Abstract:
A device for shielding a radiation source that is adapted to selectively position the source to be stored and shipped or positioned for repetitively establishing a radiation field for calibrating radiation detection devices.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to radiation shielding devices. More particularly, the invention relates to a radiation shielding device adapted to function as a shipping and storage container and as a radiation calibration source. 
     When calibrating radiation measuring devices such as radiation survey meters or dosimeters, it is common to establish a known radiation field with a radiation source and place the device to be calibrated within the field. Heretofore, it has been necessary to perform the calibration at large centralized facilities having rooms equipped with appropriate radiation sources and equipment for establishing the known field. It is highly desirable to be able to calibrate these measuring devices at the location where they are to be used, and, thus, eliminate the necessity for the large centralized facilities. To do so requires the ability to establish the known radiation field repeatably at the desired location. Additionally, there is always the problem of storing and shipping the radiation source so as to shield personnel from dangerous radiation. 
     Normally, radiation sources are stored in lead bricks, lead containers, or behind lead shields. While these devices are normally effective in shielding personnel from radiation they are bulky, heavy, and difficult to handle rendering them generally undesirable as shipping containers. More importantly, as far as can be determined, no shielding container has been devised having means for holding the radiation source in an exposed mode for establishing a known radiation field like the present invention. Rather, in the prior art, the source is removed from the container and used merely to give an indication that the measuring device is operating. Thus, a known radiation field is not established. Consequently, there is a need in the prior art to configure a storage and shipping container that is also adapted to mount the radiation source in a known position, when removed therefrom, for establishing a repeatable known radiation field for calibrating associated radiation measuring devices. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the invention is configured to a storage container for storing a radiation source so as to reduce the radiation emitted by the radiation source to levels safe for personnel in an improved manner. 
     Another object of the invention is to configure the storage container to be compact, lightweight, and capable of also functioning as an easily handled shipping container for the radiation source in an improved manner. 
     A further object of the invention is to configure the storage container so that a portion thereof is easily converted to a stand for holding the radiation source in a predetermined position for repetitively establishing at different times and locations a known radiation field for calibrating associated radiation measuring devices. 
     The foregoing objects are achieved and the shortcomings of the prior art overcome by configuring the storage container to comprise a lightweight case having an internal lead member attached thereto for receiving and shielding the radiation source when it is being stored or shipped. The case further includes a top portion for attaching the radiation source external thereto in a predetermined position for repetitively establishing the geometric relationship necessary to produce a known radiation field. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of the preferred embodiment with part of the case cut away showing details of construction and assembly. 
     FIG. 2 is an assembly drawing of the preferred embodiment in partial cut away section showing the radiation source in the shielded position for storage and shipping. 
     FIG. 3 is an assembly drawing of the preferred embodiment showing the radiation source positioned on the case at a predetermined location. 
     FIG. 4 is a diagrammatic representation of the preferred embodiment in use creating a radiation field for calibrating a radiation measuring device. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, the preferred embodiment described hereinbelow has been designed to accommodate a low level radiation source 10 of Krypton-85 gas. The radiation source 10 source is contained in an ampule 12 embedded in a rod 14 and has a strength of 5 millicuries and a radiation intensity of 5 milliroentgens per hour as measured at the bare surface of rod 14 adjacent the ampule 12. When shielded by the container of the present invention, the radiation intensity level is reduced to less than 0.5 milliroentgen as measured at the surface of the container. This level of intensity is considered acceptable for shipping between locations and handling by personnel. It is to be understood that the invention is equally applicable to other radiation sources. 
     Shown in FIGS. 1 and 2 is a radiation source shield and calibration device 16. The device includes tubular case 18 closed on one end by first closure member 20. A base plate 22 is affixed to member 20 to allow the device to stand vertically. Alternatively, base plate 22 could also function as the closure for case 18 and could be an integral part of case 18. 
     A lead internal member 24 for absorbing radiation from the source is fitted within the case and extends along the case a distant sufficient to absorb the radiation. Internal member 24 includes a cavity for receiving a liner 26 for forming a receptacle 28 to receive the radiation source 10. Receptacle 28 is disposed coaxially with liner 26 and case 18. Rod 14 slides into receptacle 28 to place the radiation 10 within the lead internal member 24. Rod 14 is kept from being separated from the device by a chain 30. 
     Still referring to FIGS. 1 and 2, case 18 is closed on its opposite end with a second closure member 32. The second closure member 32 includes an aperture 34 disposed co-axially therein and with case 18 and receptacle 28 when second closure member 32 is attached thereto. The aperture 34 is configured to threadedly receive first and second threaded portions 36 and 38, respectively, of 36 on rod 14. In the stored position, shown in FIG. 2, the road 14 is inserted through aperture 34 into receptable 28 thus shielding the radiation source 10. Threaded portion 36 secures the rod and the radiation source 10 therein. In the stored configuration, the radiation source 10 is shielded and the entire device is easily handled for storing or shipping. The preferred materials for case 18, closure members 20, 32 and base plate 22 are those that are lightweight, readily available, and easy to fabricate such as copper or plastic. Recepticle 28 is preferably copper. 
     Alternatively, the radiation source 10 may be mounted in the exposed calibration configuration, shown in FIG. 3. When this position is selected, rod 14 is removed from case 18 and turned end for end. The second threaded portion 38 thereon engages aperture 34 thereby holding the rod 14 and the radiation source 10 in a vertical position. 
     In order to repetitively establish at different times and locations the geometric relationship of a known radiation field 40, as shown in FIG. 4, the radiation source 10 must be repetitively positioned at the same known distance d in relation to a reference plane, see FIGS. 3 and 4. The reference plane is herein defined to be the surface upon which the base plate 22 is resting. Therefore, case 18 is manufactured to a predetermined length L for a particular length of the rod 14 and the radiation source 10 used, thereby positioning the the radiation source 10 at a known position relative to the reference plane each time the calibration device 16 is used to calibrate a measuring device 42 (see FIG. 4). Knowing the radioactivity level and position of the radiation source 10, the geometry of the field of radiation established is capable of being repeated at different times and at different sites. 
     As shown in FIG. 4, when calibrating measuring device 42, calibration device 16 is placed on the reference plane to establish the predetermined radiation field geometry. The center of a measuring device sensor 44 is positioned at the same predetermined distance d about the reference plane as the radiation source 10. Further, measuring device sensor 44 is positioned at the same predetermined horizontal distance x from the radiation source 10 as in prior calibrations. With the measuring device sensor 44 so placed, an indicator 46 is adjusted to indicate the radiation field intensity at that position. 
     It should be appreciated that subsequent calibrations can be made merely by placing measuring device sensor 44 at the same predetermined distances d and x. The radiation intensity does not change between calibrations because the geometry of the radiation field is held constant by calibration device 16. 
     To those skilled in the art, modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that the present invention can be practiced otherwise than as specifically described herein and still be within the spirit and scope of the appended claims.