GB2324151A

GB2324151A - Automated surveying for radiation

Info

Publication number: GB2324151A
Application number: GB9806616A
Authority: GB
Inventors: Michael Peter Stevens; Michael Mark Davies; Norman Allan May
Original assignee: AEA Technology PLC
Current assignee: Ricardo AEA Ltd
Priority date: 1997-04-02
Filing date: 1998-03-30
Publication date: 1998-10-14
Anticipated expiration: 2018-03-30
Also published as: GB9806616D0; GB2324151B

Abstract

Portable equipment for surveying an area for radiation from radioactive materials, which may be carried around the area by an operator at normal walking pace, comprises a GPS locating instrument (16) to locate the apparatus within 2.0 m, a gamma-sensitive scintillator (30) to detect gamma rays, means (18) to classify the detector signals into a plurality of different energy ranges and to count the numbers of signals in each range, and an automatic data logger (14) to record the counts and the corresponding locations at sufficiently frequent intervals that the operator has moved no more than 2.0 m between successive records. The recorded data is subsequently downloaded to a computer (34) for analysis and to generate a map displaying values of gamma rate counts. A receiver (22) for differential correction signals and a beta detector may also be included.

Description

Automated Surveying for Radiation This invention relates to a method and an apparatus for surveying an area for radiation from radioactive materials, and for recording the locations at which radiation is detected.

It is known to survey an area for the presence of nuclear radiation by scanning a geiger counter; an operator can note down his location (relative to convenient landmarks) if the count rate exceeds the expected background level. Such an instrument is portable, and might be used to search for radioactive minerals, or for localised areas of contamination. A more sophisticated survey instrument incorporates a gamma spectrometer, combined with a locating instrument utilising ground-based or satellite-based radio signals (such as Decca, Loran, or GPS), but this is both expensive and too large and heavy to be portable - it might be moved by helicopter or in a vehicle.

According to the present invention there is provided a portable apparatus for surveying an area for radiation, the apparatus comprising a GPS locating instrument, to enable the apparatus to be located to better than 1 2.0 m, a gamma-sensitive scintillator to provide signals corresponding to the energy of detected gamma rays, means to classify the signals into a plurality of different energy ranges, and to count the numbers of signals in each energy range, and automatic memory means to record the location and the said counts at intervals.

It is generally necessary to provide correction signals to the GPS positional information, the correction signals being derived from a fixed base station, to enable the required positional accuracy to be achieved.

It may be possible to achieve even better positional accuracy, for example to better than + -0.5m.

In the preferred embodiment there are three different energy ranges. The thresholds between the energy ranges may be set in accordance with the radionuclides which are to be detected, and may for example be adjusted and calibrated in comparison to signals from a gamma spectrometer prior to use of the apparatus, using a standard gamma source.

The memory means is desirably arranged to record the data at regular time intervals, for example once every second. The apparatus can be carried by an operator around an area to be surveyed, for example in a back pack, and the stored data can subsequently be downloaded from the memory means into a computer. The computer may display a map of the area, indicating any areas where radiation was detected, possibly displaying contours of equal radiation; and also indicating any areas which have not been surveyed.

Thus the invention also provides a method for surveying an area for radiation from radioactive materials, wherein an operator carries a portable surveying apparatus around the area, the apparatus comprising a GPS locating instrument to enable the apparatus to be located to better than + 2.0 m, a gammasensitive scintillator to provide signals corresponding to the energy of detected gamma rays, means to classify the signals into a plurality of different energy ranges, and to count the numbers of signals in each energy range, and automatic memory means to record the location and the said counts, the location and the said counts being recorded at sufficiently frequent intervals that the operator has moved no more than 2.0 m between successive such records, and the method also comprising subsequently downloading the recorded data, and thereby generating and displaying a map of the area showing values of gamma rate counts.

The data concerning location and counts is preferably recorded every second, which enables an operator to walk over the area, at a normal walking pace, to generate the data for a comprehensive survey. To ensure that the entire area is surveyed, the operator will usually walk to and fro from one side of the area to the opposite side, successive paths being for example parallel lines at a spacing of 1.0 m. The count rate data is preferably recorded even if no GPS signal is obtained (for example because the operator passes under a tree), and can also be subsequently downloaded; it may be possible to calculate the corresponding locations by interpolation or extrapolation from previous and/or successive locations at which a GPS signal was obtained.

Thus all the count rate data is recorded, as unprocessed, raw data, and this uncorrupted data can be retrieved subsequently if desired.

The portable apparatus desirably also includes a display to show the location as determined by GPS, so that if the operator wishes to return subsequently to a specific part of the survey area (for example because the displayed map indicates that no measurements were taken in that area) he can readily do so. It may also include a display to show the count rate.

