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I t has been shown that re-estimation of radiation dose is possible with 'LiF thermoluminescence dosemeters using ultra-violet light. The thermoluminescenoe response t o U.V. radiation and the optical absorption of 'LiF have been examined and the possibilities of this method of dose re-assessment are indicated. It is suggested that the thermoluminescence response to U.V. light is due to the presence of deep trapping centres which are bleached by suitable optical wavelengths.

The nature of the changes in TL response of COS-RAD Type-i lithium fluoride, after irradiation in a mixed field of thermal neutrons and prays, has been examined, and in particular, the modification3 observed in the glow pattern after irradiation of the phosphor a t a reactor thermal column. It has been shown that for values of the ratio of the thermal neutron fluence rate to the y-ray dose rate which are typically found at a reactor thermal column, the response of the phosphor t o thermal neutrons is significant. An attempt has been macle to explain how the observed modifications in TL behaviour arise. Recommendations are made regarding the use of Type-i LiF for the determination of the y-ray component of mixed thermal neutronly-ray fields.

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