Laser Driven Nuclear Reaction Studies

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Laser driven nuclear reaction studies: recent successes and new unique opportunities for future research Klaus M Spohr SUPA collaboration University of the West of Scotland & University of Strathclyde Overview

• Laser driven Nuclear Physics: Introductory remarks – Development of high power laser systems – History and milestone achievements in laser-nuclear research • Laser induced nuclear photo-proton reaction studies – Motivation for measuring sint(γ,p) of Mg-,Ti-, Zn- and Mo-isotopes – Methodology and setup of IOQ Jena multi TW laser system – Results for sint(γ,p) in Mg-,Ti-, Zn- and Mo-isotopes – Conclusions, opportunities and future challenges • Photonuclear reaction studies using laser induced Compton backscattering (LICB): proposed studies & vision – The principle of ‘Laser Induced Compton Backscattering’ – Motivation – LICB experiment on resonant photoabsorption of Mößbauer nuclei – Some final thoughts: induced nuclear emission (lasing) – Summary Introductory remarks Development of high power laser systems

HiPER NIF Development of high power laser systems

• Chirped Pulse Amplification (CPA) by Strickland and Mourou allowed intensities I > 1015 Wcm-2 – CPA (Strickland D and Mourou G, Opt. Comm. 56 (3) 219 (1985)) • Ultrashort laserpulse up to the petawatt level with the laser pulse being stretched out temporally and spectrally prior to amplification – CPA is the current state-of-the-art technique for all of the highest power lasers >100 TW • Currently strongest civilian systems – NIF @ LLNL, I > 1022 Wcm-2 – 2009 ASTRA/GEMINI @ CLF RAL I ~1022 Wcm-2 – Vulcan @ CLF RAL, I > 1021 Wcm-2 • HiPER project I ~ 5 ×1024 Wcm-2 (2020)

‘game-changers’ NYT, March 2009 Chirped Pulse Amplification

• Concept of Chirped Pulse Amplification (CPA) History and milestone achievements in laser-nuclear research

• 1996 Femtosecond quasi-monoenergetic keV-pulses (atomic physics) – Schoenlein R et al., Science 274 236 (1996) • 2000 Laser-induced nuclear fission of 238U – Ledingham K et al.,PRL 84 899 (2000), Cowan T et al.,PRL 84 903 (2000) • 2003 Laser-induced fusion evaporation reactions – McKenna P et al., PRL 91 (7) 075006 (2003) • 2006 GeV electron beams from a centimetre-scale 40 TW laser accelerator – Leemans W et al., Nature Physics 2 (10) 696 (2006) • 2007/08 Proton acceleration to 60 MeV and proton focussing – Robson L et al., Nature Physics 3 (1) 58 (2007), Schollmeier M et al., PRL 101 055004 (2008) • 2007 High order harmonic keV radiation (HOHG) of high brightness – Dromey B et al., PRL 99 085001 (2007) • 2009 Highest density of antimatter in solids (e+) (20 MeV) via Bethe- Heitler process n(e+)=1016cm-3 – Chen H et al., PRL 102 105001 (2009) Laser induced nuclear photo-proton reaction studies

The measurement of integral photonuclear cross-sections such as sint(γ, p) using nuclear activation is ideally suited for modern high power multi-TW laser systems

• Table-top Laser systems as competitive tool for nuclear studies – High intensity and hot bremsstrahlung spectra kT>2 MeV – Bremsstrahlung spectra spans over GDR regime ~8 - 35 MeV – Multi-TW Ti:Sapphire Laser system at the IOQ Jena, Germany Motivation for measuring sint(γ,p) of Mg-,Ti-, Zn- and Mo-isotopes • Nuclear Theory: cross-sections for p-emission and capture in plasma conditions, need to extend astrophysical data sets for low-Z isotopes: 25Mg,48,49Ti, 68Zn and 97,98Mo (feasible with method) – Hauser-Feshbach code • Applied: GDR-regime of interest for technological R&D work – nuclear power, shielding, radiation transport, radiotherapy, reactor development (transmutation studies) & medical applications – IAEA: encourages experiments esp. to retrieve reaction data in the region of the Giant Dipole Resonance (GDR) esp. for ~40 isotopes • Limitations and ‘old’ age of measurements – Values of sint(g, p) for only 40 different stable isotopes are published – Ratios: sint(g, n)/sint(g, p) for Z=12-42 needed! – Accuracy of old measurements • Probing and enhancement of nuclear models and reaction codes – EMPIRE, GNASH Methodology and setup of IOQ Jena multi-TW laser system

