NATIONAL INSTITUTE OF RADIOLOGICAL SCIENCES 9-1, 4-chome, Anagawa, Chiba-shi, Japan Lastly I would like to take this opportunity to express my great admiration for the excellent results which have been obtained under the co-operation of AEC team, Trust Territory Government and many other authorities after overcoming manydifficulties. ach C weahirk: Kumatori, foneM.D, a 218