1 Lawrence Livermore National Laboratory Anton Tonchev Low-Energy Nuclear Physics with Laser Compton  -Rays FACET-II Science Opportunities Workshops October, 2015 SLAC National Accelerator Laboratory Menlo Park, CA

2 Outline  Low-energy dipole modes of excitation  High Intensity Gamma-Ray Source (HI  S)  Experimental techniques  Experimental results:  Pygmy Dipole Resonance: Fine structure of the E1 and M1 excitation below neutron separation  Nuclear astrophysics: s-process branching point nuclei  Nuclear application  Summary

3 Characteristic Response of an Atomic Nucleus after Gamma Absorption  ( ,tot) =  ( ,Xn) +  ( ,p) +  ( ,  ) +  ( ,f)  ( ,  ) +  ( ,  ’) Individual Resonance's Electromagnetic field radiation Massless particle Photon has angular momentum / l / = 1  After the electric dipole transition excited state must have J  = 1 -  JiJi JfJf E1

4  ( ,tot) =  ( ,Xn) +  ( ,p) +  ( ,  ) +  ( ,f)  ( ,  ) +  ( ,  ’) Reaction ( ,n) is dominant Reaction ( ,n)/( ,2n)/( ,3n)  1/10/1000 Reaction ( ,p)  ( ,n) up to 20 Reaction ( ,p) rapidly declines Characteristic Response of an Atomic Nucleus after Gamma Absorption Individual Resonance's

5 Positron Annihilation in Flight Most of the data measurements have been performed at LLNL Atlas of Photonuclear Reactions Thomas-Reiche-Kuhn sum rule:

6 Arthur Holly Compton ( ) 1927 Nobel prize in physics for study of the scattering of high-energy photons by electrons: Compton Effect

7 The High Intensity  -ray Source (HI  S) based on the OK-5 storage ring FEL OK-5 wigler Computer controls of the OK-4

8 E2 E1 P High-Intensity Gamma-Ray Source Buster synchrotron 34 m long storage ring e-beam from linac

9 E2 E1 P High-Intensity Gamma-Ray Source

10 E2 E1 P Example: E e = 500 MeV  FEL = 400 nm E ph = 3.11 eV E  = 11.9 MeV (2  ) 2 High-Intensity Gamma-Ray Source

11 High-Intensity Gamma-Ray Source

12 High-Intensity Gamma-Ray Source

13 How We Do It? 100% linear or circular polarization Quasi monoenergetic Tunable beam from 1 – 100 MeV Energy selection: collimation Gamma flux on target > 10 7 s -1 AXNAXN SnSn g.s.  Excitation energy E x  Spin and parity J,   Decay width  0  Branching ratio  i /  Experimental observables In a completely model independent way ! NRF Technique High-Intensity Gamma-Ray Source N. Pietralla, at al. PRL 88 (2001) HIGS Advantages  σ el = f(E γ ) (from primary g.s. transitions)  σ inel = f(E γ ) (from secondary transitions)  σ tot = σ el + σ inel = σ abs What makes HIGS unique?

14 Photon Scattering from Light-Mass Nuclei Ne +  Ground state transitions  0 HIGS detection sensitivities: ≥ resonance states with Γ tot ≥ 1meV R.J. De Boer et al. Phys. Rev. C 82, (2010) R. Longland et al. Phys. Rev. C 80, (2009) 26 Mg( ,  ’) 26 Mg MeV J  = 1 + Angular distribution

15 Photon Scattering from Light-Mass Nuclei Ne +  Ground state transitions  0 Branching transitions  f HIGS detection sensitivities: ≥ resonance states with Γ tot ≥ 1meV Secondary transitions R.J. De Boer et al. Phys. Rev. C 82, (2010) R. Longland et al. Phys. Rev. C 80, (2009) 26 Mg( ,  ’) 26 Mg MeV J  = 1 +

16 Characteristic Response of an Atomic Nucleus to EM Radiation SnSn P,n p n (  ) ( ,Xn) Giant Dipole Resonance: E x ~ MeV, B(E1) ~ W.u. Orbital “Scissors” mode: E x ~ 3 MeV, B(M1) ~ 3  N 2 Two Phonon Excitation: E x ~ 4 MeV, B(E1) ~ W.u. Pygmy Dipole Resonance: E x ~ 4 – 8 MeV, B(E1) ~ 1% EWSR M1E1 p,nn E1 ExEx Cross Section x10 x100