• Harvest the bremsstrahlung radiation of high-intensity laser generated relativistic electrons to induce reaction

– Quasi-Maxwellian distribution: Tγ  Te , McCall G,J Phys D 15 823 (1982) – Energy distribution of γ-radiation for temperatures achievable with multi- TW lasers extends over the full GDR-region • Measure the activity of the decay of the radioactive daughter nucleus • Characteristic g-rays of decay: intensity of photopeaks allows yield determination of original daughter products, hence sint(g, p) – Efficient Ge-detector system – Adjustments for: branching, detection efficiency (system, geometry), self- absorption, abundances; irradiation-, handling- and decay-time; contaminating reaction channels, target impurities and electro- disintegration • Introduced for laser nuclear physics by Stoyer et al. – Stoyer M et al., Rev Sci Inst 72 767 (2001) Schematic setup of IOQ Jena multi-TW laser system

laser pulse E0 ~ 600 mJ Activation tlaser pulse ~ 80 fs Activation targets: MgF2,Ti,Zn,Mo λ = 800 nm thicknesses~2-4 mm P ~ 7.5 TW 9 ne per pulse ~ 2 - 5 ×10 p~ 80 bar

(Elaser / Ee) ~ 0.6 - 1.5%

~5m

Liesfeld B et al., J Phys D 79 1047 (2004) Schwörer H et al., PRL 86 2317 (2001) Setup of target chamber

Target chamber

f/2-mirror

Target & radiator holder

He gas-jet nozzle Laser-room

university-scale system! Relativistic electrons from 10TW Laser-Gas Interaction Simulated e- density Simulated e- momentum distribution for different depths PIC simulations, Pukov A and Meyer-ter-Veen, PRL 76 (21) 3975 (1996)

- Spatial confinement of e- Energy of e (measured) (measured, E=18 MeV) 2×106

1×106

250 mrad 0 from Guiletti A et al., PRL 101 105002 (2008) Simulated γ-distribution after Ta-radiator and Mo-target (GEANT4) Experimental considerations & limitations

• Extraction & detection limit: 5 min ≲ t1/2 ≲ 200 days • kT measurement necessary with activation method • Bulk targets with natural abundances • Analysis: – Uncertainty from kT & Ge-efficiency – Activity is weighted with photon distribution and needs to be referenced to well known (g, n) channel in probe

– To extract sint(g, p) the three parameters determining the GDR have to res be assumed based on models: s , res(i), Eres(I) kT measurement via Ta-activation fitted kT=2.73(22)MeV Activation spectra: MgF2-, Ti- and Zn-probes ~only 8 min of laser activation, 5000 pulses with 3-5 x1019 Wcm-2 Observed photo-proton channels Measured and simulated photo-reaction channels in 25Mg

Experimental data & EMPIRE calculations

sint (g, p) deduced from EMPIRE calculation is fully reproducing measured sint (g, p) Results for sint(γ,p) in Mg-,Ti-, Zn- and Mo-isotopes Agreement with TRK sum-rule

35 NZ • TRK Dipole Sum Rule: s ~60 (MeVmb) 0 A

• TRK=Thomas Reiche Kuhn Sum rule 1925 – A standard benchmark for E1-strengths

• Aligned with data from Wyckoff J et al., PR 137 576 (1965) ─ Values of sint up to 35 MeV relative to the classical dipole sum rule show a monotonic increase with atomic weight – Correction factor ~ 0.85 - 1.25 Agreement with TRK sum-rule

2500 σ(γ,sn) from Lit. + σ(γ,p) Exp. TRK (folded with Wyckoff) 2000 only s(g,n) only σint(g,n) known 1500

