A nonshielded, miniaturized radioisotope generator for the production of radioisotopes having a nonhazardous level of radioactivity is comprised of a closed container having an entrance port at one end, an exit port at the other end, and inner chamber communicating with the entrance and exit ports and an elutable radioactive material disposed in the generator in such a manner that the eluate can be withdrawn without contamination by the radioactive source.

Current U.S. Class:	250/436 ; 250/493.1
Current International Class:	G21G 4/00 (20060101); G21G 4/06 (20060101); G21h 005/00 ()
Field of Search:	250/106(T)

Paul A. Rose Gerald R. OBrien Charles J. Metz William R. Moran

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Claims

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1. A miniaturized radioisotope generator for the production of radioisotopes said generator comprised of in combination: a. a first section having (i) an open end and (ii) a closed end fitted with an entrance port communicating inwardly by an inner chamber with said open end, and said open end having connecting means to a second section; b. a second section having (i) an open end and (ii) a closed end fitted with an exit port communicating inwardly by an inner chamber with said open end, and said open end having connecting means to said first section; at least one of said closed ends of said first and second section being inwardly recessed and said port protrudes outwardly therefrom and is so disposed as not to extend beyond the surface formed by the outer peripheral edge of said closed end; and c. an elutable radioactive material disposed in said generator, said radioactive material being present in an amount up to the general licensed

2. The miniaturized generator of claim 1 which contains 9 microcuries of

3. The miniaturized generator of claim 1 which contains 0.9 microcuries of

4. A miniaturized radioisotope generator for the production of radioisotopes said generator having an overall length of less than 3 inches and comprised of, in combination: a. a cylindrical first section having (i) an open end and (ii) a closed end fitted with an entrance port communicating inwardly by an inner chamber with said open end, said entrance port disposed so as not to extend beyond the surface of the outer circumferential edge of said cylindrical first section, of said cylinder having retention means for a first filter which covers said inner chamber, and said open end having connecting means to a second section; b. a cylindrical second section having an open end and a closed inwardly recessed end from which outwardly protrudes a hollow, exit port communicating inwardly by an inner chamber with said open end, said exit port disposed so as not to extend beyond the surface of the outer circumferential edge of said closed end, said open end of said cylinder having retention and support means for a second filter which covers said inner chamber, said open end having connecting means to said first section; and, c. an elutable radioactive material disposed in said generator, said radioactive material being present in an amount up to the general licensed

5. The miniaturized generator of claim 4 wherein said filters have a

6. The miniaturized generator of claim 4 wherein said filters have a

7. The miniaturized generator of claim 4 having attached to the entrance port a reservoir of eluant.

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Description

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This invention relates to a miniaturized radioisotope generator. In one aspect this invention relates to a nonshielded, miniaturized radioisotope generator suitable for the production of a radioactive eluate having a nonhazardous level of radioactivity. In a further aspect, this invention relates to a miniaturized radioisotope generator which needs no special precautions for handling and hence is suitable for use as a teaching aid in the demonstration of the basic principles of nuclear theory.

In recent years there has been a marked increase in the use of radioisotopes, particularly in industrial applications such as in the measurement of slow rates, process control, radiometric chemistry and the like. Radioisotopes are also of current interest in medical research and as diagnostic agents. For example, medical investigation has shown that radioisotopes, such as indium-113m and technetium-99m, are extremely useful tools for diagnosis. High purity technetium-99m is used as a radioisotope in a variety of medical research and diagnosis. It is well suited for liver, lung, blood pool and tumor scanning, and is preferred over other radioactive isotopes because of its short half-life which results in reduced exposure of the organs to radiation.

Since the radioisotopes which are used have relatively short half-lives, it is the common practice to ship the user the parent element. The user then extracts the desired isotope as his needs require. For example, indium-113m can be shipped to the user as its parent element, i.e. neutron irradiated tin. When the radioisotope is desired, the indium-113m can be eluted from the parent element. Due to the relatively high degree of radioactivity, elaborate precautions must be taken to insure proper shielding from both the parent element and the eluted radioisotope. Lead containers are commonly employed for the storage and transportation of the radioactive materials. Hence the use of the radioisotopes is largely limited to scientists who have been trained in the special handling techniques required to minimize the hazards inherently present.

