometer life time (<50 ms). Quantum beams) and Rare-RI Ring as a beam-line, RIs can be transferred The ring was completed very re- SHARAQ is a high resolution to the Rare RI Ring (Figures 2 and cently and four seconds of revolution spectrometer (with an achieved reso- 10). This ring can be considered as a of injected particles were already ob- lution of 8,100) built by the Center of 24-sector ring cyclotron without ac- served. Real RI injection will be done Nuclear Study, the University of To- celeration cavities due to its most im- within a year. kyo. Such high resolution is achieved portant characteristic, the isochronous by using a dispersion matching tech- operation. When an RI of interest is Facilities Under Development nique, and the spectrometer is opti- detected at BigRIPS, a trigger signal SCRIT (self-confi ning RI target). mized for exothermic charge exchange is transferred to the Rare RI Ring to Located on the upper fl oor, separated from other experimental facilities sits SCRIT as shown in Figure 11. Elec- trons of 350 MeV stored in a race track type storage ring are used for electron scattering as well as to con- fi ne RIs. Ions are self-confi ned around the electron beam and in the electric mirror potential along the beam. Pres- ently, we are preparing an ISOL driven by the same electron source and have observed isotopes of Sn and Xe suc- cessfully. We are making progress on the production rate of these isotopes to realize the fi rst electron scattering ex- periment on a rare radio isotope. Figure 6. The discovery of the new magic number 34 in 54Ca. The circles show the new data obtained at RIBF. Excitation-energy (2+) systematics is shown as SlowRI (slowed-down RI beam). functions of neutron and proton numbers. SLowRI provides slow and cold RI
Vol. 25, No. 3, 2015, Nuclear Physics News 9 laboratory portrait
Figure 7. (Left) MINOS setup with the gamma detector DALI-2. (Right) Gamma ray energies before and after the Doppler correction as the function of reaction points are shown for 68Fe nuclei produced in 69Cu(p,2p)68Fe reaction. beams for users of trap, MRTOF, RILAC (Riken Linear Accelerator) suke Morita and his team successfully b-NMR, and so on. There are two and GARIS (Gas-Filled Recoil Ion observed two events of 3n(293Lv) and kinds of devices that slow down the Spectrometer) three events of 4n(292Lv) channels. Al- produced RIs. One is called PALIS On August 12, 2012, we observed though the number of events is limited, (Parasitic Laser Ion-Source) located the third decay chain of element 113 the cross-section and the life time of besides the BigRIPS beam-line, and [8] in the GARIS spectrometer using these data are totally consistent with the accepts unused beam fragments in the RILAC beam with 209B (70Zn, 1n) previously confirmed data in FLNA. the gas catcher cells. Laser ionization 278113 reaction showing beautiful de- The shift from cold fusion to hot technique is adopted for the selection cay chain with six consecutive alpha fusion experiments enabled us to pro- of the RIs of interest. This is the only decays (Figure 13). After the observa- mote more chemistry experiments device that can run parasitically with tion, we terminated the experiment to for super heavy elements. Very re- other experiments. The other is lo- synthesize element 113, and started to cently, the team headed by Dullman cated at the exit of BigRIPS, with the prepare for hot fusion experiments. We succeeded in observing the chemical RF carpet technology to collect and had 10 days of beam time in December property of Sg (Co)6, which has led to slow down RIs. Figure 12 shows the 2013 to deliver 800 pmA of 262-MeV one to conclude that seaborgium is the layout of SlowRI. The day-1 experi- 48Ca beam on the 248Cm target to cre- Group 6 element [9]. Note that such ment will be performed in 2015. ate compound nucleus of 296Lv*. Ko- an experiment can only be performed
Figure 8. (Left) The break-up spectrum of 21C* obtained with SAMURAI. (Middle) The quality of isotope separation for oxygen. (Right) The break-up spectrum of 26O.
10 Nuclear Physics News, Vol. 25, No. 3, 2015 laboratory portrait
with the experimental device like GARIS, which provides clean seabor- gium samples.
Summary The combined operation of SRC and BigRIPS at RIKEN RI Beam Fac- tory has been in effect since 2007. SRC has been fully operational since 2010, with the only temporary break in 2011 due to the Great East Japan earthquake. Up to now, the number of days approved for experiments by Figure 9. The cross-section view of SAMURAI and TPC. A simulated event of PAC is close to 500 days of which 132Sn + 124Sn collision is also shown. about 200 days are executed and 300 days are in the backlog. We are now aiming to deliver 100 user-beam-days per year. We also expect to have a 345 MeV/A uranium beam that will reach 100 pnA (2.5 times to go) within a year or two. Major characteristics of ~100 key unstable nuclei close to R-process path and/or vicinity of the magic numbers will be measured in order to solve the mystery of element genesis and to establish the ultimate picture of nucleus. The RIKEN RIBF is in its harvest time, running the world’s most intense RI beam. Most of the experimental fa- Figure 10. Rare RI Ring is often abbreviated as the R3 ring. The magnets were cilities are in place, with many experi- recycled from TURN-II at the Institute of Nuclear Study, the University of Tokyo. mental contributions from around the world. Although the current budget
Figure 11. Schematic view of SCRIT where the acronyms are as follows: RTM (racetrack microtone), eBT (electron beam transport line), IBT (ion beam transport line), ERIS (electron induced RI separator on-line), and SR2 (scrit-equipped Riken storage ring).
Vol. 25, No. 3, 2015, Nuclear Physics News 11 laboratory portrait
Figure 12. The layout of the SlowRI system. situation in Japan is still very tight due to provide you with the world’s best 2. The EURICA Collabortion home to the aftermath of the Great Tohoku RI beams. page. http://ribf.riken.jp/EURICA/ Earthquake, we will continue to try 3. G. Lorusso et al., Phys. Rev. Lett. References to operate RIBF as much as we can. 2015, 114.192501Z. 1. RIKEN Nishina Center home page. 4. D. Steppenbeck et al., Nature 502 You will never be disappointed with http://www.nishina.riken.jp/RIBF/ (2013) 207. the RIBF beam quality. We are ready accelerator/tecinfo.html. 5. The SAMURAI Collaboration home page. http://ribf.riken.jp/SAMURAI/ Collaboration/ 6. N. Kobayashi et al., Phys. Rev. Lett. 112 (2014) 242501; T. Nakamura et al., Phys. Rev. Lett. 112 (2014) 14, 142501; Y. Kondo et al., RIKEN Ac- celerator Progress Report 46 (2013) 6; T. Nakamura et al., RIKEN Accelera- tor Progress Report 46 (2013) 7. 7. The SHARAQ Collaboration home page. http://www.cns.s.u-tokyo.ac.jp/ sharaq/ 8. K. Morita et al., J. Phys. Soc. Jpn. 81 (2012) 103201 9. J. Even et al., Science, 19 September 345 (2014) 1491.
Hideto En’yo RIKEN Nishina Center for Accelerator-Based Science
Figure 13. Observed decay chain from the element 278113 produced in Zn + Bi reaction. Written on the blackboard right after the discovery.
12 Nuclear Physics News, Vol. 25, No. 3, 2015 feature article
A New Experiment to Search for Neutron–Antineutron Oscillations at the European Spallation Source
Camille Theroine, on behalf of the nn– Collaboration European Spallation Source ESS AB, Lund SE-221 00, Sweden and Institute Laue-Langevin, 6 rue Jules Horowitz BP 156, 38042 Grenoble, CEDEX 9, France
Introduction Table 1. The ESS high level parameters [2, 3]. – The discovery of neutron–antineutron (nn) oscillations Parameter Unit Value could answer crucial questions of particle physics and cos- Average beam power MW 5 mology. Why do we observe more matter than antimatter Power during pulse MW 125 in the Universe? At what energy scales do new phenomena occur? Another related intriguing subject potentially acces- Nb of target station 1 sible with this process concerns the mechanism responsible Nb of instruments in construction budget 22 for neutrino mass generation. The construction of the Eu- Nb of beam ports 48 ropean Spallation Source (ESS) offers a remarkable oppor- Nb of moderators 2 tunity to perform a sensitive experiment dedicated to the Proton kinetic energy GeV 2 search of such oscillations. Indeed, the high neutron flux Average pulse current mA 62.5 expected at this facility, combined with the important prog- Pulse length ms 2.86 ress made in neutron optics, will enable this experiment to gather all the necessary conditions for establishing possible Pulse repetition rate Hz 14 new physics coming from energy scales beyond the reach Linac length m 482.5 of colliders that can have a strong impact on our under- Annual operating period h 5000 standing of the Universe. Reliability % 95
The European Spallation Source The ESS [1] is a new research center under construction The main characteristics of ESS are its long neutron to be based on the world’s most powerful pulsed neutron pulse of 2.86 ms, its low repetition rate of 14 Hz and its source. ESS represents the largest pan-European research high peak flux comparing to today’s leading neutron re- project today, gathering at least 17 partner countries. The search centers, as shown on Figure 1. A schematic view of total construction budget is estimated at 1.8 G€ with half the ESS facility is shown in Figure 2. coming directly from Sweden, Denmark, and Norway. The facility is now under construction in Lund, Sweden. According to the current project plans, first neutrons will be available in 2019. ESS will start its user program with six instruments in 2023. In 2025, ESS construction will be complete with 22 operational instruments. At ESS neutrons will be created by spallation. A 5 MW superconducting linac will accelerate proton beam, pro- duced by an ion source, to an energy of 2 GeV. These pro- tons will hit a rotating tungsten target giving high-energy neutrons. The high level parameters of the ESS accelerator are presented in Table 1 [2]. The last two steps are to slow down these neutrons with a moderator-reflector system sur- rounding the target, and deliver the thermal and cold neu- Figure 1. Single neutron pulse brightness at 5 Å as function trons produced to the different instruments. of time at the ESS and other leading neutron facilities [2].
Vol. 25, No. 3, 2015, Nuclear Physics News 13 feature article
Standard Model (SM) of particle physics. However, it seems to not be the complete theory. Actually, there are some strong experimental evidences and theoretical argu- ments to prove it. For instance, this model does not include gravitation. It cannot explain the existence of dark matter or dark energy, which contribute as much as 25% and 70% [8], respectively, to the energy content of the Universe. Cur- rently, the SM is able to describe less than 5% of the content of the Universe [8]. For many physicists, it is crucial to test the validity of the SM by measuring its different param- eters. In this respect, precision experiments with neutrons can contribute to the understanding of the SM itself [9–12].
Why Study Neutron–Antineutron Oscillations? Figure 2. Schematic view of the ESS facility. Yellow is the The baryon asymmetry of the Universe (BAU) is one target station, red the accelerator building, green laborato- of the most important questions to solve in cosmology. ries and offi ces, purple and orange experimental halls, and Sakharov has proposed a set of three necessary conditions blue auxiliary buildings [3]. that a baryon-generating interaction must satisfy to produce matter and antimatter at different rates [13]. These require- Neutrons are a unique tool for science. With ESS, the ments are: scientifi c community can exploit new research opportuni- • Baryon number violation. ties in neutron scattering and also in fundamental physics. • Charge and charge and parity conjugation symmetry violation. • Interactions out of thermal equilibrium during the ex- Precision Studies of Fundamental Physics at ESS pansion of the Universe. Fundamental physics stands at a crossroads between particle and nuclear physics, astrophysics and cosmology. Baryon number violation appears naturally in many theo- Its main purpose is to improve our knowledge of the Uni- ries that unify quarks and leptons, such as Grand Unifi ed verse and understand its fundamental laws and evolution. Theories (GUT). The difference between the baryon num- At ESS, the high neutron fl ux will permit neutron ex- ber B and the lepton number L is required for the SM to periments to continue to advance the precision frontier [4] be renormalizable [14]. B violation in SM occurs through that consists in investigating low energy processes that can nonperturbative electroweak processes, but at a rate which be precisely predicted by theory. Deviations from expecta- is strongly suppressed at low temperatures [15]. tions in such processes would prove the existence of new To study baryon number violation, two types of experi- physics. In the precision frontier, new particles are not cre- ments have been pursued: ated in the fi nal state. The idea is to detect the footprints • Proton decay, which violates B by one unit. Observa- they leave. These traces are sought at energies below the tion close to the current limits would imply new phys- production threshold of new particles. The energy frontier ics at high energy scales ~1015 GeV [16]. To probe is based on measurements of particle interactions in colli- this, a ~100–1,000 kton detectors are needed. sion of highest energy possible aiming at the production • Neutron–antineutron oscillations. To observe a neu- of new heavy elementary particles. These scientifi c paths tron spontaneously converting into an antineutron, B are complementary. A good example illustrating this com- has to be violated by two units with no change in lep- plementarity is the discovery of the Higgs boson. Indeed, ton number. In case of discovery close to the current precision measurements performed at the Large Electron- limits, inferring the new physics is somewhat more Positron collider (LEP) and other facilities allowed to con- complex, but it could be as low as ~104 GeV [17]. strain its mass [5]. The information extracted during these For the case of nn– oscillations, this topic opens other fi elds experiments was very useful for its discovery at the Large of exploration for the physicists: Hadron Collider (LHC) at CERN [6, 7]. The established theory describing weak, strong, and • For instance, the possibility to test extensions to the electromagnetic interactions of all known particles is the Standard Model that allow violating either B or L and
14 Nuclear Physics News, Vol. 25, No. 3, 2015 1035928
@‰ En ˛
2 2 2 ˛ 2 ˛ C V Pn!n D 2 2 sinfeature– article t (2) ˛ C V p h !
