US 3385968 A
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Description (OCR text may contain errors)
y 8, 1968 R G. BRYER 3,385,968 I RADIOACTIVE RADIA'fION DOSIMETER OF THE SILVER PHOSPHATE GLASS TYPE Filed Jan. 18, 1966 10 15 10b 70a 4 I '3 I30 v \l I FIG. 2.
. ATTORNEY United States Patent 3,385,968 RADIOACTIVE RADIATION DOSIMETER OF THE SILVER PHOSPHATE GLASS TYPE Robert George lBryer, Rnislip, England, assignor to R. A.
Stephen & Company Limited, Mitcham, Surrey, England, a limited company of the United Kingdom Continuation-impart of application Ser. No. 282,039, May 21, 1963. This application Jan. 18, 1966, Ser. No. 521,284 Claims priority, application Great Britain, May 21, 1962, 19,462/ 62 2 Claims. (Ci. 250-83) The present application is a continuation-in-part application of co-pending application Ser. No. 282,039 filed May 21, 1963, now abandoned.
This invention relates to dosimeters of the locket type, for personal wear. The invention has for its object to provide an improved form thereof.
The invention is particularly applicable to a locket type dosimeter of the non-direct reading type. In such a dosirneter there is used an element of radiation-sensitive material, the effect of radiation upon which is not directly observable, so that the element must be examined by a separate reading means to ascertain the degree of radiation to which it has been subjected. An example of such a material having the desired properties is a glass containing a dissociable phosphate material, such as silver phosphate. In practice it is required to remove or expose the element in the reader, and so it is necessary that the element should be mounted in a manner to afford repeated and ready access to it.
With certain materials of this class, such as the glass mentioned above, it is necessary also to provide an adequate seal for the material when in use. The reason for this is that if the element is mounted with free access to the air, it may occur that the phosphate material will dissociate without being irradiated and will then give rise to an inaccurate indication. Also, with silver phosphate it may occur that there is superficial oxidization of the silver, producing a surface film which affects the light or radiation transmission of the glass. As it is necessary to read the dosimeter by means which depend upon the light transmission of the glass, the production of such a silver oxide will also lead to an inaccurate indication.
The present invention has for its object to provide a dosimeter locket which provides an adequate seal for the element, and which can be readily and repeatedly opened for reading.
The invention includes a dosimeter including a radiation-sensitive element, a casing for sealing said element, said casing being adapted to be opened at will to give access to said element, said casing including two separable parts and a resilient sealing member engaged between adjacent surfaces of said parts, said surfaces lying about an access opening, and a housing for receiving said casing and for imposing sealing pressure on said surfaces, said housing having two portions respectively engaging said casing parts and being relatively rotatable for imposing said pressure on said surfaces, at least one of said parts having localized engagement with its associated housing portion, whereby to permit rotation relative thereto.
The inner casing is made of steel, brass or a like metal which, unlike plastic materials, will not allow to any great extent the passage by diffusion of gases or vapors into the inner casing, will not produce emanations of a derogatory nature in the gas-containin g enclosure, and will not deform with age or temperature. It has been found that the only metal which diffuses gases much more readily than plastic is palladium. This metal is of course much too expensive to consider for use in dosimeters.
In one convenient construction of the device for read- "ice ing the element, the same is subjected to radiation directed upon it from a first direction, and the desired indication obtained as a function of a radiation, such as one of different wavelength, emerges from the element in a second direction, at an angle, preferably a right angle, to the first. This requirement means that the element must be readily removable from the locket to enable the desired reading to be made, or alternatively, the element must be so accommodated in the locket as to enable this to be done. In a preferred form of the invention described hereinafter, a locket is provided which can be located, while in its normally closed condition, in a reader and then by a simple action the element can be exposed for reading, remaining located in the reader.
Further features and advantages of the invention will be apparent from the following description of an embodiment thereof, given, by way of example in conjunction with the accompanying drawings, in which:
FIG. 1 is a half plan view of a locket; and
FIG. 2 is a medial section through the locket.
