GB2162730A - Thermosensitive shutter for radioactive source housing - Google Patents

Abstract

A shutter apparatus for a radioactive source (1) housing (4) comprises a movable member (6) and a thermosensitive releasing means (11, 13) operative normally to hold the movable member (6) in an open position but to release the movable member (6) to move to a position closing the housing (4) to contain the source (1) when the temperature exceeds a predetermined value, for example as a result of fire. <IMAGE>

Description

SPECIFICATION Thermosensitive shutter for radioactive source housing This invention relates to a shutter for a radioactive source housing.

-Precautions against unnecessary exposure to radiation are an important aspect in overall safety when dealing with radioactive sources. Typically, a radioactive source is located within a housing comprised of a suitable radiation absorbing material such -as lead. One or more outlets are provided in the housing to allow emission of radiation and suitable collimation arrangements can also be provided at the outlet. It is essential that some form of shutter arrangement is provided whereby emission from the outlets is blocked whereby work on an object or process to be irradiated can be carried out in safety.

The shutter arrangement can be moved either manually or automatically to block radiation emission, for example a block of lead can be manually moved in front of the outlet.

In taking adequate safety precautions it is necessary to consider unexpected conditions to which the source and surrounding may be exposed. A substan tial risk of radiation exposure can occur when fire breaks out. In the panic that often results during a fire situation, it can be the case that the-radioactive source is not covered or shielded so that radiation emission is not blocked. This can either occur through forgetfulness or through inability to reach the source housing because of the fire. Thus, fire fighters entering the surroundings can encounter the hazard of exposure to radiation It is an object of the invention to provide a shutter arrangement that can automatically shield an outlet of a radioactive source housing in response to a preselected temperature.

According to the invention there is provided a shutter apparatus for a radioactive source housing comprising a member movable from an open position not blocking a radiation outlet of the housing to a closed position blocking said outlet, and a thermosensitive releasing means arranged to maintain the member in the open position and to move the member to the closed position in response to a preselected temperature.

In this way, in the presence of a fire the thermosensitive releasing means when warmed by the fire to the preselected temperature moves the member to the closed position to block a radiation outlet of the housing. Consequently, the radioactive source is automatically shielded irrespective of human intervention thereby safeguarding fire fighters against exposure to radiation.

Preferably, the thermosensitive means includes a pivot arrangement locked in a non-pivoting position by means of a thermosensitive material to maintain the member in the open position and whereby melting of the material in response to the preselected temperature unlocks the pivot arrangement to produce pivoting thereof to move the member to the closed position. By having a pivoting arrangement locked in a non-pivoting position by means of a thermosensitive material, it is possible to modify the temperature response of the shutter apparatus by employing different thermosensitive materials.

Thus, the shutter apparatus can be tailored to satisfy different safety requirements dependent upon proximity to heat. Conveniently, the pivot arrangement includes a portion located and held in the thermosensitive material, the material being disposed in a horse-shoe shaped retainer and whereby in response to melting of the material the arrangement pivots to urge the portion through the opening of the retainer. By employing a horse-shoe shaped retainer a simple way is provided for locking the pivot arrangement in a non-pivoting position. Furthermore, after use the thermosensitive material can be removed and the portion relocated in the horseshoe shaped retainer and the retainer refilled with thermosensitive material. Furthermore, by employing a horse-shoe shaped retainer it is only necessary for the pivot arrangement to pivot about one point.

Conveniently the thermosensitive releasing means also includes first bias means connected to urge the pivot arrangement to pivot and second bias means connected to urge the member to move to the closed position in response to pivoting of the pivot arrangement. In this way it is unnecessary to rely on gravitational force and the bias means can be selected to ensure that sufficient urging force is provided to overcome obstructing obstacles.

A radioactive source housing can include the shutter apparatus described above.

The present invention will now be described, by way of example, with reference to the acompanying drawings, in which Figure I illustrates a side view of a shutter apparatus embodying the present invention mounted on a source housing; Figure 2 illustrates an oblique frontal view of Figure 1.

