The photoncutron ambient dose around a 18 MV medical electron lineal accelerator has been measured with LiF:Mg,Ti chips of 3 x 3 x 1 mm inside moderating spheres. During the measurements a water phantom was irradiated in a field of 40 x 40 cm2. Two methods have been considered for comparison. In the first, a TLD-600/TLD-700 pair at the centre of a 25 cm diameter paraffine sphere was used, with the system behaving as a rem meter. In the second method, TLD-600/TLD-700 pairs, bare and at the centre of 7.6, 12.7, 20.3, 25.4, and 30.5 cm diameter polyethylene Bonner spheres were used to obtain the neutron spectrum. This was unfolded using the BUNKIUT code with the SPUNIT algorithm and the UTA4 and ARKI response functions. The neutron dose was followed by multiplying the unfolded neutron spectrum by the ambient dose equivalent to neutron fluence conversion factors. Both methods result in 0.5 mSv x Gy(-1) m away from the isocentre.

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The responses of TLD-1010, TLD-700 and TLD-600 thermoluminescence dosemeters to the radiation field inside a water tank enclosing an isotopic 241Am-Be neutron source are analysed. Separate contributions coming from thermal neutrons, neutrons with energies above thermal and gamma rays to the total response of the three types of TLD are obtained. This is accomplished by assuming that the gamma responses for materials with different 6Li enrichments are identical and that the neutron response of TLD-700 is negligible compared to TLD-100 and TLD-600. The last assumption is tested by Monte Carlo simulations of the neutron energy spectrum at the points where the TLDs are irradiated.

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