may result in B violation by two units without chang- • (a/ħ) × t << 1; 1 ing L (e.g., theoretical concepts working with extra- • (V/ħ) × t << 1: VtheD quasi-free .En condition En/ (i.e., in vacuum(3) 2 dimensions, or models for baryogenesis around the and in the absence of external fields), electroweak symmetry-breaking scale) [18]. the probability of nn– transformation becomes: • The selection rule ΔB = 2 relates neutron–antineutron 1035928 2 2 oscillation to Majorana neutrino mass via (B-L). This ˛ t Pn!n D – t D (4) link could be used to discover the origin and the na- h n!n  à  à ture of neutrino masses. A simple way to understand – @‰ En ˛ with t – = ħ/
– @‰ En ˛ 2
For the following conditions:2 2 2 France [24]. The average neutron flight time was ~0.1 s and FoM˛ D N 2 ht i: t 2 (6) Pn!n D ˛– t D t (4) h n!n Pn!n D – t D (4)  h à Ân!n à  à  à Vol. 25, No. 3, 2015, Nuclear Physics News 15
2 intra D R free2 (5) intra D R free (5)
FoM D N ht 2i: (6) FoM D N ht 2i: (6) 1035928
@‰ En ˛ feature
the average velocity of the cold neutrons was ~700 m/s. In order to increase the sensitivity, the following factors 2 2 2 The quasi free condition˛ was maintained2 ˛ C withV a vacuum of are exploited: Pn!n D sin t (2) P ≈ 2 × 10–4 Pa and˛2 CtheV Earth2 magnetic fieldh– shielded down p ! • increase the free flight time of neutrons; to B < 10 nT. Antineutron appearance would be detected • increase the number of neutrons; through annihilation in a thin carbon target. Carbon has a • keep the experiment background free; high annihilation cross section (~4 kb) and a low neutron 1 • detector size can be possibly increased. capture cross-sectionV (~4D mb). .E Then annihilationEn/ reaction (3)on 2 the carbon target would have produced on average 5 pions. The first three aspects are discussed more in detail below. The target was surrounded by a detector consisting of track- ing detectors, a time-of-flight system and a calorimeter to Increase the Free Flight Time of Neutrons 2 2 reconstruct the ~1.8 GeV˛ invariant masst of the multi-pion (Observation Time) system. The Pexperimentn!n D – was t backgroundD free. After one(4) h n!n In the new experiment at ESS, the cold neutron beam year of running, no antineutron à was detectedà and no back- will propagate in a region with high vacuum and low mag- ground events were recorded. For this experiment, a limit netic field to satisfy the quasi-free condition. Equation (4) of 0.86 × 108 s was set on the free oscillation time. may then be used for the transformation probability. This 2 –5 intra D R free (5) means the vacuum should be better than ~10 Pa and the Sensitivity magnetic field must be suppressed to the few nT level at For experiments using free neutrons, the figure of merit least in the whole free flight volume. (FoM or sensitivity) is: A lower limit on the neutron velocity is imposed by 2 Earth’s gravity since very cold and ultra-cold neutrons can- FoM D N ht i: (6) not be transported over significant distance without many Here interactions with the mirrors. Indeed, each interaction re- • N is the free neutron flux reaching the annihilation sets the oscillation clock [26]. To increase the number of target and neutrons a large elliptical focusing reflector will be used • 〈t2〉 the square of the observation time. [27] to direct neutrons within large solid angle to the an- nihilation target. Cold neutrons are particularly useful due The sensitivity reached by the ILL experiment was 1.5 × to their low velocity and a long flight path (>200 m) will be 9 10 n⋅s [24]. used to increase the observation time. The next generation experiment proposed at ESS prom- ises a much-improved sensitivity and a considerable dis- Increase the Number of Neutrons covery potential. Combined with the specific advantages of A high flux of cold neutrons is expected at ESS. A large ESS, it is expected to exploit recent progress in both neu- beam port allowing the biggest possible view of the ESS tron optics and detector technologies to push the figure of moderator surface is necessary to obtain a maximum part merit to the oscillation probability by approximately three of this flux. The elliptical geometry chosen for the reflec- orders of magnitude [25]. tor increases the phase space acceptance for cold neutrons If no oscillation is seen, the expected gain in the exclu- within fixed solid angle. The cold neutron source and the sion limit would provide guidance for models aiming to ex- annihilation target will be located in the focal planes of the plain the baryon asymmetry of the Universe. It will also set ellipsoid. To increase the beam acceptance, a larger target a limit on the stability of nuclear matter at the level (at D = of ~2 m meters diameter is required. Progress made in neu- 2 mode) > 1035 years. tron optics represents an important opportunity to reach a higher sensitivity in the experiment. Even if the reflection of the super-mirrors decreases with velocity transverse to Requirements for a New Experiment at the ESS the reflector the range of reflected transverse velocities The goal of the experiment is to have neutrons travel- has been increased over Ni reflectors by a factor m thanks ing in free space for the maximum time possible without to Bragg scattering from multilayer coating of these mir- wall collisions. By a single reflection, the neutrons have to rors. Nowadays, m = 4 mirrors are industrial standard and reach the annihilation target surrounded by the detector. If m = 7 can be industrially produced [28]. One final way to a transition to an antineutron takes place, the annihilation increase the number of neutrons is to have a longer run- event needs to be detected at the end of the flight path with ning time comparing to the ILL experiment, which ran for high efficiency. one year.
16 Nuclear Physics News, Vol. 25, No. 3, 2015 feature article
would be very happy to welcome new partners and/or in- stitutions to work on the topics proposed by the different working groups [31]. D"~"4%5"m" Outlook Neutrons oscillating into antineutrons could offer a unique probe for crucial questions in fundamental phys- ics, such as the mechanisms responsible for baryon number L"~"200"300"m" violation and neutrino mass generation. The observation Figure 3. Set-up for a neutron–antineutron oscillation ex- of this process would be a discovery of primary impor- periment at ESS. tance because of its incontestable evidence for new phys- ics beyond the Standard Model. The construction of ESS in Lund, together with technological progress, offers a major Background Free Experiment opportunity to conduct a new search for this process with The experiment’s sensitivity is maximized if the detec- at least three orders of magnitude increase in sensitivity to tion of antineutrons is background free. The fast neutrons the oscillation probability compared to the ILL experiment. produced by the spallation process at ESS can be suppressed The required technologies exist and detailed simulations by using the time structure of the beam. Precise tracking to optimize the design and the technical choices are being and excellent timing resolution are needed to limit events developed by a growing collaboration. Subject to funding, to the annihilation target. Muon veto detectors are required the aim is to complete a technical design report in approxi- to reject cosmic background. MeV gammas produced by mately two years, in time to allow the experiment to take neutron capture will be suppressed by the trigger system. data not long after ESS starts the production of its fi rst cold Figure 3 presents a schematic view of the experimental neutrons as expected in 2019. set-up for a neutron–antineutron experiment at ESS. References The nn– Collaboration 1. European Spallation Source, www.esss.se In order to establish a collaboration for this experiment, 2. S. Peggs et al., ESS Technical Design Report, ESS-2013- 0001, www.esss.se a fi rst workshop took place at CERN in June 2014 [29]. At 3. H. Danared, M. Lindroos, and C. Theroine, CERN Courier this occasion, fi ve working groups were identifi ed: 54 (2014) 21. • Physics: evaluation of the scientifi c value and identifi - 4. C. Theroine, G. Pignol, and T. Soldner, eds., Phys. Procedia cation of possible new theoretical applications as well 51 (2014) 1. as additional physics processes that can be studied 5. W.-M. Yao et al., J. Physics G 33 (2006) 1. 6. CMS Collaboration, Phys. Lett. B716 (2012) 30, arXiv: with the experiment. 1207.7235 hep-ex. • Neutronics: design/optimization of the extraction op- 7. ATLAS Collaboration, Phys. Lett. B716 (2012) 1, arXiv: tics, the vacuum tube, the radiation shielding, and the 1207.7214 hep-ex. annihilation target. This group works on beam charac- 8. P. A. R. Ade, N. Aghanim, C. Armitage-Caplan, et al., Planck terization and monitoring as well. collaboration, Astronomy and astrophysics, 1303 (2013) • Magnetics: design/optimization of the magnetic 5062. shielding and magnetometry. 9. H. Abele, Prog. Part. Nucl. Phys. 60 (2008) 1. • Detector: design of the detector system, tracker, calo- 10. D. Dubbers and M.G Schmidt, Rev. Mod. Phys. 83 1111 rimeter, trigger, time of fl ight, cosmic veto, and data (2011). acquisition system. 11. V. Cirgliano and M. J. Ramsey-Musolf, eds., Prog. Part. • Software & Computing: simulation support, data man- Nucl. Phys. 71 (2013) 2–20. 12. B. R. Holstein et al., J. Phys. G 41 (2014), art. 114001 to agement, analysis tools, computing infrastructure. 114007. In February 2015, at ESS, a second workshop was orga- 13. A. Sakharov, JETP Lett. 5 (1967) 24. nized and held around these fi ve working groups [30]. 14. G. ‘t Hooft, Phys. Rev. Lett. 37 (1976) 8; Phys. Rev. D 14 The fi rst accomplishment of the collaboration will be (1978) 3432. the submission of an expression of interest to ESS in April 15. V. A. Kuzmin, V. A. Rubakov, and M. E. Shaposhnikov, Phys. 2015. At this stage, the collaboration is still forming and Lett. B 155 (1985) 36.
Vol. 25, No. 3, 2015, Nuclear Physics News 17 feature article
16. P. Nath and P. Fileviez, Phys. Rept. 441 (2007) 191. 25. D. G. Phillips II et al., arXiv:1410.1100 (2014). 17. K. Babu et al., FERMILAB-CONF-13-649-E-PPD, 31 Octo- 26. S. Marsh and K. W. Mcvoy, Phys. Rev. D28 (1983) 2793. ber (2013) 26 pp, 27. Y. Kamyshkov et al., Proceedings of the ICANS-XIII meet- 18. J. M. Arnold et al., Phys. Rev. D87 (2013) 075004. ing, PSI, Villigen, Switzerland, 11–14 October (1995) 843 pp. 19. T. Yanagida, Prog. Theor. Phys. 64 (1980) 1103. 28. Swiss Neutronics, super-mirror manufacturer, http://www. 20. R. N. Mohapatra, J. Phys. G 36 (2009) 104006. swissneutronics.ch/ 21. C. Dover, A. Gal, and J. M. Richards, Phys. Rev. D27 (1983) 29. First workshop on neutron antineutron oscillation at ESS, 1090. CERN, Switzerland, June 2014. www.nnbar-at-ess.org 22. E. Friedman and A. Gal, Phys. Rev. D78 (2008) 16002. 30. Second workshop on neutron antineutron oscillation at ESS, 23. K. Abe et al., Super-Kamiokande Collaboration, arXiv: Sweden, February 2015. www.nnbar-at-ess.org 1109.4227hep-ex. 31. www.nnbar-at-ess.org 24. M. Baldo-Ceolin et al., Z. Phys. C63 (1994) 409.
