This invention relates to radiation detection trainin apparatus for use in the training of personnel in the detectio of ionising radiation such as alpha beta and gamma ray ionisin radiation.

There is a need for an apparatus for use in the trainin of personnel in the detection of ionising radiation and i decontamination procedures once an ionising radiation sourc has been detected.

Conventionally such training is carried out using a apparatus comprising a number of sources of ionising radiation, for example short-half-life gamma ray emitters, which ar distributed over an area to be searched, or in the clothing o a person to be decontaminated, and a detector appropriate t the radiation emitted by the source or sources which is used b a person being trained to seek out the source or sources.

Such known apparatus has the disadvantage that it comprises actual sources of ionising radiation, this being particularly undesirable in the training for decontamination of a person. Further, gamma ray radiation has a much greater range in air than alpha ray radiation, making it easier to detect, and thus the use of conventional gamma ray radiation gives the person being trained an unrealistic impression of the operation of the detector in relation to the detection of alpha

ray radiation sources. A further disadvantage of such know apparatus is that the use of ionising radiation sources i costly, not only in the direct cost of the sources, but also i the indirect costs of the necessary safety procedures, and th time necessary for decontamination after training is completed.

According to this invention there is provided a apparatus for use in the training of personnel in the detectio of ionising radiation sources, comprising a number of magnet simulating ionising radiation sources, and a detecto responsive to the magnetic fields of the magnets to give a indication of detection of any one of the magnets.

The invention provides an apparatus for use in th training of personnel in the detection of ionising radiatio and in decontamination procedures, which avoids the risks, difficulties and expense of the use of actual ionisin radiation sources.

The detector can be responsive to the strengths and/o the polarity and/or the gradients of the magnetic fields, o the detected magnets.

Preferably the magnets are permanent magnets, in whic they can have a coating of a screening material which serves a a filter modifying the field of the magnet as required. Otherwise the magnets can be electromagnets, in which case eac can comprise a coil through which an oscillating current i passed, the strength of the magnetic field produced being se by frequency control of the oscillating current.

It will be appreciated that any form of magnet can be used, for example magnets constituted by magnetic liquids, powders or particles, possibly in distributed form, in addition to conventional permanent magnets or electromagnets.

The detector can comprise one or more Hall effect devices giving an output signal dependent upon field parameters of a detected magnet. The output signal can be used to drive a meter or digital read-out device and/or a speaker giving an audio output whereby the detector can stimulate and be in the form of a conventional geiger or scintillation counter. Thus, training of personnel using the apparatus of the invention can be very realistic.

This invention will now be described by way of example with reference to the drawings, in which:-

Figure 1 is a schematic diagram of the detector of an apparatus according to the invention together with an associated magnet; and

Figure 2 is a block schematic diagram of apparatus according to the invention.

The apparatus to be described comprises a plurality of permanent magnets 1 (only one shown) serving as simulations of ionising radiation sources, and a Hall effect detector 2 serving to detect the presence, polarity and field gradient of the magnetic fields of the magnets 1.

For use, the magnets 1 are distributed over an area to be 'decontaminated', and the detector 1 used to detect the

magnets by searching the area or clothing.

By detecting the three specified parameters of each of a plurality of magnets of differing strengths the apparatus can be given a relatively wide dynamic range in relation to th range of magnet strengths used.

For simplicity, consider the use of two magnets in th ratio of strengths m:l. These two magnets can be used to simulate four decades of source-strength. Clearly, it would b possible to use three or more magnets of differing strengths to simulate a greater number of source-strengths and/or a wide dynamic range.

Detection of North and South poles can be interprete differently, for example a North pole generating a detecto output one hundred times greater than that generated by an equivalent South pole, other things being equal. Further, the gradient of the magnetic field of a detected magnet can be determine .

By measuring these variables a set of two equations in a detected magnet's instrinsic strength and its distance from the detectors can be solved.

