Neutron Coincidence Counting Research Articles

Non-destructive determination of spontaneously fissioning nuclides by neutron coincidence counting using multichannel time spectroscopy

A non-destructive method for determining the amount of actinoids has been developed. The method is based on thermal neutron coincidence counting and employs a selective detection of neutrons resulting from the spontaneous fission of actinoids. The detection system is described in detail and the measurement results of ='*4Cm as an example are presented. The results show that the measured fission rate of 244 Cm is consistent with the fission rate calculated from ENDF/B-V data and that the amount of **'Cm can be determined within about 5% accuracy even in the p~esence of a large amount of actinoids, for example, up to 2.6 �9 10 6, 3.6 �9 10 4, or 1.6 �9 l0 s times in the mass ratio of sSgPu, 2, ~ Am, or s 4 o Pu to ~ * 4 Cm, respectively.

A computer controlled, high performance, neutron coincidence counting system

A circuit to implement the neutron coincidence algorithm of Böhnel is described. The circuit uses static memory devices to store the pulse trains and has a throughput of 4M pps. It has a wide range of computer controlled operating parameters. It is suitable for monitoring plutonium in bulk or in small quantities contained in crates or drums of waste. The circuit has been in use for several years and has been found to be reliable. Full circuit diagrams are included.

Experimental study of neutron multiplication in BeO by the shift-register coincidence technique

The multiplication of 14 MeV neutrons by Be, which is used as a neutron multiplier in the design of fusion reactor blankets, is of topical interest as T-breeding depends on this. Earlier investigations have shown that the experimental multiplication of 14 MeV neutrons in Be and BeO is 20–25% lower than the calculated values. Recently, a different method has been proposed to measure the leakage multiplication based on a statistical correlation technique. This note explores the applicability of such a technique to determine experimentally the leakage multiplication of Am-Be source neutrons of average energy 4.5 MeV in a BeO assembly. The experimental method uses a high-level neutron coincidence counter (HLNCC) equipped with a shift-register coincidence logic unit. The deduced value of neutron leakage multiplication for 5 and 10 cm thick BeO in near rectangular geometry is 1.12 ± 0.03 and 1.15 ± 0.03, respectively.

A High-Performance Neutron Time Correlation Counter

A new, high-performance neutron time correlation, or coincidence, counter has been developed for the measurement of nuclear materials. This detector is an improvement over the high-level neutron coincidence counter that was used previously in that it has better counting rate capability, electronic stability, noise resistance, uniform counting zone, and portability. The system uses /sup 3/He gas tubes coupled to the shift register coincidence electronics through a new hybrid charge-sensitive preamplifier/discriminator. Counting rates of 1.3 MHz have been obtained and a counting stability of 0.002% has been measured. The system has been applied to the assay of plutonium content in metal, PuO/sub 2/, and PuF/sub 4/, as well as in uraniumplutonium mixtures.

Prompt Neutron Emission Probabilities Following Spontaneous and Thermal Neutron Fission

Accurate neutron emission probability distributions (Pv) associated with spontaneous and induced fission are necessary in correcting for neutron multiplication in neutron coincidence counting. A reanalysis of previously published Pv distributions is presented as well as recent measurements. All data were obtained using a large liquid scintillator tank.

A digital random pulser for testing nuclear instrumentation

A digital random pulser circuit based on a linear feedback shift register is described. The circuit provides a wide range of discrete output rates and exhibits very little deadtime. The testing of this circuit and its use with a neutron coincidence counter electronics circuit is discussed.

A comparative study of the shift register and conventional coincidence methods for neutron coincidence counting

Nondestructive assay of spontaneous fissioning nuclides like 240Pu using passive neutron counting calls for the measurement of spontaneous fission neutrons in the presence of a background of random (α, n) neutrons. Two different systems employing two different electronic techniques, the conventional coincidence and the shift register technique, have been fabricated to carry out coincidence measurements with thermalized neutrons. The paper summarises the results of a comparative study of the performance of the two systems and establishes the superiority of the shift register technique. The limitation of the method in the assay of 240Pu is shown to arise from the effect of neutron multiplication.

A Thermal Neutron Coincidence Counting System

Thermal neutron coincidence counters are used to measure plutonium-bearing materials in-line at the Plutonium Processing Facility at the Los Alamos Scientific Laboratory. Complicated operating proc...

Neutron Coincidence Counters for Nuclear Safeguards Applications

Reliable, accurate and rapid nondestructive assay instrumentation is playing an increasingly important role in the practical implementation of nuclear material safeguards, inspection and surveillance as well as in quality control and operational safety in all types of nuclear processing facilities. The neutron coincidence counting technique has been successfully demonstrated for nondestructive assay of samples containing Pu or U. The technique involves detecting neutrons from the spontaneous fission of 240Pu and 238U with polyethylene moderated neutron coincidence counters containing 3He- or BF3-filled detectors surrounding the sample to be assayed. The coincidence counting technique is necessary for reliable assay since total neutron count rate is dependent not only on the amount of Pu in the sample but also on the chemical composition. For example, if the sample contains PuO2 the total neutron production rate would be ~100 n/sec-g; however, if the sample contained PuF4 the total rate would be ~300 times larger than this. The spontaneous fission rate of both samples would be ~25 fiss/sec-g (for 5% 240Pu isotopic composition), independent of chemical composition. By using the coincidence counting technique it is possible to distinguish spontaneous fission neutrons from the randomly produced (?,n) neutrons. Thus coincidence counting provides a powerful method for rapid and accurate assay of Pu-bearing samples. Recently, the use of fast plastic scintillation detectors has significantly extended the range of usefulness of the coincidence counting technique to materials with extremely high (?,n) activities.