Previously published particle-γ coincidence data on the 64 Ni(p, p γ) 64 Ni and 64 Ni(d, pγ) 65 Ni reactions were further analyzed to study the statistical properties of γ decay in 64,65 Ni. To do so, the γ decay to the quasicontinuum region and discrete low-lying states was investigated at γ-ray energies of 2.0-9.6 and 1.6-6.1 MeV in 64 Ni and 65 Ni, respectively. In particular, the dependence of the γ-strength function with initial and final excitation energy was studied to test the validity of the generalized Brink-Axel hypothesis. Finally, the role of fluctuations in transition strengths was estimated as a function of γ-ray and excitation energy. The γ-strength function is consistent with the hypothesis of the independence of initial excitation energy, in accordance with the generalized Brink-Axel hypothesis. The results show that the γ decay to low-lying levels displays large fluctuations for low initial excitation energies.
Particle-γ coincidence data have been analyzed to obtain the nuclear level density and the γ -strength function of 64 Ni by means of the Oslo method. The level density found in this work is in very good agreement with known energy levels at low excitation energies as well as with data deduced from particle-evaporation measurements at excitation energies above E x ≈ 5.5 MeV. The experimental γ -strength function presents an enhancement at γ energies below E γ ≈ 3 MeV and possibly a resonancelike structure centered at E γ ≈ 9.2 MeV. The obtained nuclear level density and γ -strength function have been used to estimate the (n,γ ) cross section for the s-process branch-point nucleus 63 Ni, of particular interest for astrophysical calculations of elemental abundances.
The nuclear level density and the γ-ray strength function have been extracted for 89 Y, using the Oslo Method on 89 Y(p, p γ) 89 Y coincidence data. The γ-ray strength function displays a low-energy enhancement consistent with previous observations in this mass region ( 93−98 Mo). Shell-model calculations give support that the observed enhancement is due to strong, low-energy M1 transitions at high excitation energies.The data were further used as input for calculations of the 88 Sr(p, γ) 89 Y and 88 Y(n, γ) 89 Y cross sections with the TALYS reaction code. Comparison with cross-section data, where available, as well as with values from the BRUSLIB library, shows a satisfying agreement.
The nuclear level densities and γ-ray strength functions of 138,139,140 La were measured using the 139 La( 3 He, α), 139 La( 3 He, 3 He ′ ) and 139 La(d, p) reactions. The particle-γ coincidences were recorded with the silicon particle telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these experimental results, the low-energy enhancement in the A∼140 region is discussed. The 137,138,139 La(n, γ) cross sections were calculated at s-and p-process temperatures using the experimentally measured nuclear level densities and γ-ray strength functions. Good agreement is found between 139 La(n, γ) calculated cross sections and previous measurements.
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