| Summary: | The measurement of neutron dose equivalent was made in four dual energy
linear accelerator rooms. Two of the rooms were reconstructed after
decommissioning of 60Co units, so the main limitation was the space. The
measurements were performed by a nuclear track etched detectors LR-115
associated with the converter (radiator) that consist of 10B and with the
active neutron detector Thermo BIOREM FHT 742. The detectors were set at
several locations to evaluate the neutron ambient dose equivalent and/or
neutron dose rate to which medical personnel could be exposed. Also, the
neutron dose dependence on collimator aperture was analyzed. The obtained
neutron dose rates outside the accelerator rooms were several times smaller
than the neutron dose rates inside the accelerator rooms. Nevertheless, the
measured neutron dose equivalent was not negligible from the aspect of the
personal dosimetry with almost 2 mSv a year per person in the areas occupied
by staff (conservative estimation). In rooms with 15 MV accelerators, the
neutron exposure to the personnel was significantly lower than in the rooms
having 18 MV accelerators installed. It was even more pronounced in the room
reconstructed after the 60Co decommissioning. This study confirms that
shielding from the neutron radiation should be considered when building
vaults for high energy linear accelerators, especially when the space
constraints exist.
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