Calibration and Monte Carlo modelling of neutron long counters

The Monte Carlo technique has become a very powerful tool in radiation tran sport as full advantage is taken of enhanced cross-section data. more power ful computers and statistical techniques. together with better characterisa tion of neutron and photon source spectra. At the National Physical Laborat ory, calculations using the Monte Carlo radiation transport code MCNP-4B ha ve been combined with accurate measurements to characterise two long counte rs routinely used to standardise monoenergetic neutron fields. New and more accurate response function curves have been produced For both long counter s. A novel approach using Monte Carlo methods has been developed. validated and used to model the response function of the counters and determine more accurately their effective centres. which have always been difficult to es tablish experimentally. Calculations and measurements agree well, especiall y for the De Pangher long counter for which details of the design and const ructional material are well known. The sensitivity of the Monte Carlo calcu lations for the efficiency of the De Pangher long counter to perturbations in density and cross-section of the polyethylene used in the construction h as been investigated. (C) 2000 National Physical Laboratory. Published by E lsevier Science B.V. All rights reserved.