17 Enhanced Dipole Strength Observed strength in stable nuclei with moderate neutron excess (N > Z) Below the neutron-separation energy (S n ≈ 9 MeV) 1999 Govaert et al. PRC (γ,γ`) 2000 Hartmann et all PRL (γ,γ`) 2002 Ryezayeva et al. PRL (γ,γ’) 2004 Hartmann et al. PRL (γ,γ`) 2006 Savran et al. PRL (α,α) and (γ,γ`) 2006 Voltz et al. NPA (γ,γ`) 2008 Rusev et al. PRC (γ,γ`) 2008 Schwegner et al. PRC (γ,γ`) 2009 Savran et al. PRL (γ,γ`) 2011 Savran et al. PRC (γ,γ`) PDR ≤ 1% of the Thomas-Reiche-Kuhn sum rule

18 Enhanced Dipole Strength Observed strength in radioactive nuclei with excessive neutron excess (N > Z) Above the neutron separation energy: in double-magic nucleus 2005 Adrich et al. PRL ( 132 Sn, 9 Be) 2009 Wieland et al. PRL ( 68 Ni, 9 Be) 2008 Gibelin et al. PRL ( 26 Ne, 208 Pb) PDR ~ 5 -7% of the EWSR stable radioactive

19 Enhanced Dipole Strength Predicted in nuclei with proton excess (Z > N) 2005 Paar et al. PRL 2009 Paar et al. PRL PDR is independent of the type of nucleon excess (neutron or proton) => Generic mode of excitation Z / N Predicted pygmy quadruple resonance in charge-asymmetric nuclei (Sn isotopic chain) 2011 Tsoneva et al. PLB

20 Splitting of the Pygmy Dipole Resonance KVI TUD D. Savran et al. PRL, (2006), D. Savran et al. NIMA (2006), J. Endres et al. PRL 105, (2010) Coincident experiment E  = 130 MeV High energy resolution NRF experiment Real photons E  = MeV High energy resolution

21 Fine and Gross Structure of the PDR in 138 Ba Fine structureGross structure (keV) A. Tonchev et al. PRL 104, (2010)

22 What We Have Learned  PDR is indeed E1 mode of excitation  PDR is enhanced strength below the GDR  Correlation between the PDR strength and the thickness of the neutron skin  “Soft dipole mode“ at ~7 MeV is mixture of isoscalar and isovector components N. Tsoneva, H. Lenske, PRC 77, (2008), A.P. Tonchev et al. NIM B 241, (2005); A.P. Tonchev et al. AIP 819, 350 (2006); AIP 1090, 74 (2009); A.P. Tonchev et al. PRL (2010). 

23 Nuclear astrophysics: r-process 1998 S. Goriely PLB 2003 M. Arnold et al. PR 2005 T. Rauscher NPA Neutrino-less double-beta decay physics 2004 J. Bahcall et al. PRD; 2008 J. Schiffer et al. PRL; 2009 B. Kay et al. PRC 2013 P. Goddard et al. PRC J. Beller et al. PRL. Extract the γ-ray transition matrix elements for the decay (QRPA) Study of the structure difference of the initial and final states Neutron radius: PDR provides experimental constrains on properties of nuclear matter (neutron skin and symmetry energy) 2006 Piekarewicz PRC, 2010 P.-G Reinhard et al. PR®, 2011 Piekarewicz PRC Pygmy Dipole Resonance Impact 2008 Rusev et al. PRC (γ,γ`) 2008 Schwegner et al. PRC (γ,γ`) 2010 Schwegner et al. PRC (γ,γ`)

Lawrence Livermore National Laboratory LLNL-PRES Nuclear energy: high-intensity photon beams have the potential to treat nuclear waste and enable the use of an alternative fuel, thorium, for the production of nuclear energy Clean air and water: studies show that blasts of electrons from a particle accelerator are an effective way to clean up dirty water, sewage sludge and polluted gases from smokestacks Isotope production: photon beams are needed to produce a range of radioisotopes for medical diagnostics and treatments that are routinely applied at hospitals worldwide in millions of procedures annually Semi-conductors: The semi- conductor industry relies on accelerator technology to implant ions in silicon chips, making them more effective in consumer electronic products such as computers, smart phones and MP3 players Cross section data: high- intensive photon beams are needed to address important cross sections for nuclear astrophysics and weapon related physics Gamma activation analysis: unique, fast, and non-destructive nuclear analytical method with multi- element capabilities Active photon interrogation: a noninvasive technique in order realize sort or monitoring of radioactive wastes. It consists in using high energy photons to induce on nuclei photo nuclear reactions to transform them in short live radioactive nuclei Cancer therapy: when it comes to treating certain kinds of cancer, the best tool may be a particle beam. Hospitals use particle accelerator technology to treat thousands of patients per year, with fewer side effects than traditional treatments