18 Nuclear Physics News, Vol. 25, No. 3, 2015 facilities and methods
Nuclear Physics Research at the High Intensity Gamma-Ray Source (HIgS)
The High Intensity g-Ray Source total intensity of these g-ray beams intra-cavity FEL beam as its photon (HIgS), operated by the Triangle Uni- produced in the vicinity of 10 MeV source [1], and it takes advantage of versities Nuclear Laboratory and lo- is approximately 3 × 1010 g/s, making the low emittance and large energy cated on the campus of Duke Univer- HIgS the most intense Compton g-ray acceptance of a modern storage ring. sity, is presently able to provide nearly source ever built and operated [1]. There are two different FEL systems at mono-energetic polarized gamma ray After presenting a brief description HIgS: the fi rst of these consists of two beams with energies ranging from 1 to of the HIgS facility and a few of the planar arrays of electromagnetic wig- 100 MeV. These beams are produced most exciting discoveries made using glers inside a 53.7 m long FEL resona- by Compton backscattering photons this facility, some of the future plans tor cavity whose length is equal to half produced by a free-electron laser (FEL) that could lead to even more fascinat- of the circumference of the storage from the same relativistic electron ing results will be described. ring. This length is crucial since the beam that powers the FEL inside of an The HIgS facility is unique in two round trip time of photons in the cavity electron storage ring. The maximum major ways: it uses a high-intensity is equal to the time it takes an electron
Figure 1. The schematic layout of the HIgS accelerator facility, showing the linac pre-injector, full-energy top-off booster injector (0.18–1.2 GeV), electron storage ring (0.25–1.2 GeV), and free-electron laser system. This layout shows four FEL wigglers in the 34 m long FEL straight section, with two planar OK-4 wigglers in the middle and two helical OK-5 wig- glers outboard. The typical HIgS g-ray beam operation utilizes two electron bunches, separated by one half of the storage ring circumference. Electron bunch #1 (#2) collides head-on with the FEL pulse generated by electron bunch #2 (#1) in the center of the FEL laser cavity to produce Compton gamma-rays. The gamma-ray beam passes through the fi nal beam collimator located 53 m downstream from the collision point and then enters the experimental area.
Vol. 25, No. 3, 2015, Nuclear Physics News 19 facilities and methods
bunch to complete a revolution around many experimental applications, espe- Nuclear Resonance Fluorescence the storage ring. This allows the elec- cially those involving the use of time- One of the most successful pro- tron bunch to interact with the photon of-fl ight techniques. grams at HIgS has been in the area pulse built-up by radiation of the same The energy spread and beam spot of Nuclear Resonance Fluorescence bunch in previous revolutions. The size of the g-ray beams at HIgS can be (NRF) [2]. Signifi cant results have gain of this system can be greatly en- selected by using collimators of differ- been published on studies of various hanced by means of a buncher magnet ent sizes. The minimum energy spread collective modes in nuclei including located between the two planar arrays. of the g-ray beam is limited by the the Pygmy Dipole Resonance, the Gi- This system, called the OK-4 FEL sys- energy and angular spread of the elec- ant M1 strength in nuclei, collective tem, produces linearly polarized g-ray tron beam. In the high-fl ux mode, the quadrupole–octupole coupled states, beams with the plane of polarization full-width energy resolution of a well- states of mixed symmetry, and others. in the horizontal direction and is used collimated beam is about 2.5–3.5%, As an example of the unique capabili- for g-ray production up to 60 MeV. The depending on the fl ux level. Typical ties of HIgS, we will describe a very second FEL system consists of two 4 collimator diameters are between 1 recent study that used the NRF tech- m long arrays of helical electromag- and 2 cm. nique to determine the energy splitting netic wigglers and is used primarily of the (J,T) = (1,1) parity doublet in to produce circularly polarized g-ray The Nuclear Physics Program 20Ne in the vicinity of 11.26 MeV [3]. beams. Two additional helical wiggler at HIgS The parity doublet in 20Ne was magnetic arrays are available, and a The nuclear physics program at the previously assigned energies of recent upgrade provides for a “switch- HIgS facility is very diverse and covers 11262.3(19) keV for the 1+ state and yard,” making it possible to exchange a number of different areas of nuclear 11270(5) keV for the 1– states. These the two OK-4 linear arrays with these physics. This brief report can only fea- two states are too close in energy to be two additional helical arrays. Recently, ture a few examples to illustrate the resolved with an HPGe detector hav- a new mode of operating using two novel experiments which HIgS has en- ing a resolution of ~7.5 keV at these OK-5 helical arrays has been devel- abled in the areas of Nuclear Structure energies. Therefore, only the summed oped to produce linearly polarized g- and Nuclear Astrophysics. peaks are observed. In the case of a ray beams with an arbitrary (switch- able) plane of polarization. This opens up new opportunities to users, as will be described below. The helical arrays are used for producing g-ray beams at energies up to 100 MeV, which can be either circularly or linearly polarized (<20 MeV). The layout of the facility and the beam production mechanism are shown in Figure 1. The time structure of the g-ray beams at HIgS is determined by the orbital revolution frequency of the electron bunch in the storage ring (2.79 MHz) along with the fact that the standard operating mode utilizes a symmetric two-bunch arrangement, in which two out of sixty-four RF buck- ets are fi lled with electrons separated by a distance equal to one half of the storage ring circumference. This leads Figure 2. The summed spectra for the detectors in the vertical (top) and horizon- to production of a g-ray burst every tal (bottom) planes for linear (purple) and circular (green) polarized beams. The 179 ns: a time between bursts that, as small energy shift in the vertical (top) detectors determines the energy difference will be seen below, is almost ideal for of the doublet states.
20 Nuclear Physics News, Vol. 25, No. 3, 2015 facilities and methods
linearly polarized beam, however, the Table 1. Results and comparison to literature for the deduced level energies of 1– state will show up mostly in the di- the 1+ and 1– states, their energy splitting ΔE, and their nuclear enhancement rection perpendicular to the plane of factor Fe. + polarization, while the 1 state will be Observable This work [3] Previous results seen mostly in the parallel direction. E(1+) (keV) 11258.6 (2) 11262.3 (19) The trick, therefore, is to take spectra E(1–) (keV) 11255.4 (±0.7) stat (+1.2 – 0.6) sys 11270 (5) in the two planes using both linearly and circularly polarized beams. The ΔE (keV) –3.2 (± 0.7) stat (+0.6 – 1.2) sys 7.7 ± 5.5 –1 energy difference between the two Fe. (keV ) 1.4 (±0.3) stat (± 0.2) sys 0.67 ± 0.70 states is then determined from the small energy shift between the linear of State, which describes the macro- in Figure 3. Averaging the two results and circularly polarized cases. In the scopic behavior of nuclear matter, and shown here provides an unambigu- present case, this shift is seen in the plays a dominant role in nuclear mat- ous determination of the background perpendicular plane, indicating that ter as the neutron excess increases. A term and leads to values of the energy, the 1– state lies lower in energy than knowledge of its strength and its den- width (G) and strength (IVQ-EWSR) the l+ state, as can be seen in Figure 2. sity dependence is crucial to our un- of the IVGQR almost an order of mag- The peak centroids and their re- derstanding of exotic nuclear matter nitude better than previously possible spective peak areas from all four spec- including neutron stars. The param- (Figure 3). tra allow for the determination of the eters of the IVGQR have been poorly excitation energies of the parity dou- determined, until now [4]. The intense The Second 2+ State in 12C and the blet, their energy difference, and the polarized g-ray beams of the HIgS fa- Structure of the Hoyle State ratio of their integrated cross-sections. cility, along with the realization that The second Jπ = 2+ state of 12C, The results of this work are presented the sign of the interference terms be- predicted over 50 years ago as an ex- in Table 1, which includes the value tween the IVGQR and the dominant citation of the Hoyle state, has been of the so-called parity violating effec- electric dipole background could be unambiguously identifi ed at HIgS us- fl ipped by measuring the ratio of the ing the 12C(g, a )8Be reaction. The tive nuclear enhancement factor Fe. o As seen in Table 1, the new results re- linearly polarized Compton scattered HIgS facility was used to produce vise the energetic ordering of the two g-rays perpendicular and parallel to beams between 9.1 and 11.2 MeV, states, reduce the energy difference by the polarization plane (σperp/σpar) at a and the outgoing alpha particles were a factor of about 2, and enhance the backward versus a forward angle. The detected in an optical time projection results for the case of 124Sn are shown chamber. The data allowed for the value of Fe by a factor of 2. These re- sults make this parity doublet in 20Ne an intriguing candidate for the study of parity violation in nuclear excita- tions.
Compton Scattering and the Isovector Giant Quadrupole Resonance in Nuclei Nuclei are known to exhibit giant electromagnetic resonance, the domi- nant ones being the electric dipole and the electric quadrupole modes. The Isovector Giant Quadrupole Resonance (IVGQR) is especially in- teresting because the restoring force between the oscillating neutrons and Figure 3. The ratio of the Compton scattered g-rays measured perpendicular protons that determine its properties is versus parallel to the polarization plane from a target of 124Sn as a function of a result of the symmetry energy. This Eg for detectors at 55° and 125°, respectively. The cross-over point leads to a term appears in the Nuclear Equation precise value of the energy of the IVGQR.
Vol. 25, No. 3, 2015, Nuclear Physics News 21 facilities and methods
Table 2. Parameters of a single-level Breit-Wigner resonance fit to the data with and without the level shift func- tion included for different values of ro.
ro (fm) E (MeV) Ga (keV) Gg (meV) 1.4 (w/o level-shifts) 10.13 ± 0.06 2080 ± 330 (observed) 135 ± 16 (observed) 1.6 (w/level-shifts) 10.00 ± 0.03 3360 ± 45 (formal) 226 ± 22 (formal) 1.8 (w/level-shifts) 10.06 ± 0.03 1620 ± 130 (formal) 111 ± 5 (formal)
measurement of the complete angular distributions needed to extract the E1 and E2 amplitudes and their relative phase, confirming the 2+ nature of the state near 10 MeV. The separated E1 and E2 cross-sections were fit using Breit-Wigner resonance line shapes. A preliminary report [5] of this work presented resonance parameters that were incorrect due to a sign error in the level shift parameter contained in the Breit-Wigner formula. Once this error was corrected, it was observed that the cross-section data in the vicin- ity of the 2+ resonance could not be fit using a standard Breit-Wigner line shape with energy dependent widths and the level-shift included using typi- cal values of the R-matrix parameter ro (between 1.3 and 1.5 fm). However, as pointed out by Fynbo and Gai [6], converged solutions were obtained for larger values of ro (ranging from about 1.5 to 1.8 fm), although the for- mal width had a strong dependence on the value chosen for ro. Therefore, two analyses were performed: (1) a single- level Breit-Wigner fit was performed that ignored the level-shift in order to obtain the “observed” level param- eters [7] and (2) fits were performed including the level-shift using large values of the ro parameter to obtain Figure 4. Measured E2 and E1 cross-sections and the E1–E2 phase differences the formal level parameters. The re- as a function of incident beam energy. The results shown are averaged over the sulting resonance parameters for both g-ray beam energy distribution, measured to be close to a Gaussian distribu- cases are presented in Table 2, where tion with a width of 350(40) keV. The error bars include both statistical and two cases are given for the larger systematic uncertainties. The solid lines for the 2+ resonance represent fits to values of ro to illustrate the depen- the data used to determine the “observed” resonance parameters averaged over dence of the formal parameters on its the beam width (convolved). The dashed lines are results corrected for the beam value. A formal width of around 1.62 energy spread (unfolded). Similar results are shown for the well-known 1– state MeV is preferred since the value of the at 10.9 MeV.
