Further development of the LNMRI/IRD's TNF2 thermal system for flexible dose rate irradiation.

The 'Inverse Square Law' (ISL)(  1) requires the existence of a point radiation source to be validated, but in some cases where there is more than one source, its use is possible as long as a point is determined where a virtual source can be positioned and from this point the points correspond to the ISL. Ambient dose equivalent rate values were obtained by simulation and measurements at various points along the LNMRI Thermal Neutron Flux 2 (TNF2) central axis front face, determining a function corresponding to the inverse square of the distance and the font position at the virtual point 'y0', so that the ISL is respected. This function will help in the neutron monitors calibration, previously estimating the ambient dose equivalent at a certain distance from the face.

POLYETHYLENE FILTER FOR THE TNF2 THERMAL NEUTRON FACILITY.

The Standard Thermal Neutron Flux Unit, TNF2, in (LNMRI/IRD)(1,  2), was built for neutron detector and survey meter calibrations. The facility's fluence is achieved by moderation of four 241Am-Be with a graphite core and paraffin/graphite blocks surrounding it. Due to the small channel dimensions, it is impossible to calibrate personal dosemeters and survey meters for thermal neutrons. A polyethylene filter construction was carried out to allow the external irradiation of personal dosemeters and neutron survey meters. The polyethylene filter was constructed with 29 stacked discs with diameters ranging from 5 to 34 cm. Different thicknesses were simulated to provide the desired effect. This new irradiation configuration was also experimentally tested and compared with simulation results with MCNPX(3).

Neutron metrology laboratory facility simulation.

The Neutron Low Scattering Laboratory in Brazil has been completely rebuilt. Evaluation of air attenuation parameters and neutron component scattering in the room was done using Monte Carlo simulation code. Neutron fields produced by referenced neutron source were used to calculate neutron scattering and air attenuation.