25 Summary  We unveiled the fine structure of the E1 and M1 resonances  Significant inelastic strength with increasing the incident photon energy Open questions  Is statistical analysis fully applicable for the region of PDR?  Where does the low-energy tail of the GDR end? PDR M1 E2 GDR Ringing the Resonances N. Tsoneva, H. Lenske, PRC 77, (2008), A.P. Tonchev et al. NIM B 241, (2005); A.P. Tonchev et al. AIP 819, 350 (2006); AIP 1090, 74 (2009); A.P. Tonchev et al. PRL (2010).

26 Yale V. Werner N. Cooper F. Naqvi Kentucky S.W. Yates B. P. Crider E. E. Peters A. Chakraborty F. P. Estevez A. Kumar M.T. McEllistrem TUNLke: Duke: C.R. Howell E. Kwan R. Raut C. Bhatia G. Rusev A. P. Tonchev W. Tornow N. Carolina State: J.H. Kelley M. Gooden C. Huibregtse Univ. of N. Carolina: S. Hammond Participants Germany DU Darmstadt: N. Pietralla D. Savran M. Scheck C. Roming B. Leoher T. Aumann J. Isaak J. Beller B. Loher Cologne: A. Zilges J. Endres V. Derya Giessen: N. Tsoneva H. Lenske

27 Extra slides

28 Photon Scattering from Mid- and Heavy-Mass Nuclei SnSn E  = 8.4 MeV g.s. E  = 7.2 MeV E  = 5.4 MeV A. Tonchev et al. Proceedings of the Fourteenth International Symposium, Guelph, Canada, 28 August – 2 September 2011

29 N/Z B(E1) [10 -3 e 2 fm 2 ] 536 ± ± ± ± 153 But not so strong N/Z effect ! E1 Dipole Strength Distribution in N=82 Σ B(E1) increase with N/Z asymmetry

30 M1 Dipole Strength Distribution in N = 82 Nuclei Σ B(M1) increase with N/Z asymmetry N/Z Exp B(M1) [ μ N 2 ] 0.09 ± ± ± ± ± 0.41 QPM B(M1) [ μ N 2 ]

31 Enhanced Dipole Strength: Total Integrated Strength N. Benoaret et al. PRC 79, (2009) G. Rusev et al. PRC 77, (2008) R. Schwengner et al. PRC 78, (2008) R. Schwengner et al. PRC 76, (2007) R. Massarczyk et al. PRL 112, (2014) R. Schwengner et al. PRC 87, (2013)

32 A. Richter, 1998 Motivation: How to describe the coupling between the 1 + one- phonon QRPA doorway states to more complex configurations? The closed-shell nucleus 90 Zr exhibits a strong M1 spin-flip resonance result from transitions 1g 9/2  1g 7/2 In the past, the M1 resonance in 90 Zr have been measured in (p,p′), (e,e′) and ( ,  ′) reactions and the research was focused on comparison of the total strength with predictions from theory leading to a quenching from 1.6 to 4 depending on the probe. To answer these questions high-sensitivity polarization measurements are required Fine Structure of the M1 Strength in 90 Zr: a Key for Understanding the Role of “Quenching” p n

33 Fine Structure of the M1 Strength in 90 Zr: a Key for Understanding the Role of “Quenching”  135 E1 and 53 M1 transitions identified from E = 7 to 11 MeV.   EXP B(M1) = 4.5(4)  N 2 ; E c.m. = 9.0 MeV   QPM B(M1) = 4.6  N 2 ; E c.m. = 9.1 MeV  Center of gravity of M1 strength at 9.0 MeV N. Anantaraman et al. PRL 46 (1981) 1318 G.M. Crawley et al. PRC 26 (1982) 87 G. Rusev, N. Tsoneva, H. Lenske et al. PRL (2013) E γ = 8.10MeV, ΔE γ = 0.40 MeV

34 QRPA Calculations for the M1 Strength in 90 Zr G. Rusev, N. Tsoneva, H. Lenske et al. PRL (2013)  The experiment shows a rather fragmented excitation spectrum with many 1 + states, each of them with a strength lower than 1 μ N 2  M1 transitions are calculated with a quenched effective spin-magnetic factor g eff s = 0.8 g bare s  Calculated M1 strength at excitation energies between 7 and 11 MeV contains a considerable orbital part of about 22%  The two-phonon orbital strength is about ten times larger than the one-phonon QRPA-orbital strength