22 Nuclear Physics News, Vol. 25, No. 3, 2015 facilities and methods
width tends to converge at this value applied physics problems. One ex- The first scheduled experiment as the value of ro increases above 1.8 ample of this has been the search for will be aimed at measuring the Gera- fm. Such a large ro value is not un- new means to measure the enrichment simov-Drell-Hearn (GDH) Sum Rule precedented, the R-matrix analysis of of various actinides, a problem that integrand for the deuteron below pion the Hoyle state by Barker and Treacy is of great concern to the Department threshold. First results on the value [8] required a large radius param- of Homeland Security. Studies at the of this integrand up to 20 MeV are eter (close to 1.8 fm) to reproduce the HIgS facility have shown that a mea- expected in the next year or so [12]. width of the Hoyle state. The current surement of the ratio of fission neu- Additional work on the photodisin- analysis suggests that both the Hoyle trons in the plane to those perpendicu- tegration of 3He [13] will extend our + 3 state and the 2 2 are extended objects. lar to the plane of polarization that are study of the GDH integrand for He A comprehensive multi-level R- produced when a 6.1 MeV g-ray beam to higher energies in both the 2- and Matrix theory fit to the data has been impinges on a sample consisting of 3-body channels. recently performed by Gerry Hale [9]. an admixture of 235U and 238U can be An experimental program to pro- This fit to the data indicates that this used to determine the enrichment of duce accurate values of the electric newly observed 2+ state is a Shadow the sample [11]. This is illustrated in and magnetic polarizabilities of the Pole comprised mostly (~75%) of the Figure 5, which shows the huge varia- proton and the neutron is also sched- 12 + 4.4 MeV 2+ state in C. The 2 2 state tion in the polarization asymmetry as uled for the near future. The use of po- is found to have an energy of 9.7 MeV a function of the enrichment, making larized beams will make it possible to and a formal width of 1.2 MeV. it easy to distinguish weapons-grade determine these quantities without in- The measured cross-sections and from reactor-grade uranium. voking any constraints, such as those the E1–E2 phase differences are given by the Baldin Sum Rule. Once shown in Figure 4 along with the two- these measurements are completed level fit to the data (with r0 of 1.4 fm). Future Prospects for the proton and the neutron, our at- It is interesting to note that the alpha- One of the major efforts presently tention will turn to measurements of decay width of the new 2+ state at underway at the HIGS facility is the the spin-polarizabilities via Compton 10.13 MeV exhausts 157(15)% of the commissioning of a recently installed scattering from an upgraded (scintil- Wigner limit. This strongly suggests Frozen Spin Polarized Target, intended lating) polarized deuterium target. that, like the Hoyle state, this 2+ state to provide polarized proton and polar- Beyond the next three to five years, is an a-cluster state, consistent with it ized deuteron targets. This target is we plan to commission a program on being an excitation of the Hoyle state. presently undergoing commissioning near threshold photopion production Finally, it is interesting to note that tests and calibrations, with data-taking from the proton in order to perform the predictions of the Bose-Einstein scheduled to begin in mid-2016. precision tests of the predictions of Condensate (BEC) model [10] are in reasonable agreement with the pres- + ent experimental results for the 22 + state. This model predicts a 22 state at 9.7 MeV with a reduced a-decay width of 1,200 keV, which is in rather good agreement with the observed ex- perimental value of 1,470 +160/–120 keV. This model also predicts a B(E2) value of 1.57 e2fm4 (Γϫ = 135 meV), in remarkably good agreement with the results of this experiment.
Applications In addition to confronting out- standing problems in fundamental physics, the HIgS facility has proven Figure 5. The measured values of the polarization asymmetries for a material to be a very valuable tool for many composed entirely of 235U and 238U as a function of the enrichment.
Vol. 25, No. 3, 2015, Nuclear Physics News 23 facilities and methods
the low-energy theorems of quantum 2. N. Pietralla et al., Phs. Rev. Lett., 88 chromodynamics calculated using chi- (2001) 012502. ral perturbation theory (ChPT), which 3. J. Beller et al., Phys. Lett., B 741 is based on the spontaneous break- (2015) 128. ing of chiral symmetry as well as ex- 4. S. S. Henshaw et al., Phys. Rev. Lett., 107(2011) 222501. plicit breaking due to the fi nite quark 5. W. R. Zimmerman et al., Phys. Rev. masses [14]. Lett. 110 (2013) 152502. The future of photonuclear physics 6. H. Fynbo, Inst. for Phys. and Astro., HENRY R. WELLER at the HIgS facility looks very bright, Aarhus Univ., and M. Gai, Univ. of Triangle Universities Nuclear indeed. Conn., private communication (2014). Laboratory (TUNL) and 7. W. R. Zimmerman, Ph.D. Disserta- Department of Physics, tion, U. Conn. (2013). Acknowledgments Duke University 8. F. C. Barker and P. B. Treacy, Nucl. The basic and applied nuclear Phys. 38 (1962) 33. physics research is supported by the 9. G. M. Hale, LANL, Los Alamos, NM, grants from the U.S. Department of private communication (2014). Energy, DOE (DE-FG02-97ER41033, 10. T. Yamala and P. Schuck, Eur. Phys. DE-SC0005367) and U.S. Department J. A 26 (2005) 185 and Y. Funaki, pri- of Homeland Security, Domestic Nu- vate communication (2013). clear Detection Offi ce (2010-DN-077- 11. J. M. Mueller et al., Nucl. Instr. Meth. ARI046-04). A 776 (2015) 107. 12. B. Norum, Physics Dept. U. Va., pri- vate communication (2015). M. W. AHMED References 13. G. Laskaris et al., Phys. Rev. Lett., 110 Triangle Universities Nuclear 1. Y. K. Wu e al., Phys. Rev. Lett. 96 (2013) 202501. Laboratory (TUNL); Department of (2006) 224801 and H. R. Weller et al., 14. A. Bernstein et al., Annl. Rev. Nucl. Prog. Part. Nucl. Phys. 62 (2009) 257. Part. Phys. 59 (2009) 115. Physics, Duke University; and Department of Mathematics and Physics, North Carolina Central University
More than 6500 nuclear scientists
read every issue of Y. K. WU NPN. Triangle Universities Nuclear Laboratory (TUNL) and Shouldn’t you be Department of Physics, Duke University one of them?
See the back cover to sign up for your own subscription.
24 Nuclear Physics News, Vol. 25, No. 3, 2015 facilities and methods
The g-Ray Beam-Line at NewSUBARU
NewSUBARU and Laser Compton- facility) and SACLA (X-ray free elec- the beam energy can be either accel- Scattering g-Ray Beams tron laser facility). Figure 2 depicts erated up to 1.5 GeV or decelerated The synchrotron radiation facility the g-ray production beam-line BL01 down to ~0.5 GeV. At 974 MeV, the NewSUBARU with nine beam-lines and experimental hutch GACKO. The top-up operation that keeps the beam is operated by the Laboratory of Ad- typical parameters of the gamma-ray current constant is possible as shown vanced Science and Technology for source are listed in Table 1. in Figure 3. At other beam energies, Industry, University of Hyogo, Japan. the stored current decays in time ac- Gamma-ray beams are produced in cording to beam lifetime. The beam Electron Beams the beam-line BL01 by laser Compton lifetime is determined by both scatter- In addition to the laser systems, scattering (LCS) from 0.5–1.5 GeV ing with gas molecules in the vacuum electron beams play an important role electron beams in the NewSUBARU chamber and intra-beam scattering to produce LCS photon beams. An storage ring [1]. Lasers with different due to the space-charge effect (Tous- electron beam is injected at 974 MeV wavelengths are used to produce the chek effect). The lifetime at 1.5 GeV in nominal energy from the SPring-8 LCS photon beam in the energy range is about 13 hours with an initial cur- linear accelerator (linac) [2] to the from 0.5 MeV to 76 MeV: a Nd:YVO rent 300 mA. 4 NewSUBARU storage ring whose RF laser (l = 1064 and 532 nm), a CO The spatial profile of an electron 2 frequency is 500 MHz. The electron laser (l = 10.59 mm), and an Er fi- beam is characterized by Gaussian beam involves 198 bunches along ber laser (l = 1540 nm). A new ex- functions in the horizontal and ver- the 120 m circumference that circu- perimental hutch, GACKO (Gamma tical directions. The standard devia- late at the revolution frequency 2.53 Collaboration Hutch of Konan Uni- tions s , s vary along the circum- MHz. Electrons from the linac can x y versity), was installed in the BL01 in ference of the ring as described by be injected into selected addresses. March 2012. s = √ b + (DE/E )2D2, s = √ b , An arbitrary filling from single bunch x x x 0 x y y y Figure 1 shows a bird-eye view of where , are horizontal and vertical to full-filling is feasible. After the x y the NewSUBARU facility along with emittances, b , b betatron functions, electron beam injection at 974 MeV, x y SPring-8 (8 GeV synchrotron radiation Dx horizontal dispersion function and DE/E0 energy spread of electron beams. The betatron functions calcu- lated with the MAD-X code [3] are shown in Figure 4 along the half of the ring circumference starting from the center of the straight section for the BL01, s = 0. Individual electrons oscillate around a closed orbit in both horizontal and vertical directions. The number of oscillations per betatron turn is 6.28 horizontally and 2.23 ver- tically. The natural emittance e0 at 974 MeV is 40 [nm-rad]. This value de- termined by magnet placement in the ring is a conserved quantity at a given energy and is proportional to the square of the energy. Ideally, a fi- nite emittance arises only horizontally (natural emittance) and zero verti- cally. But, in reality, a small part of the Figure 1. NewSUBARU synchrotron radiation facility. horizontal emittance is coupled to the
Vol. 25, No. 3, 2015, Nuclear Physics News 25 facilities and methods
Figure 2. The beam-line BL01 for g-ray production and the experimental hutch GACKO at NewSUBARU.
Table 1. List of energies and yields of LCS gamma-ray source at NewSUBARU.
Parameter/Lasers Nd(ω) Nd(2 ω) Er CO2 Laser wavelength λ 1064 nm 532 nm 1540 nm 10.59 mm Laser power (max) PL 35 W 20 W 4 W 7.5 W Gamma-ray energy Ee = 974 MeV 5–16.7 MeV 10–33.4 MeV 3.5–11.5 MeV 0.5–1.7 MeV (no collimator) Ee = 1470 MeV 8–37.6 MeV 15–73 MeV 5–25.7 MeV 0.7–3.9 MeV Yield (no collimator) Ee = 974 MeV 6000 γ/s/mA/W 3000 γ/s/mA/W 7000 γ/s/mA/W 7200 γ/s/mA/W Gamma-ray energy Ee = 974 MeV 15.4–16.7 MeV 30.5–33.3 MeV 10.6–11.5 MeV 1.57–1.7 MeV (3 mm φ collimator) Yield Ee = 974 MeV 2 × 106 γ/s 6 × 105 γ/s 3 × 105 γ/s 1 × 106 γ/s (3 mm φ collimator) I = 300 mA
vertical one. This factor, XY coupling Characteristics of LCS ing g-ray beams in the measurement k, is usually less than 1%. Thus, the g-Ray Beams of photonuclear reaction cross-sec- nominal horizontal and vertical emit- It is important to understand char- tions: (1) the absolute energy, (2) the tances are given by ex = e0/(1 + κ) = acteristics of laser Compton scatter- energy distribution, and (3) the fl ux. 39.6 [nm-rad], ey = e0κ /(1 + κ) = 0.4 [nm-rad]. A unique feature of the New- SUBARU is that the vertical beam size is intentionally enlarged to im- prove the Touschek lifetime during the ordinary beam time. To enlarge the beam size, we use a kicker called RF shaker that is composed of four strip- line electrodes on which RF power resonating with betatron motions is applied. As a result, the measured ver- tical beam size is a few times larger Figure 3. Variation of the electron beam current as a function of time in the top- than that without RF shaker. up operation.
