Nuclear Reactions with light ion and photon beams; Contributions to Neutrino Astrophysics

Transcription

1 Nuclear Reactions with light ion and photon beams; Contributions to Neutrino Astrophysics 1. Incompressibility and Giant Resonances (ISGMR, ISGDR) 2. Charge exchange reactions 3. Photon Beams for (g,g ), (g,n) M. Fujiwara: NNR05 Dec.2 4, 2005 CAST/SPring-8, Japan

2 In the supernova explosion processes, the iron core absorbs electrons via the electron capture process, and the core is dominated with neutron excess nuclei. This process proceeds at 0 In the region 0, the core become hard Rebounding happens Explosion Thus, an important factor for supernova explosion is the hardness of the core with neutron excess nuclei. Incompressibility snr.html Isotope dependence of Incompressiblity K sym N Z A 2

3 Two Major Unsolved Issues in Nuclear Incompressibility 1. Different K A (K )values from ISGMR and ISGDR 2. From the same GMR data, Non-relativistic and Relativistic calculations gave different K values; 220 MeV non-rel. 270 MeV rel. The first of these has been resolved. With the background-free spectra, ISGDR strength at higher Ex than before. Now, same calculations give reasonable agreement with E GMR and E ISGDR. The second issue still remained unsolved.

4 There was the consensus among the theorists that the Primary difference between the non-relativistic and relativistic calculations comes from the symmetry energy term. K A K (1+cA -1/3 ) + K sym ((Ν Ζ)/Α) 2 +Κ Coul Z 2 A -4/3 K sym = MeV; not well obtained B.A. Li, PRL 85, 4221 (2000), B.A. Li, C.M.Ko, and W. Bauer, Int. J. Mod. Phys. E7, 147 (1998). B.A.Li, W.Udo, Nova Science Publishers. R.J. Furnstahl, nucl-th/ Clearly the (N-Z)/A term is very important in nuclear structure, heavy ion collision, astronuclearphysics. The widest range of (N-Z)/A in an isotope series (in medium and heavy mass nuclei) is in Sn: 112 Sn Sn 0.194

5 Uchida et al., PRC (α,α ) spectra at 386 MeV 116 Sn ISGDR ISGDR ISGMR ISGMR MDA results for L=0 and L=1 ISGDR ISGDR ISGMR ISGMR

6 Giant Resonances By M. Itoh for RCNP experiments L=0 L=1 T=0 L=0 ISGMR L=1 ISGDR L=2 ISGQR L=3 ISGOR ISGMR L=2 L=3 ISGDR T=1 L=1 IVGDR ISGQR ISGOR

7 Giant Resonance studies at RCNP, Texas, KVI. Isoscalar 1977 Isovector 1983 Monopole Dipole Quadrupole By A. Krasznahorkay

8 Experimental data on ISGMR ISGMR energy E ISGMR Recent data Recent data

9 Grand Raiden spectrometer RCNP cyclotron facility Faraday Cup for 0 deg. Target M. Fujiwara et al., NIM A 422 (1999) He ++ beam

10 Energy Spectra GR = 0deg ND, RCNP, KVI, Kyoto, Konan collaboration GR = 0deg 124 Sn 116 Sn Counts 112 Sn 118 Sn Counts 114 Sn 120 Sn Excitation Energy (MeV) Excitation Energy (MeV)

11 Data Analysis Background rejection with the focal plane detector system of the spectrometer Grand Raiden. (a) one-dimensional spectrum along the vertical direction. Background events correspond to the hatched area.true and background events are in the central region. (b) The energy spectra for the true + background events, and for the background Events. (c) Difference spectrum for true events.

12 Multipole-decomposition analysis 124 Sn(, ) σ exp ( x = L L x calc L θ, E ) a ( E ) σ ( θ, E ) x Cross sections DWBA calculations (L=0 15) and IVGDR cross section

13 L=0 Breit-Wigner function σ ( E ) σ = m ( E E 2 m ) + Γ m 112 Sn 114 Sn 116 Sn 118 Sn 120 Sn 122 Sn 124 Sn E m (MeV) m (MeV) ,114,118,120,122,124 Sn : this work 116 Sn : Uchida et al.

14 ISGMR energy E ISGMR Final data analysis

15 E K A m < r = ISGMR h 2 > K A K (1+cA -1/3 ) + K sym ((Ν Ζ)/Α) 2 +Κ Coul Z 2 A -4/3 c =-1 K Coul = -5 G. Colo et al. PRC (2004) -580 < K sym < -380

16 Effects of the in-medium nucleon-nucleon cross sections Free -space xsection -550 < K asy < -450 MeV close to that extracted from Osaka giant resonance data in-medium xsection 0.7 < γ < 1.1 in fitting E sym =32( / 0 ) γ Bao-An Li et al., ND workshop July 14-15, 2005; Bao-An Li and L.-W. Chen nucl-th/

17 Calculated by Jorge Piekarewicz

18 208 Pb(γ pol,γ), E γ =7.8 MeV 80 Counts/ 4 kev ,E ,E ,E ,E σ(0 ) Positive Parity σ(90 ) Negative Parity Photon Energy (MeV) Baumer et al., Phys.Rev. C 71, (2005) KVI Fujiwqara et al., Phys.Rev.Lett. 85 (2000) RCNP (d, 2 He), (t, 3 He), ( 7 Li, 7 Be) SN explosion, nuclear Synthesis, (e,e ), (g,g ), (p,p ), (a,a ) Supernova, (p,n), ( 3 He,t) Solar neutrino detection, Double beta decay,

