Charge exchange reactions and photo-nuclear reactions

Transcription

1 Charge exchange reactions and photo-nuclear reactions σ( 7 Li, 7 Be) and σ(γ,n) S. Nakayama (Univ of Tokushima) Determination of σ(γ,n) from CE reactions (CE reaction = Charge Exchange reaction) Application of the ( 7 Li, 7 Be) reaction to σ(γ,n) Astrophysical phenomena Deduction of σ(γ,n) as a function of Ex 006/1/11-4. Dec., 005 NNR05 1

2 Motivation Interactions of CE reaction are similar to weak and EM interactions. Astrophysical interest Low-multipole transitions in CE reaction GT/M1 and E1-transitions. Application to deduce σ(γ,n) Astrophysical phenomena BB-nucleosynthesis of deuteron SDR/GDR in 1 C (SN ν-heating of 4 He) 006/1/11-4. Dec., 005 NNR05

3 Nucleon-nucleon interactions of Charge Exchange Reactions Central part: T T S 10 LJ S 11LJ = g = g S 10LJ S 11LJ τ τ Non-central part: Tensor force ; V [ ] L L i r Y [ ] L L i r Y σ S T = V T L L L ; Electric type excitation J ( r) τ S ; Magnetic type excitation ( S = 1) 1 ( σ ; S = 3 1 ( S = 0) 1 r)( σ r r) σ Tensor force has a sizable contribution for unnatural-parity transitions. 1 σ 006/1/11-4. Dec., 005 NNR05 3

4 Probe for Nuclear Weak and EM Responses Weak operators ; EM operators ; 10-3 T T T T W 10 LJ W 11 LJ E E 10 LJ = g 10 LJ τ 3 M 11 LJ = = = g g g g W 1101 W 10 W 11 M 11 LJ LJ LJ W / g 1000 τ τ 3 τ [ ] L L i r Y L L [ L L i r Y σ ] 1. 4 L [ L L i r Y ] L L [1 + f ( µ )] {[ ] [ ] L L L L i r Y σ + i r Y l } L Spin part Orbital part Their contributions are strongly dependent on the relevant states. J for L=0 transition J L J 006/1/11-4. Dec., 005 NNR05 4

5 Charge Exchange Reactions T=1, T = -1 (p,n) ( 3 He,t) ( 6 Li, 6 He) etc T=1, T = +1 (n,p) (d, He) (t, 3 He) ( 7 Li, 7 Be) etc 006/1/11-4. Dec., 005 NNR05 5

6 ( 7 ( Li, 7 Li, 7 Be) 7 Be) 7Li 7Be transition and spin-selectivities 1/ - 3/ - 7 Li / - (Be1) : S= 1 3/ - (Be0) : S= 0,1 7 Be 0.0 Ejectile excitation 7 Be-γ coincidence Separation between Be0 and Be1 Be0 : Without 7 Be- coincidence Be1 : With 7 Be- coincidence Electric-type Excitation ( S=0) Magnetic-type Excitation ( S=1) σ ( S σ ( S = 0) = σ (Be = 1) = σ (Be ) / B 1 0 ) σ (Be ) R GT 1 (Be Charge exchange Spin-flip & Spin-nonflip Reaction 1 ) COUNTS Nakayama, S. et al. Nucl. Instrum Methods A404 (1998) 34. Phys. Rev. Lett. 83 (1999) 690. Phys. Rev. Lett. 85 (000) 6. Phys. Rev. Lett. 87 (001) Li + A 7 Be + B T z = +1/ T z = -1/ J = 3/- 7Be (J = 3/-) T z = +1 S=0/ S=1 Be* (J =1/-) T z = +1 R = BGT( Be0)/ BGT(Be1) = 1.30 /1.1 = /1/11-4. Dec., 005 NNR05 EXCITATION ENERGY (MeV ) S=1 Be + GT, 1 + -, 4-7 SDR (0 -, 1 -, - ) GDR, 1 -

7 Experimental procedure - Beam: 455 MeV, 7 Li at RCNP, Osaka Univ. - Targets: CH, CD, 6 Li, 1 C, - 7 Be:Grand RAIDEN θ L <1 deg. E ~ 400 kev - γ-rays: NYMPHS ε ~ 0% for 0.43-MeV γ 006/1/11-4. Dec., 005 NNR05 7

8 Contents Characteristics of ( 7 Li, 7 Be) reaction at 455 MeV - NN interaction - σ(0 ) and B GT -value Two applications to deduce σ(γ,n) - σ M1 γ,n of H near the threshold energy region - GDR in 1 C(γ,n), GDR/SDR SN ν-heating of 4 He 006/1/11-4. Dec., 005 NNR05 8

9 Nucleon-Nucleon Interactions in the H( 7 Li, 7 Be)n reaction β-decay of neutron : B F =1, B GT =3 N τ D, N D σ * F, σ * GT στ ; distortion unit cross factors sections Assuming distortion factors of N Dτ =N D στ, ; Ratio of central nteractions V στ /V τ 006/1/11 9

10 006/1/11-4. Dec., 005 NNR05 10

11 GT strength in the ( 7 Li, 7 Be) reaction Relation between B GT and cm / N D [ = A 1 A / (A 1 +A ), N D = exp(-.5a 1/3 ) ] dσ o B( GT) (0 ) / µ dω for discrete transitions Accordingly, one gets a relationship db(gt) de N D d σ o = k (0 ) dedω for continuum transitions where k is a proportional coefficient. 006/1/11-4. Dec., 005 NNR05 11

