Overview of the Rare Isotope Science Project of the Institute for Basic Science

New Physics: Sae Mulli, Vol. 66, No. 12, December 2016, pp. 1458∼1464 http://dx.doi.org/10.3938/NPSM.66.1458

Sunchan Jeong∗ Rare Isotope Science Project, Institute for Basic Science, Daejeon 34047, Korea

(Received 16 November 2016 : revised 13 December 2016 : accepted 13 December 2016)

The Rare Isotope Science Project of Institute for Basic Science was launched in 2011 with the unprecedented aim of constructing a heavy-ion linear accelerator complex in Daejeon, Korea. The goal of the accelerator complex, named RAON, is to produce a variety of stable and rare isotope beams for studies in basic sciences and various other applications. Powered by a 400 kW superconducting linac, the facility is intended to establish In-flight Fragment and Isotope Separation On-Line facilities and to run those facilities simultaneously to become the most effective producer of rare isotope beams worldwide. The prototype construction of the major accelerator components is almost complete, and subsequent testing is ongoing. We briefly introduce the RAON accelerator and the experimental systems, together with RAON’s theoretical activities. The current status and the short-term prospects of the Rare Isotope Science Project are also presented.

PACS numbers: 81.05.Ea, 85.30.Tv Keywords: Astrophysics, Condensed matter physics, Nuclear physics, Particle physics, Physics education

I. INTRODUCTION ISOL (Isotope Separation On-Line) system and a post- accelerator also for the ISOL system. The ISOL and Under the International Science Business Belt (ISBB) the IF systems can be operated simultaneously and in- project by Korean Government, Institute for Basic Sci- dependently for most effective production of RI (rare iso- ence (IBS) was established in November 2011 to provide tope) beams in the world. In addition, the rare isotopes a creative research environment for basic science and produced in the ISOL can be injected into the Driver thereby to promote basic sciences in Korea. Just one Linac for accelerating the rare isotope beam (RIB) to month after IBS, Rare Isotope Science Project (RISP) even higher energies or for use in IF system to produce was launched with a challenging goal to construct a rare even more exotic rare isotopes. Therefore, RAON will isotope beam facility as a key research facility of IBS, certainly provide unique research opportunity worldwide called RAON. RISP is going to complete RAON by De- for nuclear physics and nuclear astrophysics as well as cember 2021 and its total budget is 1.44 billion USD including accelerator and experiment systems, civil en- applied fields such as bio- and medical-science, neutron gineering and conventional facilities. Out of 1.44 BUSD, science, and materials science. For a recent overview of 460 million USD was initially assigned for accelerator and RISP, we refer to [1]. experimental apparatus. The total budget including the budget for civil engineering and conventional facilities was approved in June 2014. II. RAON ACCELERATOR SYSTEMS RAON will be equipped with a heavy ion linear ac- The goal of the RAON accelerator complex is to pro- celerator as the driver for the IF (In-flight Fragmenta- tion) system, a proton cyclotron as the driver for the duce variety of stable and rare isotope beams to be used for researches in basic science and various appli- ∗E-mail: [email protected] cations. The RAON consists of three superconducting

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. ≪ Review Article ≫ Overview of the Rare Isotope Science Project of the Institute for ··· – Sunchan Jeong 1459

Fig. 1. (Color online) Layout of RAON.

