Measurement of the 14 Be(p,n) 14 B(1 + ) Reaction in Inverse Kinematics

Transcription

1 XXVII Texas Symposium on Relativistic Astrophysics, December 8-13, Dallas, TX Measurement of the e(p,n) (1 + ) Reaction in Inverse Kinematics Y.Satou, Seoul National University e Y.Satou, et al., PL697(2011)459. Na Mg Si Al Ne Z=2 Z=8 H N=2 He N=8 Li e O N C N=16 (new) F 1. Spectroscopy of 2. Proportionality relationship: dσ dω q = 0 ~(GT) 3. Energy dependence of J στ 1

2 Relevance of weak processes in stars Weak interaction theory Neutrino hypothesis (Pauli) The first theory of weak interaction (Fermi, 1934) The universal V-A theory (Feynman, Gell-mann, 1958) Neutral weak current (1973) Weinberg-Salam theory (1967) Astrophysical implication Neutrino production as a cooling mechanism of stellar interiors [Urca Process] (Gamow, Schoenberg, 1940) remsstrahlung radiation of neutrino pairs by electrons (Pontecorvo, 1959) Neutrino trapping during a type-ii supernova (Freedman, 1974, Mazurek,1975, Sato, 1975) Accurate cross sections for weak processes among elementary particles, but not for processes involving nuclei For a calculation (involving nuclei) to be more reliable, experimental data must be available which test, constrain, and guide the models. K.Langanke and G. Martines-Pinedo, RMP 75 (2003)

3 β-decay (p,n) reaction β-decay rates and reduced transition probabilities (F) and (GT) ft = 67 F + g A g V F = 1 2I i + 1 f τ ± k Fermi Non-spin-flip GT = 1 2I i + 1 f σ k kτ ± Gamow-Teller k Spin-flip k 2 (GT) i i 2 2 Forward-angle (p,n) cross sections and (F) and (GT) dσ dω μ q = 0 = πħ 2 α = F, GT 2 ND J α 2 α Matrix element for charge-exchange reaction is similar to that of β decay in spin-isospin space. Examined for stable target (p,n) studies. Yielded (GT) inaccessible with β decay. C.D.Goodman et al.,prl44(1980)1755. T.N.Taddeucci et al., NPA469(1987)125. Limited applications for unstable nuclear beams. 3

4 Objectives of this work 1. Test the proportionality between σ(p, n) and GT for an unstable nuclear beam The e(p,n) reaction at 69 MeV N.Aoi et al., PRC66(2002)0301. log ft = 3.68(5), (GT)=0.80(9) dσ dω ΔL=0 q=0 = E i E f ħ 2 c 2 π 2 N D J στ 2 (GT) Z=2 2. Spectroscopy of ( F) V.Z.Goldberg et al., PL692(2010)307. F Z=8 H P.Maris et al., PRC81(2010)021301(R). He Li e O N C N=16 (new) F Ne Na Si Al Mg Sn=0.97(2)MeV 4

5 β-decay measurement γ-ray detector eam 17 Plastic counter β γ n n Neutron detector 17 β 17 C n 16 C γ β 16 N n 15 N γ β γ Stopper C Ueno et al., PRC87(2013)

6 In-flight charge-exchange decay measurement γ-ray detector eam e Target γ Magnet Neutron detector n Fragment Charged particle detector e S n E ex Charge Exchange n 13 M inv = E F + E n 2 P F + P n 2 E rel = M inv M F M n E ex = S n + E rel + E γ γ e Advantages: Daughter nucleus is subsequently removed. No limitation in excitation energy, dσ dω q GT/F, angular momentum l. High energy decay products focused along the beam axis (inverse kinematics). 6

7 ADC Z F1: Energy degrader (Al, 4.6 mm) Experiment at RIKEN-RIPS e e 69AMeV 13 RIPS: RIken Projectile fragment Separator Experimental apparatus TOF F0: Production target (e, 6 mm) P/P ±2% Intensity Secondary Target LH2 Target 7 kcps LH 2 : 229 mg/cm 2 A/Z neut DALI DC HOD 18 O 100AMeV e OMAG 7

8 σ (mb) Invariant mass spectra 1 + s 1/2 p 1/2 p 3/2 s 1/2 π 0-16 Positive parity ν DWA calculation scheme dσ dω X( ) χ b Φ V ba X (+) 2 χ a Φ A Optical potential: ruyeres potential (JLM): E.auge et al.,prc63(2001) KD02: A.J.Koning et al., NPA713(2003)231. CH89: R.L.Varner et al., PhysRep201(1991)57. Effective interaction: M3Y (ALTSO parameter): G.ertsch et al.,npa284(1977)399. One body transition density: WT interaction (0ħω): E.K.Warburton et al., PRC46(1992)923. Shell model code: OXASH:.A.rown et al., NSCL Report No. MSUCL DWA code: DW81: J.R.Comfort extended version. 8

9 σ (mb) Invariant mass spectra ? 0-16 Negative parity DWA calculation scheme dσ dω X( ) χ b Φ V ba X (+) 2 χ a Φ A Optical potential: ruyeres potential (JLM): E.auge et al.,prc63(2001) KD02: A.J.Koning et al., NPA713(2003)231. CH89: R.L.Varner et al., PhysRep201(1991)57. Effective interaction: M3Y (ALTSO parameter): G.ertsch et al.,npa284(1977)399. One body transition density: WT interaction (0ħω): E.K.Warburton et al., PRC46(1992)923. Shell model code: OXASH:.A.rown et al., NSCL Report No. MSUCL DWA code: DW81: J.R.Comfort extended version. 9