12 Application I σ(γ,n) (M1) in deuteron M1-cross section of H(γ,n) reaction - Astrophysics (BB-nucleosynthesis) - Neutrino physics (SNO detector) Deduction from the ( 7 Li, 7 Be) reaction - Analogous interaction to M1γ excitation - σ γ (M1) as a function of Ex 006/1/11-4. Dec., 005 NNR05 1

13 GT excitation ( S=1) in H n CD ( 7 Li, 7 Be) E L =455 MeV, θ L < 1 H C, g.s S=0 S=1 EXCITATION ENERGY (MeV) 006/1/11 13

14 DWBA for H( 7 Li, 7 Be) at θ L < Ex=. MeV in D L=0 L= L=0+ Including Tensor force Knock-on exchange effect 10 4 GT-strength distribution in deuteron S=1 spectrum GT-strength (L=0) θ cm (deg.) 1000 θ L < db(gt) d σ o = k (0 ) de dedω d σ σ γ (M1) = 0.1k Eγ (0 dedω /1/11-4. Dec., 005 NNR05 14 EXITATION ENERGY in deuteron (MeV) EXCITATION ENERGY in deuteron (MeV) o )

15 σ γ from ( 7 Li, 7 Be) 1 CD ( 7 Li, 7 Be) E L =455 MeV, θ L < W. Tornow, et al., Phys. Lett. B574 (003) 8 E. Schreiber, et al., Phys. Rev. C61 (000) Effective field theory (EFT) Eγ (MeV) 006/1/11 15

16 Application II GDR and SDR of 1 C Excitation of self-conjugate closed shell nuclei - No Gamow-Teller transition in 4 He - GDR and SDR of 4 He is not still unknown Deduction from the ( 7 Li, 7 Be) reaction - Analogous interaction to ν-excitation - Equal contribution of GDR/SDR to ν-heating W W g111 J / g ? for L = 1 transitions 006/1/11-4. Dec., 005 NNR05 16

17 GDR in 1 C 1 C( 7 Li, 7 Be) 1 B EL =455 MeV, θ L < 1.5 τ σ GT, 1 + -, 4 - τ σ ry 1 SDR (0 -, 1 -, - ) S=0 S=1 Dipole excitation τ ry 1 GDR, 1 - d σ σ γ (GDR) Eγ EXCITATION ENERGY (MeV) dedω 006/1/11 17

18 σ γ (GDR) (arbitrary unit) S=0 spectrum and (γ,n) in 1 C σ γ (GDR) E γ d σ dedω 1 C( 7 Li, 7 Be) 1 B E L =455 MeV, θ L < 1.5 Eγ ( S=0) Eγ ( S=1) GDR(γ,n) L 1, IVGMR? IVGQR? EXCITATION ENERGY IN 1 C 006/1/11 18

19 Summary CE reaction is feasible to deduce the σ(γ,n) as a function of excitation energy. σ ( 7 Li, 7 Be) σ(γ,n) Application to the H(γ,n) reaction σ[ H γ,n ] near the threshold energy region Application to deduce σ(γ,n) to dipole excitations GDR and SDR in 1 C ( 4 He) 006/1/11-4. Dec., 005 NNR05 19

20 DWBA calculations Knock-on exchange effect for V and V Optical potentials for MeV 1. MeV. MeV 006/1/11-4. Dec., 005 NNR05 0

21 Isospin dependence of final states of n-p and n-n Difference between n-n and n-p two-nucleon systems is assumed to be due to their different scattering lengths. a a s s ( np) ( nn) 3. fm 18.7 fm σ γ (mb) From the Blatt-Weisskopf s formula, (zero range approximation) E γ (MeV) 006/1/11-4. Dec., 005 NNR05 1

22 Interaction of GT/M1 excitation GT-excitation: n ( 7 Li, 7 Be) V H V 1 S,0+ 3 S,1+ V = V στ st M1γ-excitation: µ π π ν = [( gl l + gs s) + ( gl 3 S 1 S excitation in deuteron: µ = ( g π s s + g ν s s) µ N l + g ν s s)] µ N Accordingly, db(m1) 3( µ = de 8π db(gt) de where db(gt)/de is given in units of p µ n ) db(gt) =.64 de µ N / MeV. 006/1/11-4. Dec., 005 NNR05

23 σ γ from M1γ strength M1 γ width [=Γ γ (M1)] is described in terms of B(M1) For a discrete transition: 16p 3 Γγ (M1) = D µ (M1) 9 B N D = hc/ E?, E? = hω Application to a continuum transition: One replaces B(M1) into db(m1)/de γ p 3 db(m1) Γγ ( Eγ,1 0 ) = D µ N 9 de Here the cross section σ is defined with Γ γ as follows.5 MeV continuous γ-ray (ω, ω + ω ) > g.s db(m1) = Eγ Finally one gets deγ d σ s ( E, γ ) = 0.1k Eγ d (0 de Ω k is determined by normalizing σ(0 ) to the (γ,n) data around Ex=3 MeV. 006/1/11-4. Dec., 005 NNR05 3 H M p+n s ( E γ +,1 0 + ) = π D Γ γ ( E γ γ +,1 0 γ + ) o )

24 GDR and SDR in 4 He - Huge abundance of 4 He 4 He, 1 C(γ,γ α), 16 O(γ,γ α), - 4 He may play an important role In ν-heating during SN explosion. - How do the GDR and SDR of 4 He distribute? - The ( 7 Li, 7 Be) may provide relative distribution of GDR and SDR. 006/1/11-4. Dec., 005 NNR05 4