is going to have both the Isotope Separation On-Line (ISOL) and In-Flight (IF) fragmentation methods to produce rare isotope beams far from the valley of stability. As summarized in Fig. 2 the two methods are comple- mentary. For the production of radioactive nuclei, the ISOL has a much greater advantage (about 104 times) than the in- flight method due to the target thicknesses and primary beam intensities available for production. For the in- Fig. 2. (Color online) Comparison of the two RIB pro- flight method, only an electromagnetic separator isnec- duction methods. essary. However, more factors are involved for the ISOL method including the efficiencies of extraction from the linacs of which superconducting cavities are indepen- target materials and ionization. dently phased and operating at three different frequen- To go one step further, RAON has a challenging plan cies. In order to meet the diverse demands on beam to combine the ISOL and IF system to produce the more species and energies, it can deliver various stable ions exotic RI beams with a greater intensity, namely 80% of from protons to uranium atoms and rare isotope beams all isotopes predicted to exist for elements below ura- with energies variable from the injector energy. For the nium. The ISOL system, probably with actinide tar- extensive discussion on RAON accelerator systems, we gets, is to be used to produce high-intensity beam of refer to [2]. neutron-rich isotopes of the easiest-to-extract elements (i.e., fast diffusion and effusion in the target materials), III. RAON RI PRODUCTION SYSTEMS and then the produced RIB is to be accelerated to an energy enough for projectile fragmentation. The in-flight The primary goal of RAON is to study unexplored technique for fast separation can be then applied to ob- territory of the nuclear landscapes. To this end, RAON tain beams of very neutron rich nuclei. 1460 New Physics: Sae Mulli, Vol. 66, No. 12, December 2016

Produced rare isotopes will be used for and will be studied at various experimental facilities of RAON. Now, we give a brief introduction of the ISOL and IF systems. For the extensive discussion on RAON RI production and experimental systems, we refer to [3].

1. ISOL

The ISOL technique has been mainly developed at CERN/ISOLDE in order to separate rare isotopes of interest from the produced target fragments. This type Fig. 3. (Color online) Science territory of RAON. of facility requires some additional complicated systems including an ISOL-system and an accelerator for radioac- acceptances and two-staged separation. The large accep- tive ions. High efficiencies are required at each stage of tances allow RI beams produced by projectile fragmen- production; ionization, separation, and transportation. tation as well as U-fission fragmentation method. The These developments are inter-related and thus many de- RAON IF uses an electromagnetic separator to separate velopments are still necessary. Especially, one has to and guide rare isotope beams to experimental halls for extract the rare isotope of interest from the bulk of the further studies. production target. The rate-determining steps are the The major technical challenges will be a high power diffusion and effusion of the rare isotope in the target production target, high power beam dump for removing materials, the rate of which depends on the combina- primary beam, a HTS (high temperature superconduct- tion of target material and element to be extracted, and ing) magnet in a hot cell region, and large aperture su- is often slow compared to the lifetime of the nuclide of perconducting magnet. The design of the IF system has interest. been completed and the prototyping of each component The ISOL system of RAON will be derived by a 70- is currently underway. MeV cyclotron that will induce fission on a direct fissile The rare isotope beams separated from the IF sepa- 14 target with a rate of 10 fissions/s. Short-lived neutron- rator will be delivered to the high energy experimental rich isotopes mostly with mass range 80 < A < 160 are facility; for instance, LAMPS to study exotic state of expected to be produced by fission in a hot (about 2000 nuclear matter and nuclear symmetry energy. ◦C) target. The fission-product beam isolated by ISOL will be post-accelerated by a superconducting linear accelerator SCL3 for low energy experiments. Recently, we IV. RAON EXPERIMENTAL SYSTEMS successfully extracted Sn-isotopes via a laser ionization and made a large LaCx target with 50 mm in diameter. The science programs of RAON include the study of exotic nuclei, hadrons in nuclei or in nuclear matter, equation of state of nuclear matter, origin of heavy ele- 2. IF ments, limits of nuclear existence, energy generation of stars, chemical history of the universe, compact stellar IF system is another main device to produce and sep- objects like neutron stars, etc. Though there may not be arate RI beams using 400 kW primary beams at RAON a great chance, together with supercomputers, RAON and is derived by a 400kW superconducting linear accel- might be able to contribute significantly to understand- erator system, where U beam could be accelerated up to ing nuclear physics in terms of its underlying theory such 200 MeV/u. The RAON IF separator is featured by large as QCD (quantum chromodynamics). ≪ Review Article ≫ Overview of the Rare Isotope Science Project of the Institute for ··· – Sunchan Jeong 1461

Fig. 4. (Color online) RAON experimental systems.

