GB2254990A

GB2254990A - Alpha-radioactivity, radon and thoron daughter detector

Info

Publication number: GB2254990A
Application number: GB9107541A
Authority: GB
Inventors: Denis Lee Henshaw
Original assignee: TRACK ANALYSIS SYSTEMS Ltd
Current assignee: TRACK ANALYSIS SYSTEMS Ltd
Priority date: 1991-04-10
Filing date: 1991-04-10
Publication date: 1992-10-21
Also published as: GB9107541D0

Abstract

A method of measuring alpha-radioactivity from any source in air including radon, thoron and their daughter nuclei in which the identity of emissions from individual nuclei is uniquely determined by measuring their energy i.e. track size, in a plastic track detector. A method of measuring alpha-radiation dose to the skin by measuring the plateout of alpha-radionuclides from their presence in air on a plastic track detector, worn on the body. <IMAGE>

Description

Alpha-radioactivity, radon and thoron daughter detector This invention relates to a method of measuring any alpha-radioactive particle in air including radon and thoron short-lived daughter nuclei.

Radon and thoron are gases and respectively the common names for the isotopes 222Rn, and 220Rn. These nuclei are alpha-radioactive as are certain of their shortlived daughter nuclei: 214po, 218pot 216po, 212Bi, 212po. Radon and thoron are naturally present in room air and in some cases relatively high levels are present In the UK the average levels of indoor radon is estimated as 20 Bq.m-3.

The National Radiological Protection Board, UK recommends an action limit of 200 Bq.m3 above which remedial action to reduce indoor radon should be taken.

Although it is radon and thoron themselves that enter indoors the radiation dose to most organs of the body arises from the presence of the alpha-emitting radon and thoron daughters. These daughters are rarely in equilibrium with radon and thoron. They are present in air in the form of ions which may land on and be retained by surfaces, a process known as plateout. They may also land on the skin delivering a radiation dose to sensitive cells beneath the skin.

Radon detectors of the passive type used for surveys of indoor radon such as in houses generally measure 222Rn only: 220Rn is poorly detected and free radon and thoron daughters are not detected.

Radon detectors have been devised which measure radon daughters by counting the presence of tracks of alpha-particles from radon daughters on a plastic track detector.

Other radioactive particles may exist in air from either natural or man-made sources and these may also plateout on surfaces including the skin.

The present invention allows radon, and radon and thoron daughter nuclei, and alpha-radioactive particles from natural or man-made sources to be uniquely identified by measuring the energy of their alpha-particle emissions recorded on a plastic track detector, such as that commercially available under the trademark TASTRAK.

The present invention hangs a piece of TASTRAK in air which records radon, thoron and their alpha-emitting daughter nuclei in air and the daughter nuclei 214po, 218po, 212gi, 212pro. which become plated out on the plastic.

The present invention may use TASTRAK moulded into any shape or form mounted anywhere so as to have a face exposed to air.

The present invention hangs a piece of TASTRAK in air, which may be overlaid with a layer of degrader made of any material, which records and assists in the discrimination of radon, thoron and their alpha-emitting daughter nuclei in air and the daughter nuclei 214po, 218pro, 212Bi, 212pro. which become plated out on the plastic.

The present invention hangs a piece of plastic in air which may record alpharadioactivity from any alpha-radioactive particle landing on its surface.

The present invention etches latent alpha-particle tracks in such a way that the emissions from the above radon and thoron daughter nuclei, and any other alpha-radioactive particles that are plated out on the plastic have a unique conelike shape which may be identified by measurement.

The present invention etches latent alpha-particle tracks in such a way that the emissions from the above daughter nuclei that are present in air within alphaparticle range of the surface and are not plated out on the plastic, have a family of cone-like shapes which fall into a well defined category, which may be identified by measurement.

The present invention uses a piece of TASTRAK, moulded into any shape or form, which may be worn anywhere on the body or on clothing on the body so as to act as a personal dosemeter for the radiation dose to the skin from radon, and radon and thoron daughter nuclei, and from any other alpha-radioactive particle.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a photomicrograph which shows the general appearance alphaparticle etch tracks in TASTRAK a commercially available plastic track detector.

These have been revealed by etching latent tracks in a suitable etchant such as NaOH.

Figure 2 shows a computer simulation of an alpha-particle track in TASTRAK plastic track detector in which 5 measurable parameters are illustrated.

Figure 3 shows a scatter plot of the longest axis versus the minor axis of an etch track in TASTRAK. All possible combinations of size of track from alphaparticles incident with different energy and angle with the plastic surface fall into a well-defined envelope as outlined. Each dot represents the location of the parameters of a given alpha-particle etch track.

Figure 4 shows a similar plot to figure 3 but for tracks of alpha-particles emitted from alpha-radioactive particles plated out on the plastic surface. Examples of two alpha-particle energies are given, that emitted from the thoron daughter 212po and that emitted from the radon daughter 214pro. In this case the parameters of the given alpha-particle etch tracks lie on well-defined trajectories, illustrated by the solid lines, within the envelope.

We may consider the envelope of sizes of tracks recorded from a piece of TASTRAK held in air. Referring to figure 3, for alpha-particles emitted from radon, thoron and their daughter nuclei in air, the plastic will record the total alpha-activity in air from these particles. When used with a conventional radon dosemeter which measures radon only, the activity from radon and thoron daughters in air may be determined.

At the same time radon and thoron daughters will plateout on the surface of the plastic and will be recorded as illustrated in figure 4. The sizes of tracks are such that individual radon and thoron daughter nuclei can be identified. This additionally gives a direct measure of the radon and thoron dose to the skin.

At the same time any other alpha-radioactive particulates in air, for example from man-made sources in an industrial environment, may be deposited on the plastic. These may be uniquely identified in a similar manner to that shown in figure 4 and for such particles deposited on the skin will provide a direct measure of the radiation dose to the skin.

Claims

1. A method of measuring alpha-activity in air from any source in which the energy of the alpha-particles emitted from that source is measured in a plastic track detector, such as that available under the name TASTRAK, such that the nature of the source is identified.

2. A method of measuring alpha-activity from any source as in claim 1 that is plated out or otherwise deposited on the surface of a plastic track detector.

3. A method of measuring radon, and radon and thoron daughter nuclei, in air in which the energy of the alpha-particles emitted from these nuclei is measured as in claims I and 2 such that the presence of radon and individual radon and thoron daughters are identified.

4. A method of measuring alpha-radioactivity in air, radon, and radon and thoron daughter nuclei in air in claims 1, 2 and 3, which may be used in any outdoor situation.

5. A method of method of measuring alpha-radioactivity in air, radon and radon and thoron daughter nuclei in air in claims 1,2 and 3, which may be used in any indoor situation, domestic, commercial or military.

6. A method of measuring alpha-radioactivity in air, radon and thoron daughter nuclei in air in claims 1, 2 and 3, which may be used in any underground facility including mines, caves, storage facilities or places of work military or civil.

7. A method of measuring alpha-radioactivity in air, and radon and thoron daughter nuclei in air in a plastic track detector in claims 1, 2 and 3, which may be worn anywhere on the body in any situation as in claims 4,5 and 6, and which may act as a personal radiation dosemeter.