Assume that the axial field from a detector magnet is that of an ideal dipole. Then

B. = k/z ^*

SB _Z = -3K ^ z z ⁴

These equations can be solved for k and z:

Now suppose two magnets in the strength ratio m:l are used to represent detector outputs in the ratio 10:1. The exponent is defined by πf*- β 10, <=><- = l/log _1Q m).

Let f(z) be the function relating field-strength to detector output for the North pole of a magnet of strength k=l. Let p be an integer representing magnet-polarity, being +1 for North,

-1 for South. Then we can write an expression for detector output in the general case:

Output - k^fCz) x 10 ^p_1

With two magnets and two polarities, we can scale f(z) by factors of from 0.001 to 10.0, covering four decades of source-strength.

There are some complications and approximations involved in implementing this algorithm.

Instead of a local measurement of δBz/δz, Bz is measured at two distinct points, the two values subtracted. Call these values B _f and B. ;

_ . . B _f ^4βt f' ( B _f ) x 10 ^P_1

Output = ± ,_. (1)

( _Bf -B _b ) * (B _f -B _b )

The first term, which is an approximation for k, is not in fact constant for a given magnet. However, it retains the important property that, for a given magnet-detector separation, the

^B f ratio — is constant, and the output is proportional to

Bf-B _b

B^, i.e. to k*S as required. Equation (1) can be simplified to

Output = B _f ^ g' ( Bf ) x lO ^5"1 (2)

(Bf-B _b)

where g ¹ (x) == x f ^* (x) .

Referring now to Figure 1 of the drawing, as shown the detector 2 comprises two planar arrays 3 and 4 of Hall effect devices 5, held in spaced parallel relationship by spacer members 6. Each array 3 or 4 has an electrical power supply as indicated. The combined outputs of the devices 5 in each array 3 or 4 are passed to respective comparators 7 and 8 where they are compared with an input reference voltage 9. The outputs of the comparators 7 and 8, indicated as V, and V _f indicate the strength of a detected magnet 1, and can be processed to obtain the gradient of the magnetic field of the magnet 1 across the spacing between the arrays 3 and 4. Further, the output of the comparator 8 is supplied to a polarity detector 10 the output of which indicates the polarity of a detected magnet 1.

The three outputs thus obtained can be processed in the manner discussed above to provide an output signal for driving

a visual and/or audible signal output device, as discussed aboveby which detection of a magnet and the comparative strength of the detected magnet can be signalled to the user of the apparatus.

Preferably the detector is in the form of a conventional geiger or scintillation counter with the visual and/or audible indication given being similar to that given by such a counter whereby use of the apparatus simulates use of such a counter as closely as possible.

Referring now to Figure 2 of the drawings, here is shown a magnet 1 and detector apparatus 2, for example as shown in Figure 1. The outputs from the detector apparatus 2 are supplied to a microprocessor 11 for processing as discussed above, which microprocessor 11 provides a first output which drives a meter 12 and a second output which is passed by way of an audio amplifier 13 to drive a speaker 14.

Although in the apparatus described above the detector comprises two spaced planar arrays of Hall effect devices, it is otherwise possible to use a single planar array while still detecting up to four different strengths of simulated ionising radiation sources. With such apparatus the processing circuitry which receives the output of the Hall effect device array will serve to detect the maximum magnet field strength of either polarity sensed anywhere in the array. Such a single array detector is used with simulated sources comprising, for the two weakest ranges to be detected, single North and South pole magnets as for the above apparatus, while the sources for

the two strongest ranges to be detected each comprise a mai magnet with one or more adjacent auxiliary magnets, with th main magnets being of opposite polarity. When the detecto array detects a simulated source for one of the two stronges ranges the processing circuitry serves to sense whether th detected field strength is above a threshold indicating that main magnet with one or more adjacent auxiliary magnets ha been detected, that is that a 'strong' source has bee detected, and distinguishes between the two strong sources o the basis of the polarity of the main magnet thereof. Thus such apparatus using only a single planar array of Hall effec devices can distinguish between four different simulate sources.