radiation shielding progress

The unwanted radiation of the reactor core has to be absorbed to shield people and the instrument from this radiation. For people the instrument should not introduce more than 1uSv/h above the background level in the reactor hal. For the instrument the requirement is a good-as-possible signal to noise (S/N) ratio (for instance 0.001). To verify that the current setup is feasible shielding-wise from these requirements, MCNP calculation have been performed on this instrument. This includes the core, the reactor shielding and the instrument shielding (with the current level of detail).

The figure below shows the logarithmic levels of the neutron flux according to these calculations. A standard iron-PE-boron mixture has been used in these calculations. The picture below shows the beam from the reactor coming from the left. The germanium crystal monochromator (not displayed) reflects the wanted part of the neutron beam to the sample (in blue circle). The neutrons scattered from the sample are reflected to (green) detector. The detector is situated in an acceptable background flux of 1n/s/cm2. Collimation will improve this level of the background.

top view of instrument with shielding in grey

Fast, epi-thermal neutron, and gamma flux levels are higher but not unacceptable.

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