[MeVmb] 1000 int

s s 500

0 25Mg 48Ti 49Ti 68Zn 69Zn 98Mo Isotope

Total σint values ~ σint (g,sn) + σint (g,p) show good to excellent agreement with the TRK-sum rule. For 97Mo no σint (g,n) known Agreement with known σint-values

this work Aligned acc. to branching 250 Literature 200 No errors given in 150 Literature values

[MeVmb] 100 int s 50

0 64Zn (g, 2n)62Cu 70Zn (g, n)69mZn Ivanchenko V et al., Carlos P et al., Goryachev A et al., P.ZHETF1 11 452 (1966) NP A258 3652 (1976) Yad.Fiz. 38 121 (1982) Reaction All three measured σint-values for different targets and particle channels that can be benchmarked with known data show good agreement

Known σint(g,n)/ σint(g,p) ratios (IAEA) p)

g, Experiment added 15% (

int towards all existing data!

 this work σ

n)/

(

int σ Conclusions, opportunities and future challenges • We measured a total of 6 new sint (g,p) values and hence deduced six new sint (g,n)/sint (g,p) ratios for light nuclei – First time laser driven research adds new data to nuclear physics – almost 15% of previously published data – Spohr K et al., New J Phys 10 043037 (2008) & New J Phys Best of 2008 collection • Conclusively proven that nuclear reactions can be produced and cross-section can be measured using table-top Laser systems – data agrees with TRK-sum rule – data agrees with EMPIRE calculations – data agrees with three previously known data-sets • A good base for a more extensive research investigation Conclusions, opportunities and future challenges

• Opportunity for extended campaign: – Determination of >110 new sint (g, p) measurable with university- scale multi-TW laser systems is possible

• ~90 lifetimes 5 min < t1/2 < 300 days (feasible)

• Challenge ~25 lifetimes t1/2 < 5 min • Challenges: – Use of isotopic enriched targets – Rapid transport mechanism (@ e.g. ELBE) – On-line measurement of prompt g-radiation – Deflection of electrons, separation with small Halbach magnets – Lowering the uncertainties of kT measurement – Multi-Ge-system in coincidence – Particle detectors in coincidence, radiation resistant detectors Conclusions, opportunities and future challenges

• Conjoined ELBE/Laser @ FZ-Dresden Rossendorf – SUPA has allocated beam-time quota – Elinac (40MeV) and 150 TW laser system (mid-2009) • We could use both systems and compare • 150 TW laser ~ E(e-) = ~80-90 MeV endpoint – Proposal to study sint (g,p) reaction of stable p-nuclei: • p-nuclei are neutron deficient (except 176Lu) nuclei that are shielded by their isobaric neighbours from production via the r-process and can not be produced by the s-process either • p-nuclei of astrophysical interest: 96Ru, 120Te, 130Ba, 156Dy, 162Er, 168Yb and 176Lu are feasible to study, yield improvement with new system ~103 • Understand formation of p-nuclei and support Hauser-Feshbach calculations • Higher power will give laser competitive edge over Elinacs Using different kT for evaluation of s(E)

Unfold cross-section by using different kT values, 1 MeV

K. Spohr J.J. Melone R. Chapman M. Shaw K. Ledingham W. Galster L. Robson P. McKenna T. McCanny K-U. Amthor B. Liesfeld R. Sauerbrey H. Schwoerer J. Yang The future strategy: harvest the unique capabilities of newly developed laser driven accelerator systems

Photonuclear reaction studies using laser induced Compton backscattering (LICB): proposed studies & vision Photonuclear reaction studies using laser induced Compton backscattering (LICB): proposed studies & vision

• Laser Inverse Compton Backscattering (LICB) – Cobald/ERLP system @ Daresbury (May 2009) & ELBE(40MeV)/150TW Laser (Spring 2010) – High brightness, ultra short, energy tunable source for low-lying quasi coherent, polarised gamma-radiation <30 keV (2009) – Proof of concept: Schoenlein R et al., Science 274 236 (1996) – Brightness: – Total Photons: – Brightness comparable to proposed 4th generation light sources (only approched by SPring8 in the moment) – Comparison with synchrotrons • + Much smaller (cheaper) systems • + Better time resolution • - lower repetition rate 10 Hz and hence total yield 10 to 100 lower – Cobald/ERLP: Priebe G, Spohr K et al., Las Part Beams 26 (4) 201 (2008) Photonuclear reaction studies using laser induced Compton backscattering (LICB): proposed studies & vision