26 Nuclear Physics News, Vol. 25, No. 3, 2015 facilities and methods
tral wave length of the P(20) transition is known (l = 10.5915 mm ± 3 Å) [7] with the bandwidth 1.3 Å in the full width at half maximum FWHM [8]. Including the bandwidth, the accuracy of the wavelength of CO2 laser is 4.1 × 10–5. A coaxial HPGe detector (64 mm in diameter × 60 mm in length) was used to measure the low-energy LCS g-rays. The HPGe detector was cali- brated with the standard g-ray sources, 60Co including the sum peak, 133Ba, 137Cs, and 152Eu and a natural radio- activity 40K. After the injection of 974 MeV electrons into the NewSUBARU storage ring, the electron beam was Figure 4. Betatron functions of the NewSUBARU storage ring. either decelerated to the nominal en- ergy 550 MeV or accelerated to 1460 MeV followed by a production of the For the determination of the absolute ing of laser photons from relativistic LCS g-ray beam and a measurements energy, electron beam energies of the electrons. LCS g-rays form a high- with the HPGe detector at every NewSUBARU storage ring were cali- energy edge by Lorentz-boosting laser energy. brated with high accuracy of the order photons that are Compton-scattered The response function of a HPGe of 10–5 [4]. The energy distribution is at 180° in the rest frame of electrons. detector to low-energy LCS g-ray determined by a Monte Carlo analy- Since the wavelength of laser photons beams is characterized by a full-en- sis of response functions of a large- is fixed with high precision, the edge ergy peak with a sloped high-energy edge reflecting the energy resolutions volume LaBr3(Ce) detector to LCS g- energy is sensitive only to the electron rays [5], while the flux determination beam energy. of the electron beam and the HPGe for pulsed g-ray beams is based on a To calibrate electron beams of the detector. The edge energy was de- Poisson fitting analysis [6] of pile-up NewSUBARU storage ring, a few termined by means of Monte Carlo spectra measured with a large-volume MeV LCS g-ray beams were produced simulation. The EGS4/PRESTA code [9], which simulates laser-Compton NaI(Tl) detector with 100% detection with a CO2 laser. As shown in Figure efficiency. 2, the beam-line BL01 has two colli- backscattering and interactions of g- The energy calibration of g-rays is mators; one (C1) in the storage ring rays with detector materials, was used. not a straightforward issue in the re- vault and the other (C2) in Hutch 1. Figure 5 shows an example of the de- gion of a few tens of MeV for a lack Both collimators are made of 10 cm pendence of the Monte Carlo simula- of proper calibration sources. A high- thick Pb. In the calibration experi- tion on the electron beam energy. The resolution germanium detector may ment, we used the C1 collimator with best fit to an experimental spectrum be used for calibration. However, an aperture of 6 mm diameter. The C2 with the electron beam energy Ee = the standard g-ray sources can cover collimator with an aperture of 2 mm 860.72 MeV is shown in comparison only low energies so that a linear ex- diameter defined scattering angle for with Ee = 860.72 ± 0.50 MeV and Ee trapolation to high energies may cause laser Compton backscattering. = 860.72 ± 1.00 MeV. Thus, the elec- uncertainties of ~50 keV around 10 An electron beam was injected tron beam energy was calibrated with MeV. Furthermore, a large-volume from the linear accelerator into the accuracy of the order of 10–5 in the Ge detector is needed to detect a high- NewSUBARU storage ring at the nominal energy ranges 974–550 MeV energy edge corresponding to the full- nominal energy 974 MeV. A grating- [4] and 974–1460 MeV [10], which energy peak for 10 MeV g-rays if it fixed CO2 laser (INFRARED IN- offers a standard for the energy cali- may fail to isolate a peak. STRUMENTS, IR-10-WS-GF-VP) bration of LCS g-ray beams produced Energies of LCS g-rays follow the oscillated at a single line of the stron- with a Nd:YVO4 laser (l = 1064 nm kinematics of the Compton scatter- gest master transition P(20). The cen- in the fundamental mode and 512 nm
Vol. 25, No. 3, 2015, Nuclear Physics News 27 facilities and methods
recorded with the LaBr3(Ce) detector along with the GEANT4 simulations of the detector response function (red dot- ted lines) and the incident g-ray beam (gray lines) [5]. Note that the energy of the response function is calibrated by the electron energy in the Monte Carlo simulation. The response functions are well reproduced by the GEANT4 simulation. Energy spreads of 1.2%, 1.4%, and 1.6% in the full width at half maximum (FWHM) were obtained for the three incident g-ray beams of 6.5, 10.0, and 13.0 MeV maximum energy, respectively. Thus a large-size Figure 5. Dependence of the Monte Carlo simulation on the electron beam en- LaBr (Ce) detector serves as a profi le ergy for the experimental response function of a HPGe detector to the LCS g- 3 monitor for the LCS g-ray beams. ray beam produced at the nominal electron energy 850 MeV. The best fi t was The fl ux of LCS g-ray beams is obtained with the electron beam energy E = 860.72 MeV. The sensitivity of the e currently monitored with a 8 × 12 simulation to E is shown in steps of DE = ±0.5 and ±1.0 MeV. e e NaI(Tl) detector to ensure 100% de- tection effi ciency for high-energy g- in the second harmonics) in the energy the response function of a 3.5 × 4.0 rays above several MeV. The electron region of a few to several tens of MeV. LaBr3(Ce) detector. For this purpose, beam bunches have a time structure We remark that the electron beam en- the effect of the electron beam emit- of 2 ns interval (500 MHz) and 60 ps ergy is excellently reproduced in ev- tance in the kinematics of inverse width. Both CW and Q-switch lasers ery routine of injection of an electron Compton scattering of laser photons are used to produce continuous and beam at 974 MeV followed by decel- from relativistic electrons was incor- pulsed LCS g-ray beams. The fl ux of eration and acceleration. porated into the GEAMT4 code in a continuous g-ray beam is determined The energy profi le of quasi-mono- conjunction with the ELI-NP project by direct counting of individual pho- chromatic LCS g-ray beams is deter- [11]. Figure 6 shows typical spectra tons. mined by a Monte Carlo analysis of of LCS g-ray beams (dark solid line) PHOTONEUTRON CROSS SECTIONS FOR SAMARIUM . . . PHYSICAL REVIEW C 90, 064616 (2014) Pulsed LCS g-rays are generated in bunches at the frequency of the Q-switch laser. The number of LCS g-rays per bunch is given by a Pois- son distribution [12] with a mean that depends on the probability of inter- action between the laser photons and the relativistic electrons. The number of recorded photons is obtained with an empirical formula of the “pile-up method” [6] based on the Poisson fi t- ting [12, 13]. The uncertainty of the Poisson fi tting is estimated to be 3%, which is attributed to the fi tting and the energy linearity of the g-ray detec- tor in its response to multiphotons. A typical example of the experimental Figure 6. Experimental response functions of a 3.5 × 4.0 LaBr (Ce) detector pile-up energy spectrum is shown in FIG. 3. (Color online) Energy calibration of the LaBr3 : Ce de- FIG. 5. (Color online) Typical spectra of the γ -ray beams3 137 60 138 to LCS g-ray beams (dark solid lines), GEANT4 simulations (red dotted lines), Figure 7 along with the single-photon tector with Cs, Co, and La and the maximum energies of LCS recorded with the LaBr3 : Ce detector (solid lines) and the simulations γ -ray beams produced using a Nd : YVO4 laser and electron beamsand energyof the distributions response function of LCS (dotted g-ray lines)beams and (gray of the lines). incident γ -ray beam spectrum. at energies between 573 and 850 MeV. (gray lines). A double collimation with a C1 collimator of 6-mm aperture and a C2 collimator of 2-mm aperture was employed. 28 Nuclear Physics News, Vol. 25, No. 3, 2015 is a systematic difference of approximately 10 MeV between the nominal electron energy given by the beam optics of the function (dotted line) and the incident γ -ray beam (gray storage ring and the calibrated energy. line). The spectra are renormalized for better visualization. The Compton backscattering of laser photons on relativistic The experimental response function was obtained without the electrons and the electromagnetic interactions of the γ -ray C1 collimator. One can see a broad low-energy bump around beams inside the LaBr3 : Ce detector were simulated by using 3 MeV in the response function. This bump is characteristic the GEANT4 Monte Carlo code [16,17]. The kinematics of of spectra obtained without the C1 collimator, which was the inverse Compton scattering is implemented in the Monte confirmed experimentally under the presence and absence of Carlo code with inclusion of the effect of the electron beam the C1 collimator. The bump corresponds to the laser photons emittance. The energy spectra of the LCS γ -ray beams incident Compton-scattered around 0◦ with large cross sections in on the targets were obtained by reproducing the LaBr3 : Ce the rest frame of electrons which, after a Lorentz boost by detector response. A detailed description of the GEANT4 relativistic electrons in the laboratory frame, punched through simulation is given in a separate paper [18]. the 10-cm C2 collimator. The punch-through component is Figure 4 shows a typical spectrum of the LCS γ -ray seen in the low-energy region of the incident γ -ray spectrum. beam recorded with the LaBr3 : Ce detector (solid line) Figure 5 shows typical spectra of the LCS γ -ray beams along with the GEANT4 simulations of the detector response recorded with the LaBr3 : Ce detector (solid lines) along with the GEANT4 simulations of the detector response function (dotted lines) and the incident γ -ray beam (gray lines). The experimental response functions were obtained by using the double collimation system with a C1 collimator of 6-mm aperture. The low-energy component is absent in the response function obtained with the double collimation system, which confines the scattering angles into a narrower cone along the electron beam axis with a total thickness of 20 cm. The experimental response functions are well reproduced by the GEANT4 simulation. Energy spreads of 1.2%, 1.4%, and 1.6% at full width at half maximum (FWHM) were obtained for the three incident γ -ray beams of maximum energy of 6.5, 10.0, and 13.0 MeV, respectively. Thus the LaBr3 : Ce detector is suitable for recording energy spectra of the γ -ray beams.