10 Differential cross sections Good reproduction of the angular distribution shapes for the 1 + and 4 - states Corroborating earlier J π assignments Tentative J π assignment of 3 + or 3 - for the 4.06 MeV state 1 + state at 1.28 MeV M.elbot et al., PRC56(1997)3038. N.Aoi et al., PRC66(2002) state at 2.08 MeV R.Kalpakchieva et al., EPJA7(2000)451. G.C.all et al, PRL31(1973)

11 Relative energy Invariant mass spectra or e Q β =16.2 MeV 4.06(5) MeV? 2.08 MeV #2 4 - Resonance parameters Er (MeV) Ex (MeV) r (MeV) l (ħ) J π 0.304(4) 1.27(2) 0.16(2) (5) 4.06(5) [1.0(3),1.2(5)] (1,2) (3 +,3 - ) 1.27(2) MeV #1 Sn=0.97(2)MeV 1 + (1 - ) n #1: Reported to be 1.28(2) MeV in Refs. M.elbot et al., PRC56(1997)3038. Aoi et al., PRC66(2002)0301. #2: Taken from Refs. R.Kalpakchieva et al., EPJA7(2000)451. G.C.all et al, PRL31(1973)

12 (GT) from 0-degree (p,n) cross section J στ = ± 3.1 stat ± 9.3 syst MeVfm 3 from 12 C(p,n) 12 N(1 + ; 61.9 MeV J στ = MeVfm 3 at 61(40) MeV W.G.Love in The (p,n) reaction and the nucleonnucleon fource (1980) Volume integral of the στ term of the NN int. dσ dω ΔL=0 q=0 = E i E f ħ 2 c 2 π 2 N D J στ 2 (GT) Method (GT) Comment Reduced transition probability for e(β - ) (1 +,1.27 MeV) β decay Kinematical 0.80(9) factor Aoi dσet dω (q al., = PRC66(2002) ) DW (p,n) reaction 0.79±0.03(stat)±0.09(syst) N D = This dσ work dω (q = 0) PW Shell model 0.88 Quenching factor of is included, W.-T.Chou et al., dσ dσ dω (q = 0) ΔL=0 dσ PRC47(1993)163. = dω ΔL=0 dσ q=0 dω (θ, q) dω θ, q exp From experiment 12

13 Energy dependence of J στ dσ dω ΔL=0 q=0 = E i E f ħ 2 c 2 π 2 N D J στ 2 (GT) M3Y J στ = ± 13.4 MeVfm 3 Franey & Love 13

14 Summary Measurement of the e(p,n) reaction in inverse kinematics. The CE reaction accompanied by neutron decay provides an alternative approach for nuclear structure to beta-delayed neutron spectroscopy. Er (MeV) Ex (MeV) r (MeV) l (ħ) J π 0.304(4) 1.27(2) 0.16(2) (GT)=0.80(9) (GT) (p,n) =0.79±0.03(stat) ±0.09(syst) 3.09(5) 4.06(5) [1.0(3),1.2(5)] (1,2) (3 +,3 - ) Energy dependent J στ (q = 0) was discussed. The e(g.s.) (1 + ) transition exhausts only a minor fraction of the GT sum rule: 3(N-Z)=18. Further studies locating the major GT strengths, together with studies on their astrophysical relevance, is appreciated.

15 Collaborators: RIKEN, R364n Seoul National University Y.Satou Tokyo Institute of Technology T.Nakamura, T.Sugimoto, Y.Kondo, N.Matsui, Y.Hashimoto, T.Nakabayashi, T.Okumura,M.Shinohara RIKEN N.Fukuda, T.Motobayashi, Y.Yanagisawa, N.Aoi, S.Takeuchi, T.Gomi, H.Sakurai, H.Otsu, M.Ishihara Rikkyo University Y.Togano, S.Kawai Tokyo University H.J.Ong, T.K.Onishi Center of Study (CNS) Tokyo University S.Shimoura, M.Tamaki Tohoku University T.Kobayashi, Y.Matsuda, N.Endo, M.Kitayama 15

16 Introduction Weak interaction plays a key role on astrophysical processes. Elementary weak processes are well understood. Weak interaction processes involving nuclei reduces the calculation to a nuclear structure problem. Small coupling parameters allow a perturbative treatment. For a calculation to be more reliable, experimental data must be available which test, constrain, and guide the models. Most of the data for exotic nuclei came from β-decay. The availability of radioactive beams will facilitate acquiring relevant data by energetic nuclear reactions, e.g., (p,n) reaction, with unique and different sensitivities. 16

17 E (MeV) E (MeV) Energy history of a 22M star as a function of time until core collapse Nuclear weak-interaction processes in stars K.Langanke and G. Martines-Pinedo, RMP 75 (2003) 819. Urca Process eta decay 15 Electron capture backresonances e + Z + 1, A Z, A + ν 2 Z, A Z + 1, A + e + ν 0 Finite T A~45 65 (Z,A) 1 GT + (Z+1,A) 5 0 8/29