The results of a preliminary study on the dosimetric characteristics of three different grades of commercial sintered beryllium oxide are reported. among useful features of this promising thermoluminescent material a very low sensitivity to thermal neutrons (0.2 y-rads equivalent per 10'" neutrons cm-a), a fairly high sensitivity to y-rays. and a good energy response, are emphasized. These properties enable beryllium oxide to be used successfully in mixed fields of t'hermal neutrons and y-rays, such as exist in nuclear reactor facilities.

A number of European laboratories studying the late effects of ionizing radiation in animals have established an effective cooperation within the European Late Effects Project Group (EULEP) since 1970. To facilitate the exchange of biological results several techniques, including quality control of the experimental animals, pathology and dosimetry, have to be standardized. The most important aspects of the procedures for X-irradiation and dosimetry of small animals are summarized. These include recommendations on irradiation conditions, dosimetry methods, characteristics of phantoms and factors affecting X-ray dosimetry. X-irradiation procedures employed by the participating institutes are described and the results of five X-ray dosimetry intercomparisons are reported. The introduction of a common dosimetry protocol has resulted in improvements in exposure arrangements and absolute dosimetry.

An analysis of the literature shows a lack of data about basic biological parameters regarding cytogenetic dosimetry as applied to neutron fields, in the dose range below 50 rad. Human peripheral blood lymphocytes were exposed in vitro to a degraded fission neutron spectrum of mean energy 0.4 MeV. The dose-range was 0.2--50 rad delivered at a dose-rate of about 0.2 or 7 rad/min. The results were processed using a computer programme. Both experimental data for dicentric induction, and theoretical considerations indicate the first-order polynomial as the best fitting dose--response function. The implications of these results for cytogenetic dosimetry are discussed. A comparison with 250 kV X-ray data in the same range gives an r.b.e. of 18.5 +/- 3.1.

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