Brief comments are given on in-situ and/or sample measurements in the environment.

  The main aim of this review is to provide an overview of the techniques which have been developed for measuring radon and radon progeny in the atmosphere. Overviews are first provided of the content of so-called radon problem and characteristics of radon. The various measurement techniques are then described by classification as follows ; active methods for radon, active methods for thoron, techniques for radon and thoron progenies, techniques for unattached atoms of radon progeny, passive methods and other methods.

  JAERI has developed a dose evalution method using a NaI (Tl) scintillation detector and a spectral weighting function for low-level gamma rays in the environment. This method has the following advantages : (a) the detection efficiency is high ; (b) information on energy spectra can be used ; (c) the method is easily applied to the estimation of effective dose equivalent ; and (d) small and highly efficient instruments using this method can be produced because of recent development of IC technique. In this paper, the principle of the method, derivation of the weighting function, and the practical application of this method to the environmental measuring instruments are described. Further, the characteristics of dose rates in the urban environments examined with a portable dose rate meter using this method are briefly explained.

  Various Measuring Methods of Environmental Radioactivity are reviewed with information on the recently established Japanese standard analytical methods of radioactive nuclides in the environment. The following topics are specially explained from the view point of applied physics with references to the papers published. (Ⅰ) Cerenkov radiation measurements of β ray emitters such as ⁹⁰Sr (⁹⁰Y) and ¹⁴⁴Ce (¹⁴⁴Pr). (Ⅱ) Liquid scintillation measurements of β ray emitters, including tritium in different chemical species. (Ⅲ) Determination of α ray emitters by their radiations after radiochemical purifications. (Ⅳ) Mass spectrometric measurements (especially by ICP-MS) of long-lived nuclides.

  Techniques are presented capable of evaluating the bulk density, porosity, weight and uniformity of large structural materials using cosmic-rays. Feasibilities are also described of cosmic-ray radiography and inspecting ancient mounds.

  The Life Span Study (LSS) of the atomic bomb survivors in Hiroshima and Nagasaki has provided invaluable qualitative data on the late effects of ionizing radiations to human beings. For the study, the best possible estimates of the atomic bomb radiations received by the organs or tissues of survivors were principally required. The first dose estimates for the survivors were designated as Tentative 1957 Doses (T57D). In 1965, a revised dosimetry system was constructed on the basis of experimental data from a field measurement with the Health Physics Research Reactor (HPRR) at Nevada and from the thermoluminescence measurements of ceramic material and the radioactivity measurements of iron materials in Japan. These dose estimates were designated as Tentative 1965 (T65D). The T65D system was used with a great deal of confidence for risk assessment throughout the 1970s. In 1980, however, two scientific groups in the United States challenged the validity of the T65D system. In the fall of 1981, a Working Group on Atomic Bomb Dosimetry Reassessment was organized both in the United States and in Japan. After four US-Japan Joint Workshops for Reassessment of Atomic Bomb Radiation Dosimetry, the new dosimetry system which is desigated as Dosimetry System 1986 (DS86) was constructed.

  Recently, the Radiation Effects Research Foundation (RERF) has published the results of LSS which focussed on a comparison of the radiation-related risks of site-specific cancer mortality based on the DS86 and the T65D and deaths from cancer in the years 1950 to 1985. The International Commission on Radiological Protection (ICRP) has issued its basic recommendations as ICRP Publication 60 including the revised dose limits in occupational exposures.

  This paper reviews the dosimetry system of survivors for the LSS and discusses the physical basis for the DS86.

  In order to improve image quality in positron emission tomography (PET), a PET device needs to achieve full utilization of emitting photons, and it must be intimately linked to any 3D image reconstruction algorithm. Both the analytical and the iterative 3D reconstruction algorithms suitable for 3D PET systems are classified and evaluated from a computational point of view. For the analytical algorithms, the computation time is analyzed briefly and the required performances of a computer for 3D PET systems are provided. It is suggested that successful utilization of their algorithms depends not only on the performances of a computor, but also on the size of the image space due to the practical constraints of detected photon counts. Some guidelines are provided for the choice of an appropriate reconstruction algorithm in a given situation.