GB2255177A - Personal radiation dose indicators with sensors for different levels of radiation penetration - Google Patents

Abstract

The radiation dose meter/indicator apparatus comprises a plurality of electronic radiation detectors (2) each sensitive to a different radiation range. A signal processor receives a signal from each of the detectors and provides a signal indicative of penetrating dose and superficial dose. A second signal processor, display (3) and alarm means (4) is also provided, the said second signal processor providing drive signals for the display (3) to facilitate the selective display of digital data indicative of any one of the following parameters; superficial dose, superficial dose rate, cumulative superficial dose, penetrating dose, penetrating dose rate, or cumulative penetrating dose, and to provide an alarm signal if one of these parameters exceeds a predetermined threshold. The apparatus may include a standby mode of operation to optimise battery life and optical means for the input and/or output of data. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO PERSONAL RADIATION DOSE INDICATORS This invention relates to personal radiation dose meters/indicators for measuring radioactivity doses and/or levels to which personnel are exposed and more especially it relates to electrically operated dose meters. Known dose meters or dose indicators comprise thermo-luminescent devices (TLD's) or film badges which exhibit predetermined characteristics when they are exposed to a predetermined cumulative radiation dose.

Such devices tend to have limited sensitivity and moreover will provide a warning indication only when the devices are processed.

Thus dangerous short term radiation peaks may go undetected unless additional peak level alarm apparatus is used. Additionally TLD's or film badges must be processed to determine a reading and thus there is a delay before information concerning dose is available.

One object of the present invention is to provide a personal dose meter/indicator which will give timely a warning signal either when the cumulative dose reaches a specified level or when the dose rate reaches a predetermined threshold, and which affords the facility of providing for spot checks of either parameter.

According to the present invention, radiation dose meter/indicator apparatus comprises a plurality of electronic radiation detectors each sensitive to a different radiation range so that detection of radiation over a total range covered by the different radiation detectors in combination is facilitated, a first signal processor which receives a signal from each of the said detectors and which provides a first signal indicative of penetrating dose and a second signal indicative of superficial dose, a second signal processor, display means and alarm means, the said second signal processor being responsive to the first and second signals for providing drive signals for the display means thereby to facilitate the selective display of digital data indicative of any one of the following parameters; superficial dose, superficial dose rate, cumulative superficial dose, penetrating dose, penetrating dose rate, or cumulative penetrating dose, and to provide an alarm signal if a predetermined one of these parameters exceeds a predetermined threshold.

The apparatus may comprise non volatile store means effective to store cumulative data appertaining to one or more of the said parameters and a threshold detector, the said threshold detector being responsive to data in the non volatile store means for initiating operation of the alarm means when data appertaining to a predetermined parameter exceeds a threshold level which relates thereto.

The apparatus may comprise a battery power supply, and in order to conserve power the signal processors may be arranged to operate in a standby mode when not in use whereby battery life is optimised.

The apparatus may comprise optical detector means responsive to externally injected optical signals for setting the said threshold levels and or sensitivity of the apparatus, also for reading dose/rate data from the unit.

Some embodiments of the invention will now be described with reference to the accompanying drawings, in which; Figure 1 is a perspective view of a dose meter according to the present invention, Figure 2 is a front view of a digital display panel forming a part of the dose meter shown in Figure 1, Figure 3 is a generally schematic block diagram, showing in operative association, parts of the dose meter shown in Figure 1, and; Figure 4 is a more detailed block schematic diagram showing parts of the dose meter shown in Figure 3.

Referring now to Figure 1, the personal radiation dose meter comprises a magnesium alloy case 1 in which are accommodated radiation detectors 2 for detecting both gamma and beta radiation.

The radiation detectors 2 provide signals for a CMOS micro computer, 24 (not shown) contained within the case 1 which is powered by a lithium battery 22. Circuitry within the case including the computer 24 provides signals for an optical digital liquid crystal display (LCD) panel 3 and an audible alarm warning sounder 4. Display selection is effected by means of control mode buttons 5 and 6. In order to facilitate setting up of the circuitry contained within the case 1, optical communication ports 7 and 8 are provided which facilitate the injection/extraction of data by optical means.

The digital display panel 3 is shown in greater detail in Figure 2.

The display panel 3 comprises a 4 X 7 segment digital display panel 9 which is capable of providing several different display modes which are selectable sequentially by operation of the mode buttons 5 and 6.

The mode selected is indicated by means of characters on the display panel which display is used also for alarm purposes, and thus the following modes or alarm indications as shown in Figure 2 are available; penetrating dose 10 as shown by the letters HP (alarm only), superficial dose 11 as shown by the letters HS (alarm only), penetrating dose rate 12 as shown by the letters HP/h (alarm only), superficial dose rate 13 as shown by the letters HS/h (alarm only), cumulative penetrating dose 14 as shown by the enlarged letters HP and total accumulated superficial dose 15 as indicated by the enlarged letters HS (display mode only).

An intermittent flashing "heart beat" lamp indicator 16 is provided which serves to indicate that the apparatus is operational, and a battery state indicator 17 is also provided together with an alarm indicator 18 and a "calibration required" indicator flag 19.

During calibration, a test legend 20 is illuminated. The calibration flag 19 is illuminated when the calibration period has expired.

