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% ~5m 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 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)/ g, ( 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 <kT <10 MeV Collaborators K.