Referring to the drawings, a housing 4 houses a radioactive source 1 at the centre thereof. A collimator shaft 2 communicates between the radioactive source 1 and the exterior of the housing. The collimator shaft together with the housing can comprise lead or other suitable radioactive shielding material.

A shutter member 7 comprising suitable shielding material is attached to a rotatable shaft 5 mounted in bearings on the housing (not shown). A bias spring 8 is located around the shaft 5 to press between the housing front face and a restraint 7 connected to the shutter member 6. Consequently, this spring bias urges the shaft 5 and hence shutter member 6 to rotate in the direction of the arrow X shown in the drawings. It will be apparent that by suitable arrangement of the weight of the shutter member 6 it would be possible to employ gravitational force to urge the shutter member to rotate in the direction of the arrow X.

Furthermore, some suitable arrangement of pistons could also be employed.

A lever arm 9 is connected between the shaft 5 and a further shaft 10. The shaft 10 is mounted in the lever 9 to run substantially parallel to the shaft 5. A horse-shoe shaped retainer 13 is mounted on the side of the housing 4 and orientated such that on rotation of the shaft 5 the shaft 10 rotates in the direction X and can pass through the opening 14of the horse-shoe shaped retainer 30.

A low melting point disc 11 can be located within the retainer 13. The disc has a central hole to receive the shaft 10 which can be retracted away from the housing 4 by pulling on a knob 15 provided at the end of the shaft 10. A bias spring 12 is located to urge the shaft towards the housing 4to urge the end ofthe shaft 10 into the hole in the low melting point disc.

Consequently, the end porition of the shaft 10 is locked in the low melting point disc 11 which is itself locked in the horseshoe shaped retainer 13. Therefore, pivoting of the shaft 5 and lever 9 is prevented so that the shutter member 6 remains in the position shown in Figure 1 whereby the member 6 does not block radiation emission from the source along the collimator 2. On exposure to heat, at a preselected temperature the low melting point disc 11 melts sufficiently to allow the bias of the spring 8 to pivot the lever 9 and shaft 5. Therefore, the shaft 10 advances through the opening 14 of the retainer 13 to allow rotation of the shutter 6 in the direction of arrow X whereby the shutter member 6 moves to a position blocking the emission of radiation along collimator 2. Thus, in this closed position emission of radiation-from the radioactive source 1 is blocked therefore, by selecting the melting point of the disc 11 it is possible to tailor the thermosensitive response of the closing of the shutter member 6. The selection of a suitable alloyforthe low melting point disc 11 will be apparent to one skilled in the art.

Claims (7)

CLAIMS:

1. Shutter apparatus for a radioactive source housing comprising a member movable from an open position not blocking a radiation outlet of the -housing to a closed position blocking said outlet, and a thermosensitive releasing means arranged to maintain the member in the open position andto move the member to the closed position in response to a preselected temperature.

2. Apparatus as claimed in Ciaim 1, wherein the thermosensitive means includes a pivot arrangement locked in a non-pivoting position by means of a thermosensitive material to maintain said member in the open position and whereby melting of the material in response to the preselected temperature unlocks the pivot arrangementto produce pivoting thereof to move the member to the closed position.

3. Apparatus as claimed in Claim 2, wherein the pivot arrangement includes a portion located and held in said thermosensitive material, the material being disposed in a horse-shoe shaped retainer and whereby in response to melting of the material the arrangement pivots to urge said portion through the opening of said retainer.

4. Apparatus as claimed in Claim 2 or 3, wherein the thermosenstivie releasing means includes first biased means connected to urge the pivot arrangement to pivot and second biased means connected to urge the member to move to the closed position in response to pivoting of the pivot arrangement.

5. A radioactive source housing including a shutter apparatus according to any preceding claim.

6. A shutter apparatus for a radioactive source housing substantially as herein described with reference to the accqmpanying drawings.

7. A radioactive source housing substantially as herein described with reference to the accompanying drawings.