GB2148490A - A survey vehicle for radioactive contamination - Google Patents

Abstract

The ground survey vehicle comprises a self-propelled unit carrying arrays of radiation detectors at the front thereof. The arrays, in their operative positions, extend outwardly beyond the sides of the unit and are supported in close proximity to the ground. Conveniently three in-line arrays of detectors are employed with the two outer arrays being hingedly connected to the centre array. The arrays can be moved into and out of their operative positions by hydraulically operable means 8. <IMAGE>

Description

SPECIFICATION A survey vehicle for radioactive contamination The present invention concerns a survey vehicle for the monitoring of radioactive contamination.

According to the present invention a survey vehicle for the monitoring of radioactive contamination comprises a self-propelled unit with an hydraulic lift mechanism at the front of the unit carrying a plurality of radiation detectors.

Conveniently, the detectors are gas-flow proportional counters which can be arranged in three arrays on the hydraulic lift mechanism to extend across the front of the vehicle. In their operative positions the arrays are supported a short distance above the surface of the ground to be monitored and preferably the arrays are enclosed within a skirt to shield the detectors against background radiation. Conveniently the skirt can be a lead-loaded plastics material. The arrays are arranged in line to extend across the front of the vehicle and conveniently the two outer arrays are hingedly connected to the ends of the centre array. In operation the outer arrays extend beyond the sides of the vehicle and can be retracted when not required for use to thereby reduce the overall width of the vehicle. The unit comprises a cab for an operator or operators.The cab houses controls for the operation of the vehicle and the hydraulic lift mechanism and contains a display and control panel associated with the detectors.

The invention will be described further, by way of example, with reference to the accompanying drawings: in which: Figure 1 is a side elevation of a road survey monitor vehicle; Figure 2 is a front elevation of the vehicle; Figure 3 is a diagrammatic gas flow arrangement for the vehicle.

Figs. 1 and 2 show a self-propelled vehicle 1 having detector arrays 2 mounted at the front of the vehicle. The vehicle is conveniently four-wheel drive and four-wheel steering and can be powered by a water-cooled, propane-fuelled, four stroke engine. A cab 3 is provided for a driver and passenger and the detector arrays are carried by an hydraulic lift mechanism 8.

The detector arrays comprise ten double gas flow proportional counters arranged in three groups, namely a centre group 4 of four between two side groups 5 and 6 each of three double detectors. The side groups 5 and 6 are hingedly connected to the centre group 4 and can be raised individually to an upright inoperative position when not required for use. The detectors in each group are contained within a ground-engaging skirt 7.

When not in use to survey the ground the side groups 5 and 6 will be in their upright elevated positions and the centre group 4 will be raised clear of the ground.

Each double proportional counter comprises a lower counter having a thin window and which is beta/gamma sensitive and an upper counter which is gamma sensitive only. The double counter arrangement compensates for normal background gamma radiation, the difference signal from the counters in each pair being the result of beta radiation. The signals from the twenty detectors, ie ten beta/gamma and ten gamma, are fed to twenty separate counting channels. For each channel the counts are totalled at regular intervals, for example every - second, and the sum of the four most recent totals provides a running average (counts/second) for that channel. In the operative position the window of the lower counter of each double counter can be located approximately 10 cms above the ground.

Fig. 3 is a gas flow diagram for the arrangement of the three groups of counters. The counters in each group are series connected and supplied from a common gas supply cylinder 10 carried by the vehicle, the gas being 90% Argon, 10% methane mixture.

The gas supply is controlled by a pressure regulator 11 and the flow to the three groups of counters is indicated by a flowmeter 1 2.

On leaving the flowmeter the gas passes along lines 13, 1 4 and 1 5 to the respective groups of counters. A flow adjusting needle valve 1 6 is provided in each line upstream of the counters. The flow from the counters passes through a bubbler 1 7 before venting to atmosphere. The bubblers provide a visual indication of the flow of gas. Th-e bubblers each contain a depth of fluid which maintains a positive gas pressure of about 1 inch water gauge. Each of the lines has a low pressure switch 1 8 which functions to operate an alarm if the pressure in the associated line falls below a certain predetermined valve, for example, 3 inch water gauge. The various valves, switches, bubblers and flowmeter are mounted within the cab.A display and control panel in the cab includes 1. Red light emitting diode lamps, each linked to a counter, which light up when contamination is detected and remain lit until reset.

2. A loudspeaker operable to emit an audible signal when contamination is detected by any counter.

3. Amber light emitting diode lamps to indicate a failure associated with any counter.

4. Further light emitting diodes operable to indicate high background contamination.

5. Reset means for 1 and 2.

6. A ten-position rotary switch capable of connecting two analogue 30 segment bar displays to any gas flow detector channel.

One display shows the count rate from the gamma background counter for the channel and the other display gives the count rate from the beta/gamma counter after gamma background subtraction. The rotary switch also permits inclusion or exclusion of a channel by pressing an enable/disable button whilst the channel is selected. The status of each channel is indicated by a green light emitting diode which lights up when a channel is enabled.

7. A single amber light emitting diode lights up when the gas pressure in one of the three lines falls below a predetermined value, such as T inch water gauge.

In use, the vehicle is driven at a slow operating speed along a road or other surface to be monitored. The arms are lowered and with the outer arms in their operative positions the vehicle can survey a width of approximately nine feet. The operating speed of the vehicle can be held at about 1 mph.

Claims (6)

1. A ground survey vehicle for the monitoring of radioactive contamination comprising a self-propelled unit, radiation detectors mounted in arrays at the front of the unit and means on the unit for selectively moving the arrays into and out of their operative positions, the arrays in their operative positions extending across the front of the unit and projecting beyond the sides of the unit and being supported in close proximity to the ground.

2. A ground survey vehicle as claimed in Claim 1 including hydraulically operable means for moving the arrays.

3. A ground survey vehicle as claimed in claim 1 or 2 in which the detectors are arranged in three in-line arrays with the two outer arrays being hingedly connected to the centre array.

4. A ground survey vehicle as claimed in any preceding claim in which each array is contained within a skirt.

5. A ground survey vehicle as claimed in any preceding claim in which each detector array comprises upper and lower counters, the upper counters being gamma sensitive and the lower counters being beta/gamma sensitive.

6. A ground survey vehicle for the monitoring of radioactive contamination substantially as herein described with reference to and as illustrated in the accompanying drawings.