BS ISO 8529-1:2021 pdf download – Neutron reference radiations fields Part 1: Characteristics and methods of production 4 Broad spectrum neutron reference radiation fields produced with radionuclide sources 4.1 Overview In this clause, neutron reference fields produced with radionuclide sources are specified, which are particularly suited for the calibration of neutron‑measuring devices (see Reference [2]). Thermal neutron reference radiation fields are achievable by moderating radionuclide sources, but are covered by Clause 6. 4.2 Types of calibration sources The radionuclide sources given in Table 1 shall be used to produce neutron reference radiation fields. The numerical values given in Table 1 are to be taken only as a guide to the prominent features of the sources, since the properties of a specific source vary with the construction of the source, because of scattering and absorption of neutron and gamma radiation, and with the isotopic impurities of the radioactive material used. Hence details of the source encapsulation are specified (see 4.3), and the method for determining the anisotropy of the neutron emission is specified (see Annex E). 252 Cf has a high specific neutron emission rate and 252 Cf sources are therefore comparatively small. Because of their short half‑life of 2,647 years, they need regular replacement. The D 2 O‑moderated 252 Cf source is ideally composed of a point 252 Cf source located in the centre of a 300 mm diameter heavy‑water sphere, surrounded by a) a 0,8 mm thick iron shell, and b) a1 mm thick cadmium shell. In practice, a number of designs have been developed in reference laboratories, being slightly different in terms of construction details, such as the guide used to locate the source in the sphere centre, the material used to contain the heavy water, and the structure used to suspend or hold the moderating sphere. In addition, every moderating assembly has specific D 2 O purity and 252 Cf source capsule. The experience of reference laboratories suggests that variability in the construction of D 2 O‑moderated 252 Cf sources results in non‑negligible differences in the energy distribution of the neutron fluence [3] . Laboratories should characterize their D 2 O‑moderated 252 Cf sources by simulations and spectral measurements. The energy distribution of the neutron emission rate and spectrum‑averaged quantities of these fields should be checked through comparisons. A representative spectrum of the D 2 O‑ moderated 252 Cf source was derived, for the purposes of this...

Download Address

  • Download