Relating to monitoring

1. A method of monitoring emissions from radioactive decay, the method comprising:

providing an instrument, the instrument including a plurality of detectors for detecting emissions from radioactive decay;

obtaining a data set using the instrument, the data set including a record of an emission event, together with an indication of the time of the emission event and the detector which detected the emission event, the data set including a plurality of such records from the plurality of detectors; and

processing the data set by:

analysing at least a part of the data set according to a first set of criteria to provide a first analysed data set, the first set of criteria including a first length of time between an emission event and the start of a time period, the time period being the time period providing a count of real and accidental coincidence emission events; and

analysing at least a part of the data set according to a second set of criteria to provide a second analysed data set, one or more criteria of the second set being different to the criteria of the first set, the second set of criteria being different to the criteria of the first set by providing a different length of time between an emission event and the start of the time period, the time period being the time period providing a count of real and accidental coincident emission events.

2. The method according to claim 1 in which one or more of the criteria are the time between an occasion and the start of the time period and/or the time between an occasion and the end of the time period and/or the time period between the start of the time period and the end of the time period.

3. The method according to claim 1 in which the first set of criteria includes a first length of time between the start of a time period and the end of a time period and the second set of criteria includes a second different length of time between the start of the time period and the end of the time period.

4. The method according to claim 3 in which the first time period is a measure of the real and accidental coincidences in the events, with the second time period being a measure of the accidental coincidences.

5. The method according to claim 4 in which the distribution of the number of events falling within the time periods is considered.

6. The method according to claim 1 further comprising:

reviewing the first analysed data set and the second analysed data set; and

selecting one of the analysed data sets in preference to the other, the set of criteria for the selected data set being selected to give a length of time period which excludes times at which only accidental coincidences occur.

7. The method according to claim 1 further comprising:

reviewing the first analysed data set and the second analysed data set; and

selecting one of the data sets in preference to the other, the set of criteria for the selected data set being selected to give a length of time period which excludes times for which real coincidences occur below a threshold rate.

8. The method according to claim 1 in which

the first set of criteria is the time between an event and an event which is n events later, where n is a positive integer and

the second set of criteria is the time between an event and an event which is m events later, where m is a positive integer and is different to n.