A non- Slip Extremity Dosimeter
The current invention relates to the field of radiation health physics and dose uptake measurement.
Radiation workers perform many manual operations, and in the course of these, accrue an ionising radiation dose. Whilst a whole body dose is reasonably easy to calculate by the use of thermoluniinescent dosimeter (TLD) etc, it is also important to calculate extremity doses, particularly when the worker is working in a glovebox environment, when TLD's may be shielded.
Extremity doses are currently measured by fixing a small TLD in a band that is worn around the finger. This band is typically made of nylon or similar materials and may be adjusted by means of Velcro(RTM) strips or any other simple fastening.
Current devices have a failing, however, in that they are prone to slip around or along the finger, or to become completely dislodged as the hand moves around in the glove. Furthermore, it is often easier to fasten such devices so that the device sits on the back of the hand. In this position it will be shielded by the fingers and thus will erroneously record a lower extremity dose rate, especially for the more easily attenuated types of ionising radiation, such as Beta rays and low energy x-rays. This has the potential to lead to harm to operatives in manual contact with ionising radiation sources, through under estimating the accrued dose. The object of this invention is to overcome some of the failings in the prior art by devising a dosimeter that will not become dislodged when carrying out glovebox operations and the like.
Accordingly, the current invention provides for a dosimeter capable of being mounted on a digit, comprising a radiation detector and a mounting therefor, characterised in that said mounting is formed into a sheath that fits closely around said digit, the sheath having a proximal end and a distal end.
The advantage of such a device is that by employing the sheath construction, the device is less likely to slip off the digit or to move around it, whilst in a glove or at other times. The radiation detector may be of any suitable design including but not limited to radiation sensitive films, and thermoluminescent detectors. The mounting for the dosimeter may be of any length from a short sheath to one stretching along the length of a digit, but should be of sufficient length and sufficient tightness to be capable of inhibiting movement of the dosimeter around the finger without resorting to adjusting mechanisms. The material forming the sheath may be selected for the amount of friction or slippage between the sheath and the digit it is being worn on. Typical materials for the sheath may include, but not be limited to, resilient materials (those that return to their original shape following deformation), such as rubber and flexible plastics and less rigid materials such as elasticated fabrics.
In a second embodiment, the invention provides for a dosimeter comprising a radiation detector and a mounting as described above, wherein the proximal end is configured so as to provide an opening into which a digit can be inserted, and the distal end is closed so as to limit movement of the digit within the sheath.
In this configuration, the mounting for the dosimeter may typically resemble a thimble. This configuration introduces additional adhesion between the dosimeter and the finger by creating a vacuum effect. In order to maintain the benefit of the vacuum effect, the dosimeter mounting may advantageously be made from non-porous materials such as rubber. Performance may be further enhanced by selecting a material with suitable non- slip properties when in contact with the skin.
In order to further inhibit the movement of the dosimeter around the digit, one part of the sheath can be further tightened. This could be achieved by incorporating some elasticated band along a part of the dosimeter mounting, or by incorporating a fasteneble portion, e.g. with Velcro(RTM) into the sheath. Such a fastenable portion could advantageously be worn tightened above a knuckle, to prevent the device slipping along a digit. By equipping a dosimeter with such a fastening to be tightened around a digit, and employing sheath closed at one end as described above, movement of such a dosimeter would thus be doubly constrained. In such a configuration, the radiation detector could advantageously be situated in such a position that it sits at the most suitable position for dose measurement when the sheath is fastened in the normal way. In a further embodiment, the radiation detector is situated right at the end of the sheath. This has the advantage allowing the true extremity dose to be calculated, and since the device will be much less likely to be shielded by the finger, will record a dose rate more accurately.
In a further embodiment, the sheath is stored pre-roUed with the dosimeter in place, or is rolled up before use (from the proximal end to the distal end where the detector may be located), in order to facilitate the application of the dosimeter. In this embodiment, the mounting might advantageously be made from latex or a synthetic rubber, so as to be tight over the digit when worn. Such devices could conveniently be pre- rolled and packaged in this state by the manufacturers. When required, a new dosimeter could be simply taken from its packaging, and rolled over a finger into position.
An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, wherein
Fig 1. shows the device in the form of a thimble with the radiation detector mounted on the end- side elevation.
Fig 2. shows a cross section through the device along the line A-A in the direction shown.
Figure 3 shows the device in the form of a sheath in side elevation.
Referring first to figure 1 , the dosimeter mounting (4) is open at the proximal end (2) to allow a finger to be inserted. The distal end (6) is closed so that the sheath forms a thimble. This ensures that the device is kept in place through the vacuum effect at the end of the thimble, and by choosing a material that has a high coefficient of friction with the wearer's skin. In the embodiment shown, the material selected is rubber, and is in contact all around the tip of the finger.
At the distal end (6) a housing (8) for a radiation detector (10) is provided, recessed so that it is substantially flush with the surface of the sheath. The radiation detector (10) is worn so that it is over the pad of the finger so that during any manipulation it will be between the finger and the source.
Figure 3 shows a different embodiment of the invention. In this embodiment, the dosimeter mounting is formed into a sheath (14) of a diameter selected so that it is tight when worn over a finger. In this example, the sheath is formed from latex or a synthetic rubber, so that it does not inhibit movement of the finger. In this embodiment, the radiation detector (10) and its housing (8) are located at the distal end (12) near the finger tip, and to further restrict movement of the dosimeter in relation to the finger, a band of elasticated material (16) is incorporated towards the proximal end of the finger.