James M. Adams

A New Methodology for Adjustment of Iron Scattering Cross Sections Using Time-of-Flight Spectroscopy

Monte Carlo analysis of a time-of-flight experiment was performed to investigate the iron scattering cross section. Experimental data were utilized to build a Monte Carlo source for simulation of a time-of-flight (ToF) experiment with a spherical iron shell, different source spectra, and different angular beam source alignments. For this study, two pointwise cross section libraries, ENDF/B-VI and JEFF 3.0 are examined. Comparison of calculation and experimental results indicates differences that are larger than experimental and calculation errors. To reduce the observed discrepancy, pointwise data in the ENDF/B-VI iron scattering cross section file were adjusted at a few energy intervals using a utility code developed for this purpose. Adjusted cross sections resulted in closer agreement of calculated results with the experimental Time-of-Flight data. Multigroup cross sections were generated with the adjusted cross sections and results indicate pressure vessel fluence may be underestimated.

Novel Investigation of Iron Cross Sections via Spherical Shell Transmission Measurements and Particle Transport Calculations for Material Embrittlement Studies

Abstract We have carried out a multifaceted research project to improve our knowledge of the iron nonelastic scattering cross sections. Spherical shell transmission measurements were made using time-of-flight techniques with neutrons from the 15N(p,n)15O and D(d,n)3He source reactions. For the 15N(p,n)15O work, measurements were made with a proton energy of 5.1 MeV. Measurements were made from 3 to 7-MeV deuteron energy for the D(d,n)3He work. For both source reactions, the angular range was as large as 15 to 135 deg. Two shell thicknesses were used. Comparisons are given between Monte Carlo predictions and experimental data. Utilizing a new tallying option, the estimated total iron cross sections at energies corresponding to the peak of the spectra for the 0-deg experiments were calculated to within 1% of the data in the ENDF/B-VII library. A processing code was developed to adjust ENDF format files to obtain closer agreement between measurements and calculations. Sensitivity analyses were performed at energies corresponding to the 0-deg beam angle neutrons. Using cross sections where the nonelastic and elastic cross sections were adjusted while constraining the total cross section to be constant, differences between experiment and calculation were reduced by ~;40% for a pressure vessel calculation. Such fluence calculations with adjusted cross sections indicate possible underestimation of neutron fluence, and therefore more material damage.

Final Report - Novel investigation of iron cross sections via spherical shell transmission measurements and particle transport calculations for material embrittlement studies.

OAK B204 We have been pursuing a multi-year project, funded by the U.S. Department of Energy, to study neutron scattering interactions in iron. The principal objective of this work is to investigate the well-known deficiency that exists for reactor pressure vessel neutron fluence determinations. Specifically, we are using the spherical-shell transmission method, employing iron shells with different thicknesses, and neutron time-of-flight (TOF) measurements of the scattered neutrons, in an effort to precisely determine specific energy regions over which deficiencies in the non-elastic scattering cross section for neutron scattering in iron appear to exist.

Measurement of Neutron Transmission Through Iron Spheres

We have measured the transmission of neutrons through iron spheres with several different neutron sources. The D(d,n) reaction and the 15N(n,p) reaction were found to be the best candidates for nearly monoenergetic sources at energies below 11 MeV. We have used a quasi monoenergetic source with 3.0‐, 5.0‐, and 7.0‐MeV deuterons incident on a deuteron gas cell and 5.1‐MeV protons incident on a 15N gas cell. The Ohio University Beam Swinger Facility was used in these measurements. This allowed a single fixed detector in a well‐shielded time‐of‐flight (TOF) tunnel to be used for measurements at all angles. This allows a great reduction in the background from room scattered neutrons. The detector, either NE‐213 or lithium glass, was calibrated relative to the neutron spectrum from the B(d,n) or the Al(d,n) source reaction. These spectra have been measured relative to the primary neutron standard, 235U(n, f). The transmitted neutrons have been measured for all source reactions at several angles. The data will ...

Development of a Methodology for Analysis of the Fe‐56 ENDF‐B/VI Cross Sections with a Time‐of‐Flight Experiment

This paper discusses a methodology developed for analysis of a time‐of‐flight (TOF) experiment performed for examination of iron cross sections. The methodology combines measurements from several experimental setups and Monte Carlo simulations. Neutron TOF spectra are obtained via the spherical shell transmission method with iron shells of two thicknesses and using both 15N(p,n) and D(d,n) neutron source interactions at various beam angles. Experimental data were used to determine a source distribution for Monte Carlo Simulations. Comparison of experiments and calculations identified discrepancies over several energy ranges that may be attributed to inaccuracies in the Fe‐56 inelastic scattering cross‐section. To further investigate this issue, the Fe‐56 scattering cross sections were adjusted, and used in the Monte Carlo simulations. The results of these simulations demonstrate that the adjusted cross‐sections result in significant reductions (as large as ∼40%) in the discrepancies between experimental a...

A New Investigation of Iron Cross Sections via Spherical-Shell Transmission Measurements and Particle Transport Calculations

We are engaged in a multi-year project to study neutron scattering interactions in iron, the principal objective of which is to investigate the well-known deficiency that exists in reactor pressure vessel neutron fluence determinations. Specifically, we are using the spherical-shell transmission method, employing iron shells with different thicknesses, and neutron time-of-flight measurements of the scattered neutrons, in an effort to precisely determine specific energy regions over which deficiencies in the non-elastic scattering cross section for neutron scattering in iron appear to exist. The analysis of the experimental data involves correlating the data with theoretical calculations of neutron transport through the iron spheres in order to evaluate the degree to which the calculated neutron spectra predict the measured spectra relative to different types of particle interactions. In doing so, we have developed new methodologies for performing neutron transport calculations that will be useful to a range of transport problems. Preliminary results show good agreement between the experimental data and the calculated distribution of neutron flight times over much of the data range, except for the contribution due to breakup neutrons.

New Particle Transport Methods for Design and Optimization of Spherical-Shell Transmission Measurements

This paper discusses new particle transport methods developed for accurate investigation of iron non-elastic scattering cross sections using the spherical-shell transmission method, employing iron shells with different thicknesses, and neutron time-of-flight spectroscopy of the scattered neutrons. New calculational techniques based on the deterministic and Monte Carlo methods have been developed for design and optimization of the experiment, and for identification and reduction of experimental uncertainties. The new methods include a new tallying option for the MCNP code and new quadrature sets for the 3-D parallel Sn code PENTRAN. The new tallying option is used to determine the optimum source energy versus target thickness, and among the new quadrature sets, the Pn-Tn with ordinate-splitting technique has resulted in accurate flux distributions as compared to Monte Carlo prediction.