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Investigation of the implications of 250Cf and 248Cm in 252Cf neutron sources.

Roberts, N J; Jones, L N (2004) Investigation of the implications of 250Cf and 248Cm in 252Cf neutron sources. NPL Report. DQL-RN 005

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Abstract

One of the most common radionuclide neutron sources used for calibration of detectors is 252Cf. However, these sources are not isotopically pure and also contain the neutron emitting isotope 250Cf. This has a longer half-life than 252Cf and so becomes a more significant fraction with time. 248Cm, formed as the daughter of 252Cf via a-decay, also emits neutrons through spontaneous fission. Consequently, as the source becomes older, the emission rate does not follow the decay curve of 252Cf. The impact of this effect on measurements made at NPL has been investigated in this report. The emission rate of a source can be underestimated by over 10% if the presence of 250Cf and 248Cm are not taken into account. The solution adopted at NPL is to make frequent emission rate measurements using a manganese bath and to fit a function to the data in order to extrapolate forward in time. The importance of this problem to other calibration laboratories and users of 252Cf sources is emphasised.

Item Type: Report/Guide (NPL Report)
NPL Report No.: DQL-RN 005
Subjects: Ionising Radiation
Ionising Radiation > Neutron Metrology
Last Modified: 02 Feb 2018 13:16
URI: http://eprintspublications.npl.co.uk/id/eprint/3129

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