Use of passive detectors to characterize neutron field hardness.

Most personnel neutron dosimeters and field monitors suffer from an energy dependence. The knowledge of the energy distribution of the measured neutron field is necessary to correct the response of the detectors. However, the response of the detectors can be significantly improved when only a simple idea of the spectrum hardness is available. This paper describes a way of characterizing the neutron spectrum hardness in a large variety of neutron fields (with energies extending from thermal to 100 MeV) by using the various indications of different types of passive neutron detectors. These indications allow the choice of the appropriate factors established by calibration measurements or taken from the literature to correct the energy dependent response of personnel neutron dosimeters and field monitors.

The fission track detector revisited: application to individual neutron dosimetry.

A system based on fission fragment tracks had previously been developed for individual neutron dosimetry. The dosimeter detects both fast neutrons by means of the 232Th(n,f) reaction, and thermal and albedo neutrons by means of the 235U(n,f) reaction. The fission tracks produced in a plastic foil are chemically etched and counted by spark discharges. The response of the dosimeter has recently been re-investigated in 36 different neutron fields: monoenergetic beams, reference fields near isotopic sources, and radiation fields encountered in a variety of situations inside nuclear power plants. The results obtained have been compared to those computed by convolution of the neutron spectra with the energy response functions of the dosimeters. In practical situations, it is essential to know the shape of the neutron spectrum, approximately at least, in order to perform an acceptably accurate dose evaluation. For that purpose, the neutron fields encountered inside nuclear power plants have been grouped into four categories, for which algorithms for dose evaluation have been developed. Concerning the neutron equivalent dose, the error associated with this approach does not exceed a factor of 2, a performance which is comparable to other detection systems used in the field of individual neutron dosimetry.

Return to normality after a radiological emergency.

Some preliminary considerations from the management of post-accident situations connected to large scale and high land contamination are presented. The return to normal, or at least acceptable living conditions, as soon as reasonably achievable, and the prevention of the possible emergence of a post-accident crisis is of key importance. A scheme is proposed for understanding the dynamics of the various phases after an accident. An attempt is made to characterize some of the parameters driving the acceptability of post-accident situations. Strategies to return to normal living conditions in contaminated areas are considered.

Appraisal of individual radiation risk in the context of probabilistic exposures.

There exists a growing desire to base safety criteria in different fields on the same principles. The current approach by the international Commission on Radiological Protection (ICRP) to control radiation exposure touches many aspects such as social, psychological, or economic factors that are important for such principles. This paper attempts to further explore possible ways of defining a common basis for dealing with radiation risks and other safety problems. Specifically, it introduces the following issues: (1) different types of risk are judged differently. To account for this, the concept of risk categories is introduced. (2) The dimension of time may play an important role. There is a difference between an immediate death and a death occurring 20 years after exposure to radiation. Effects such as reduced quality of life after exposure and reduction of lifetime expectancy are discussed. The paper suggests to introduce an individual risk equivalent which allows to compare risks as defined in various fields. Furthermore, it suggests the use of risk acceptance criteria which depend on the different categories of risk.