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Data from manganese bath measurements of the neutron emission rates from commercial 252Cf sources over a period of 40 years have been used to derive an accurate value for the 252Cf half-life. Particular care was taken to account for the presence of other californium and curium isotopes in the sources, and the resulting value has an uncertainty of 0.05%. The present value has been compared with earlier measurements in a review of this important half-life. [ABSTRACT FROM AUTHOR]

A Bonner Sphere spectrometer employing a large, 11 mm diameter × 3 mm thickness, 6 LiI(Eu) scintillator (LL-BSS), was assembled. The purpose was to produce a BSS similar in sensitivity to those based on 3 He sensors, but using alternative sensors. With respect to the traditional BSS based on the 4 mm (diameter) × 4 mm (height) 6 LiI(Eu), this new BSS is a factor of 3 more sensitive. LL-BSS response matrix, determined with MCNPX, was experimentally evaluated with monoenergetic reference neutron fields of 144 keV, 565 keV and 1.2 MeV available at NPL (Teddington, UK). The results of the experiment confirmed the correctness of the response matrix within an overall uncertainty lower than ±2%. [ABSTRACT FROM AUTHOR]

Americium–beryllium neutron sources are certainly the most widely used in neutron dosimetry laboratories, basically due to their long half-life and their energy distribution, which covers the energy domain of interest for many applications in ambient and personal dosimetry. Nevertheless, the spectrum of this source depends on the materials and dimension of the capsule and on the amount and physical–chemical properties of the active material, thus affecting relevant quantities such as the spectrum-averaged fluence-to-dose equivalent conversion coefficient. A EURAMET (European Association of National Metrology Institutes) project (n. 1104) was initiated to experimentally investigate how the neutron spectrum changes for different source sizes and encapsulations with a view to providing improved data for a planned revision of the ISO 8529 Standard Series. The experimental campaign was carried out in the low scatter facility at NPL. Here three different Bonner sphere spectrometers, BSSs, were exposed to the neutron fields produced by three different neutron sources formats: one X3 capsule (1 Ci) and two X14 capsules (10 Ci and 15 Ci). The specific advantage of the BSS is the large sensitivity to low-energy neutrons ( E <0.1 MeV) which is the component expected to be most affected by the capsule-to-capsule variations and the component which is least well known. This paper summarises the results of the campaign with emphasis on (1) estimating the low-energy component of the Am–Be neutron spectrum, according to the encapsulation type; (2) evaluating the coherence between the Bonner spheres data and the previous studies performed with high-resolution spectrometers but limited in energy to E >0.1 MeV; (3) understanding whether the ISO-recommended Am–Be spectrum needs to be amended, and for which source formats. [ABSTRACT FROM AUTHOR]

Abstract: The discrimination of neutron and -ray events in an organic scintillator with the pulse gradient analysis (PGA) method is verified against that achieved via the digital measurement of time of flight (TOF). Events arising from the reaction have been detected with an LS-301 organic liquid scintillator and recorded with a fast digital sampling oscilloscope. Both qualitative (via the cross-referencing of scatter diagrams) and quantitative (via the neutron/-ray ratio) comparisons are reported. Discrimination afforded by the PGA method is observed to be consistent with that achieved by digital TOF. [Copyright &y& Elsevier]

All available measured data for the response characteristics of the Leake counter have been gathered together. These data, augmented by previously unpublished work, have been compared to Monte Carlo simulations of the instrument''s response characteristics in the energy range from thermal to 20 MeV. A response function has been derived, which is recommended as the best currently available for the instrument. Folding this function with workplace energy distributions has enabled an assessment of the impact of this new response function to be made. Similar work, which will be published separately, has been carried out for the NM2 and the Studsvik 2202D neutron area survey instruments. [Copyright &y& Elsevier]

Abstract: The UK national standards laboratory, the National Physical Laboratory (NPL), provides an extensive range of facilities for measurements on neutron sources and neutron-sensitive devices. This paper describes recent improvements and extensions to the neutron standards. Correction factors used in source strength measurements have been improved, as have the scatter corrections used in monoenergetic and source-based irradiations. Characterisation of the thermal field facility has been improved by activation measurements. Experimental facilities developed recently include a system for measuring personal dosemeter responses at several energies simultaneously, and a neutron source tailored to simulate typical workplace fields. [Copyright &y& Elsevier]