Comparison of the neutron spectra of reference neutron sources for the improvement of the ISO 8529 Standard series

Project Description

The ISO working group for reference radiation fields (TC85/SC2/WG2) has recently expressed the need for accurate measurements of the neutron spectra of reference 241Am-Be neutron sources having different source activity, encapsulations and constituting materials. For these sources, the spectra and related dosimetric quantities may differ significantly from the data recommended in the actual ISO Standard 8529-1, due to different 241Am activity, fabrication method and encapsulation type. In addition, the low-energy spectra (< 1 MeV) of these sources have not been measured but only estimated by interpolation or calculation. One of the projects of ISO (see resolutions of ISO/TC85/SC2/WG2 meeting, 16-18 June 2008, Orlando, FL) is the revision of the ISO Standard 8529-1, including the formulation of new recommendations on the mentioned topics.

Recent work performed by IRSN, NPL and PTB (see Section 8) allowed evaluating, with high-resolution spectrometry techniques (such as NE213 and BC501), the high-energy spectra (> 1 MeV) of 241Am-Be sources having different 241Am activity and encapsulation type.

This project proposes the use of the Bonner Sphere Spectrometry (BSS) technique to determine the low-energy spectrum of 241Am-Be sources with different encapsulations and 241Am activity, focusing on the commercially available formats (e.g. 1 Ci (X3), 10 Ci - 15 Ci (X14)). These data will be matched with those available at high-energy. Preferably, sources whose high-energy spectrum is known through high-resolution techniques will be selected for BSS measurements. A pre-evaluation computational study is planned to predict the performance of BSSs when exposed to the mentioned sources.

The experimental campaign will be hosted by NPL, where a relevant number of 241Am-Be sources of different formats (particularly those commercially available) are available. Measuring time at no cost will be provided.

BSSs based on different central detectors and having different spheres (especially small diameters suitable to detect low-energy neutrons) should be used. The INFN-LNF, PTB, IRSN, NPL and UAB groups agreed to undertake the measurements. After a final elaboration phase, the "typical" 241Am-Be spectra for different source formats will be published and included in the revised ISO Standard.

Final Report 2016-06-22

Results are published in Nuclear Instruments and Methods A 10.1016/j.nima.2014.06.040


Further Information

The works on the high-energy 241Am-Be spectra are: Radiat. Prot. Dosim. 125 (1-4) 69-72 (2007); Radiat. Prot. Dosim. 126 (1-4) 3-7 (2007); Radiat. Prot. Dosim. 126 (1-4) 413-417 (2007).

This project, together with a computational study to derive the neutron spectrum from encapsulation type and materials, are the result of two meetings of a group of European neutron dosimetry experts (Bologna, Oct. 12th 2007 and Paris, Jan. 24th 2008). Minutes available from the proposer.

The project will be piloted jointly by INFN-LNF (Roberto Bedogni) and NPL (Neil Roberts)

Ionising Radiation (IR)
Neil Roberts, NPL (United Kingdom)
Phone: +44 20 8943 6869
Coordinating Institute
NPL (United Kingdom)
Participating Partners
Further Partners
Instituto Nationale di Fisica Nucleare, Laboratori Nazionali di Frascati, INFN-LNF (Italy)
Universitat autonoma de Barcelona, UAB (Spain)