35 Capture reaction n + target  population of compound nucleus (CN) Subsequent decay by competition of  emission and neutron evaporation Theoretical description Hauser-Feshbach (HF) formalism: T  is the gamma transmission coefficient Challenge for calculations Accurate description of competition requires:  –ray strength function level densities optical model for n+target A+1 A E top EE CN populated SnSn  where T n is the neutron transmission coefficient n T  (E, J,  ) =

36 Direct measurement of the  strength function via ( ,  ’) measurement The  strength function is governed by low-energy transitions !!! The  strength function is governed by low-energy transitions !!! A+1 A E top EE CN populated SnSn n  Applicable for systems where A is stable and A-1 is a radioactive nucleus

37 HI  S facility neutron counter gamma counter m = g, 99.4% enriched

38 Obtained by statistical (HF) model HI  S facility R. Schwengner et al., PRC 87, (2013)

39 Fine Structure of the Electromagnetic Dipole Strength in 206 Pb Measured:  99 E1 levels (40 new)  28 M1 levels (23 new)

40 Fine Structure of the Electromagnetic Dipole Strength in 206 Pb 208 Pb Number of E1 states = 12 ΣB(E1)  = 1.23±0.11 e 2 fm 2 ΣB(E1) QRPA = 1.13 e 2 fm Pb Number of e1 states = 99 ΣB(E1)  = 0.91±0.17 e 2 fm 2 ΣB(E1) QRPA = 0.8 e 2 fm Pb Number of M1 states = 9 ΣB(M1)  = 13.09±0.30 m N Pb Number of M1 states = 28 ΣB(M1)  = 13.3±3.0 m N 2 N. Tsoneva, Preliminary QRPA calculations C. Bhatia et al. In preparation

41 Nuclear Dipole Polarizability from Tin isotopes PDR GDR σ 0 is the integrated cross section σ -1 is the first moment of the integrated cross section σ -2 is the second moment of the integrated cross section J. Piekarewicz 83, (2011)  -2 ~ e 2 R 2 A / 40 K

42

43 Experimental Technique: NRF SnSn 142 Nd E x = 9.2 MeV Fluence = 2.3x10 12 cm -2 Ground state transitions  0 Experimental Asymmetry g.s.

Lawrence Livermore National Laboratory LLNL-PRES-xxxxxx 44 Investigation of Photon-Strength Functions: 90 Zr case Zr( ,  ) spectrum at HIGS  Photon-strength function describes energy distribution of photon emission from high-energy states. f (E  ) =  Importance: Astrophysical network calculations; new fast nuclear reactors, statistical models. Preliminary results  E1 is the dominant multipolarity transition  Primary transitions are strongly dictated by the microscopic properties of the low-lying levels.  PSF is not smooth curve below the B n and E  > 4 MeV.  G. Rusev et al. PRC 77, (2008) 90 Zr

Lawrence Livermore National Laboratory LLNL-PRES-xxxxxx 45 Spin and Parity Determination

Lawrence Livermore National Laboratory LLNL-PRES-xxxxxx 46 Spin and Parity Determination B. Löher et al. NIMA 723, 136 (2013)

47 z y x Parity Measurements with a Linear Polarized Photon Beams DipoleAzimuthal distribution x z y 0 +  1 -   1 +  0 + M1‏ E E E Experimental Asymmetry of 0.96 Quadruple 0 +  2 +  0 + E z y x (θ,φ) = (90 0, 90 0 ) (θ,φ) = (135 0, 90 0 ) c E M2 0 +  2 -  0 + z x, 2 +, 2 - E1 E2 EiEi J=J= N. Pietralla et al. NIMA 483, 556 (2002), A. Tonchev, NIM B 241 (2005) 51474, G. Rusev et al. Phys. Rev. C 79, (2009), B. Löher et al. NIMA 723, 136 (2013)

48 Magnetic isoscalarisovector Electric monopole ΔL=0 dipole ΔL=1 quadruple ΔL=2 isoscalarisovector Classification of Giant-Resonance Modes

49 Schematic diagram of reaction network for the s-process

50  What is the character of the PDR? Electric or Magnetic?  What is the strength and energy distribution of the PDR?  What is the decay pattern of the PDR governed by the photon-strength function and level density?  Is the PDR a collective mode of excitation?  How this mode evolve with the excitation energy to the Giant Dipole Resonance? Experimental probe: photons (monoenergetic and 100% linearly polarized)‏ Experimental technique: Nuclear Resonance Fluorescence Motivation