B. Target preparation 144 147 148 149 150 FIG. 4. (Color online) A typical spectrum of the γ -ray beam Enriched samples of Sm, Sm, Sm, Sm, Sm, 152 154 recorded with the LaBr3 : Ce detector (solid line) and the simulations Sm, and Sm in oxide form (Sm2O3) placed in pure of the response function (dotted line) and of the incident γ -ray beam aluminum containers with inner diameter of 8 mm were (gray line). A single collimation with a C2 collimator of 2-mm irradiated by the γ -ray beams. The samples were dehydrated aperture was used. by baking in vacuum at temperatures up to 393◦C for 4 h before
064616-3 D. M. FILIPESCU et al. PHYSICAL REVIEW C 90, 064616 (2014)
TABLE I. Enrichment and areal density of samples. collimator aperture, and the probability of interaction between the laser photons and the relativistic electrons. Sample Purity Areal density The number of recorded γ photons was obtained by using (%) (mg/cm2) the “pile-up method” described in [21], which is based on the Poisson fitting method originally developed at the Electrotech- 144Sm 88.80 1102 nical Laboratory [22,23]. The uncertainty of the Poisson fitting 147Sm 94.00 1042 method is estimated to be 3%, which is attributed to the 148 Sm 99.94 2102 fitting and the energy linearity of the γ -ray detector in its 149 Sm 97.72 2242 response to multiphotons. For each neutron measurement run 150Sm 94.68 862 152 we recorded the γ -ray spectra, when the laser is on in the full Sm 99.47 1959 power mode. Multiple photons were detected simultaneously, 154Sm 98.69 2253 generating a so-called pile-up spectrum. Before or after each neutron measurement run the laser power is reduced in order to obtain a single-photon spectrum, where it is most likely being placed inside the aluminum containers. The sample to measure only one photon at a time. A typical example masses were determined by weighing the containers before and of the experimental pile-up energy spectrum, along with the after the filling. The γ -ray beam was positioned at the center single-photon spectrum, is shown in Fig. 6. of the target by monitoring the visible synchrotron radiation as The number of γ rays detected in the NaI detector, Nγ,det, a guide. According to the GEANT4 simulation, the beam spot is given by on target is 2.3 mm in diameter, which is sufficiently smaller than the diameter of the target. The enrichment and the areal i pileup Nγ,det ⟨ ⟩ ni , (1) density of each sample are listed in Table I. = i single pileup ⟨ ⟩ where i ( xi ni )/( ni ) gives the average channel of C. Neutron detection ⟨ ⟩ = the pile-up and single-photon spectrum, and ni is the number The number of (γ,n) reactions was determined by detecting of counts in the ith channel. Note that the ratio of i in the reaction neutrons with a calibrated neutron detection array. Eq. (1) gives the average number of γ photons involved⟨ ⟩ in The samarium samples were mounted at the center of a 4π 3 a γ -ray beam pulse, while the sum pile-up events give the neutron detector composed of 20 He proportional counters number of γ -ray beam pulses. As the targets are quite thick, embedded in a 36 36 50 cm3 polyethylene moderator. 3 × × the attenuation of the γ rays in the target amounts to 2%–3%. The He counters were placed in three concentric rings of four, Furthermore, to calculate the average γ -ray flux incident on eight, and eight proportional counters located 3.8, 7.0, and the target we have to take into account the attenuation in the 10.0 cm from the beam axis, respectively. The moderator was NaI detector as well, surrounded by additional polyethylene plates with cadmium to suppress background neutrons. Every 100 ms of γ irradiation, Nγ,det Nγ , (2) facilities and methods reaction plus background neutrons were recorded for 80 ms µt µNaI = exp tt 1 exp tNaI of laser-on and background neutrons were recorded for 20 ms − ρt − − ρNaI of laser-off. The average energy of the reaction neutrons was obtained using the “ring ratio technique” originally developed by Berman and Fultz [19] and used to determine the detection efficiency. More details of the neutron detection are found in the literature [20]. Neutron detection efficiencies of the three rings were measured after the present experiment by using a calibrated 252 4 1 Cf source with an emission rate of 2.27 10 s− with 2.2% uncertainty at the National Metrology Institute× of Japan. The measurement excellently reproduced the results obtained HIROAKI UTSUNOMIYA in 2006 at the same institute, which can be seen in Ref. [20]. Department of Physics, Konan University, Kobe, Japan D. Beam flux monitoring
The γ -ray beam flux was monitored with a 6′′ 5′′ NaI(Tl) detector placed at the end of the LCS γ -ray beam line.× The Nd : YVO4 (λ 1.064 µm) laser operated at 20-kHz frequency = produces pulses of light of 60 ns in duration. The electron beamFigure 7. AFIG. pileup 6. (Color spectrum online) of a Experimental pulsed beam pile-up of LCS energy g-rays spectrum measured of with a bunches have a time structure of 2-ns interval (500 MHz) and6 × 5 NaI(Tl)the LCS detectorγ -ray beam and a obtained single photon with a spectrum. 6′′ 5′′ NaI(Tl) detector. 60-ps width. Thus, the LCS γ rays are generated in bunches A single-photon spectrum is also shown by× the dashed line. The corresponding to each laser light pulse. The number of LCSSummarymaximum energy of the LCS γ -ray 5. beam D. M. is Filipescu 13.03 MeV et al., (electron Phys. Rev. C 90 SATOSHI HASHIMOTO γ rays per bunch is given by a Poisson distribution [21] with aThe beamfundamental energy of characteristics 860.8 MeV). The average(2014) number 064616. of photons per LASTI, mean which depends on the laser and electron beam intensity,of LCS beamg-ray pulsebeams is 1.78.produced at the 6. T. Kondo et al., Nucl. Instrum. Meth. in Phys. Res. A 659 (2011) 462. University of Hyogo, NewSUBARU facility are examined Hyogo, Japan and064616-4 established well. Quasi-mono- 7. C. K. N. Patel, Phys. Rev. Lett. 13 (1964) 617. chromatic g-ray beams with energy 8. R. L. Abrams, Appl. Phys. Lett. 25, spreads of 1–2% in FWHM are pro- (1974) 609. duced with intensity of the order of 9. H. Ohgaki et al., Nucl. Instrum. Meth- 5 10 cps. One can gain higher intensity ods in Phys. Res. A 455 (2000) 54. at the cost of the monochromaticy 10. T. Shima and H. Utsunomiya, in Pro- by choosing a larger collimator. First ceedings of the Nuclear Physics and measurements of (g,n) cross-sections Gamma-ray Sources for Nuclear Se- were carried out for Nd [14] and Sm curity and Nonproliferation, January [5] isotopes. The LCS g-ray beam is 28–30, 2014, Tokai, Japan, ed. T. Hay- SHUJI MIYAMOTO LASTI, applicable to basic and industrial sci- akawa et al., World Scientifi c Publish- University of Hyogo, ence and technology from nucleosyn- ing, Singapore, 151–160. 11. I. Gheorghe et al. (unpublished). Hyogo, Japan thesis, photonuclear data, gamma ra- 12. T. Kii et al., in Proceedings of the 12th diograph, to nuclear security. Symposium on Accelerator Science and Technology, ed. Yasushige Yano References (The Institute of Physical and Chemi- 1. http://www.spring8.or.jp/en/about_us/ cal Research (RIKEN), Wako, Japan, whats_sp8/facilities/accelerators/linac 1999), 484–485. 2. http://www.lasti.u-hyogo.ac.jp/NS- 13. H. Toyokawa et al., IEEE Trans. Nucl. en/ Sci. 47 (2000) 1954. 3. http://mad.web.cern.ch/mad/ 14. H.-T. Nyhus et al., Phys. Rev. C 91 4. H. Utsunomiya et al., IEEE Trans. (2015) 015808. Nucl. Sci. 61 (2014) 1252.
Vol. 25, No. 3, 2015, Nuclear Physics News 29 meeting reports
11th International Spring Seminar on Nuclear Physics—Shell Model and Nuclear Structure: Achievements of the Past Two Decades
efi t of his suggestions, has maintained cialized seminars, going through four this tradition. The title “Shell model main topics: (1) From nuclear forces and nuclear structure: achievements to nuclear structure; (2) Exploring of the past two decades” recalls that nuclear structure toward the drip line; of the 2nd International Spring Semi- (3) Role of the shell model in the study nar “Shell Model and Nuclear Struc- of exotic nuclei; (4) Nuclear structure ture: where do we stand?” (1989). Its aspects outside the shell model. Focal scope has been, in fact, to discuss the points of current developments in the changes of the past two decades on study of nuclear structure and future our view of nuclei in terms of shell challenges have been highlighted from Figure 1. Map of Ischia (1590) shown structure as well as the perspectives of the experimental and theoretical point on the conference poster. the shell model, which has been one of view. Several talks have shown how of the key points in Aldo’s research. the advent of radioactive beams has This facet is well accounted for by the substantially improved our knowledge The 11th International Seminar on Opening Speech of Igal Talmi, one of of nuclear structure and how the next Nuclear Physics was held in Ischia the fathers of the shell model. generation facilities will open the way from 12 May to 16 May 2014. It was The program of the meeting con- to new perspectives. On the theory dedicated to Aldo Covello, who has sisted of general talks and more spe- front, the discussion focused on the been the promoter of this series of Seminars, which started in Sorrento in 1986 and continued with meetings held every two or three years in the Naples area. The main aim of these meetings was to offer to both theorists and ex- perimentalists the opportunity to dis- cuss their points of view on current achievements and future develop- ments of nuclear structure in a lively and informal way. We may read, in fact, as one of the motivations for Aldo’s election as Fellow of the American Physical Society in 2008 “... for his outstand- ing contributions to the international nuclear physics community by provid- ing, for over two decades, a venue for theorists and experimentalists to share their latest ideas” (ASP Fellowship, http://www.aps.org/units/fip/fellow ship/index.cfm). Figure 2. Pictures taken during the conference. From left to right, top to bottom: The 11th Seminar, organized by Al- 1. N. Itaco, L. Coraggio, T. T. S. Kuo; 2. M. J. G. Borge; 3. F. Iachello; 4. A. do’s former students and with the ben- Gargano; 5. I. Talmi; 6. A. Faessler.
30 Nuclear Physics News, Vol. 25, No. 3, 2015 meeting reports
progress made toward a microscopic is the fact that more than 50% of the theory capable of describing the prop- present participants attended one or erties of nuclei and nuclear reactions, more of the previous Seminars. with particular attention on our un- The presentations made at the derstanding of nuclear forces and on conference are available at the con- the new/improved methods to perform ference website: http://ischia2014. microscopic calculations. The role of na.infn.it, and the proceedings have symmetries in nuclear physics was been published by IOP in the open ac- also emphasized. cess Journal of Physics: Conference A session was dedicated to special Series, Vol. 580, 2015. topics as, for instance, the nuclear The Seminar took place in a pleas- astrophysical frontier and that of the ant thermal hotel located in Ischia, a neutrino physics, while the main con- volcanic island in Gulf of Naples, and clusions of the meeting were drawn was sponsored by the University and in two final keynotes talks given by the Department of Physics of Naples, Amand Faessler and Franco Iachello. and the Italian Institute for Nuclear The meeting has greatly benefited Physics. from the expertise of scientists who have significantly contributed to the Acknowledgments advancement of nuclear physics re- This report is written in Honor of search as well as from the large inter- Aldo Covello. national participation. In fact, the con- ference had about 90 participants from Figure 3. Aldo Covello at the confer- some 20 countries. This is well in line Angela Gargano ence dinner. with the tradition of these meetings, as INFN, Sezione di Napoli, Italy
Figure 4. Group photo from the 11th International Spring Seminar on Nuclear Physics, May 2014.
Vol. 25, No. 3, 2015, Nuclear Physics News 31 meeting reports
15th International Conference on Nuclear Structure: NS2014
TRIUMF was honored to host International Advisory Committee, fessor George D. Dracoulis, a pioneer the 15th international conference on 44 were selected to complement the in this field and a regular participant Nuclear Structure (NS2014) which 21 invited speakers. An additional 70 in this conference series, who passed was held from 20–25 July 2014 on contributions were presented as post- away in June 2014 at age 69. Although the campus of the University of Brit- ers. During the poster session an in- it is difficult to select highlights from ish Columbia (UBC) in Vancouver, ternational ad-hoc committee selected this comprehensive program, some of Canada (Figure 1). This biennial con- the best student presentations with the more intriguing experimental re- ference series has evolved to cover the the top three students receiving cash sults included decay spectroscopy of latest results on experimental and the- prizes and diplomas. the Element 115 daughters, the influ- oretical research into the structure of The conference began with invited ence of new beta-decay measurements nuclei at the extremes of isospin, ex- talks on experimental and theoretical with EURICA on r-process nucleo- citation energy, mass, and angular mo- investigations of the role of three-nu- synthesis, and direct evidence for a mentum. Special emphasis was given cleon forces in medium-mass nuclei. strong prolate deformation in the self- to the physics and techniques associ- The measured and predicted structure conjugate nucleus 72Kr. The confer- ated with gamma-ray spectroscopy; of neutron-rich nuclei were strongly ence concluded with updates on major however, atomic, mass, and charged- represented in the program. There gamma-ray detector arrays around the particle spectroscopy were also rep- were also selected sessions devoted world and nuclear physics research resented. This series is organized by to topics such as octupole and quad- facilities in North America. Electronic North American national laboratories, rupole collectivity, mirror or nearly versions of the oral presentations can and returned to Canada for the first mirror nuclei, nuclear tests of funda- be freely accessed through the website time since 1992. mental forces and symmetries, and su- http://ns2014.triumf.ca. Of the 180 abstracts contributed, perheavy nuclei. A session on high-K Outside of the lecture hall, the del- based on the recommendations of the isomers was dedicated to the late Pro- egates had the chance to visit some of
Figure 1. Attendees of the 15th International Conference on Nuclear Structure (NS2014).
32 Nuclear Physics News, Vol. 25, No. 3, 2015 meeting reports
UBC’s and Vancouver’s attractions, delayed neutron emission in 1939 including a tour of TRIUMF, an ex- with 12 talks dedicated to the ongoing cursion to Grouse Mountain or a boat and future projects in many radioac- cruise up the Indian Arm, and a visit tive-beam facilities around the world, including the conference dinner at the including TRIUMF’s ISAC and future UBC Museum of Anthropology. ARIEL facility. Representatives of the current and The organizing committee thanks prior organizing committees selected the International Advisory Committee Oak Ridge National Laboratory as the for their wise guidance, and thankfully GREG HACKMAN host of the next conference in this se- acknowledges generous funding from TRIUMF ries in 2016. our sponsors: Canberra, the Canadian Following the conference, about Institute for Nuclear Physics, the Divi- 25 participants joined the 1.5 day “3rd sion of Nuclear Physics of the Cana- North American Workshop on Beta- dian Association of Physicists, Simon Delayed Neutron Emission.” This Fraser University, University of Brit- year’s workshop celebrated the 75th ish Columbia, AAPS, Nordion, and anniversary of the discovery of beta- TRIUMF.