Although radioisotopes would be of great assistance in teaching the principles and applications of nuclear technology, they have not been employed as a teaching aid primarily due to the need for special handling techniques and the hazards associated therewith. In this respect, the Atomic Energy Commission has set certain license requirements regarding the possession and use of radioactive materials. The only quantities of radioactive materials which are exempt from an AEC license are those which exhibit such a low level of radioactivity that are not considered to be a radiation hazard. Since such quantities are of little value for industrial or medical uses, to date there are few, if any, commercial generators available for their production.

It is therefore an object of this invention to provide a miniaturized, radioisotope generator. Another object of this invention is to provide a nonshielded, miniaturized radioisotope generator which produces an eluate having a relatively low degree of radioactivity. A further object of this invention is to provide a miniaturized generator which can be employed as a teaching aid with a complete degree of safety. A still further object of this invention is to provide a generator that virtually precludes radioactive contamination even with gross physical or chemical misuse. These and other objects will readily become apparent to those skilled in the art in the light of the teachings herein set forth.

The objects of the invention and the preferred embodiments thereof, will best be understood by reference to the accompanying drawing wherein:

FIG. 1 is a perspective view of the separate components that comprise one embodiment of the invention.

FIG. 2 is a view of the miniaturized radioisotope generator having attached thereto a syringe for the introduction of the eluant.

With respect to the drawings, FIG. 1 shows a perspective view of a miniaturized generator consisting of a first section 10, having a port 11, through which the eluting solution can be introduced into the generator; a second section 12, having a port 13 through which the eluate exits. The radioactive parent element 14, is disposed between filters 15 and 16 which permit passage of the eluting solution while at the same time maintaining the parent element in place. An additional optional retainer 17 provides support for filter 16 and prevents passage of the parent element in the event of a rupture in filter 16.

FIG. 2 shows a view of the actual size of a typical miniaturized generator having attached thereto a reservoir of eluant contained in a syringe.

By the term "miniaturized" as employed throughout the specification and appended claims, is meant a radioisotope generator of such size that it can be easily transported and stored in a minimum of space and having an overall length of less than about 3 inches and a width or diameter of less than about 2 inches. Although the particular design of the generator is not critical, it is preferred that it be constructed in such a manner that the area in which the radioactive material is disposed is easily accessible. In practice, it has been found that if the generator is constructed of two sections which can be coupled or screwed together, the introduction of the radioactive material and the assembly of the unit is greatly facilitated.

As indicated in FIG. 1, one embodiment of the invention is directed to a generator comprised of two threaded sections which can be joined together to from a leakproof container. The first section contains the entrance port and an inner chamber connecting to the port, while the second section contains the exit port and a similar inner chamber. When the two sections are coupled together one continuous chamber is formed leading from the entrance to exit ports. Retaining means are provided in the section walls of the chamber for positioning the elutable radioactive material. As indicated above, filters are provided on either side of the radioactive source to permit passage of the eluting solution and the daughter radioisotope. The filters can also be supported and held in place by a porous face on the inner chambers of each of the sections. In one embodiment, either or both of the entrance and exit ports are recessed so that they do not extend beyond the outer circumferential edge of the generator. Particularly, when the exit port is recessed, the generator can be placed in an upright position even while the syringe is filled with little danger of tipping over. The exit should however protrude from the bottom of the generator so that the drops of eluate emerging can easily be observed. This is particularly useful since due to the size of the generator, very small amounts of eluant are used. If the surface of the exit section of the generator is concave or otherwise recessed, the exit port can be fashioned of a tube which protrudes above the surface but not beyond the circumferential edge of the section.

The entrance port can also be recessed so that it does not protrude beyond the edge of the first section. In this manner, the generator can easily be stored in a minimum of space and without damage to the port. In a preferred embodiment, the entrance port is threaded so that the end of the syringe can be screwed onto the port to provide a leakproof connection.

In practice, the generator can be composed of most any material which is unreactive with the eluting solution and radioactive materials. Glass, metal, ceramics, or a wide variety of other materials can be employed. However, for practical purposes it is preferred to use a nonbreakage inert material such as one or more of the many plastics currently available. For example, polyethylene, polypropylene, polystyrene, and the like can be used. When plastic is employed, the sections of the generator and ports can be molded as single units. Similarly, a plastic syringe can also be employed so that the entire system is essentially unbreakable. It should be noted that the entrance and exit ports of the generator are always open. However, if desired for shipping or storage purposes, plastic guards such as a plug or cup can be used to cover the ports.