• Motivation: – ‘Finest’ g-source available • Highest intensity & shortest steerable pulse duration – A new class of (g, g’) reactions allowing precise study of nuclear transitions (as of 2009: E<40 keV) • Population of isomeric states • Nuclear spectroscopy with high energy resolution • Nuclear lifetime measurements (direct measurements of fs-lifetimes and below!) , spectroscopic information – Coherent ensembles of gamma excitations in nuclei (excitons) • New quantum phenomena (quantum beats), ‘coherent nuclear physics’ • Enhancement of decay width – Resonance reactions to probe for existence of materials in probes The principle of Laser Induced Compton Backscattering

Superconducting Elinac

Cobald/ERLP @ Daresbury ELBE/150TW system is similar Cobald @ Daresbury LICB photons: the principle

• Laser light works like undulator on electrons • Electrons are deflected ~ 104 more often than in conventional magnetic undulators • LICB scattered photons remain partially coherent

Principle of SCAPA (SUPA2) project Laser/e-beam collision geometry

Normalised vector potential of the laser field ~undulator deflection parameter of static field

from Priebe G, …, Spohr K et al., Laser and Particle Beams 26 (4) 201 (2008) Spatial distribution of photon-energy

30 ]

kev

[ 2 γ 10

E ] [ 0 θ 0 0

100 collision angle 200 -2 Φ [] 300 scattered angle head on configuration transverse configuration

   2 E 2 g Eg  4g EL  30 keV E  15 keV g 2 Photon-energy vs scattered angle

Simulation

θ = π Motivation for studying isomers with LICB • Laser inverse Compton Backscattering present an unique opportunity for studies into the laser induced pumping of nuclear states – Ideal cases: short lived Möβbauer isomers:161Dy, 57Fe,181Ta – Questions: feasibility and efficiency, new coherent phenomena? |2>

LICB E1

|1> Baldwin G and Solem J, Rev Mod Phys 69 (4) 1085 (1995) 161Dy Einstein A, Phys Zeit 18 121 (1917) LICB experiment on resonant photoabsorption of Mößbauer nuclei

• High brightness of impacting pulsed photon-beam complicates detection of resonant absorbed and re-emitted γ-radiation – Target spins within ultra-fast rotating spindle, mapping of time into spatial domain – Röhlsberger R et al., PRL 87 (4) 047601 (2001) Nuclear Lighthouse Effect

e.g.161Dy Rotors up to 70kHz LICB - γ

fast rotor

Avalanche Photo Diode LICB experiment on resonant photoabsorption of Mößbauer nuclei

• Will reveal insight into new coherent nuclear physics phenomena – Ensemble (>1000) of coupled nucleons in the same state of excitation (excitons) – Exciton stationary or migrates through the probe with slow speeds (polaritons) • E.g. Nuclear Lighthouse effect • Quantum beats as different hyperfine components interfere – Decay rate is increases, hence the absorption line-width – Even more so, if an ensemble of polaritons is created – Estimate: 161Dy ~ 2 x 108 detectable 25.7 keV g-rays in 5 days experiment, 181Ta ~5000 detectable 6.2 keV g-rays in 5 days • Based on natural and measured line-widths, conversion coefficients, resonant excitation cross-section, mass attenuation coefficient, recoilless f- fraction of Mossbauer nuclei, brightness and spatial beam distribution • Cobald functional May 2009, Future in STFC? .... A word on controlled amplification

nuclear systems Some final thoughts: induced nuclear emission (lasing) • Cross section at resonance: • Radiative width  |2> -> |1> into stable g.s.: – For lasing: problem population inversion, many nuclei in g.s. level – Small for long lived isomers! Never feasible for bulk targets • Decay from unstable state |2> into unstable state |1>:

