Characterization of the collimated output fluence , in a thermal neutron field, in terms of ambient equivalent dose H*(10,0)

The Brazilian Neutron Laboratory at the Institute of Radioprotection and Dosimetry (IRD) developed and built a new standard facility for thermal neutron flux, seeking to provide a new homogeneous fluence to calibrate neutron detectors and personal dosimeters. The purpose of this work is therefore to characterize the collimated output fluence, in a thermal neutron field, in terms of ambient equivalent dose H*(10,0) for calibration and irradiation of personal monitors and neutron survey meters.  The neutron fluence in the system irradiation field needs to be well known for personal monitors and neutron survey meters calibrated used in nuclear reactors in addition to studies and development of new materials for neutron dosimetry. The characterization of neutron thermal energy fields at the usual calibration points is one of the recommendations of the International Organization for Standardization ISO 8529, 2001 for international intercomparison of neutron fluence measurements. The determination of the ambient equivalent dose of the new facility was estimated based on a secondary transfer standard internationally known as Long Counter and properly characterized and traced back to the Neutron Laboratory primary standards

A feasibility study of a H2O-moderated 252Cf source for metrology

The new edition of ISO 8529 series reduced from 4 to 3 standard neutron reference field. Recent studies have highlighted the increasing importance of characterizing neutron source spectra at different energies to obtain appropriate fluence-to-dose-equivalent conversion coefficient. This study presents the determination of neutron energy fluency from a free and moderated 252Cf (120 µg) source placed within spheres of different diameters containing distilled water. The spectrum determination is based on both Monte Carlo simulations and experimental measurements with Bonner Sphere Spectrometer (BSS) of multiple diameters: 5.08 cm (2"), 7.62 cm (3”), 12.70 cm (5”), 20.32 cm (8”), 25.40 cm (10”), and 30.48 cm (12”). The aim was to characterize the new water-moderated spectra, obtaining reference values for operational quantities that represent realistic radiation fields for testing, calibrating, and irradiation of personal dosimetry and survey meters