As previously indicated, the source of the desired radioactive isotope is maintained in place within the inner chamber in such a manner that the eluting solution can pass over or through it and elute the desired isotope without carrying out any of the parent element. This can best be achieved by sandwiching the parent element between two filtering plates or discs. Although a wide variety of filters can be employed, such as a glass frit, and the like, it is preferred to use a filter paper having a porosity of less than about 15 microns, and more preferably, less than about 1 micron. Filters having a porosity of about 0.22 microns are particularly preferred.

It has been found that the miniaturized generator of this invention is useful for producing a wide variety of radioactive isotopes from their parent element. In all instances, both the parent element and the eluted radioactive isotope have such a low degree of radiation, that no shielding is necessary for either the generator or the eluate. Illustrative parent elements and their "daughter" radioisotopes, i.e., the radioisotope which has been eluted, include among others, .sup.113 Sn/.sup.113m In; .sup.137 Cs/.sup.137m Ba; .sup.144 Ce/.sup.144 Pr; .sup.90 Sr/.sup.90 Y; .sup.68 Ge/.sup.68 Ga; .sup.140 La/.sup.140 Ba; and the like.

In practice, the parent element from which the desired radioisotope is eluted is contained on a substrate or matrix. The choice of substrate will, of course, be dependent upon the particular parent element employed. The preferred substrate chosen is one which has a greater capacity to retain the parent element than the daughter radioisotope. Hence, when the eluting solution is introduced, the desired radioisotope is selectively withdrawn from the substrate. The preferred choice of eluting solution will likewise be dependent upon the particularly parent-daughter elements. Although a variety of substrates and eluting solutions can be employed, table I below sets forth several radioisotopic systems and their preferred substrates and eluting solutions. ##SPC1##

To use the generator, a quantity of the eluant, usually a few milliliters, is taken up in the syringe, and the syringe screwed onto the entrance port. By the slow application of pressure on the piston, the eluant is forced into the generator where the desired radioisotope is taken up and then leaves through the exit port into an appropriate vessel such as a beaker. Thus the miniaturized generators provide an inexpensive source of short-lived radioisotopes. They can deliver well over 1,000 times their license-exempt loading during their useful lifetimes which is many years for the Cesium-137/Barium-137m generators and about two years for the Tin-113/Indium-113m generator. In addition, the generators can be eluted whenever desired and repeatedly during a given laboratory period. This characteristic virtually eliminates the supply and demand problems often associated with other commercially available radioisotopes

As hereinbefore indicated, the miniaturized radioisotope generator of this invention is constructed to contain quantities of radioisotopes which are AEC general licensed and which virtually precludes radioactive contamination even with gross physical or chemical misuse. Under title 10 of the Code of Federal Regulations, Part 31, Section 31.4, a general license is issued to transfer, receive, acquire, own, possess, use and import the quantities of byproduct materials listed in Section 31.100, Schedule A thereof. For a nonsealed source a general license is issued for byproduct materials having as little as 0.1 microcurie (Polonium 210) up to a maximum of 250 microcuries (Tritrium). For example, for a nonshielded source of barium-137m 1 microcurie is generally licensed, whereas for a nonshielded source of indium-113m 10 microcuries are licensed. For beta and/or gamma emitting byproduct material not specifically listed in Schedule A a general license is issued for a nonsealed source of 1 microcurie and a sealed source of 10 microcuries. The low levels or radiation used in the generator permit them to be stored with other school supplies and with no special precautions in storage and handling. In addition, there is no danger of contamination of the work area even if the eluate is spilled during experimentation because the eluate contains such small quantities of a short-lived radioisotope, a feature that precludes longterm radioactive contamination.

The following examples illustrate the uses of the miniaturized radioisotope generator as an aid for teaching some of the fundamentals of nuclear theory.

EXAMPLE 1

Study of Activity Buildup in .sup.137 Cs/.sup.137m Ba Generator

In this example, a study was made of the activity buildup in a .sup.137 Cs/.sup.137m Ba miniaturized radioisotope generator. Cesium-137 is a fission product of Uranium-235 which has a half-life of 30 years. When it emits a beta particle its atomic number increases by one with no change in atomic mass to produce .sup.137m Ba. The unstable condition of this isotope's nucleus makes it a gamma emitter with a short half-life in the range of minutes.

