WO2008080753A1

WO2008080753A1 - Radon monitoring dosimeter

Info

Publication number: WO2008080753A1
Application number: PCT/EP2007/063415
Authority: WO
Inventors: Paolo Orlando
Original assignee: Paolo Orlando
Priority date: 2006-12-29
Filing date: 2007-12-06
Publication date: 2008-07-10
Also published as: ITRM20060713A1

Abstract

A dosimeter (1) is described for monitoring radon, comprising: a first part (2) provided with a housing seat (12), which is suitable to receive a detector (9) including a free surface (9s) sensitive to the impact against alpha particles produced by the decay of radon and daughter products thereof, a second part (3) that can be coupled to the first part (20), which is provided with a diffusion chamber (20) having an opening (27) facing the first part (2), said chamber (20) being such that it can receive radon therein by diffusion from the external environment, coupling means (4,7) for coupling the first part (2) and second part (3) to each other, The coupling means (4,7) allow operatively coupling the first (2) and second (3) parts such that they can take at least one first and one second operating positions (ON, OFF) relative to each other in order to stop or restart monitoring the decay of radon and daughter products thereof that are present in the diffusion chamber (20).

Description

"Radon monitoring dosimeter"

DESCRIPTION

The present invention relates to a radon monitoring dosimeter. More particularly, the present invention relates to a dosimeter of the type including a diffusion chamber and a detector that is sensitive to the impact with alpha particles that are emitted by the decay of radon and by the decay of the daughter products thereof.

As is known, the requirement of monitoring radon concentrations has been felt for a long time in work, domestic or recreational environments, since a prolonged exposure to radon, mainly when high concentrations of the latter are present in an environment, is a serious danger for human health. Radon is a natural radioactive gas and is a product of the radioactive decay of radium, which, in turn, derives from uranium. Radon decays and originates other decay products. These products, the so-called "radon daughter products" are solid radio-active isotopes which are the greatest danger for human health as they are inhaled while breathing and are deposited in the lungs, where they, by decaying in turn, emit radiations that damage the lung tissue.

For monitoring the concentration values of radon and daughter products thereof passive dosimeters have been used for a long time, of the type including a diffusion chamber and a trace detector that is sensitive to the impact with alpha particles that are emitted by the decay of radon and daughter products thereof. The detector exposure is carried out within the diffusion chamber that radon enters by diffusion from the external environment. Practically, within the diffusion chamber, the alpha radiations emitted by the decay of radon and daughter products thereof upon impact against the detector produce surface damages, or "traces", therein. Subsequently, after the exposure has been completed, it is possible to amplify the damages produced in the detector by means of a chemical treatment of the latter, such as to allow reading these traces via a manual system (optical microscope) or an automatic scan system, which for example provides an automatic count of the traces by means of a vectorialisation program.

An example of a dosimeter such as described above is the one which has been initially developed at the end of the eighties by NRPB (National Radiation Protection Board, UK) and then improved by SSI (Swedish Radioprotection Institute) . This dosimeter, for example described in the publication "The NRPB radon personal dosimetry service", in "Journal of Radiological Protection", 1988 vol. 1, pagg. 19-24 consists of two parts: a base provided with a recess for housing a trace detector, and a cover element that can be coupled to the base and is dome-shaped. The dome-shaped cover element, when coupled to the base, forms a diffusion chamber containing the detector, and which the radon gas enters by diffusion from the external environment. A dosimeter of the type indicated above can be placed in a fixed location within an environment or can be worn by a person, such as fixed to the helmet or belt of a miner. While prior art dosimeters of the type described above are advantageously used, they suffer from a drawback in that they do not allow stopping and restarting according to the requirements the monitoring operation, by means of the trace detector, of the radon contained within the diffusion chamber and hence they do not allow monitoring the radon concentration only at the times of dwelling within an environment, for example a working environment. In other words, these dosimeters do not allow monitoring a person' s exposure to radon and daughter products thereof in a selective manner relative to the actual period of stay within one or more (e.g. working) environments.

The object of the present invention is to provide a radon monitoring dosimeter, which is capable of solving the drawback mentioned above with reference to the prior art .

This object is achieved by means of a dosimeter as generally defined in the annexed claim 1. Preferred and/or advantageous embodiments of a dosimeter according to the present invention are as defined in the annexed dependent claims.