The invention will now be further and more particularly described by way of example only and with reference to the accompanying drawings in which: Figure 1 is a block diagram of surveying apparatus; and Figure 2 is a circuit diagram of part of the surveying apparatus of Figure 1.

Referring to Figure 1, a surveying apparatus 10 includes a backpack 12 (indicated by a broken line) to be carried by an operator. All the equipment in the backpack 12 is powered by batteries (not shown). The backpack 12 includes a data logger 14 which at one second intervals stores digital data from a GPS receiver 16, and a signal processor 18 (described below in more detail with reference to Figure 2).

The GPS receiver 16 is a Trimble GPS Pathfinder (trade mark) which has twelve channels to receive signals via an aerial 20 from three or more GPS satellites at once. The aerial 20 can also receive marine band (300 kHz) differential correction information from a base station such as a lighthouse, if such information is broadcast without encryption, so enabling the GPS receiver 16 to determine its position to about + 1 metre.

In some parts of the world differential correction information is broadcast in encrypted form (for example by Trinity House/Scorpio Marine), or is broadcast as an RDS signal on a non-marine band wavelength (for example by Classic FM), the radio transmitter being indicated at 21, and the backpack 12 includes a radio receiver 22 for receiving such signals and providing them to the GPS receiver 16, so the receiver 16 can continuously and accurately determine its position. The data logger 14 may incorporate a display co show the current position.

If neither source of differential correction information is available then the apparatus 10 would include a second, identical GPS receiver 24 with an aerial 25 and a data logger 26, situated at an accurately known position, referred to as a base station 27.

The data logger 14 in the backpack 12 not only stores signals from the GPS receiver indicating its position, but also signals from the signal processor 18 which receives signals from a high efficiency 75 mm diameter sodium iodide scintillator 30 with a photomultiplier 32. The scintillator 30 detects gamma rays, and the photomultiplier 32 generates electrical pulses whose magnitude is related to the energy of the detected gamma rays. The signal processor 18 receives this series of analogue pulses, counts the numbers of pulses in each of three different energy ranges, and provides these counts as digital signals to the data logger 14 every second.

After an operator has walked to and fro with the equipment in the backpack 12 over the area to be surveyed, the data from the logger 14 is down-loaded into a computer 34. The computer 34 analyses the data and can for example provide a map output displaying the gamma ray intensity at different parts of the area, highlighting any parts of the area which have not been surveyed. The gamma ray counts at different energy windows can allow specific radio isotopes to be identified. If it had been necessary to use a base station 27, then the data from the data logger 26 is also downloaded to the computer 34, which corrects the positional information provided by the GPS receiver 16. Thus the generation of a map displaying the measured values of gamma counts can be performed automatically by the computer 34. A contour map showing variations in gamma intensity over the surveyed area may also be displayed.

Referring now to Figure 2, this shows a circuit diagram of part of the signal processor 18. The analogue pulses from the photomultiplier 32 are supplied via a buffer (not shown) and input lead 40 to the positive inputs of three differential amplifiers 41, 42 and 43.

The negative inputs of the amplifiers 41, 42 and 43 are connected to adjustable resistor contacts 44, 45 and 46 respectively which form part of a potential divider network 47 between two fixed voltage levels V and V2.

The contact 44 is set so the amplifier 41 gives an output signal for any input pulse above the noise level. The contacts 45 and 46 are set so the amplifiers 42 and 43 give output signals for any input pulses larger than respective thresholds, the threshold for the amplifier 43 being the higher of the two. The output signals from the amplifier 41 are supplied via a buffer 48 to a microcontroller 50, and the output signals from the amplifiers 42 and 43 are supplied via respective buffers 48 to bistable latch units 52 which provide output signals to the microcontroller 50.

When the microcontroller 50 detects the back edge of a pulse from the amplifier 41 it reads the state of each latch unit 52 to see if it has received a pulse, and then transmits a reset signal via lead 54 to each latch unit 52. The microcontroller 50 counts the numbers of pulses received via each amplifier 41, 42 and 43, and once a second these three counts are transmitted (as digital signals) to the data logger 14 via the output lead 55, and the stored counts are reset to zero. The signal processor 18 also includes a liquid crystal display 56 which may be switched to display the number of counts per second in both digital and pseudo-analogue form. It may be arranged to display the total count rate (i.e. those provided by amplifier 41), the count rate below the lower threshold (i.e. the count from amplifier 41 minus the count from amplifier 42), the count rate in the energy window between the two thresholds (i.e. the count from amplifier 42 minus the count from amplifier 43), or the count rate above the upper threshold (i.e. the count from amplifier 43). The microcontroller 50 also provides an output digital signal for every pulse received from the amplifier 41, which can be supplied to headphones 58 for the operator.