A generally schematic block diagram of the apparatus of Figures 1 and 2 is shown in Figure 3 wherein parts corresponding to those shown in Figure 1 and Figure 2 bear as appropriate the same numerical designations. Referring now to Figure 3 signals from the radiation detectors 2 are fed to the amplifier 21. The amplifier 21 includes detector amplifiers and discriminators as will hereinafter be described with reference to Figure 4, for detecting beta and gamma radiation which exceeds predetermined thresholds. The amplifier 21 also includes a monitor circuit for monitoring the condition of the lithium battery 22. An A.S.I.C 23 is provided which serves to receive and transmit signals to the optical communication ports 7 and 8 as well as to receive control signals from the mode buttons 5 and 6 and to interface between the A.S.I.C and microcomputer.The A.S.I.C 23 is coupled to a microcomputer 24 which includes a RAM, a ROM and interface circuitry for the LCD display panel 3. The microcomputer 24 is additionally coupled to a programmable read only memory 25 which contains pre-programmed data appertaining to signal processing constants required for operation of the apparatus.

Turning now to Figure 4 wherein parts of the apparatus shown in Figure 3 are shown in greater detail, the radiation detectors 2 comprise three detector diodes 26, 27 and 28. Radiation sensed by the diode 26 is filtered by a zinc screen 29 whereby the detector 26 tends to provide useful signals only for higher energy levels of gamma radiation, and thus signals from the detector 26 might be described as providing hard gamma channel data signals. Radiation for the detector 27 is filtered by a combination of the magnesium case 1 and a perspex screen 30 such that the detector 27 provides useful signals for lower energy level gamma radiation and some beta radiation. The detector 28 is exposed to radiation via a screen 31 which comprises a polyimide substrate coated with aluminium whereby the detector provides useful signals for beta and gamma radiation. Signals from the diodes 26, 27 and 28 are fed via preamplifiers 32, 33 and 34 respectively to pulse shapers 35, 36 and 37 respectively. An output signal from the pulse shaper 35 is fed to a discriminator 38 which passes pulses indicative of hard gamma radiation to a counter 39 if they exceed a predetermined threshold level as determined by a signal applied on line 40. Output signals from the pulse shaper 36 are fed to two discriminators 41 and 42 which are fed on lines 43 and 44 respectively with different threshold level signals whereby an output signal from the discriminator 41 is fed to a counter 45 indicative of soft gamma channel signal levels. An output signal from the discriminator 42 is fed to a counter 46 which registers signals indicative of some beta and gamma radiation signals.Similarly output signals from the pulse shaper 37 are fed to a discriminator 47 which is fed with a threshold signal on a line 48 whereby a counter 49 fed therefrom registers signals indicative of beta and gamma radiation. The discriminators 38, 41, 42 and 47 are digital discriminators and the threshold level signals fed on lines 40, 43, 44 and 48 are digital threshold signals fed from the micrcomputer 24 shown in Figure 3 which indicate the appropriate threshold levels.

Output signals on lines 50, 51, 52 and 53 from the counters 39, 45, 46, and 49 respectively are fed to count loss correction circuits 54, 55, 56 and 57 which serve to compensate for detector dead time as will be appreciated by the cognoscenti. The count loss correction computation may simply be done by taking an average, for example, of the count which might have been expected during the dead time loss period using a look up table.Output signals from the count loss correction units 54, 55, 56 and 57 are fed on lines 58, 59, 60 and 61 to a microcomputer 62 which operates in accordance with a predetermined algorithm to provide output signals on lines 63 and 64 respectively indicative of the HP level and HS level respectively which signals are utilised by the unit 24 which integrates with time and/or applies alarm thresholds as necessary thereby to provide signals to drive the LCD display 3 in Figure 3. The detectors, the amplifiers and pulse shapers shown in Figure 3 form part of the Analogue amplifier 21 whereas the counters and counter loss and count loss correction circuits form part of the A.S.I.C 23.

The various units such as the amplifier 21 and A.S.I.C 23, and microcomputer 24 which are fed from the battery 22 are arranged to consume significant power only when computing demands are made and at other times to operate in a low power consumption standby mode whereby battery life is optimised. The construction and manner of manufacturer of such power economy circuits is well known to those skilled in the art and will not be described herein.

Various modifications may be made to the arrangement just before described without departing from the scope of the invention and for example any suitable discriminator, counter and microcomputer may be utilised to produce the desired results.

Claims (6)

1. A radiation does meter/indicator apparatus comprises a plurality of electronic radiation detectors each sensitive to a different radiation range so that detection or radiation over a total range covered by the different radiation detectors in combination is facilitated, a first signal processor which receives a signal from each of the detectors and which provides a first signal indicative of penetrating dose and a second signal indicative of superficial dose, a second signal processor, display means and alarm means, the said second signal processor being responsive to the first and second signals for providing drive signals for the display means thereby to facilitate the selective display of digital data indicative of any one of a plurality of parameters; and to provide an alarm signal if a predetermined one of the parameters exceeds a predetermined threshold.

2. Apparatus as claimed in Claim 1, wherein the parameters include: superficial dose, superficial dose rate, cumulative superficial dose, penetrating dose, penetrating dose rate, or cumulative penetrating dose.

3. Apparatus as claimed in Claim 1 or Claim 2, including non volatile store means effective to store cumulative data appertaining to one or more of the said parameters, and a threshold detector, said threshold detector being responsive to data in the non volatile store means for initiating operation of the alarm means when data appertaining to a predetermined parameter exceeds a threshold level which relates thereto.

4. Apparatus as claimed in any preceding claim, including a battery power supply, and in order to conserve power the signal processors may be arranged to operate in a standby mode when not in use whereby battery life is optimised.

5. Apparatus as claimed in Claim 4, including optical detector means responsive to externally injected optical signals for setting the said threshold levels and or sensitivity of the apparatus, and for reading dose/rate data from the apparatus.

6. Apparatus substantially as hereinbefore described with reference to Figures 1 to 4 of the accompanying drawings.