Pyrochemical multiplicity counter development

Impure plutonium-bearing materials from pyrochemical processes often display both significant self-multiplication and variable ({alpha},n) reaction rates. Standard neutron coincidence counting techniques usually fail to accurately measure these materials. Neutron multiplicity counters measure the third moment of the neutron multiplicity distribution and thus make it possible to deduce the fertile plutonium mass of a sample even when both the self-multiplication and the ({alpha},n) reaction rate are unknown. A multiplicity counter suitable for measuring pyrochemical materials has been designed and built. This paper describes the results of characterization studies for the new counter. The counter consists of 126 helium-3 tubes arranged in 4 concentric rings in a polyethylene moderator; the average spacing between the tubes is 1.59 cm. The end plugs for the counter are made of graphite, and the 24.1- by 37.5-cm sample cavity is cadmium lined. The counter consists of two distinct halves from which the neutron counts are summed. The counter is capable of operation in either a freestanding mode with the two halves coupled together by an external cabinet or in a glove-box mode with the two halves placed around a glovebox well and then mated. For a {sup 252}Cf source centered in the sample cavity, the measured efficiency of the new multiplicity counter is 57.7% and its die-away time is 47.2{mu}s. 8 refs., 9 figs

High energy, heavy ion nuclear microprobe for ion beam research on the tandem accelerator at ANSTO.

A comprehensive review is given on the production and use heavy ion beams with spot sizes of a few μm. The development of a high energy, heavy ion microprobe at ANSTO and its possible applications are discussed

Characterization of sputtered SmCo thin films for light element contamination using RBS and HIERDA techniques

Samariurn cobalt films were prepared on silicon substrates with and without a chromium buffer layer at room temperature and 600degreesC using direct current unbalanced magnetron sputtering. For obtaining ideal magnetic properties, the films should be free from impurities, such as O, Al and others. Rutherford backscattering spectrometry and heavy ion elastic recoil detection analysis were used to determine the composition and film thickness and to monitor the light element contamination across film thickness. X-ray diffractometer and superconducting quantum interference device were employed to characterize the structure and magnetic properties of the films, respectively. The results obtained led to an improved design of the ground shield and the use of a sorption pump to effectively minimize aluminium and oxygen concentration in the films, respectively

Characterisation of single-crystal mercuric iodide.

The mobility-lifetime product of electrons and holes in single-crystal mercuric iodide for detector applications was measured to be 4×10−5 and 3×10−5 cm2/V respectively. The charge carriers were optically induced by a near band gap excitation using a GaP (560 nm) light emitting diode. Optical Deep Level Transient Spectrometry measurements of trapping states showed three dominant energy levels at 0.26, 0.8 and 1.4 eV. There is little correlation between trapping levels reported in the literature. © 2004, Elsevier Ltd

Neutron multiplicity counter development

We have designed and built two multiplicity counters to test the usefulness of multiplicity counting for the safeguards assay of plutonium-bearing materials. The first prototype counter has been characterized and a variety of plutonium-bearing materials have been measured with it. Assays accurate to {approximately}0.7% have been obtained for both pure and impure plutonium oxide samples in reasonable measurement times. Assays accurate to {approximately}5% have been obtained for metal samples. A second multiplicity counter has been designed using experience gained from the first as well as Monte Carlo simulations. The second counter was designed to be more suitable for in-plant measurement of pyrochemical process materials. This paper presents the results of characterization studies of the two instruments. 10 refs., 9 figs., 2 tabs