Determination of fission neutron transmission through waste matrix material using neutron signal correlation from active assay of {sup 239}Pu

The accuracy of TRU (transuranic) waste assay using the differential die-away technique depends upon significant corrections to compensate for the effects of the matrix material in which the TRU waste is located. The authors have used a new instrument, the Combined Thermal/Epithermal Neutron (CTEN) instrument for the assay of TRU waste, to develop methods to improve the accuracy of these corrections. Neutrons from a pulsed 14-MeV neutron generator are moderated in the walls of the CTEN cavity and induce fission in the TRU material. The prompt neutrons from these fission events are detected in cadmium-wrapped {sup 3}He neutron detectors. They report new methods of data acquisition and analysis to extract correlation in the neutron signals resulting form fission during active interrogation. They use the correlation information in conjunction with the total number of neutrons to determine the fraction of fission neutrons transmitted through the matrix material into the {sup 3}He detectors. This determination allows them to cleanly separate the matrix effects into two processes: matrix modification upon the neutron interrogating flux and matrix modification upon the fraction of fission neutrons transmitted to the neutron detectors. This transmission information is also directly applied in a neutron multiplicity analysis in the passive assay of {sup 240}Pu

pi-NN Coupling Constants from NN Elastic Data between 210 and 800 Mev

High partial waves for $pp$ and $np$ elastic scattering are examined critically from 210 to 800 MeV. Non-OPE contributions are compared with predictions from theory. There are some discrepancies, but sufficient agreement that values of the $\pi NN$ coupling constants $g_0^2$ for $\pi ^0$ exchange and $g^2_{c}$ for charged $\pi$ exchange can be derived. Results are $g^2_0 = 13.91 \pm 0.13 \pm 0.07$ and $g^2_c = 13.69 \pm 0.15 \pm 0.24$, where the first error is statistical and the second is an estimate of the likely systematic error, arising mostly from uncertainties in the normalisation of total cross sections and $d\sigma/d\Omega$.Comment: 21 pages of LaTeX, UI-NTH-940

Chiral perturbation theory calculation for pn -> dpipi at threshold

We investigate the reaction pn -> dpipi in the framework of Chiral Perturbation Theory. For the first time a complete calculation of the leading order contributions is presented. We identify various diagrams that are of equal importance as compared to those recognized in earlier works. The diagrams at leading order behave as expected by the power counting. Also for the first time the nucleon-nucleon interaction in the initial, intermediate and final state is included consistently and found to be very important. This study provides a theoretical basis for a controlled evaluation of the non-resonant contributions in two-pion production reactions in nucleon-nucleon collisions.Comment: 24 pages, 3 figures, 3 table

Subcritical Neutron Multiplication Measurements of HEU Using Delayed Neutrons as the Driving Source

A new method for the determination of the multiplication of highly enriched uranium systems is presented. The method uses delayed neutrons to drive the HEU system. These delayed neutrons are from fission events induced by a pulsed 14-MeV neutron source. Between pulses, neutrons are detected within a medium efficiency neutron detector using {sup 3}He ionization tubes within polyethylene enclosures. The neutron detection times are recorded relative to the initiation of the 14-MeV neutron pulse, and subsequently analyzed with the Feynman reduced variance method to extract singles, doubles and triples neutron counting rates. Measurements have been made on a set of nested hollow spheres of 93% enriched uranium, with mass values from 3.86 kg to 21.48 kg. The singles, doubles and triples counting rates for each uranium system are compared to calculations from point kinetics models of neutron multiplicity to assign multiplication values. These multiplication values are compared to those from MC NP K-Code calculations

Analysis of fissionable material using delayed gamma rays from photofission

The energetic gamma-ray spectra from the fission products of photofission have been investigated to determine whether photofission can identify heavily shielded fissionable material. Target samples of natural thorium, 93% enriched /sup 235/U, natural uranium, and 93% enriched /sup 239/Pu were irradiated with bremsstrahlung gamma rays produced by 10-MeV electrons from a small linear accelerator. The gamma-ray spectra for each of the four isotopes studied reveals a distinctive intensity distribution. For example, the intensity ratio of the pair of gamma rays at 1436 keV (/sup 138/Cs) and 1428 keV (/sup 94/Sr) is 1.9 for /sup 235/U, 2.4 for /sup 238/U, 1.7 for /sup 232/Th and 1.4 for /sup 239/Pu. 6 refs., 2 figs., 1 tab

Measurement of K/sub NN/, K/sub LL/ in p vector d. -->. n vector X and p vector /sup 9/Be. -->. n vector X at 800 MeV

The spin transfer parameters, K/sub NN/ and K/sub LL/, have been measured in p vector d ..-->.. n vector X and p vector /sup 9/Be ..-->.. n vector X at 0/sup 0/ and 800 MeV. The rather large values of K/sub LL/ demonstrate that this transfer mechanism will provide a useful source of polarized neutrons at LAMPF energies

Measurement of K/sub NN/, K/sub SS/, K/sub SL/, and K/sub LL/ in polarized np. -->. polarized pn at 800 MeV in the CEX region

The spin transfer parameters K/sub NN/, K/sub SS/, K/sub SL/, and K/sub LL/ have been measured for np elastic scattering at 800 MeV between 165/sup 0/ and 180/sup 0/ c.m. The parameters K/sub NN/ and K/sub LL/ are in good agreement with the quasi-free reaction polarized pd ..-->.. polarized npp at 180/sup 0/

Polarimeter for protons between 300 and 800 MeV

A polarimeter for protons between 300 and 800 MeV has been constructed. It uses a carbon block analyzer of variable thickness and 6 drift chambers for particle tracking