19 Zegers et al, NSCL, RCNP, KVI, ORSAY

20 Anglo Australian Observatory SN1987A About 50 kpc distance from the earth Neutrinos were detected about 2 hrs later than the optical observation. ν? e ~20 events were confirmed at Kamiokande and IMB First (and only so far) neutrino detection from outside of the solar system Because of water Cerenkov method, almost all the neutrinos were n e :? e + p n+ e +

21 Nakanishi et al., RCNP, KVI, ORSAY, Kyoto, Konan, Neutrino Flavors and Energy Distributions Cross Section: Coupling constant of weak interaction σ ~10-42 cm 2 ~10 15 Smaller than cross sections in ordinary nuclear reaction More neutrons than protons at core + n p+ e? e + p n+ e CC reactions (n p exchange) easily happen. The radii of Neutrino sphere are different in flavors. Prediction of neutrino energy distribution <E(n e )> = 11 MeV <E(n e )> = 16 MeV <E(n x )> = 25 MeV Average energies depend on supernovae explosion model.? e + The first purpose is to measure energy distributions. Equation of neutrino state and transimissivity can be known. A. Burrows, Annu. Rev. Nucl. Part. Sci 40, 181 (1990).

22 Neutrino Detection via 208 Pb CC & NC reaction can be detected using nuclei with a low neutron decay threshold. Cross section is relatively higher. n s n s Q [ 208 Pb(n,n 2n) 206 Pb] = MeV Q [ 208 Pb(n,n n) 207 Pb] = -7.4 MeV n s Available to measure n m & n t Playing as Flavor Filter. Neutral Current (NC) reaction ν ν i e Pb e Bi * 208 Pb 207 Bi Q [ 208 Pb(n e,e + n) 207 Bi] = -9.8 MeV * Pb ν ' i + Pb Pb + γ or Pb + n or Pb ν p ν + p ( i = e, µ, τ ) Charged-Current (CC) reaction ν e e + e + + p e + n 1-2 neutron decay from excited nuclei become neutrino signal. 207 Bi + n or 206 Bi + 2n Reaction thresholds + 2n

23 Excitation Energy Spectra A) Singles measurement B) Neutron coincidence C) γ-ray coincidence D) Decay neutron ratio E) Decay γ-ray ratio (Scattering angle 0 o < <2 o ) 208 Pb( 3 He,t)

24 Statistical Decay and Model Calculation Direct Decay p Statistical Decay n Compound nucleus Ex p n p n p n grand state or excited state Ex p n p n p n p n Comparison of statistical-model calculation and measurement

25 Energy distribution is compatible with statisticalmodel calculation. As fitting by using Maxwell- Boltzman distribution function for neutron evaporation from a nuclei, f ( E) E exp( ae) the center energy became MeV. Energy Distribution of Decay Neutron

26 Kawase et al., kev NRF γ-ray peak 1. Direct counting of NRF yields 2. Both E1 and M1 excitations are used. 3. Self-corrections for experimental error 4. Circular polarized beam with high stability and high emittance is needed. 1 ev kev In the case of 19 F ½- ½+ Α γ = 2 T(E1) T(M1) A RL = 2 E H PNC 1 2 1/ 2 + µ 1 / 2 1 / / 2 O( E1) 1 / 2 µ 1 / 2 ( 1 + cosθ ) kev

27 Facility for Inverse Compton g-ray beam at New-Subaru at SPring GeV TOP up operation 1-30 MeV photons 10 7 photons/sec. g Application: Astrophysics, Nuclear Physics Straight line for Inverse Compton scattering

28 Hayakawa et al., Nucleosynthesis by high energy photons Heavy elements have been produced by stars in the Galaxy. Massive stars have contaminations of heavy elements synthesized at early generation stars. New isotopes are produced by photons in supernova explosions. Temperature: 3x10 9 K!

29 Summary 1) ISGMR in 112,114,116,118,120,122,124 Sn via (α,α ). We obtained the ISGMR cross section distribution and peak positions. sym. is most likely -580 < < -380 MeV. 2) Selected results from ( 3 He,t). (d, 3 He), (t, 3 He) results are shown. 3) Charge exchange reaction for supernova neutrino detector 4) γ-ray beam facility at SPring-8.

30 April kev ½+ 1/2- transition in 19 F Kawase et al.,

31 Density-dependent N- interaction V ( r r ', ρ 2/3 2 0( r' )) = V (1 + βv ρ 0( r' ) )exp( r r' / αv ) iw(1 + β W ρ 2 /3 2 0 ( r' ) ) exp( r r' / α W ) Interaction parameters were obtained for 124 Sn by fitting the elastic scattering. The angler distributions were calculated with the DWBA code ECIS95

32

33 112 Sn 2 + (1.257MeV) 112 Sn 3 - (2.360MeV)

34 120 Sn 2 + (1.171MeV) 120 Sn 3 - (2.399MeV)

35 124 Sn 2 + (1.131MeV) 124 Sn 3 - (2.614MeV) 124 Sn 4 + (3.158MeV)