Introduction

In its Publication 60 (1991), the International Commission on Radiological Protection (ICRP) recommended annual limits in terms of effective dose and equivalent dose to the skin, to the lenses of eyes the and to extremities. Due to the tissue weighting factors in its definitions, the effective dose is destined to be an instable quantity. In fact, its values strongly depend on the geometrical conditions of irradiation and can only be determined using anthropomorphic phantoms approaching the human body.

For monitoring purposes, the International Commission on Radiation Units and Measurements (ICRU) and the ICRP recommended so-called operational quantities [ICRU Report 39 (1985), ICRU Report 51 (1993) and ICRP Publication 74 (1996)] ^[4]. The operational quantity recommended for area monitoring of strongly penetrating radiation is the ambient dose equivalent.

Unfortunately the ambient dose equivalent does not give a conservative estimate of the effective dose for all the energies of interest for neutron radiation [ICRP Publication 74 (1996)] ^[4] and, at high energies, both for neutron and photon radiation. Moreover, the ambient dose equivalent has not been introduced for shielding purposes.

All the experimental data found in literature are expressed in terms of maximum dose equivalent, a quantity based on superseded Q vs LET relationship [ICRP Publication 21 (1971)] ^[3].

This International Standard makes use of the ambient dose equivalent as radiation protection quantity, based on the new Q-L relation as recommended in ICRP Publication 60. Due to the above-mentioned limitation, the field of application is restricted to neutrons of energy below 20 MeV.

For practical purposes, some data expressed in terms of maximum dose equivalent are also included in this International Standard. It is recommended that these data be conservatively multiplied by a factor 2 if used for purposes of shielding calculations [ICRU Publication 51 (1993)].

To establish an operational neutron radiation protection shielding system, several consecutive steps should be performed:

- choice of the radiological objectives and other design criteria;
- characterization of the radiation sources;
- identification of the constraints on placement and construction;
- choice of the shielding materials and arrangement within the shielding;
- implementation of a calculation method;
- choice of the final solution;
- experimental verification.

This International Standard outlines, in the body of the text, the basic requirements and the general provisions for the implementation of each of these previous steps.

Detailed annexes complete these general considerations, especially in the following fields:

- characterization of neutron sources;
- criteria for the choice of neutron shielding materials;
- review of shielding calculation methods (manual methods or computer codes).

NOTE The general principles provided in this International Standard are mainly applicable to simple slab geometries. For neutron shielding of complex geometries, including local lessenings such as service penetrations, ducts, labyrinths, zigzag mountings, the guidance given in this International Standard apply, but are generally not sufficient. For that purpose, special calculation techniques and arrangement of the shielding materials are needed. These specific considerations are out of the scope of this International Standard.

The same remark can be made for criticality shielding, for which the principles given in this International Standard apply, but are generally not sufficient. In this case additional considerations should be taken into account.

For these two items (criticality shielding and neutron radiation protection shielding of complex geometries), further standards will be studied in the near future.

BS ISO 14152:2001

Neutron radiation protection shielding. Design principles and considerations for the choice of appropriate materials

Current

Published:

9 Dec 2002