A New Neutron Multiplicity Deadtime Scheme
- Canberra Industries Inc., Meriden, CT (United States)
Deadtime corrections for passive neutron coincidence counting are traditionally formulated in terms of the Totals counting rate. The deadtime correction is exponential in form with the effective deadtime being linear in terms of observed Totals rate. The deadtime coefficient for the Reals rate is traditionally fixed at four times that of the Totals rate parameter. When it comes to multiplicity counting, however, more complex expressions are typically used for the Doubles and Triples rates based on mathematical actions to the multiplicity histograms with the Singles (or Trigger) rate being treated rather simplistically. Since the Totals and Singles and Reals and Doubles, respectively, are effectively equivalent measures, the difference in deadtime treatment results is an inconsistency. Furthermore, additional empirical correction factors are often applied in the case of the multiplicity deadtime corrections and these do not follow from the underlying theoretical framework. The purpose of this paper is to re-examine the semi-empirical deadtime correction expressions from a fresh perspective. We propose to a scheme whereby Totals and Singles are treated equivalently with the correction having the transcendental form of the paralysable model. The impact of correlations on the Totals deadtime correction is shown to be modest. The deadtime correction factor for Reals and Doubles are again treated similarly also using an exponential form in terms of the corrected Total event rate but with a deadtime parameter which is not fixed ahead of time to be four times that used in the Totals correction. In the case of the Triples correction, which is evaluated from a composite expression, the deadtime corrections for the Singles and Doubles are used as appropriate but a new empirical correction, again given in terms of the corrected rate, is introduced. The new correction acts only on the part of the Triples expression which is does not represent the correlated-accidentals. The new scheme is not based on an elaborate mathematical model for deadtime losses and consequently does not involve a deadtime-function-weighted sum of histogram elements. In that sense it is simpler to understand and implement. Determination of the free deadtime parameters is based on first extracting the deadtime parameter for the Singles for which several options are available. The Doubles deadtime parameter is then based on rendering the corrected Doubles to Singles ratio for Cf-252 invariant to trigger rate. Similarly the Triple deadtime parameter is extracted from Cf-252 data given the Singles (or Trigger) and Doubles parameters. In this article we briefly review current practice, lay out the new concept and illustrate their application with experimental data of a passive neutron multiplicity counter. (authors)
- Research Organization:
- WM Symposia, 1628 E. Southern Avenue, Suite 9 - 332, Tempe, AZ 85282 (United States)
- OSTI ID:
- 21323120
- Report Number(s):
- INIS-US-10-WM-08383; TRN: US10V0578064311
- Resource Relation:
- Conference: WM'08: Waste Management Symposium 2008 - HLW, TRU, LLW/ILW, Mixed, Hazardous Wastes and Environmental Management - Phoenix Rising: Moving Forward in Waste Management, Phoenix, AZ (United States), 24-28 Feb 2008; Other Information: Country of input: France; 10 refs
- Country of Publication:
- United States
- Language:
- English
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