Restricted spin-range correction in the Oslo method: The example of nuclear level density and γ -ray strength function from Pu239(d,pγ)

Abstract

The Oslo Method has been applied to particle-γ coincidences following the 239 Pu(d,p) reaction to obtain the nuclear level density (NLD) and γ-ray strength function (γSF) of 240 Pu. The experiment was conducted with a 12 MeV deuteron beam at the Oslo Cyclotron Laboratory. The low spin transfer of this reaction leads to a spin-parity mismatch between populated and intrinsic levels. This is a challenge for the Oslo Method as it can have a significant impact on the extracted NLD and γSF. We have developed an iterative approach to ensure consistent results even for cases with a large spin-parity mismatch, in which we couple Green's Function Transfer calculations of the spin-parity dependent population cross-section to the nuclear decay code RAINIER. The resulting γSF shows a pronounced enhancement between 2-4 MeV that is consistent with the location of the low-energy orbital M 1 scissors mode.

Simultaneous Determination of Neutron-Induced Fission and Radiative Capture Cross Sections from Decay Probabilities Obtained with a Surrogate Reaction

“…These values are very close to literature [40,44,45]. In addition, we obtained a normalization factor for the γSF of 2.8 AE 0.3, which, combined with the model of [41], gives a γSF for 240 Pu that compares well with the experimental results of [46]. The good agreement of these model ingredients with previous work demonstrates the validity of our adjustment procedure.…”

Statistical properties of the well deformed Sm153,155 nuclei and the scissors resonance

“…This again influences the primary γ -ray spectra P(E x , E γ ). A slope correction of the γ SF might therefore be necessary in particular for sub-Coulomb barrier reactions [12][13][14][15][16][17]58]. To verify whether such a correction is necessary, the J π distribution populated by the (d, pγ ) reaction has been investigated with the statistical nuclear reaction code TALYS (v1.95) [59] for the deuteron absorption compound reaction formation assuming isotropic emission.…”

“…Since then, many heavy deformed even-even and odd-mass rare-earth nuclei have been systematically investigated. So far, the SR mode has been experimentally observed in vibrational and rotational [8], as well as in γ -soft nuclei [9,10] and has also been observed in the actinide region [11][12][13][14][15][16][17], as well as in the rare-earth mass region [4,[18][19][20][21][22][23][24][25][26][27].…”

Statistical properties of the well deformed $^{153,155}$Sm nuclei and the scissors resonance

“…This again influences the primary γ-ray spectra P(E x , E γ ). A slope correction of the γSF might therefore be necessary in particular for sub-Coulomb barrier reactions [12][13][14][15][16][17]58]. To verify whether such a correction is necessary, the J π distribution populated by the (d,pγ) reaction has been investigated with the statistical nuclear reaction code TALYS (v1.95) [59] for the deuteron absorption compound reaction formation assuming isotropic emission.…”

“…Since then, many heavy deformed even-even and odd-mass rare-earth nuclei have been systematically investigated. So far, the SR mode has been experimentally observed in vibrational and rotational [8], as well as in γ-soft nuclei [9,10] and has also been observed in the actinide region [11][12][13][14][15][16][17], as well as in the rare-earth mass region [4,[18][19][20][21][22][23][24][25][26][27].…”