I. N. Borzov IPPE, Obninsk

1
I. N. Borzov IPPE, Obninsk GSI,
DarmstadtWeak interaction rates for nuclei
near the r-process paths Hirschegg,
19.01.06

• 1. The ß-half-lives and ß-delayed neutron
  emission near N50, 82
• Sef-consistent CQRPA calculations of the
  GT and FF ß-strength functions.
• Supression of the Pn-values in nuclei
  crossing the major N50,82 shell.
• I.N. Borzov Phys.ReV. C71(2005)065801
• 2. Charged-current neutrino induced fission
  near N126, 184
• Y.Qian Astron.J 569 (2002) L103
• ltEgt 10-12 MeV, A gt200 , Ex (F, GT)
  20-30 MeV gt Bf
• Fission and n-evaporation may occur after
  the r-process freeze-out.
• E.Kolbe et al . PRL 92 (2004) 111011
• A.Kelic' et al P.L 616 (2005) 48
• Collaboration K. Langanke, G.
  Martinez-Pinedo, A. Kelic, N.Zinner

2
Self-Consistent Ground State
M/M1

• Skyrme-HF
• S. Goriely, F. Tondeur, J.M. Pearson ADNDT
  77(2001)311
• MSk7- 10 parameters Skyrme force, 4 parameters
  ?-function pairing, 2 parameters Wigner term. The
  rms error of the fit to 1988 masses (Audi-Wapstra
  1995) is 0.738 MeV.

• EDF
• I.N. Borzov, S.A. Fayans, E. Kromer, D. Zawischa
  Z. Phys. A335(1996) 117
• DF3 local energy-density functional by S.A.
  Fayans et al. 3 parameters ?-function pairing.
• Fitted to the g.s. properties near magic cross
  at 132Sn.

3
CQRPA description of the pn-excited states
Q2eq2 st 0.8 Quenching of st-vertexes -
the same for all A, eq 2?5 1.4
S Q2
3(N-Z)

• continuum
• no pairing

pairing in the valence space
T0 A.P. Platonov, E.E. Saperstein, ?? 1987
Nucl.Phys. A486(1988)63. T0 N. Van Giai, Nucl.
Phys. A482 (1988) 473c. T1 I.N. Borzov, E.L.
Trykov Izv.AN SSSR 53(1989) 2468
I.N. Borzov, S.A.Fayans, E.L. Trykov
Sov.J.Nucl.Phys. 52(1990) 33
4
Particle-hole effective NN-interaction
(dp?)
REPULSION ATTRACTION
93 ? 5 (p,n), (n,p) Ep295 MeV R?NP 1999
Q2??Q2??0.81 (20) moderetely soft p
60 ? 10 (p,n), Ep120 MeV IUCF
199 Q2??Q2??0.64 (40) stiff p
Particle-particle effective NN-interaction
(pn T0)
F? reduces ?-strength , P.Vogel, 1984
F??? - 2C0 g? ?(r12) ? 1 ? 2
?--decay half-life vs. g?
g? is fixed from (n,p), (p,n) spectra at
Ep,n 300 MeV in 54Fe, 60Ni ... Neglecting F?
in BCSRPA causes cevere QRPA symmetry
violation (see H.DeWitte Phys.Rev. C69 (2004)
044305)
T1/2 (exp)
gx critical
5
One-quasiparticle levels near Z28, N50
0.0
-------- µ(n)
protons
____ 2d5/2
____ 1g7/2
N50
-5.0
____ 1g9/2
____ 2d5/2
FF , L1
____ 1f5/2
-10.0
____ 1p1/2
____ 1g9/2
GT, L0
____1p3/2
____ 2p1/2
-15.00
____ 1f5/2
____1f7/2
____ 2p3/2
µ(p)
--------
-20.00
neutrons
____ 1f7/2
6
Suppression of the delayed neutron
emission beyond N50, 82 shells
A,Z precursor
1 - Q-B-window
Q?
A-1, Z1 product
Ni-isotopes
7
Half-lives and Pn-values for Ni isotopes
a) MSU-05 , P.T.Hosmer et.al.
PRL 94 (2005) 112501 b) CERN
98 A Tth, ms MSU-05,ms 75 340
34420-24 76 255 23815-18 77
166 12827-33 78 133 110100
-60 For Alt78, the half-lives are well
described in the GT approximation only
(DF3CQRPA) ( c f P.T.Hgt Alt78 GT FF
shell quenching ) For Agt78, a regular
behavior of the T1/2 can be provided if the
GTFF transitions are included. The FF
transitions outside the Qßn suppress the
Pn-values compared to the GT case.
I.N. B, nucl-th/0409019 (2004)
Phys.ReV. C71(2005)065801
8
N82 nuclei at Z 50
More examples Ga, Ge, As, Br, Cd I.N.B,
Nucl.Phys. (npa 10142, 2005)
Experimental data

G. Rudstam et al. 1993, ADNDT 53,
1 R. Shergur et al. 2002,Phys. ReV. C 65,
034313
9
(II) GT and FF strength functions for
experimentally unknown unstable nuclei at
Agt200, N126 and 184
What are the benchmarks for full strength
functions incl. the continuum region ?

• Sum rules for charge-exchange excitations

Multipole projection operators
10
GT and FF strength functions in 275Am (q0)
E sysIAS EGT
11
GT strength function at finite momentum transfer
(q)
12
Comparison with RPA for Am-chain
Neutrino capture cross sections
sJLS(E? , q0)
275Am, Qß 8.2 MeV

• N.Zinner

Cross section folded with the neutrino spectrum
(F- D, µ0, T4MeV)
in 10( - 42) cm2
cQRPA (q0) RPA (q0)
0.913(3) 0.660(3)
cQRPA gives more strength at Ex lt15-20MeV
13
Nn and s for Agt280 Am-chain. (ALBA-code,
K.-H. Schmidt et al.)

• N.Zinner

U, Cm and Am-chains
14
The self-consistent DFCQRPA approachhas been
used to simultaniously calculate the different
weak rates for the r-process relevant nucleiat
N50, 82 and 126,184 regions

• The impact of the first-forbidden decays on
  T1/2 and Pn at N50,82
• A suppression of the delayed neutron
  emission
• Where? Why?
• In nuclei with
  N-ZgtN0 , due to the high-energy FF transitions
• to the states outside the neutron emission window
• T1/2 in N126 region GSI current experments
  (talk by T.Kurtukian-Nieto)
• Contribution of the first-forbidden decays is
  found to be important for neutrino-induced
  fission
• Perspectives
• Deformed DFQRPA
• Collaboration K.Langanke, G.Martinez-Pinedo,
  A.Kelic', N.Zinner