Also, RAON is going to play important roles in applied energy and angular distribution, and the determi- sciences; some of such applications include finding new nation of nucleon occupancy in single particle or- materials, mutating cells or DNA, nuclear data evalua- bit (inelastic scattering, (d,p) reaction, nucleon re- tions, and development of new heavy ion cancer therapy moval reaction, etc). methods. √ Study of soft dipole and Pygmy dipole resonances Fig. 3 summarizes the scientific scope of RAON. using nuclear probe, e.g., α, Ca and Pb. To achieve such scientific goals, RISP has been devel- √ oping experimental systems along with the accelerator Direct measurement of charged-particle capture and RI production systems. Those seven experimental cross section, e.g., for 15O(, γ) reactions at < 1 systems are pictured in Fig. 4. MeV/nucleon. Among them, we briefly touch on the main science √ topics of KOBRA and LAMPS. Indirect measurement of radiative capture cross The main physics goal of KOBRA is to gain complete section, e.g., for (d,p) reaction at a few understanding on the structure of exotic nuclei and nu- MeV/nucleon. clear reactions important in astrophysics. Since the nu- LAMPS is another key experimental system for nuclei are closed or open quantum many-body system to be clear physics. The main physics to be probed by LAMPS ultimate playground of non-perturbative QCD, it should is the properties of nuclear matter above the saturation be very important to understand clearly the properties densities with large isospin asymmetry. Isospin asymme- of nuclei and their interactions, such that we can sense try is defined as the neutron and proton number differ- our nature and figure out the laws of nature from fun- ence divided by the sum of the two. Attractive phenom- damental principles. Now, we list some specific topics of ena associated with isospin asymmetric nuclear matter KOBRA. include nuclear symmetry energy, phase transitions in √ Study of shell evolution in proton- and neutron- nuclear matter, in-medium modification of chiral con- rich nuclei such as the measurements of excitation densate and hadron masses, and finding new exotic state 1462 New Physics: Sae Mulli, Vol. 66, No. 12, December 2016

Fig. 5. (Color online) RAON theory flow chart. Fig. 6. (Color online) The comparison of the results about various s-shell and p-shell nuclei from JISP16 and of nuclear matter. As well known, understanding nu- Daejeon16. The figure it taken from the talk by J. Vary clear symmetry energy is one of key issues for studying at RISP in 2015. neutron stars. Idaho N3LO nucleon-nucleon (NN) interaction and ap- ply to it phase-equivalent-transformation (PET) which V. RAON THEORY remains scattering phase shift and bound state energy of two-body systems intact but can modify other properties The theory group at RISP was launched in September, of many-body systems. The optimal set of PET parame- 2012 with primary goals to achieve a thorough under- ters are determined to describe the binding energies (and standing on rare isotopes using traditional and modern spectra for some cases) of several selected light nuclei. theoretical frameworks, to interpret the results of forth- We call this newly optimized nuclear force ‘Daejeon16’; coming experiments and to help planning future experi- Daejeon is from the location of RISP and 16 is from 16 O ments at RAON. Since then, theoretical tools have been which is heaviest nuclei used in fitting process [4]. Dae- attached to RAON theory group starting with the DNS jeon16 provides improved data about light s-shell and (Di-nuclear system) model for the production of exotic p-shell nuclei compared with other existing interactions. nuclei and synthesis of SHE (super heavy elements) and Furthermore, neutron rich isotopes located far from sta- the ab initio no core shell model for structure of light nu- ble valley are also well described. For example, in the clei. We have developed nuclear transport codes to un- case of He isotopes, not only stable 4He but also unsta- derstand physics involved in heavy ion collisions in terms ble 6He and 8He results agree mostly with experimental of experimental data, based on the quantum molecu- values. We are currently working on Li and Be isotope lar dynamics and the Boltzmann-Uehling-Uhlenbeck ap- chains using the Dajeon 16 interaction. Also, the reso- proach (Daejeon BUU). Also, to sharpen the scientific nance state of tetra-neutron can be expected from the goals of the experimental systems of RAON, the RAON ab initio calculation using Daejeon16 with the help of a theory group keeps intimate collaborations with experi- recently developed technique. mentalists at RISP. The theoretical methods of RAON theory group as of 2016 and some correlations among different approaches are summarized in Fig. 5. VI. PRESENT STATUS AND Among theoretical achievements made so far by SHORT-TERM PROSPECTS RAON theory group, we briefly discuss an improved nuclear force developed by RAON theory group through Developments of the RAON accelerator and experi- international collaborations, which will be useful for a mental systems stays on track with civil constructions. wide range of applications to nuclear structure and reac- Prototyping of major components of the accelerator sys- tions. To obtain improved nuclear force, we start from tem is almost finished and their test is on-going. We ≪ Review Article ≫ Overview of the Rare Isotope Science Project of the Institute for ··· – Sunchan Jeong 1463