Further characteristics and the advantages of a dosimeter according to the present invention will be apparent from the description given below of non-limiting exemplary embodiments thereof, in which:

Fig. 1 is a top perspective view of a dosimeter according to a particularly preferred embodiment of the present invention;

- Fig. 2 is a top perspective view of a first part of the dosimeter in Fig. 1 ;

- Fig. 3 is a bottom perspective view of a second part of the dosimeter in Fig. 1 ;

- Fig. 4 is a further top view of the dosimeter from Fig. 1; - Fig. 5 is a side sectional view of the dosimeter in Fig. 1, in a first operating configuration; and - Fig. 6 is a side sectional view of the dosimeter in Fig. 1, in a second operating configuration.

In the figures, equal or similar elements will be designated with the same numerals. With reference to the annexed figures, and particularly Fig. 1, with 1 has been generally designated a radon monitoring dosimeter according to a particularly preferred embodiment of the present invention. As may be seen in Fig. 1, the dosimeter 1 includes a first part 2, or more simply, a base 2, and a second part 3, or cover element 3, in the form of two pieces that are separated from each other and removably couplable to each other by removable coupling means 4, which in the particular example as represented herein include, without being limited thereto, a screw 4. In a particularly preferred embodiment, the base 2 and cover element 3 are made from plastics, such as by means of moulding techniques. More preferably, the base 2 and cover element 3 are made from conductive plastics, such as carbon- filled polypropylene.

Advantageously, the means 4 for coupling the base 2 to the cover element 3 allow fastening the base 2 and cover element 3 to each other while allowing a relative movement between these parts. Preferably, these coupling means 4 allow pivotally fastening the base 2 to the cover element 3.

The base 2, which is shown in greater detail in Fig. 2, includes a housing seat 12 for a so-called trace detector 9. The latter has, when received within the housing seat 12, a free surface 9s that is sensitive to the impact against alpha particles that are produced by the radioactive decay of radon and daughter products thereof. This free surface 9s, in the example illustrated in the figures, faces the cover element 3.

Preferably, though not being limited thereto, the trace detector 9 is in the form of a substantially rectangular plate, such as about 1 mm thick, which is made of polymeric material, for example made of poly- allyl diglycol carbonate (also known as CR-39) The use of this polymeric material to manufacture trace detectors sensitive to the impact against alpha particles has been long known to those skilled in the art.

Preferably, the base 2 is substantially plate-shaped and provided with a recess, such as a blind cavity, which is formed in the thickness thereof and defines the housing seat 12 for the trace detector 9. More preferably, the base 2 includes a substantially flat, essentially disc-shaped part 5, the recess 12 being defined in the thickness thereof, and includes a peripheral edge 6a, 6b that is raised relative to the flat part 5. In the example as illustrated in the figures, this raised peripheral edge 6a, 6b has first 6a and second 6b half-portions having different heights and forming two arcs that are consecutive to each other. Due to the different heights of the two arc-shaped half- portions 6a and 6b, the raised peripheral edge 6a, 6b includes two steps 10. In the example, the base 2 further includes a central pivot 7 which projects from the base 2 to the cover element 3 and has an internally threaded cavity on the head thereof, which is suitable to receive the screw 4 (shown in Fig. 1) . In a possible alternative embodiment, the base 2 may be provided with, in replacement of the pivot 7, a central hole suitable to receive an end portion of the screw 4 or removable coupling means that are similar or equivalent to the screw 4.

The base 2 further includes hooking means 8 to allow the dosimeter 1 to be worn by a person. In the particular example as represented herein, these hooking means are, though in a non-limiting manner, embodied by a simple eyelet 8, for example suitable to allow a person to wear the dosimeter 1 in a pendant fashion, such as attached to a key case or band. Alternatively, or additionally to this eyelet 8, a clip may be for example provided which is suitable to allow fixing the dosimeter 1 to a belt, pocket, helmet, etc.

Fig. 3 shows in greater detail the other part of the dosimeter 1 in Fig. 1, i.e. the cover element 3. Particularly, in Fig. 3, the lower face of the cover element 3 can be seen. This lower face is practically the side of the cover element 3 facing the base 2 when the cover element 3 and base 2 are coupled to each other.

The lower face of the cover element 3, which preferably has an outer periphery 24 of a substantially circular shape, has a substantially plane portion 21, which, when the base 2 and the cover element 3 are coupled to each other, results to be substantially parallel to the substantially flat part 5 of the base 2. Preferably, the lower face of the cover element 3 includes a central portion 23 that is slightly more protruding towards the base 2 than the plane portion 21 and intended to abut against the base 2 when the cover element 3 is coupled to the base 3. In the particularly preferred embodiment in Fig. 3, two hollow pockets 25 are provided in the cover element 3, the only function of which is to lighten the cover element 3.

