M. S. Basunia

Investigation of the tungsten isotopes via thermal neutron capture

�5 ( 184 W m ,8.33 µs) = 0.0247(55) b; �0( 184 W) = 1.43(10) b and �11/2+( 185 W m ,1.67 min) = 0.0062(16) b; and, �0( 186 W) = 33.33(62) b and �9/2+( 187 W m ,1.38 µs) = 0.400(16) b. These results are consistent with earlier measurements in the literature. The 186 W cross section was also independently confirmed from an activation measurement, following the decay of 187 W, yielding values for �0( 186 W) that are consistent with our prompt -ray measurement. The cross-section measurements were found to be insensitive to choice of level density or photon strength model, and only weakly dependent on Ecrit. Total radiative-capture widths calculated with DICEBOX showed much greater model dependence, however, the recommended values could be reproduced with selected model choices. The decay schemes for all tungsten isotopes were improved in these analyses. We were also able to determine new neutron separation energies from our primary -ray measurements for the respective (n,) compounds: 183 W (Sn = 6190.88(6) keV); 184 W (Sn = 7411.11(13) keV); 185 W (S n = 5753.74(5) keV); and, 187 W (S n = 5466.62(7) keV).

Radiative Capture Cross Sections of 155,157 Gd for Thermal Neutrons

Abstract Thermal neutron radiative capture cross sections σ0γ of 155,157Gd are determined by summing the transition cross sections feeding the ground states of the respective product nuclei. The transition cross sections feeding the ground states from the discrete states in the low-excitation region, where the decay schemes are known completely, were measured using a guided cold neutron beam at the Budapest Research Reactor. Transitions from the states at the higher excitation, the so-called quasi-continuum levels, are determined from simulations with the extreme statistical model normalized to the intensity balance through the low-lying discrete levels. A significant non-1/v correction was applied to 155,157Gd, leading to σ0γ(155Gd) = 56 700(2100) b and σ0γ(157Gd) = 239 000(6000) b.

Surrogate measurement of the 238Pu(n,f) cross section

The neutron-induced fission cross section of 238 Pu was determined using the surrogate ratio method. The (n,f) cross section over an equivalent neutron energy range 5‐20 MeV was deduced from inelastic α-induced fission reactions on 239 Pu, with 235 U(α, α � f )a nd 236 U(α, α � f) used as references. These reference reactions reflect 234 U(n,f )a nd 235 U(n,f) yields, respectively. The deduced 238 Pu(n, f) cross section agrees well with standard data libraries up to ∼10 MeV, although larger values are seen at higher energies. The difference at higher energies is less than 20%.

Photon Strength and the Low-Energy Enhancement

Several measurements in medium mass nuclei have reported a low-energy enhancement in the photon strength function. Although, much effort has been invested in unraveling the mysteries of this effect, its physical origin is still not conclusively understood. Here, a completely model-independent experimental approach to investigate the existence of this enhancement is presented. The experiment was designed to study statistical feeding from the quasi-continuum (below the neutron separation energy) to individual low-lying discrete levels in 95Mo produced in the (d, p) reaction. A key aspect to successfully study gamma decay from the region of high-level density is the detection and extraction of correlated particle-gamma-gamma events which was accomplished using an array of Clover HPGe detectors and large area annular silicon detectors. The entrance channel excitation energy into the residual nucleus produced in the reaction was inferred from the detected proton energies in the silicon detectors. Gating on gam...

Data evaluation methods and improvements to the neutron‐capture γ‐ray spectrum

Improved neutron‐capture γ‐ray spectra, not only of interest to the nuclear structure and reactions communities, are needed in a variety of applied and non‐proliferation programs. This requires an evaluation of the existing experimental capture‐γ data. Elemental neutron‐capture data taken from direct measurements at the Budapest Reactor have been used to collate the Evaluated Gamma‐ray Activation File, a database of capture γ‐ray cross sections. These cross sections are then compared to Monte Carlo simulations of γ‐ray emission following the thermal neutron‐capture process using the statistical‐decay code DICEBOX. The aim of this procedure is to obtain the total radiative neutron‐capture cross section and confidently increase the number of levels and γ rays that can be assigned to a given isotope in the neutron data libraries. To achieve these goals and provide as complete information as possible in the neutron data libraries, it is also necessary to remain current with recent advances in nuclear structur...

Study of the (3He,t) Charge Transfer Reaction as a Surrogate for Neutron Energy Between 10 to 20 MeV

We have indirectly determined the 237Np(n,f) cross section over an equivalent neutron energy range from 10 to 20 MeV using the surrogate reaction 238U(3He,tf). A self‐supporting ∼761 μg/cm2 metallic 238U foil was bombarded with a 42 MeV 3He2+ beam from the 88‐Inch Cyclotron at Lawrence Berkeley National Laboratory (LBNL). Outgoing charged particles and fission fragments were identified using the Silicon Telescope Array for Reaction Studies (STARS) consisted of two 140 μm and one 1000 μm Micron S2 type silicon detectors. These results were compared with the 237Np(n,f) cross section data from the direct measurements, the Evaluated Nuclear Data File (ENDF/B‐VII.0), and the Japanese Evaluated Nuclear Data Library (JENDL 3.3) and found to closely follow those datasets.

Measurement of cross sections for {alpha}-induced reactions on {sup 197}Au and thick-target yields for the ({alpha},{gamma}) process on {sup 64}Zn and {sup 63}Cu

We have measured the cross sections for the {sup 197}Au({alpha},{gamma}){sup 201}Tl and {sup 197}Au({alpha},2n){sup 199}Tl reactions in the 17.9- to 23.9-MeV energy range, and {sup 197}Au({alpha},n){sup 200}Tl reaction in the 13.4- to 23.9-MeV energy range using an activation technique. Thick-target yields for the {sup 64}Zn({alpha},{gamma}){sup 68}Ge (7- to 14-MeV) and {sup 63}Cu({alpha},{gamma}){sup 67}Ga (7-MeV) reactions were measured. For all measurements, natural elements were bombarded with He{sup +} beams from the 88 In. Cyclotron at the Lawrence Berkeley National Laboratory (LBNL). Irradiated samples were counted using a {gamma}-spectrometry system at LBNLs Low Background Facility. Measured {sup 197}Au({alpha},{gamma}){sup 201}Tl cross sections were compared with the NON-SMOKER theoretical values. The thick-target yields for the {sup 64}Zn({alpha},{gamma}){sup 68}Ge and {sup 63}Cu({alpha},{gamma}){sup 67}Ga reactions are also compared with the theoretical yield, calculated numerically using the energy dependent NON-SMOKER cross section data. In both cases, measured values are found to follow a trend of overlapping the predicted value near the alpha nucleus barrier height and fall below with a slowly widening difference between them in the sub-barrier energy points.