– Inversion population if N(|2>) > N(|1>)

• Possible for T2 > T1 • Favourable ‘pumping reaction’ to enhance population of |2> • Favourable branching b=1 and low conversion a small

– Decay times are somewhat similar, as for T2 >> T1, ss is small – Resembles Four-level pumping scheme of optical lasers Some final thoughts: induced nuclear emission (lasing)

Pumping nuclear reaction e.g. photonuclear type High energetic levels Laser induced!

|2> LICB

g |1>

g.s. Some final thoughts: induced nuclear emission (lasing) • Stedile generated population inversion via NRF in stable 103Rh – |2> = 357 keV, (5/2-) t=107 ps and |1> = 295 keV, (3/2-) t=9.8 ps – ‘Generating an inversion on a nuclear transition - Photopumping of 103Rh’, Stedile F, Hyper Inter. 143 (1-4) 133 (2002) • A thought… for something new: Use bremsstrahlung radiation to create population inversion via NRF with high yields (high rep rate) and then impinge quasi-monochromatic matching γ- energy from LICB on target! – For the moment: yields by far to small – Need effective high yield pump (high power and repitition laser accelerator) and LICB laser system – Identification of favourable isotope 103 • Rh not ideal, Eγ=62 keV too high …, – 2 high power laser systems: MBI Berlin (~2011) Summary • Laser Nuclear physics offers promising research into new phenomena at the interface of two very diverse areas of research – Will it become a mainstream field in Nuclear Physics in the UK? – As of March 2009: 4 researchers (Strathclyde & UWS) • Laser driven nuclear physics has just begun to deliver the goods for applied and fundamental new nuclear research – Integrated cross-section measurements – Ability to reach high kT values and hence to derive effective photodisintegration rates in high temperature plasma • Though facing tremendous challenges, British-led efforts could be crucial for the exploitation of new systems using Laser Inverse Compton backscattering – LICB systems have the potential to add a new unique quality to nuclear research – Study of resonant photoabsorption is ideally suited to harvest these systems – Something really new and challenging

In Memory of Dr Wilfred Galster 1948-2009

The next generation IOQ Jena multi-TW laser system

Single diode pump station of 150TW-system (5 total) @IOQ Start: 04/2008 Simulated bremsstrahlung-spectra in Ta-radiator (MCNPX) 1

0.1

0.01

0.001

0.0001 Flux(MeV/cm^2)

0.00001

0.000001 0 1 2 3 4 5 6 7 8 9 10 Energy(MeV)

kT=2.91MeV kT=5MeV kT=7MeV kT=4MeV kT measurement

• First to be determined: kTg – By activation method

– Very well known cross-sections allow best-fit of kTg – Two independent measurements • 181Ta(γ,n)180Ta and 181Ta(γ,3n)178Ta

– Intensities: I103keV with t1/2=8.15 hrs and I426keV with t1/2=2.36 hrs – N (178Ta) / N (180Ta) = 3.06(48) x 10-4, with Ge-detector

– Uncertainty: I103keV, literature value, influence of electro-disintegration reactions (e,e’) was ~20% (no e--rejection) – Measured kT=2.73(33) MeV • 12C(γ,n)11C and 63Cu(γ,n)62Cu – Both β+ giving rise to 511 keV annihilation • Influence of electro-disintegration (e,e’) dramatically reduced – N (11C) / N (62Cu) = 8.58(13) x 10-3, with NaI coincidence system – Uncertainty: low intensity in 11C, ~ 2 counts/s – Measured kT=3.09(23) MeV • Accepted result: kT=2.90(23) MeV Measured and simulated photo-reaction channels in 66,67Zn

Experimental data & EMPIRE calculations

sint (g, p) deduced from EMPIRE calculations are reproducing measured sint (g, p) Spatial distribution of photons

0 Y (mrad)

-5

-10

-15

-20 -30 -20 -10 0 10 20 30

X (mrad)

Backscattering angular distribution; each colour is a 1 keV energy band with 20- 21 keV on outside and 30-31 keV at centre Photon brightness vs photon energy

Simulation