It will be appreciated that a surveying apparatus may differ from that described above while remaining within the scope of the invention. For example the scintillator might be of caesium iodide, and might be of a different size to that described. The location and the count rates might be recorded at different intervals, such as every 10 seconds, or every 0.5 second. All the components to be carried by the operator were described as being in the backpack 12, but it will be appreciated that an operator might instead carry some of the components separately, connected electrically to the components in the backpack 12. For example he might hold the display 56 in one hand, to be able to see what count rate is being recorded, and he might carry the scintillator 30 and photomultiplier 32 on a shoulder strap, adjusted so the scintillator 30 is about 0.5 m above the ground.

A surveying apparatus might include other types of detectors, for example a diode to detect beta radiation, along with a signal processor similar to the processor 18 described above including a microcontroller to count the detected beta rays. A surveying apparatus might thus include a plurality of microcontrollers; and these may be connected in cascade, so the stored counts from one are transmitted to the next in the chain, to be transmitted on along the chain along with its own stored counts. The last one in the chain would then transmit to the data logger 14 the counts detected by each signal processor.

Claims

1. A method for surveying an area for radiation from radioactive materials, wherein an operator carries a portable surveying apparatus around the area, the apparatus comprising a GPS locating instrument to enable the apparatus to be located to better than + 2.0 m, wherein the apparatus also comprises a gamma-sensitive scintillator to provide signals corresponding to the energy of detected gamma rays, means to classify the signals into a plurality of different energy ranges, and to count the numbers of signals in each energy range, and automatic memory means to record the location and the said counts, the location and the said counts being recorded at sufficiently frequent intervals that the operator has moved no more than 2.0 m between successive such records, and the method also comprises subsequently downloading the recorded data, and thereby generating and displaying a map of the area showing values of gamma rate counts.

2. A method as claimed in claim 1 wherein the operator carries the apparatus at normal walking pace, and the location and the counts are recorded at least once every second.

3. A method as claimed in claim 1 or claim 2 wherein the map indicates any parts of the surveyed area from which count rate data was not obtained.

4. A portable apparatus for surveying an area for radiation, the apparatus comprising a GPS locating instrument to enable the apparatus to be located to better than + 2.0 m, and also comprising a gammasensitive scintillator to provide signals corresponding to the energy of detected gamma rays, means to classify the signals into a plurality of different energy ranges, and to count the numbers of signals in each energy range, and automatic memory means to record the location and the said counts at intervals.

5. An apparatus as claimed in claim 4 also comprising means to provide correction signals to the GPS positional information, the correction signals being derived from a fixed base station.

6. An apparatus as claimed in claim 4 or claim 5 wherein there are three different energy ranges.

7. An apparatus as claimed in claim 6 including means to enable the thresholds of the energy ranges to be adjusted.

8. An apparatus as claimed in any one of claims 4 to 7 wherein the memory means is arranged to record the location and the count data at least once every second.

9. An apparatus as claimed in any one of claims 4 to 8 also comprising a display to indicate the current location of the apparatus as determined by the GPS locating instrument.

10. A portable apparatus for surveying an area for radiation from radioactive materials substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

10. An apparatus as claimed in any one of claims 4 to 9 also comprising means to indicate to the operator a current value of count rate.

11. A method for surveying an area for radiation from radiactive materials substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

12. A portable apparatus for surveying an area for radiation from radiactive materials substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.

Amendments to the claims have been flied as follows 1. A method for surveying an area for radiation from radioactive materials, wherein an operator carries a portable surveying apparatus around the area, the apparatus comprising a GPS locating instrument to enable the apparatus to be located to better than t 2.0 m, wherein the apparatus also comprises a gamma-sensitive scintillator to provide signals corresponding to the energy of detected gamma rays, means to classify the signals into three different energy ranges, and to count the numbers of signals in each energy range, and automatic memory means to record the location and the said counts, the location and the said counts being recorded at sufficiently frequent intervals that the operator has moved no more than 2.0 m between successive such records, and the method also comprises subsequently downloading the recorded data, and thereby generating and displaying a map of the area showing values of gamma rate counts.

4. A portable apparatus for surveying an area for radiation, the apparatus comprising a GPS locating instrument to enable the apparatus to be located to better than + 2.0 m, and also comprising a gammasensitive scintillator to provide signals corresponding to the energy of detected gamma rays, means to classify the signals into three different energy ranges, and to count the numbers of signals in each energy range, and automatic memory means to record the location and the said counts at least once every second.

6. An apparatus as claimed in claim 4 or claim 5 including means to enable the thresholds of the energy ranges to be adjusted.

7. An apparatus as claimed in any one of claims 4 to 6 also comprising a display to indicate the current location of the apparatus as determined by the GPS locating instrument.

8. An apparatus as claimed in any one of claims 4 to 7 also comprising means to indicate to the operator a current value of count rate.

9. A method for surveying an area for radiation from radioactive materials substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.