R.E. Slovacek

Photoneutron target development for the RPI linear accelerator

Abstract Two new photoneutron targets have been developed for neutron time-of-flight experiments, the axial water-moderated target (AWMT) and the bare bounce target (BBT). These targets operate without any lead shielding nearby and both have superior neutron resolution compared to the older bounce target. The BBT has been selected over the AWMT for general time-of-flight measurements because it exhibited lower neutron background in the keV energy region.

Design and construction of a thermal neutron target for the RPI linac

Abstract To perform thermal cross section measurements the low energy neutron intensity from the RPI linac facility was increased. A new Enhanced Thermal Target (ETT) was designed, constructed and tested. The thermal flux of the new target was up to six times greater than the flux from the previous RPI Bounce Target (BT). This additional gain allows transmission measurements to be performed in the energy range of 0.001 to 15 eV with high statistical accuracy in a short time (∼ 40 h). The ETT was also designed to be coupled to a cold moderator that will give an additional flux increase factor of about 9 below 3 meV. Design calculations for the cold moderator including neutronics and cryogenics are also given.

Design of a spent-fuel assay device using a lead spectrometer

The neutron slowing-down-time method for nondestructive assay of light water reactor spent fuel has been under development for many years. Results for a newly optimized design of a lead slowing-down-time spectrometer for spent-nuclear-fuel assay are presented. Monte Carlo analyses were performed to optimize the design of the assay device, determine its main parameters, investigate the effects of the spent-fuel assembly and the detector impurities on its performance, determine the fission signatures of the fissile isotopes in spent-fuel elements, and simulate the assay signal as a function of the slowing-down time, assuming threshold fission chambers for the assay detectors. The assay signals from the threshold detectors were analyzed to predict the unknown masses of the fissile isotopes in a typical spent commercial light water reactor fuel element. The broadened resolution of the system caused by the presence of the spent fuel inside the spectrometer pile was found sufficient to separate the signatures of the U and Pu fissiles in spent fuel.

Neutron Total Cross-Section Measurements and Resonance Parameter Analysis of Holmium, Thulium, and Erbium from 0.001 to 20 eV

The Rensselaer Polytechnic Institute linear accelerator with the enhanced thermal target was used for neutron transmission measurements of rare earth metal samples of holmium, erbium, and thulium and isotopically enriched oxide samples of 166 Er2O3 and 167 Er2O3 in the energy range from 0.001 to 20 eV. The measurements were done with a 15-m time-of-flight spectrometer and provided high-quality data in the thermal and subthermal region as well as in the low energy resonance region. The effect of paramag- netic scattering on these cross sections is discussed. The data were corrected for paramagnetic scattering, and resonance parameters were obtained by fitting the transmission with the SAMMY multilevel R-matrix code. These results were compared to the ENDF0B-VI evaluation and to other measurements.

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.

Hafnium Resonance Parameter Analysis Using Neutron Capture and Transmission Experiments

Abstract The focus of this work is to determine the resonance parameters for stable hafnium isotopes in the 0.005- to 200-eV region, with special emphasis on the overlapping 176Hf and 178Hf resonances near 8 eV. Accurate hafnium cross sections and resonance parameters are needed in order to quantify the effects of hafnium found in zirconium, a metal commonly used in reactors. The accuracy of the cross sections and the corresponding resonance parameters used in current nuclear analysis tools are rapidly becoming the limiting factor in reducing the overall uncertainty on reactor physics calculations. Experiments measuring neutron capture and transmission are routinely performed at the Rensselaer Polytechnic Institute LINAC using the time-of-flight technique. Lithium-6 glass scintillation detectors were used for transmission experiments at flight path lengths of 15 and 25 m, respectively. Capture experiments were performed using a 16-section NaI multiplicity detector at a flight path length of 25 m. These experiments utilized several thicknesses of metallic and isotope-enriched liquid Hf samples. The liquid Hf samples were designed to provide information on the 176Hf and 178Hf contributions to the 8-eV doublet without saturation. Data analyses were performed using the R-matrix Bayesian code SAMMY. A combined capture and transmission data analysis yielded resonance parameters for all hafnium isotopes from 0.005 to 200 eV. Additionally, resonance integrals were calculated, along with errors for each hafnium isotope, using the NJOY and INTER codes. The isotopic resonance integrals calculated were significantly different from previous values. The 176Hf resonance integral, based on this work, is ~73% higher than the ENDF/B-VI value. This is due primarily to the changes to resonance parameters in the 8-eV resonance; the neutron width presented in this work is more than twice that of the previous value. The calculated elemental hafnium resonance integral, however, changed very little.