Referring back to Fig. 3, the cover element 3 includes a diffusion chamber 20, which has an opening 27 that is defined in the lower face of the cover element 3. The opening 27 of the diffusion chamber 20, preferably of a substantially semi-circular shape, practically faces the base 2 when the cover element 3 is coupled to the base 2. Preferably, this opening 27 is co-planar with the plane portion 21.

For the purposes of the present description, by

"diffusion chamber" 20 is meant any chamber being defined in the cover element 3 and suitable to receive radon gas- containing air from outside the dosimeter 1 by diffusion.

In the example illustrated in the figures, the cover element 3 is provided with a central hole 22 that is suitable to receive the pivot 11 with which the base 2 is provided, to allow the pivoting coupling between the base 2 and the cover element 3, which coupling is practically provided by means of the pivot 11 and screw 4.

In a dosimeter 1 in accordance with the present invention, the cover element 3 and base 2 can be operatively coupled to each other such as to be capable of taking, upon coupling:

- at least one first operating position in which the free surface 9s of the detector 9 is such as to cooperate with the opening 27 of the diffusion chamber 20 to monitor the decay of radon and daughter products thereof which are present in the diffusion chamber 20;

- at least one second operating position in which the free surface 9s of the detector 9 is substantially noninterfering with the opening 27 of the diffusion chamber 20 to stop the monitoring of the decay of radon and daughter products thereof which are present in the diffusion chamber 20.

As may be appreciated from what has been described above, and can also be seen in Fig. 4, these operating positions, in the particularly preferred embodiment as illustrated in the figures, are achieved by rotating the cover element 3 relative to the base 2, such as to either superimpose the diffusion chamber 20 or not to the housing recess 12 that accommodates the detector 9.

For example, referring back to Fig. 4, these operating positions, during the movement of the cover element 3 relative to base 2, are two opposite end-of- travel positions, that can be for example achieved by means of two rotations of about 180° in opposite directions. For example, these end-of-travel positions are achieved, respectively, when a first projecting pin pi provided in the cover element 3 abuts against the one of the two steps 10 of the outer peripheral edge 6a, 6b of the base 2, and when a second projecting pin p2 provided in the cover element 3 abuts against the other of the two steps 10 of the outer peripheral edge 6a, 6b of the base 2. In the example in Fig. 4, this second condition occurs when the cover element 3 is rotated relative to the position illustrated in Fig. 4 in the direction of arrow fl and by an angle of about 180°. It should be observed that suitable (preferably snap) locking means can be provided, for example magnetic or mechanical, not described further herein and not shown in the figures, which are suitable to selectively lock the base 2 and the cover element 3 to each other in the two operating configurations as discussed above. It is believed that particular implementations of these locking means are within reach of those skilled in the art.

In Fig. 5 is shown a side sectional view of the dosimeter in Fig. 1. In this figure, with Z-Z has been designated the axis about which the mutual rotation takes place between the base 2 and cover element 3.

In Fig. 5, the base 2 and cover element 3 are shown in the operating configuration, the so-called "ON" configuration, in which the detector 9 is such as to monitoring the decay of radon and daughter products thereof which are present in the diffusion chamber 20. Particularly, in the "ON" operating position in Fig. 4, the decay of radon and daughter products thereof, which are contained within the chamber 20, emits alpha particles impacting against the surface 9s of the detector thus causing damages (the so-called "traces") to the detector 9.

As may be seen in Fig. 4, in a particularly preferred embodiment, the cover element 3 includes a substantially dome-shaped portion 32 which accommodates the diffusion chamber 20. The diffusion chamber 20, on the opposite side relative to the opening 27, also has an internally rounded roof.

The remaining portion of the cover element 3 is essentially the plane wall 21 and is preferably, hence not limited thereto, provided with a stiffening border 33 and one or more stiffening ribs 13 (which can be best seen in Fig. 1 and 4) .

In Fig. 6, since the base 2 and cover element 3 have been relatively rotated by 180° about the axis Z-Z relative to the "ON" operating configuration in Fig. 5, they are shown in the so-called "OFF" operating condition, in which the monitoring operation by means of the detector 9 of the decay of radon and daughter products thereof within the diffusion chamber 20 is interrupted. This is practically due to the fact that in this operating configuration, the detector 9 is substantially noninterfering with the opening 27, and accordingly substantially isolated from the diffusion chamber 20.

It should be further observed that, advantageously, in the OFF operating configuration, the plane wall 21 of the cover element 3 protects the detector 9, and particularly the surface 9s thereof, from the impact with alpha particles produced by the decay of radon and daughter products thereof, which are present in the external environment, i.e. which are present outside the dosimeter 1. This plane wall 21 is thus a protective shield to at least partially protect the detector 9 in the OFF operating position.

