Speaker
Description
The International Standard ISO8529 on Neutron Reference neutron radiations fields, that constitutes the reference for the neutron calibration laboratories is under revision. Part 1 and 3, covering characteristics and methods of production, and the calibration of area and personal dosemeters respectively have already been updated. Part 2: Calibration fundamentals of radiation protection devices related to the basic quantities characterizing the radiation field is under revision by the working group responsible for the standard, ISO/TC85/SC2/WG2 (Reference Radiation Fields)/SG2(Neutrons).
Part 2 deals with the methods proposed to calibrate radiation protection devices in the neutron fields recommended by Part 1, mainly radionuclide sources $^{252}Cf$, $^{241}Am-Be$ and $D_2O$-moderated $^{252}Cf$, with special attention on the corrections necessary to determine their direct contributions. These corrections are related with the contribution of the scattered neutrons as consequence of the presence of walls, air, and other structures and geometry corrections that take into account the finite size of source and detector.
This work covers the studies carried out with MCNP simulations to validate the equations proposed in ISO 8529-1:2000 to define the geometry correction factor, $F_1(l)$, for the three radionuclide neutron sources described in Part 1 and two generic survey meters, spherical and cylindrical. These are idealized neutron detectors that consist of a spherical or cylindrical $^3He$ detector surrounded by a spherical or cylindrical moderator respectively. In both cases a thin Cd shell is included inside the polyethylene moderator to reproduce similar responses to those obtained by commercial devices.
From these six cases the three equations proposed in the standard have been fitted using statistical tools (like R) and new recommendations for the parameters $\delta$, $a4$ and $a5$ have been proposed to validate and complement the old values that were determined by analytical methods and limited to spherical devices and, in some circumstances, to point or spherical sources.