Neutron Transmission and Capture Measurements and Resonance Parameter Analysis of Neodymium from 1 to 500 eV

Abstract Neodymium is a 235U fission product and is important for reactor neutronic calculations. The aim of the present work is to improve upon the existing neutron cross-section data of neodymium. Neutron capture and transmission measurements were performed by the time-of-flight technique at the Rensselaer Polytechnic Institute (RPI) linear accelerator (LINAC) laboratory using metallic neodymium samples. The capture measurements were made at the 25-m flight station with a 16-segment NaI multiplicity detector, and the transmission measurements were performed at 15- and 25-m flight stations, respectively, with 6Li glass scintillation detectors. After the data were collected and reduced, resonance parameters were determined by combined fitting of the transmission and capture data with the SAMMY multilevel R-matrix Bayesian code. The resonance parameters for all naturally occurring neodymium isotopes were deduced within the energy range of 1 to 500 eV. The resulting resonance parameters were used to calculate the capture resonance integrals from this energy. The RPI parameters gave a resonance integral value of 32 ± 1 b that is ˜7% lower than that obtained with the ENDF/B-VI parameters. The current measurements significantly reduce the uncertainties of the resonance parameters when compared with previously published parameters.

Neutron tomographic fissile assay in spent fuel using the lead slowing down time spectrometer

Abstract A tomographical fissile assay technique for light water reactor spent fuels was developed based on the lead slowing down time spectrometer (LSDTS). The Monte Carlo method was used for system performance and for simulation of the sensitivity of detection of fissile materials using neutron emission tomography. A typical spent PWR fuel element was simulated and the spatial and mass sensitivity of the fissile components were investigated. From these studies, the LSDTS system is shown to be a very sensitive device for analyzing the spatial distribution of total fissile materials of a spent fuel assembly in a properly selected assay neutron energy range. This method is also applicable to nuclear waste assay.

Neutron capture and total cross-section measurements and resonance parameter analysis of zirconium up to 2.5 keV

Abstract Neutron capture and transmission measurements were performed by the time-of-flight technique at the Rensselaer Polytechnic Institute LINAC using metallic zirconium samples. The capture measurement was made at the 25-m flight station with a multiplicity-type capture detector, and the transmission total cross-section measurements were performed at the 25-m flight station with a 6Li glass scintillation detector. Resonance parameters were determined by a combined analysis of all 11 data sets (4 capture and 7 transmission) using the least-squares multilevel R-matrix code REFIT. The present measurements were undertaken to resolve discrepancies between common usage (ENDF/B-VI) and the recent measurements of Salah et al. for the 300-eV zirconium doublet. The present measurements support the Salah et al. conclusions. Specifically, the results confirm the assignment of J = 3 for the 91Zr 292.5-eV resonance and include all significant resonances up to 2.5 keV. The zirconium resonance parameters Γγ and Γn, determined in the present measurement, are compared with the ENDF/B-VI parameters.

Neutron Capture and Total Cross Section of Thorium-232 from 0.006 to 18 eV

The neutron total cross section and the shape of the neutron capture cross section of /sup 232/Th have been measured in the energy range from 0.006 to 18 eV at the Rensselaer Polytechnic Institute Gaerttner Linac Laboratory. The neutron total cross section was obtained from transmission measurements using metallic /sup 232/Th samples and a /sup 6/Li glass neutron detector. The first goal of this work is to determine the total cross section to an accuracy of a few percent. The second goal is to measure the shape of the low-energy capture cross section and to resolve the rather large discrepancy between the results of the two previous measurements. 23 refs.