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Neutron coincidence methods
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  • If a sample is surrounded with neutron detectors and neutrons are detected in one detector at the same time, then each such coincident event will represent the detection of one fission.
  • The rate of such coincidences appearing is proportional to the concentration at the spontaneous fissioning material.
  • A protocol such as the following is used.
    • a neutron is detected;
    • there is a short delay to allow the detector to stabilise (0.25 - 64 ms);
    • count for a short period to collect real and accidental coincidences (4 - 1024 ms). These counts are collected in an up down counter;
    • wait for a 'long' period (4 ms);
    • collect another count for the same time interval as the first, but in this case collect counts negatively in the up down counter, thus subtracting the accidental rate;
    • repeat until the net number of counts, the real coincidences, is significant to the required statistical degree.
 

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