GB2228610A

GB2228610A - Measuring radioactivity: radon detector

Info

Publication number: GB2228610A
Application number: GB8829414A
Authority: GB
Inventors: R Denis Lee Henshaw; R Geoffrey Charles Camplin
Original assignee: CAMPLIN DR GEOFFREY CHARLES; HENSHAW DR DENIS LEE
Current assignee: CAMPLIN DR GEOFFREY CHARLES; HENSHAW DR DENIS LEE
Priority date: 1988-12-15
Filing date: 1988-12-15
Publication date: 1990-08-29
Anticipated expiration: 2008-12-15
Also published as: GB8829414D0; GB2228610B

Abstract

A method of measuring alpha activity uses a plastic track detector, and a 1cm square box is scribed on the plastic track detector (1) so that the user may count the number of recorded alpha-particle tracks in a fixed area without need to measure that area. Tracks of alpha-particles recorded on the plastic detector are etched in such a way as to be uniquely identifiable (2) when projected on a screen by placing the plastic in a slide projector. A particular configuration of a radon detector houses the plastic track detector in a pot 70 mm high by 50 mm in diameter, such as that commonly used as a yogurt pot, which is exposed for six days either in or around the home. In this configuration the number of recorded tracks falling within the 1cm square is equal to the radon activity in Becquerels per cubic metre of radon in air. The plastic track detector with these features may be used separately for measuring total alpha-radioactivity in the ground. <IMAGE>

Description

Do-it-yourself Radon/Alpha-radiation Detector Technical Field This invention relates to a method of measuring radon and alpha-radiation in and around the home.

Background Passive dectectors consisting of a small plastic box containing an alpha-particle sensitive nuclear track detector are in common use by radiation protection agencies for measuring radon in houses. These are calibrated in a known radon atmosphere so that the radon concentration may be calculated from the density of alpha-particle tracks recorded on the plastic.

Detectors in current use are relatively expensive and are supplied ready assembled and the recorded radiation level is read-out from the track detector in the laboratory.

Passive detectors of a self-assembly type have been used for teaching radioactivity in schools in which the plastic track detector is housed in the bottom of a small plastic pot such as a yogurt pot which is covered in thin food wrapping film and held in place by an elastic band.

Essential technical details The present invention uses a self assembly radon detector in which the plastic track detector-has a 1 cm square scribed on the plastic surface allowing the user to count recorded tracks in a fixed area.

The present invention etches latent alpha-particle tracks in such a way that when the detector is placed in a slide projector the tracks have a unique appearance and may be counted on the projector screen.

The present invention can be used with any size or shape of small plastic pot of which the use of a yogurt pot is only one example.

According to the present invention the radon detector may be exposed for any period greater than three days inside or outside the home.

According to the present invention the track detector when used in a plastic pot of dimensions 70 mm high and 50 mm in diameter, being also the size of a yogurt pot in common use, and exposed as a radon detector for six days is calibrated such that the subsequent track count on the projector screen is equal to the radon activity in becquerels per cubic metre of radon in air.

According to the present invention the plastic track detector may be used separately to measure the total alpha-radioactivity in the ground, allowing the user to view and count the tracks in the same way as for that used in the radon detector.

Example A specific embodimemnt of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a plan view of the plastic track detector with the 1 cm square box scribed in the middle. The name of the detector, TASTRAKTM which is a commercially available alpha-sensitive plastic track detector, and a number is also shown.

Figure 2 shows in perspective the radon detector consisting of the track detector housed in the base of a yogurt pot covered with food wrapping film for example "clingfilm".

Figure 3 shows a plan view of the processed plastic detector when projected onto a screen.

Referring to figure 1 the scribed 1 cm square on the plastic detector allows the user to count the number of recorded alpha-particle tracks within a fixed area when the square is projected to any size without the need to calibrate that area.

The plastic track detector is supplied in a metallised plastic bag to avoid contamination from environmental alpha-radioactivity such as from radon prior to use.

In order to construct the radon detector the plastic track detector is housed in the bottom of a suitable plastic pot such as a yogurt pot held in place by "Blu-tak" or similar adhesive. The pot is covered with thin food wrapping film, for example "Clingfim", which is held in place by an elastic band as shown in figure 2. The radon detector is placed in a room in the house for six days. Alternatively, the radon detector may be left in place for any period of time ideally exceeding five days, provided that the user notes the period of time to the nearest day.

Alternatively, the radon detetor may be placed in the ground to measure the local radon concentration.

Alternatively, the plastic detector may be placed on its own in the soil in the garden or any similar location in order to record the total environmental alpha-radioactivity.

After exposure the plastic detector is returned to its metallised bag and returned to the supplier. The supplier reveals tracks of alpha-particles by etching in 6.25 M NaOH at 98 "C for 4 hours, after which their size falls within a well-definded envelope as illustrated in figure 3. The supplier then mounts the plastic detector in a 35mm slide holder and returns it to the user.

The user can place the slide in a conventional slide projector of any kind and project the recorded alpha-particle tracks onto a screen. The size and shape of the tracks is such that they may be unambiguously recognised. By way of example, if the scribed 1 cm square is projected to 50 cm in size, the tracks will be approximately 3 mm in diameter and will have the appearance of small black craters with a white middle. The user can count the number of tracks in the square.

The inventors have calibrated the plastic detector when used in a conventional cylindrical yogurt pot of dimension 70 mm high by 50 mm diameter. For this configuration of radon detector which has been exposed for six days, the track count within the scribed square is equal to the radon activity in the units Becquerels per cubic metre of radon in air. In this configuration the user can determine the radon activity from the track count without further calculation. For other sizes of plastic pot and different exposure times the user may determine the radon activity using an appropriate calibration and conversion formula.

The inventors have calibrated the plastic track detector for use in measuring total alpha-radioactivity in the ground. For an exposure period of six days the activity in the units Becquerels per kilogram is twice the track count within the scribed square. For exposure periods of other than six days a simple formula exists for converting track count to activity.

Claims

1. A do-it-youself method for measuring radon in houses or in the ground in which the plastic alpha-radiation detector, such as that commercially available under the name TASTRAKTM and housed in a suitable small plastic pot, has scribed a 1 cm square on its face so that recorded alpha-particle tracks within a fixed area may be counted without the need to calibrate that area.

2. A do-it-youself method for measuring radon in houses or in the ground in Claim 1 in which alpha-particle tracks recorded in the detector are revealed by etching in 6.25 M NaOH at 98 C for 4 hours so that they fall into a welldefined size range.

3. A do-it-youself method for measuring radon in houses or in the ground in Claim 1 and Claim 2 in which alpha-particle tracks recorded in the detector are revealed by etching in 6.25 M NaOH at 980 C for 4 hours so that they are uniquely distinctive on a projector screen when the plastic detector is placed in a conventional slide projector.

4. A do-it-youself method for measuring radon in houses or in the ground as in Claim 2 in which for a pot of dimensions 70 mm high by 50 mm diameter exposed for six days, the radon activity in units of Becquerels per cubic metre of air is equal to the track count within the scribed square, to an accuracy governed by the counting statistics and calibration accuracy of the radon detector.

5. A do-it-youself method for measuring total alpha-radioactivity in the ground which uses a plastic track detector which has a 1 cm scribed square as in Claim 1 and Claim 2.