C. A. Goulding

Differential neutron production cross sections and neutron yields from stopping-length targets for 113-MeV protons

We have measured differential (P,xin) cross sections, d/sup 2/sigma/d..cap omega..dE/sub n/, from thin targets and absolute neutron yields from stopping-length targets at angles of 7.5/degree/, 30/degree/, 60/degree/, and 150/degree/, for the 113--MeV proton bombardment of elemental beryllium, carbon, aluminum, iron, and depleted uranium. Additional cross-section measurements are reported for oxygen, tungsten, and lead. We used time-of-flight techniques to identify and discriminate against backgrounds and to determine the neutron energy spectrum. Comparison of the experimental data with intranuclear-cascade evaporation-model calculations with the code HETC showed discrepancies as high as a factor of 7 in the differential cross sections. These discrepancies in the differential cross sections make it possible to identify some of the good agreement seen in the stopping-length yield comparisons as fortuitous cancellation of incorrect production estimates in different energy regimes. 13 refs., 20 figs., 4 tabs.

Differential neutron production cross sections for 256-MeV protons

In this paper differential (p, xn) cross sections d{sup 2}{sigma}/d{Omega}E{sub n}, from the thin targets of beryllium, carbon, oxygen, aluminum, iron, lead, and {sup 238}U for 256-MeV protons are measured. Time-of-flight techniques are used to identify and discriminate against backgrounds and to determine the neutron energy spectrum. Comparison of the experimental data with intranuclear-cascade evaporation-model calculations using the HETC code showed discrepancies of as much as a factor of 7, notably at 7.5 and 150 deg.

Neutron Yields from Stopping- and Near-Stopping-Length Targets for 256-MeV Protons

We have measured absolute neutron yields at angles of 30/degree/, 60/degree/, 120/degree/, and 150/degree/, for the 256-MeV proton bombardment of elemental carbon, aluminum, and iron and of depleted uranium. We used time-of-flight techniques to identify and discriminate against backgrounds and to determine the neutron energy spectrum. Comparison of the experimental yields with intranuclear-cascade evaporation-model calculations with the codes HETC and ISABEL showed very good agreement over the entire neutron energy range except at 150/degree/. 16 refs., 31 figs., 4 tabs.

Linear Accelerator‐Based Active Interrogation For Detection of Highly Enriched Uranium

Photofissions were induced in samples of highly enriched uranium (HEU) with masses up to 22 kg using bremsstrahlung photons from a pulsed 10‐MeV electron linear accelerator (linac). Neutrons were detected between pulses by large 3He detectors, and the data were analyzed with the Feynman variance‐to‐mean method. The effects of shielding materials, such as lead and polyethylene, and the variation of the counting rate with distance for several configurations were measured. For comparison, a beryllium block was inserted in the beam to produce neutrons that were also used for interrogation. Because both high‐energy photons and neutrons are very penetrating, both approaches can be used to detect shielded HEU; the choice of approach depends on the details of the configuration and the shielding.

Neutron Yields from Stopping-Length Targets for 256-MeV Protons

In this paper absolute neutron yields from stopping-length targets at angles of 7.5, 30, 60, and 150 deg for the 256-MeV proton bombardment of elemental beryllium, carbon, aluminum, and iron are measured. Time-of-flight techniques are used to identify and discriminate against backgrounds and to determine the neutron energy spectrum. Comparison of the experimental data with intranuclear-cascade evaporation-model calculations using the HETC code showed good agreement, indicating that transport probably dominates production effects in the calculations.

Photon and Neutron Active Interrogation of Highly Enriched Uranium

The physics of photon and neutron active interrogation of highly enriched uranium (HEU) using the delayed neutron reinterrogation method is described in this paper. Two sets of active interrogation experiments were performed using a set of subcritical configurations of concentric HEU metal hemishells. One set of measurements utilized a pulsed 14‐MeV neutron generator as the active source. The second set of measurements utilized a linear accelerator‐based bremsstrahlung photon source as an active interrogation source. The neutron responses were measured for both sets of experiments. The operational details and results for both measurement sets are described.

Effects of proton beam quality on the production of gamma rays for nuclear resonance absorption in nitrogen

We describe a method for performing nuclear resonance absorption with the proton beam from a radio frequency quadrupole (RFQ) linear accelerator. The objective was to assess the suitability of the pulsed beam from an RFQ to image nitrogen relative to that of electrostatic accelerators. This choice of accelerator results in tradeoffs in performance and complexity, in return for the prospect of higher average current. In spite of a reduced resonance attenuation coefficient in nitrogen, we successfully produced 3D tomographic images of real explosives in luggage the first time the unoptimized system was operated. The results and assessments of our initial laboratory measurements are reported.

Radiation dosimetry through spectral definition

Abstract We have developed a fieldable instrumentation system for determining from measured flux spectra, both the neutron and gamma ray dose rate distributions associated with radioactive sources. This system includes the sensors, the computer-based data acquisition and analysis hardware, and the requisite software for unfolding the sensor response functions to obtain the flux spectra, and for folding the resultant flux spectra with appropriate flux spectrum-to-dose conversion factors. We use bismuth germanate scintillators that have experimentally measured and analytically interpolated response functions to determine the gamma ray flux spectra, and a suite of neutron sensors, based on proton recoil and 3 He capture, to determine the neutron flux spectra. In addition, gamma ray peak identification is done using HPGe sensors. We describe the equipment and procedures and present some recent results.