As may be appreciated from what has been described above, it is understood that a dosimeter according to the invention allows overcoming the drawbacks mentioned above with reference to prior art dosimeters. For example, a dosimeter of the type described above can be brought to the "ON" operating condition and worn by an individual during his/her work time such as to allow monitoring the actual exposure to radon of this individual in his/her working environment. At the end of the work shift, the dosimeter can be brought to the "OFF" position such as to substantially stop the monitoring operation. Obviously, inevitably, it will happen that in the "OFF" operating configuration, mainly due to the radon which will penetrate within the dosimeter 1 by diffusion between the wall 21 and base 2, the detector will keep on measuring a so-called "background noise" which is due for example to the decay of radon and daughter products that are present within the gaps that are provided between the base 2 and cover element 3 and that are proximate to the detector 9. The contribution of this "background noise" to the measurement can be, however, eliminated, for example by arithmetic subtraction (or "cancellation") , by providing a second dosimeter in the environment, for example identical to the one described above, which has to be constantly held in the "OFF" position and by providing an individual, at the end of his/her work shift, to leave his/her personal dosimeter in the working environment in the "OFF" position in a place next to the one in which the second dosimeter is stored.

Obviously, those skilled in the art, in order to meet contingent and specific requirements, will be able to make a number of modifications and variants to the dosimeter described above, all of which are contained within the scope of the invention as defined by the following claims.

For example, in a possible variant embodiment, anti- tampering means can be provided in the dosimeter 1 in order to prevent or restrain the possibility of access to the trace detector by unauthorized operators. For example, with reference to the examples described above, the screw 4 may be made in the form of a special screw or a pivot that can be handled only via special tools to be provided to the authorized operators.

Claims

1. A dosimeter (1) for monitoring radon, comprising: a first part (2) provided with a housing seat (12), which is suitable to receive a detector (9) including a free surface (9s) sensitive to the impact against alpha particles produced by the decay of radon and daughter products thereof, a second part (3) that can be coupled to the first part (20), which is provided with a diffusion chamber (20) having an opening (27) facing the first part (2), said chamber (20) being such that it can receive radon therein by diffusion from the external environment, coupling means (4, 7) for coupling the first part (2) and second part (3) to each other, characterized in that the coupling means (4, 7) allow operatively coupling the first (2) to the second part (3) such that they can take at least one first operating position (ON) relative to each other in which the free surface (9s) is such as to co-operate with the opening (27) for monitoring the decay of radon and daughter products thereof which are present in the diffusion chamber (20) and a second operating position (OFF) in which the free surface (9s) is substantially noninterfering with the opening (27) to stop monitoring the decay of radon and daughter products thereof that are present within the diffusion chamber (20) .

2. The dosimeter (1) according to claim 1, wherein the second part (3) includes shielding means (21) to at least partially protect, in the second operating position

(OFF), the surface (9s) free from the interaction with radon and the daughters products thereof which are present in the environment external to the dosimeter (1) .

3. The dosimeter (1) according to claim 2, wherein the shielding means include a plane wall (21) which is substantially co-planar to this opening (27).

4. The dosimeter (1) according to any preceding claim, wherein the coupling means (4) allow fastening the first (2) and second (3) parts to each other while allowing for a relative movement between these parts.

5. The dosimeter (1) according to claim 4, wherein in this movement, the first and second operating positions (ON, OFF) are two opposite end-of-travel positions.

6. The dosimeter (1) according to any preceding claim, wherein the coupling means are pivoting coupling means and wherein the first (2) and second (3) parts are such as to be capable of being brought to the first (ON) or second (OFF) operating positions by means of a relative rotating movement about an axis of rotation (Z-Z) .

7. The dosimeter (1) according to claim 6, wherein the first part (1) includes an essentially disc-shaped plate-like main body (5) , and wherein the second part (3) includes a lower face that is intended to face the first part (2) and having an essentially circular outer periphery, said opening (27) being defined in this lower face .

8. The dosimeter (1) according to claim 8, wherein said opening (27) is approximatively semicircle-shaped.

9. The dosimeter (1) according to any preceding claims, wherein the second part (3) includes an essentially dome-shaped portion (32), said diffusion chamber (20) being defined in said dome-shaped portion (32) .

10. The dosimeter (1) according to any preceding claim, including means for removably locking the first (2) and second (3) parts in the first and second operating positions, respectively.

11. The dosimeter (1) according to any preceding claim, further including anti-tampering means for preventing or limiting the possibility of access to said detector (9) by unauthorized operators.