R.W. Hoff

Fission Cross-Section Measurements of 247 Cm, 254 Es, and 250 Cf from 0.1 eV to 80 keV

The fission cross sections of Cm, Es, and Cf are measured with the Rensselaer intense neutron spectrometer from 0.1 eV to 80 keV. The cross sections are normalized to the U ENDF/BV broadened cross section. Fission areas and resonance widths are determined for lowenergy resonances in Cm. The Es and Cf fission cross sections are the only reported measurements for these isotopes. The Es isotope is the heaviest odd-odd isotope ever measured over this energy range. The thermal fission cross sections for Cm, Es, and Cf are determined by extrapolation of the low-energy region of the cross section and are in good agreement with other reported measurements. Resonance integrals are reported for the energy range of 0.1 eV to 80 keV, and the areas for Cm and Cf resonances are also reported. The previously reported Cm fission cross section was corrected for fission in Cm.

The availability of enriched stable isotopes: Present status and future prospects

Abstract The ORNL Electromagnetic Isotopic Enrichment Facility (EMIEF) has the foremost capability in the world for large-scale enrichment of stable isotopes. Despite the importance of these isotopes in research and medical applications, the funding levels for EMIEF operation since 1982 have decreased significantly, forcing operation at rates far below replacement of isotopes sold or loaned. The availability of enriched stable isotopes is presented, along with a summary of EMIEF User Group concerns and activities.

Intermediate structure in the fission cross sections of the even curium isotopes

Abstract The neutron-induced fission cross sections of Cm-244, Cm-246, and Cm-248 which were measured with the RINS lead spectrometer system at RPI have been analyzed for intermediate structure. Gross structure is observed in Cm-244 near 200, 400, 800, and 2000 eV and in Cm-246 near 350, 800, and 3300 eV. For Cm-248 a very broad type of structure is observed near 10 keV. Assuming double-barrier fission, the Cm-244 and Cm-246 structure is consistent with the outer potential well lying 2 to 3 MeV above the inner potential well. The broad structure observed in Cm-248 fission implies significantly different barrier parameters than for Cm-244 or Cm-246.

Experimental Assessment of the Performance of a Proposed Lead Slowing‐Down Spectrometer at WNR/PSR

In November 1989, we carried out a measurement of the fission cross section of {sup 247}Cm, {sup 250}Cf, and {sup 254}Es on the Rensselaer Intense Neutron Source (RINS) at Rensselaer Polytechnic Institute (RPI). In July 1990, we carried out a second measurement, using the same fission chamber and electronics, in beam geometry at the Los Alamos Neutron Scattering Center (LANSCE) facility. Using the relative count rates observed in the two experiments, and the flux-enhancement factors determined by the RPI group for a lead slowing-down spectrometer compared to beam geometry, we can assess the performance of a spectrometer similar to RINS, driven by the Proton Storage Ring (PSR) at the Los Alamos National Laboratory. With such a spectrometer, we find that is is feasible to make measurements with samples of 1 ng for fission 1 {mu}g for capture, and of isotopes with half-lives of tens of minutes. It is important to note that, while a significant amount of information can be obtained from the low resolution RINS measurement, a definitive determination of average properties, including the level density, requires that the resonance structure be resolved. 12 refs., 5 figs., 3 tabs.

Search for low-spin superdeformed states in nuclei☆

Abstract Since the first discovery in 1986 of a rotational band at high angular momentum with deformation parameters near β =0.6, a great deal of research has been devoted to the study of these superdeformed (SD) bands in nuclei leading to the identification of similar bands in numerous nuclei in the mass 130, 150, and 190 regions. While superdeformed shape isomers have been observed at low spin in the actinides via spontaneous fission and in a few cases via γ decay, below mass 200 the low-spin members of the SD bands have not been observed. Theoretical calculations are able to account for the relative stability of the superdeformed bands in the nuclei where they have been observed. These calculations suggest that in the Hgue5f8Pb region the SD shape should be stable at a rotational frequency of 0. Several experiments have been performed to search for the population and decay of the lower spin members of the SD bands in the mass 190 region and some are still in progress. To this date, none has provided conclusive observation of the 0 + bandhead of a superdeformed band. The experimental techniques utilized in several of these are described.

Reaction cross-section calculations using new experimental and theoretical level structure data for deformed nuclei

A technique for modeling level structures of odd-odd nuclei has been used to construct sets of discrete states with energies in the range 0 to 1.5 MeV for several nuclei in the rare-earth and actinide regions. The accuracy of the modeling technique was determined by comparison with experimental data. Examination was made of what effect the use of these new, more complete sets of discrete states has on the calculation of level densities, total reaction cross sections, and isomer ratios. 9 refs.