Fig. 7. (Color online) Time-line of the project. Some important milestones are also marked. extracted successfully stable beams from ion sources for 500keV/u (RFQ linac energy) to the energies in maxi- the SCL1 and the ISOL system at the end of 2015 at ion mum around 18.5 MeV/u (U) and 90 MeV (p) according source test benches, and accelerated beams at the off-site to their A/q values, to the very low- and low-energy ex- test facility are expected in 2017. perimental halls. This facility, though part of the whole The construction site for the facility was confirmed in facility, is supposed to be unique and hence highly com- the middle of 2014 as Sindong, located about 10 km from petitive in terms of available beam energies and variety the center of Daejeon. Currently, RAON site preparation of beams. is under progress. For the conventional facilities, the site To show the entire plan of RISP and to visualize which will be available for buildings accommodating accelerator is available when, we finish this section with the RISP complex at the beginning of 2017, for utilities at the end milestone schedule given in Fig. 7. of 2018. Installation and commissioning of accelerator and experimental systems will be going on accordingly. From next year, the fabrication of major components VII. SUMMARY will start. Especially, putting the highest priority on early completion of the low-energy facility by the end of The RISP, launched for the construction of the RAON 2019 as strongly recommended by the RISP-IAC (inter- heavy ion accelerator complex, has reached the half national advisory committee) in this August, we are on way stage of the project period. Various R&D issues the process of the procurements of major components of have been addressed from scratch through our persis- the SCL3 for starting fabrication of those major com- tent efforts. In this short article, we briefly introduced ponents next year. The low-energy facility consisting of RAON accelerator and experimental systems together the cyclotron, ISOL system and SCL3 will deliver various with RAON theory activities. We also summarized stable and RI beams with variable energies from around present status and short-term prospects of the RISP. In 1464 New Physics: Sae Mulli, Vol. 66, No. 12, December 2016 closing, it is hoped that RAON will be a major play- REFERENCES ground for those who have genuine sprit of sciences and be a key player in basic sciences in the world. [1] S. Jeong, in Proceedings of the IPAC 2016 (Busan, Korea, 2016), p. 4261. [2] J. Kim, W.-k. Kim, H.-m. Jang, Y. Kim and I. Shin ACKNOWLEDGEMENTS et al., New Phys.: Sae Mulli 66, 1491 (2016). [3] T. Shin, B. H. Kang, G. D. Kim, Y. J. Ki and Y. K. This work was supported by the Rare Isotope Science Project of Institute for Basic Science funded by Ministry Kwon et al., New Phys.: Sae Mulli 66, 1500 (2016). of Science, ICT and Future Planning and National Re- [4] A. M. Shirokov and I. J. Shin, Phys. Lett. B 761, 87 search Foundation of Korea (2013M7A1A1075764). (2016).