Monitoring a sample containing a neutron source
AssigneeBritish Nuclear Fuels plc
InventorsJohn Paul Ronaldson, Robert Jonathan Sharpe
Life of this patent
Estimating the term…
Abstract
The invention considers the frequency distributions of singles, doubles and triple neutron emission events from a sample under assay. The count rates are equated to mathematical functions related to the spontaneous fission rate, self-induced fission rate, detection efficiency and α,n rate with probability distribution assigned to each of those factors, the value of the product of all the probability distributions being increased to give an optimised solution and so provide a value of the spontaneous fission rate which is linked to the mass of the neutron source. The technique aims to provide increased accuracy and certainty compared with neutron coincidence counting based techniques.
Claims12
A method of monitoring a sample containing a neutron source in which:—
- i) signals from a plurality of neutron detectors are analysed and the count rates for single, double and triple incidence of neutrons on the detectors are determined;
- ii) the single, double and triple count rates are equated to a mathematical function related to the spontaneous fission rate, self-induced fission rate, detection efficiency and α,n rate;
- iii) a probability distribution is assigned to each of the self-induced fission rate, detection efficiency and α,n reaction rate and each of the counting rates to provide a probability distribution factor for any given value;
- iv) and the value of the product of all the probability distribution factors is increased to give an optimised solution and so provide a value for the spontaneous fission rate which is linked to the mass of the neutron source.
A method according to any preceding claim in which the doublet counting rate is related to the spontaneous fission rate, the self-multiplication factor, where
- 29 m = 1 - p ( 1 - p ) υ I
- and p=probability first neutron causes induced fission;
- the detection efficiency and the α,n reaction rate by the function
- 30 R 2 = ϵ 2 · F s · M 2 · v s2 · ( 1 + ( M - 1 ) ( 1 + α ) v s1 v s2 v s2 ( v s1 - 1 ) ) .
- .
A method according to any preceding claim wherein the triplet counting rate is related to the spontaneous fission rate, the self-multiplication factor, where
- 31 m = 1 - p ( 1 - p ) υ I
- and p=probability first neutron causes induced fission;
- the detection efficiency and the α,n reaction rate by the function
- 32 R 3 = ϵ 3 · F S · M 3 · v S 3 · ( 1 + 2 ( M - 1 ) v S 2 V I 2 v S 3 ( v I 3 - 1 ) + ( M - 1 ) ( 1 + α ) v S 1 v I 3 v S 3 ( v I 1 - 1 ) ( 1 + 2 ( M - 1 ) v I 2 2 v I 3 ( v S 1 - 1 ) ) ) .
- .
A method according to any preceding claim in which the probability distribution assigned to individual variables or counting rates is a normal distribution or a flat distribution or a triangular distribution.
A method according to any preceding claim in which the distributions are constrained within certain applied constraints/boundaries, such that the probability distribution factor is zero beyond the constraints or such that the probability distribution factor rapidly tends to zero beyond certain values.
A method according to any preceding claim in which the increasing, and preferably maximisation, of the product of the probability distribution factors (pdf's) is preferably performed as an iterative process.
Dependencies are inferred from the claim text.