Thermal neutron multiplicity counting of samples with very low fission rates

When samples with very low fission rates are assayed using thermal neutron multiplicity counting, shift register electronics, and the moments formalism for the singles, doubles, and triples count rates, large counting statistics errors can occur in the triples rates because of cosmic ray events. These counting statistics errors can be greatly reduced using gate multiplicity analysis when cosmic ray events produce high multiplicity neutron bursts. The gate multiplicity analysis method, measurement data, and results are presented

Shift-register coincidence electronics system for thermal neutron counters

An improved shift-register, coincidence-counting logic circuit, developed for use with thermal neutron well counters, is described in detail. A distinguishing feature of the circuit is its ability to operate usefully at neutron counting rates of several hundred kHz. A portable electronics package incorporating the new coincidence logic and support circuits is also described

Metal enrichment processes

There are many processes that can transport gas from the galaxies to their environment and enrich the environment in this way with metals. These metal enrichment processes have a large influence on the evolution of both the galaxies and their environment. Various processes can contribute to the gas transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy interactions and others. We review their observational evidence, corresponding simulations, their efficiencies, and their time scales as far as they are known to date. It seems that all processes can contribute to the enrichment. There is not a single process that always dominates the enrichment, because the efficiencies of the processes vary strongly with galaxy and environmental properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 17; work done by an international team at the International Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke

Birdcage neutron coincidence counter manual

A thermal neutron coincidence counter has been constructed for the assay of fast critical assembly fuel plates stored in birdcages. Standard coincidence counting electronics are used. This manual describes the birdcage, the measurement system, and its performance characteristics. 3 refs

Pulse generator for testing shift-register coincidence electronics

A multi-function electronic pulser has been implemented as a nuclear instrument module for the checkout and debugging of neutron coincidence counter shift-register electronics. The pulser has five different outputs: random, correlated, periodic, burst, and a long-delay circuit check. The frequency for the random and periodic is selectable from frequency of 5 kHz and consists of pulse pairs produced randomly at a rate of 2.5 kHz. The second pulse of a pair follows the first with a probability proportional to exp(-t/{tau}). The correlated pulser produces an exponential die-away after 0.5 {mu}s following the first pulse of the pair. The burst pulser produces a fixed burst of 16 at a rate of 16 MHz; the burst rate is 100 Hz. The long delay is used to check the long delay of a shift-register. The long delay consists of pulse pairs separated by 4096.5 {mu}s produced at a rate of 100 Hz

Multiplicity sorter for shift-register coincidence electronics

A multiplicity sorter for the latest Los Alamos National Laboratory version of shift-register coincidence electronics is described. The multiplicity information taken from the coincidence-gate up-down counter is decoded and gated onto the output lines by prompt real-plus-accidental (R+A) and delayed accidental (A) strobes. Multiplicities of 0-7 and greater than or equal to 8 are sorted for both the R+A and A gates

Measurement of enriched uranium and uranium-aluminum fuel materials with the AWCC

The active well coincidence counter (AWCC) was calibrated at the Chalk River Nuclear Laboratories (CRNL) for the assay of 93%-enriched fuel materials in three categories: (1) uranium-aluminum billets, (2) uranium-aluminum fuel elements, and (3) uranium metal pieces. The AWCC was a standard instrument supplied to the International Atomic Energy Agency under the International Safeguards Project Office Task A.51. Excellent agreement was obtained between the CRNL measurements and previous Los Alamos National Laboratory measurements on similar mockup fuel material. Calibration curves were obtained for each sample category. 2 refs., 8 figs., 15 tabs

A two-fold reduction in measurement time for neutron assay: Initial tests of a prototype dual-gated shift register

Neutron coincidence counting (NCC) is used routinely around the world for nondestructive mass assay of uranium and plutonium in many forms, including waste. Compared with other methods, NCC is generally the most flexible, economic, and rapid. Many applications of NCC would benefit from a reduction in counting time required for a fixed random error. We have developed and tested the first prototype of a dual- gated, shift-register-based electronics unit that offers the potential of decreased measurement time for all passive and active NCC applications