This locket comprises an outer casing 10 suitably made of a molded synthetic plastic material and having a central recess 11 which accommodates a lead shield 12 and an inner casing 13 of metal. The lead shield 12 is located on casing 10 by means of an annular projection 10a formed integrally with casing 10 and engaging in a central opening 14 in the shield 12. The casing 13, and with it the shield 12, are secured against axial movement relative to casing 10 by a pin 15 attached to inner casing 13 and passing through outer casing 10 into a recess 10b, the pin being held, for example, by deforming its free end over a washer 16, or alternatively by a spring ring engaging in a groove formed in the pin. For reasons that will appear later in the description, the casing 13 is free to rotate. The portion 10c of casing 10 defining the opening to the recess 11 is screw-threaded to receive a lid 17 having a screwthreaded peripheral portion 17a. Supported on lid 17 are a lead disk 18 and an inner casing lid 20; the outer edge 20a of lid 20 is depressed as shown and fits within an annular recess 17b of the lid 17 and thus provides a receptacle for a sealing O-ring 21. O-ring 21 cooperates with a flanged outer edge 13a of the casing 13 to provide a completely sealed enclosure between inner casings 13 and 20 when the lid 17 is screwed into the access opening of casing 10. For clarity of illustration, a rather large gap is shown between flanged edge 13a and casing 20. In practice this gap will be very small or nonexistent, since during assembly O-ring 21 is deformed until edge 13a and casing 20 come in contact with each other.
The seal which is formed by O-ring 21 does not prevent gases from diffusing into the inner casing, but it occupies a minute fraction of the total surface area of the inner casing, and accordingly, the amount of gases which can diffuse through the seal is minute and negligible for all practical purposes.
Within the enclosure there is accommodated, by means of a clip fastening not shown, a small block 22 of glass which contains silver metaphopshate. The lead shields 12 and 18 may have in them perforations of suitable size in order to equalize the response of the glass 22 to different energy levels.
The outer casing 10 also has an integrally formed projection 10d provided with a hole 25 for supporting cord or the like.
Holes 23 in lid 17 enable the locket to be located, unopened, on corresponding locating pins in the reader; the casing 10 is then unscrewed from the lid 17 without the use of a separate tool, leaving the glass block exposed for reading in the manner previously described.
Instead of screw-threaded engagement between casing 10 and lid 17, the casing 10 may be formed with an interrupted groove or grooves which can receive projections formed on the peripheral portion of the lid 17 when it is angularly rotated with respect to the casing 10.
With the construction described, the glass 22 is completely sealed and is thereby protected against contamination by the atmosphere, or against any migration of a constituent of the casing 10 or its lid 17; operation of the dosimeter is thereby stabilized over long periods.
Further, by making the inner casing 13 rotatable, objectionable rubbing between the O-ring 21 and flange 13a, when the lid 17 is being screwed into or out of the casing 10, is eliminated; the casing 13 being free to rotate with the lid 17.
While the invention has been described in detail with respect to a certain now preferred example and embodiment thereof, it will be understood by those skilled in the art, after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended, therefore, to cover all such changes and modifications in the appended claims.
What is claimed is:
1. A portable dosimeter comprising in combination:
(a) a casing made of a gas diffusion pervious material and having a generally cup-shaped bottom part and a lid screwable into the rim of the bottom part;
(b) an inner casing made of a substantially gas impervious material and having an imperforate generally cup-shaped bottom part nested in the outer casing bottom part and an imperforate lid fitted between the lid of the outer casing and the peripheral rim of the bottom part of the inner casing, said rim terminating in an outwardly extended flange and said inner casing lid having a set-off peripheral rim disposed in parallel superimposition with said flange spaced apart therefrom to define an annular space between said flange and said rim;
(0) a sealing ring fitted in said space, sealing pressure being applicable to the ring by screwing the outer casing lid into the outer casing bottom part;
((1) a substantially imperforate cup-shaped lead shield interposed 'between said two casing bottom parts;
(e) a substantially disc-shaped imperforate lead shield interposed between two lids; and
(f) a radiation-sensitive element disposed within said inner casing.
2. A dosimeter according to claim 1, wherein said cup-shaped shield has an aperture, and comprising fastening means securing said bottom parts to each other and extending through said aperture.
References Cited UNITED STATES PATENTS 2,415,031 1/1947 Kuhn et al. 220-46 2,580,057 12/1951 Wilhelm 220-46 X 2,879,914 3/1959 Fleckenstein 220-46 X 3,042,802 3/1962 Just et al. 250-83 3,100,262 8/1963 Shenker et al. 25083 2,750,515 6/1956 Shurcliff 250-83 ARCHIE R. BORCHELT, Primary Examiner.