ISO 8529-1:2001 pdf download
ISO 8529-1:2001 pdf download.Reference neutron radiations一
Part 1: Characteristics and methods of production.
The shape of the source should be spherical or cylindrical and, in the latter case, it is preferable that the diameter and length are approximately the same. The thickness of the encapsulation should be uniform and small compared to the external diameter. For a 241Am-Be(a,n) source, the spectral distribution, mainly in the energy range below approximately 2 MeV, depends, to some extent, on the size and the composition of the source. Sources should comply with the encapsulation requirements in ISO 2919.
The 241Am-Be(a,n) source may be wrapped in a 1 mm thick lead shield. This reduces the photon dose-equivalent rate to less than 5 % of the neutron dose-equivalent rate. The lead shield produces a negligible change (less than 1 %) in the neutron dose-equivalent rate. In the absence of the lead shield, the photon dose-equivalent rate (mainly from y-rays having an energy of 59,5 keV) will depend upon the source construction, but may be comparable with the neutron dose-equivalent rate.
4.3 Characteristics of calibration sources
4.3.1 Types
Preferably 241Am-Be (a,n) and/or 252Cf spontaneous fission sources should be used for routine calibration (see ISO 8529-3). 252Cf sources generally have a high specific source strength and are therefore comparatively small. Because of their half-life of 2,65 years, they need occasional replacement. The americium-based neutron source shall consist of an americium alloy or a homogeneous, compressed mixture of americium oxide and beryllium or boron as appropriate, americium alloys may also be used.
4.3.2 Energy distribution of neutron source strength
The energy distributions of neutron source strength for 241Am-Be (a,n), 252Cf, 252Cf(D20-moderated) and 241 Am-B (c,n) sources are given in annex A (Tables A.1 to A.4 and Figures A.1 to A.4). The energy distribution of the neutron source strength, BE, of 252Cf, is given in annex A. In the energy range from 100 keV to 10 MeV, it can be described by the following formula:
where Tis a spectrum parameter given by T= 1,42 MeV )[4] (see Figure A.1).
The neutron spectra given in annex A are those recommended for lightly encapsulated sources (see 4.2.2). The spectrum-averaged fluence-to-dose-equivalent conversion coefficients contained in Table 1 and in ISO 8529-3 have been calculated for these spectra. For the cases of heavy encapsulation, or special construction of the D20-moderated 252Cf source, spectra may change significantly. If such source strength spectra, BE, or fluence spectra, 1’E are known from calculation or measurement, specific spectrum-averaged conversion coefficients should be calculated using:
where is taken to be proportional to BE.
4.4 Neutron fluence rate produced by a source
The fluence rate produced by a neutron source is determined primarily from the neutron source strength and the distance between the source centre and the point of test. Neutron sources generally show anisotropic neutron emission in a coordinate system fixed in the geometrical centre of the source. For cylindrical sources, the angular source strength, B1 in a direction .0, which is characterized by the angles 6and a(see Figure 1), does not depend noticeably on the azimuth angle a, but only upon angle 6. As the angular source strength dB/d.0 varies least for 6= 90°, this direction should be used for calibrations.
There is the possibility, however, that, with time, the constituent components of the americium-beryllium and americium-boron powder sources may shift with respect to each other, with a resultant change in the neutron source strength. It is therefore recommended that these sources be recalibrated every five years.