IRIS DILLMANN TRIUMF
READ LEARN DISCUSS PARTICIPATE
Vol. 25, No. 3, 2015, Nuclear Physics News 33 news and views
Extreme Light Infrastructure–Nuclear Physics (ELI–NP)
The project Extreme Light Infra- ration the scientific interest of ELI–NP tivities and it will host the main re- structure–Nuclear Physics (ELI–NP) is covering a broad range of key top- search equipment, the experimental [1], to build in Romania a European ics in frontier fundamental physics areas, laboratories and workshops, research center to study ultraintense and nuclear physics. The total cost of control rooms, and user area. The lasers interaction with matter and the facility will be 300 million euro, high spatial accuracy of the laser and nuclear science using gamma and without value-added tax (VAT). In gamma beams requires a special de- laser beams, ends in December 2014 September 2012, the project was ap- sign of the concrete base plate of the the second year of its implementa- proved by the European Commission building to prevent vibrations. The tion. The new research center will and the first phase was financed with state of the art equipment will require be located in Magurele, a town a few 180 million euro, with 83% financial special clean-room, temperature, and kilometers away from Bucharest, Ro- support from the existing Structural humidity conditions. The architect’s mania. The project is implemented by Funds cycle, which ends in 2015 and vision of the main buildings complex “Horia Hulubei” National Institute 17% from the Romanian National is shown in Figure 1. Other build- for Physics and Nuclear Engineering Budget. The second phase of financ- ings under construction are the office (IFIN-HH). ELI–NP will host two 10 ing will be granted in the next Struc- building, a guest house and a canteen. PW lasers and a gamma beam system tural Funds cycle which will start in The construction of the building com- producing gamma beams with param- 2015. The entire facility will be opera- plex started in May 2013 and will be eters beyond those available at the tional in 2018. completed in 2015. Figure 2 shows the present state of the art machines. At status of the construction in December ELI–NP two well-established scien- of 2014. tific communities, high-power lasers ELI–NP Buildings Complex and ELI–NP hosts two major research and nuclear physics, have joined their Major Equipment equipment with beyond state-of-the efforts to build a new interdisciplinary The ELI–NP main buildings com- art characteristics: a high-power la- facility and to define its research pro- plex, covering more than 15,000 m2, ser system (HPLS), with two arms— gram [2–4]. As a result of this collabo- is dedicated to the experimental ac- reaching up to 10 PW for each arm— and a gamma-beam system (GBS) that will provide very intense and narrow- band gamma-rays with energies up to 19 MeV. The high–power laser system of ELI–NP consists of two 10 PW lasers based on Optical Parametric Chirped Pulse Amplification (OPCPA) [5, 6] at about 820 nm central wavelength, with a dual front-end architecture with two parallel amplification arms. Each of the two parallel chains includes Ti: Sapphire amplifiers to bring the final output energy to the level ofa few hundreds of Joule. Subsequently, the pulses are compressed to around a 20 fs pulse duration that implies a peak power of 10 PW at a repetition rate of 1 shot per min for each of the Figure 1. The architect’s vision of the main buildings complex at ELI–NP. two arms [7]. Along the two amplifi-
34 Nuclear Physics News, Vol. 25, No. 3, 2015 news and views
Italy. A layout of the Gamma Beam system is displayed in Figure 4.
The ELI–NP Scientifi c Program The scientifi c case for ELI–NP was elaborated by an international collaboration of more than 100 scien- tists from 30 countries and published as the ELI–NP White Book [10]. It is based on the unique features of the high–power laser and gamma beams. The main research topics of inter- est are: laser driven nuclear physics experiments, characterization of the laser–target interaction by the means of nuclear physics methods, photonu- clear reactions, exotic nuclear physics and astrophysics. In addition to funda- Figure 2. View of the construction site of ELI–NP in December 2014. mental themes, applications of HPLS and GBS are under study. Accelerated cation chains, additional outputs with low cross-section for Compton scat- particles produced by laser-matter corresponding optical compressors tering will be compensated in obtain- interaction radiation-induced damage, will be installed. Their corresponding ing high brilliance gamma beam by and gamma beams–induced nuclear power levels are 0.1 PW and 1 PW very intense high repetition rate pho- reactions are major active research at repetition rates of 10 Hz and 1 Hz, ton beam, very intense low emittance areas in nuclear physics and engineer- respectively. For the two 10 PW out- electron beam and a very small and ing. Their applications extend from puts an unprecedented level of inten- precise interaction volume. The ELI– the nuclear power plants to medicine sity of about 1023–1024 W/cm2 will be NP GBS is being constructed by Euro- and from space science to material achieved. Out of the six possible out- GammaS [8], a European Consortium science. puts on the two arms, two of them, one of academic and research institutions The ELI–NP team, together with from each arm, can be provided simul- and industrial partners with expertise their collaborators from the interna- taneously for experiments, combined in the fi eld of electron accelerators tional scientifi c community, shaped in the same experimental setup or to and laser technology from 8 European the future scientifi c program of ELI– be used independently in two differ- countries, consortium led by INFN NP in a series of workshops and de- ent setups. The HPLS is being built by Thales Optronique France and Thales Romania (Figure 3). The Gamma Beam System (GBS) for ELI–NP was designed to provide a very intense and brilliant gamma beam with tunable energy based on the incoherent inverse Compton scat- tering of a high repetition pulsed laser beam on a high intensity, low emit- tance, relativistic electron beam. The electron accelerator will be a warm linac, with two acceleration stages of 360 MeV each [8, 9]. The gamma beam up to 19 MeV will have a band- width smaller than 0.5%. The very Figure 3. Schematic layout of the ELI–NP High Power Laser System (HPLS).
Vol. 25, No. 3, 2015, Nuclear Physics News 35 news and views
tures such as production of beams with solid target densities and large acceleration over very short distances. Laser acceleration of heavy ions will be investigated and the possibility to use it for nuclear reactions. The fl agship experiment involves production of neutron rich isotopes using fi ssion of Th and subsequent fu- sion process [12], to shed light on the Figure 4. General layout of the ELI–NP Gamma Beam System (GBS). formation of heavy elements (beyond Fe) in the universe. The needed data for the formation of heavy elements in fi ned ten development directions for liver accelerating gradients more than the region of lead (Z = 82) and beyond the facility. The Technical Design 1,000 times higher than in conven- are those related to very neutron-rich Reports (TDRs) are being fi nalized tional accelerator technology, reduc- isotopes. The fusion cross-section and in the fi rst part of 2015 will be ing the required accelerator length by even with secondary beams of radio- approved by the scientifi c community the same factor. This large increase in isotopes is so low that in practice these and by the ELI–NP International Sci- accelerating gradient for laser technol- key measurements are not within entifi c Advisory Board. ogy is the key to reducing the size up reach today. Using HPLS with a CD2 Eight experimental areas will be to a tabletop scale and reducing asso- production target and a very thin Th available for performing experiments ciated cost over conventional acceler- target, one may reach fusion of two using the laser beams, the gamma ators. It is expected that the compact, very neutron-rich isotopes originating beams or combined. high repetition rate, tabletop laser from the fi ssion of Th (e.g., fusion of will defi ne the future for laser-driven Z = 35) leading to this unknown mass Laser-Driven Nuclear Physics nuclear and particle phenomena [11]. region. First circular polarized laser Experiments The observation of high brilliance beam incident on production target One of the most exciting driving beams of multi-MeV protons from produces, through Radiation Pres- forces behind the studies of the high- solid targets has stimulated an enor- sure Acceleration (RPA) mechanism, intensity laser interaction with matter mous amount of studies. However, the a high density bunch of 232Th, 12C, is the perspective of obtaining laser- laser-driven beams have yet to achieve and D ions. Then fi ssion reactions will driven particles beams with charac- the quality of conventional accelerator take place. 232Th ion bunches interacts teristics similar to those obtained beams and, consequently, systematic with 12C (or 1H) in the 1st layer and with conventional accelerators but, studies should be performed in or- 12C and D nuclei interacts with 232Th potentially, much less expensive. The der to obtain mono-energetic particle in the 2nd layer of reaction target. Fol- present energy frontier of high energy beams. This novel technology must lowing their production, the two light physics is several TeV, but colliders be followed by the development of fi ssion fragments fuse in the reaction capable of reaching this regime are diagnostics and suitable detectors for target and neutron rich nuclei (close to very costly to build. Relatively expen- such beams with 108–1012 particles in N = 126) are produced. Such experi- sive are also the accelerators used for 1 ps pulse at 1–200 Hz repetition rate. ments require signifi cant experimen- science, hadron-therapy, or synchro- For this purpose, typical nuclear phys- tal development in the fi eld of laser- trons for material studies. Virtually all ics studies, with specifi c methods and driven ion acceleration in order to of today’s accelerators are using the tools, are extremely important for the produce intense heavy-ion bunches in electric fi eld generated between con- development of this new fi eld. the 5–10 MeV/u energy range relevant ducting electrodes or electromagnetic As a leading facility in laser-driven for fi ssion and fusion reactions. cavities. In this approach electrical nuclear physics, ELI–NP will take Experiments related to strong-fi eld breakdown limits the maximum fi eld advantage of the high intensity la- quantum electrodynamics are also to less than 100 MV/m. Laser-based ser beams. Acceleration of ions with planned. The tightly focused beams accelerators have the potential to de- high–power lasers offers unique fea- up to 1023 W/cm2 on solid targets will
36 Nuclear Physics News, Vol. 25, No. 3, 2015 news and views
be used for electron positron pair cre- citation energies, level widths, decay nation of the E1 or M1 type of excita- ation studies. The pair production can branching ratios, or spin quantum tion for the observed structures. be enhanced by combining the laser numbers and parities of the excited Photo-fission is also a topic where and gamma beams. nuclear states. ELI–NP gamma beam will bring sig- The high-repetition rate 0.1 PW The high brilliance, small band- nificant advances. So far bremsstrah- and 1 PW beams, where laser pulses width, and tunable energy of the lung was used to induce fission of produce relatively broadband spec- low-energy gamma beam may revo- actinide nuclei. Two classes of experi- trum of secondary radiation (elec- lutionize the characterization of nu- ments have been identified: investiga- trons, gamma, protons, neutrons and clear materials. The tunable-energy tion of the fission potential barrier and positrons), are proposed to study the gamma-ray beam can be locked on the the high efficiency production of neu- material behavior under extreme con- known excitation energy of the isotope tron rich nuclei through photo-fission ditions of radiation. to be located and identified (each iso- of U nuclei. High-resolution photo- tope has a unique fingerprint) and the fission of the second and third poten- energy response of the detectors will tial minima in actinide nuclei, angular Nuclear Science and Applications clearly indicate the location and pres- and mass distribution, cross-sections, with High Brilliance Low-Energy ence or absence of the isotope in the studies of rare photo-fission events, Gamma Beams bulk material (e.g., in a nuclear waste such as triple fission and highly asym- The ELI–NP gamma beam ex- container). This technique will be ex- metric fission will be investigated. perimental program will explore new tremely useful in the management of Gamma beams of 15 MeV are territory in the field of Nuclear Reso- sensitive nuclear materials and radio- highly efficient for producing short- nance Fluorescence (NRF) [13] and active waste for isotope-specific iden- lived and refractory elements in thin experiments above the particle separa- tification such as 238U/235U or 239Pu. U targets using a gas-cell catcher tion threshold such as studies of giant It will allow the scan of containers for (IGISOL technique). After their sepa- resonances, nuclear astrophysics reac- nuclear material and explosives, the ration, the nuclei of interest can be tions, and photo-fission experiments. inspection of spent fuel elements, and transported to different measurement The narrow bandwidth beam excites the quantitative measure of the final stations. a single excited state, whose decay is 235U/238U content in order to optimize The ELI–NP facility provides studied in the experiment. The excited the geometry toward the longer use unique opportunities for nuclear as- state can be below or above the par- (20%) of fuel elements in the reactor trophysics research. Gamma-induced ticle separation energy. In the former core. nuclear reactions of astrophysical in- case, the NRF method is applied and, An intense and high-energy resolv- terest still represent a challenge due to in the latter case, induced reactions, ing g–ray beam from ELI–NP will their very low cross-sections as the re- such as (g, n), (g, p), open up new horizons for the inves- actions occur deep below the Coulomb The low-energy gamma experi- tigation of the nuclear photo-response barrier. The study of these reactions ments (Eg < 3.5 MeV) shall be mainly at and above the separation threshold. will benefit from the use of the high dedicated to NRF experiments and Both the GDR and the PDR can be intensity gamma beams at ELI–NP. applications. Due to the brilliance of covered within the energy range of the Laboratory astrophysics experiments the gamma-ray beam, significantly in- ELI–NP beams. In the experiments the aiming at explaining the nucleosynthe- creased with respect to existing facili- excitation functions for elastic and in- sis processes will be possible, through ties, experiments on isotopes whose elastic scattering will be measured, re- direct or inverse reactions. To advance availability is very limited will be- vealing possible fine-structures/split- the explanation of the formation of a come feasible. This opens up an entire ting of the Giant Dipole Resonance large part of the known elements in the new area of applicability of the NRF (GDR) and the Pigmy Dipole Reso- Universe, reactions relevant for the p- method to isotopes that may be avail- nance (PDR). The excitation function and r-processes will be investigated. able only in quantities of a few mg, with high resolution for (g, n) and (g, All p-nuclei can be synthesized from like long-lived radioactive isotopes of charged-particle) channels, allows the the destruction of pre-existing nuclei heavy actinides. The NRF technique determination of the branching ratios of the s- and r-type by a combination allows the measurements of several for various decay channels. The polar- of (p, g) captures and (g, n), (g, p) or physical quantities, such as: the ex- ized beam will also allow the determi- (g, a) photo-reactions [14]. In particu-
Vol. 25, No. 3, 2015, Nuclear Physics News 37 news and views
lar, charged-particle detector systems, time. The gamma beams will also be The ELI–NP project is co-financed needed to measure nuclear reaction used to produce pozitrons in a con- by the Romanian Government and Eu- cross-sections of the proton and alpha verter foil via the (γ, e−e+) process. ropean Union through the European burning processes and—most impor- After moderation, the positrons will Regional Development Fund. tantly—the 12C(α, γ) reaction cross- be used for material science, as probes section relevant for stellar helium for defect spectroscopy to depths up to References burning, will be investigated. several 100 nm. 1. www.eli-np.ro In order to carry out the scientific 2. D. Habs, T. Tajima, and V. Zamfir, program discussed above, a number Conclusions Nucl. Phys. News 21 (2011), 23. of different state-of-the-art instru- The ELI–NP facility combines two 3. N. V. Zamfir,EPJ Web of Conferences ments are being considered. These in- major research equipment with beyond 66 (2014) 11043. clude: a high-resolution spectrometer 4. N. V. Zamfir, EPJ Special Topics 223 state-of-the-art parameters, namely a of (segmented) large HPGe (clover) (2014) 1221. high power laser system with two am- detectors, combined with good tim- 5. D. Strickland and G. Mourou, Opt. plification arms to deliver 10 PW and ing, for example, LaBr3 detectors, a Comm. 56 (1985) 219. intensities on the target in the range of spectrometer with medium resolu- 6. I. N. Ross et al., Opt. Commun 144 1023 W/cm2 at least every minute and, tion of large LaBr3 detectors and a (1997) 125. a gamma beam system to deliver up to 7. D. Ursescu et al., Proc. of SPIE 8780 neutron detector array, a tape station 19 MeV photons with extremely good (2013) 87801H-1. and a close-geometry spectrometer brilliance and bandwidth. Their out- 8. O. Adriani et al., Technical Design for high-resolution decay studies, a 4p standing performances will allow the Report; EuroGammaS proposal for charged-particle array of segmented exploration of new frontiers in nuclear the ELI-NP Gamma beam System, DSSSD detectors and a TPC gas cell physics. Benefiting from the support arXiv:1407.3669v1 [physics.acc-ph]. for astrophysics reaction measure- 9. C. Ur et al., Zakopane Conference on of a large number of specialists across ments. Nuclear Physics, 2014, Poland. the globe, the ELI–NP facility is on In addition, a variety of applied re- 10. ELI-NP White Book, eds. D. Habs track with TDR and construction of search experiments are proposed using et al. (2010), http://www.eli-np.ro/ the experimental areas. Commission- low-energy brilliant intense gamma, documents/ELI-NP-WhiteBook.pdf ing is expected to take place in 2018. neutron, and positron beams, which 11. G. A. Mourou, C. P. J. Barry, and M. D. Perry, Phys. Today 51 (1998) 22. will open new fields in materials sci- 12. P. G. Thirolf et al., EPJ Web of Con- ence and life sciences. The new pro- Acknowledgments ferences, 38 (2012) 08001. duction schemes of medical isotopes The ELI–NP project is the result 13. Ulrich Kneissl, Norbert Pietralla, and 99 [15] (e.g., Mo currently used in ther- of an international collaborative ef- Andreas Zilges, J. Phys. G: Nucl. apies, 195mPt for nuclear imaging to fort of more than 100 scientists from Part. Phys. 32 (2006) R217. determine efficiency of chemotherapy, 20 countries and their contribution to 14. K.-L. Kratz et al., Astrophys. J. 403 and 117mSn, an emitter of low-energy the definition and implementation of (1993) 216. Auger electrons for tumor therapy) the project scientific program is grate- 15. D. Habs and U. Köster, Applied Phys- via (γ, n) processes may also reach fully acknowledged. The tremendous ics B103 (2011) 501. socioeconomical relevance. Comput- work of the ELI–NP scientific team erized tomography with gamma-ray and the essential contribution of my Victor Zamfir beams for non-destructive inspection enthusiastic and tenacious colleagues ELI-NP, “Horia Hulubei” of objects will also benefit from high- from the Management team in the National Institute for Physics and energy quasi-monochromatic and high implementation of the project are also Nuclear Engineering (IFIN-HH), beam intensity to shorten the scanning deeply acknowledged. Bucharest-Magurele, Romania
______Be sure to check the Calendar for upcoming ______events of interest to nuclear scientists.
______38 Nuclear Physics News, Vol. 25, No. 3, 2015 news and views
IUPAP Young Scientist Prize in Nuclear Physics
This prize was established by IU- are open to all experimental and theo- contribution to and its direct impact PAP in 2005 at the time of the General retical nuclear physicists. The nomi- on the field. Assembly in Capetown, South Africa. nation package should contain, other Nominations for prizes to be The purpose of this prize, which con- than the nomination letter, at least two awarded at the next International sists of 1,000€, a medal, and a cer- additional letters of support, the cur- Nuclear Physics Conference, 11–16 tificate citing the recipient’s contribu- riculum vitae of the nominee contain- September 2016, in Adelaide, Austra- tions, is: ing also the list of publications. Three lia, are to be sent by e-mail by 1 De- To recognize and encourage very prizes will ordinarily be awarded at cember 2015 to the Chair of the IU- promising experimental or theo- the time of the tri-annual International PAP Commission of Nuclear Physics retical research in nuclear physics, Nuclear Physics Conference. (C12): Professor Alinka Lépine-Szily, including the advancement of a Nominations are due 1 December Institut of Physics, University of São method, a procedure, a technique, 2015 and are valid only until then. Paulo, [email protected], subject “IU- or a device that contributes in a The additional letters supporting the PAP prize nomination.” significant way to nuclear physics research. Candidates for the prize nomination should detail the expected must have a maximum of eight significance of the contributions of the years of research experience (ex- nominee to nuclear physics. To un- cluding career interruptions) fol- derline this, additional material such lowing the Ph.D. (or equivalent) as published articles can be added to degree. the nomination package. Especially Alinka Lépine-Szily Nominations by one or two nomi- information that allows the selection Institut of Phyics, University of nators (and distinct from the nominee) committee to evaluate the nominee’s São Paulo, São Paulo, Brazil
2015 - 2016 Free Event Listings
Conferences Workshops Schools
If you are planning a future event, ensure that the nuclear physics community is aware of it by sending the dates, location and contact details as soon as they are available to:
Vol. 25, No. 3, 2015, Nuclear Physics News 39 calendar
2015 November 10–13 July 11–15 Washington, DC, USA. 12th In- Halifax, Canada. DREB 2016 September 27–October 3 ternational Topical Meeting on Nu- http://conferences.triumf.ca/ Kobe, Japan. Quark Matter 2015 clear Applications of Accelerators DREB2016/index.html http://qm2015.riken.jp/ (AccApp’15) http://aad.ans.org/meetings.html August 8–12 October 1–3 Aarhus, Denmark. 23rd Euro- Osaka, Japan. “Frontiers of November 12–13 pean Conference on Few-Body Prob- gamma-ray spectroscopy” (Gamma Caserta, Italy. Workshop on Nu- lems in Physics 15) clear Asprophysics at SPES http://owww.phys.au.dk/~fedorov/ http://www.rcnp.osaka-u.ac.jp/ https://agenda.infn.it/ EFB23/ indico/event/829/ conferenceDisplay. py?confId=9725 August 28–September 4 October 4–11 Zakopane, Poland. Zakopane Kemer (Antalya), Turkey. Fifth December 1–5 Conference on Nuclear Physics 2016 International Conference on Nu- Medellín, Colombia. The XI http://zakopane2016.ifj.edu.pl/ clear Fragmentation NUFRA2015 Latin American Symposium on Nu- http://fias.uni-frankfurt.de/ clear Physics and Applications August 29–September 2 historical/nufra2015/ http://www.gfnun.unal.edu.co/ Helsinki, Finland. 9th Interna- LASNPAXI/ tional Conference on Nuclear and October 8–10 Radiochemistry (NRC9) Sofia, Bulgaria. Shapes and Dy- December 15–20 http://nrc9.it.helsinki.fi/ namics of Atomic Nuclei: Contem- Honolulu, HI, USA. International porary Aspects SDANCA-15 Chemical Congress of Pacific Basin September 4–10 http://ntl.inrne.bas.bg/events/ Societies, PACIFICHEM 2015 Kazan, Russia. VIII Interna- sdanca15/ http://www.pacifichem.org/ tional Symposium on Exotic Nuclei EXON2016 October 12–16 http://exon2016.jinr.ru/ Shanghai, China. 12th Interna- 2016 tional Computational Accelerator September 11–16 Physics Conference, ICAP’15 February 22–28 Adelaide, Australia. Interna- http://icap2015.csp.escience.cn/ Bormio, Italy. Third Topical tional Conference on Nuclear Phys- dct/page/1 Workshop on Modern Aspects in ics 2016 - INPC2016 Nuclear Structure http://www.physics.adelaide.edu. October 17–23 https://sites.google.com/site/ au/cssm/workshops/inpc2016/ Melbourne, Australia. 15th In- wsbormiomi2016/ ternational Conference on Accelera- September 11–16 tor and Large Experimental Physics March 6–11 Bruges, Belgium. International Control Systems (ICALEPCS 2015) Kanazawa, Japan. 12th Interna- Conference on Nuclear Data for http://www.icalepcs2015.org/ tional Conference on Low Energy Science and Technology ND2016 Antiproton Physics (LEAP2016) http://www.nd2016.eu/ October 19–23 http://leap2016.riken.jp/ Tokyo, Japan. Fifth Interna- October 30–November 4 tional Workshop on Compound- June 2–7 Fort Worth, Texas, USA. 24th Nuclear Reactions and Related Top- Kraków, Poland. 14th Interna- Conference on the Application of ics, CNR*15 tional Workshop on Meson Pro- Accelerators in Research and In- http://www.nr.titech.ac.jp/~chiba/ duction, Properties and Interaction dustry CAARI 2016 CNR15/index.html MESON2016 http://www.caari.com/ http://meson.if.uj.edu.pl/ November 1–7 Paphos, Cyprus. Electromag- June 19–24 netic Interactions with Nucleons Niigata, Japan. 14th Interna- and Nuclei (EINN) tional Symposium on Nuclei in the http://www.cyprusconferences.org/ Cosmos (NIC-XIV) einn2015/ http://nic2016.jp/
More information available in the Calendar of Events on the NuPECC website: http://www.nupecc.org/
40 Nuclear Physics News, Vol. 25, No. 3, 2015
View all the new and forthcoming physics titles at www.crcpress.com
.
SUBSCRIBE
Please photocopy this form and mail to:
Taylor & Francis -‐ Nuclear Physics News Subscriptions 530 Walnut Street, Suite 850 Philadelphia, PA 19106 USA
Tel: +1 215 625 8900 Fax: +1 215 207 0050 ☐ Nuclear Physics News: ISSN -‐ 1050 6896 Quarterly, € Volume 25 (2015)
☐ € ☐ Institutional Subscription (print + online) -‐ £669/ 885/$1109 Personal Subscription -‐ £80/ 109/$132 Complimentary Subscription for nuclear physicists ☐ ☐ from ☐ contributing countries Please print: BILL TO/SHIP TO: CHARGE: VISA MC AMEX
Name______Card#______Institution______Exp. Date______Address______Signature______Required for credit card ____ purchase. ______Telephone______
City______P.O. #______State______Date______Zip/Post______Country______☐ Make checks payable to Taylor & Francis in US funds only. E-‐mail______CHECK OR MONEY ORDER ENCLOSED