A miniaturized generator was employed which contained a general licensed amount (0.9 microcurie) of Cesium-137 coated on a substrate. A background count was first recorded with a scintillation counter. Thereafter, the activity reading of the .sup.137 Cs/.sup.137m Ba generator was taken before elution. This value represented the equilibrium activity. Four milliliters of one molar HCl was taken up in the syringe and the generator slowly eluted, while the activity reading of the generator was recorded for 1 minute and thereafter at 2 minute intervals over a 10 minute period. Milking the generator with one molar HC1 selectively removes the daughter Barium-137m from the parent Cesium-137. As soon as the barium has been eluted from the generator its radioactivity drops to a very low level, but immediately begins to build up as additional cesium is transmuted to barium. This experiment investigates this buildup until equilibrium between the constituents of the generator is again achieved.

EXAMPLE 2

Determination of the Half-Life of Barium-137m

In this example the half-life of Barium-137m was determined using the miniature generator. Barium-137m is a metastable isomer formed by the emission of a beta particle from the nucleus of Cesuim-137. It exists in this radioactive isomeric state emitting gamma rays until the nucleus achieves a stable ground state. Most metastable isomers emit all their potential gamma rays in a small fraction of a second. Some, however, including Barium-137m, exhibit delayed gamma emission and have half-lives ranging from seconds to months. The gamma rays emitted have energies measured in thousands of electron volts (kev.) and these are attributable to the rearranging of the nucleus and its quantum descriptions (particularly angular momentum) in coming to the ground state. Barium-137m emits a 661 kev. gamma ray.

A miniaturized generator was employed which contained a general licensed amount (0.9 microcurie) of Cesium-137 coated on a substrate. A background count was first recorded with a scintillation counter. Thereafter, the generator was eluted with about 3 milliliters of HCl in the syringe and the eluted liquid collected in a 10 milliliter beaker. The beaker was placed in the counter and a 1-minute reading of the activity recorded. After a 1- minute interval, 1-minute readings were taken every other minute for approximately 10 minutes. After correcting for background count, the readings were plotted as activity vs. time curve on semilong-arithmetic graph paper. Any two convenient activities on the graph are then selected which show the earlier-occurring reading exactly twice as active as the later reading. Perpendicular lines are then drawn from these points to each axis so that the line in the Y plane represents a decrease of one-half in the activity and the line in the X plane represents the half-life of .sup.137m Ba (that is, the time required for the activity of a radioactive sample to decrease to half its original value). The half-life of the .sup.137m Ba was found to be 2.6 minutes.

EXAMPLE 3

Determination of the Half-Life of Indium-113m

In this example the half-life of Indium-113m was determined using the miniaturized generator. Tin-112, which exists naturally making up less than 1 percent of a sample of natural tin, when exposed to neutron bombardment in a nuclear reactor, absorbs a neutron to become Tin-113. This isotope has a half-life of 118 days and transmutes itself to Indium-113m by k-electron capture. This metastable isomer is a gamma emitter similar to Barium-137m but with a longer half-life.

A miniature generator was employed which contained a general licensed amount (9 microcuries) of tin-113 on a substrate. A background count was first recorded with a scintillation counter. Thereafter, the generator was eluted with 5 milliliters of 0.03 molar HCl into a 10 milliliter beaker. Two 1-minute readings were taken on the eluted indium followed by continuous readings each half hour for at least 3 hours. After correcting for background count, the readings were plotted as activity vs. time on semilogarithmic graph paper and the half-life determined as in the previous example. The half-life of Indium-113m was found to be 1.73 hours.

EXAMPLE 4

Use of Radioisotopes for Density Gauging

In this experiment, a miniature .sup.113 Sn/.sup.113m In generator was employed to gauge the density and thickness of opaque objects and to trace the internal system of an object lacking accessibility.

An aluminum cylinder was packed with alternating layers of sand and lead shot. Their positions are not visible from the outside. Using the miniature .sup.113 Sn/.sup.113m In which contained a general licensed amount (9 microcuries) of tin-113 as a a gamma source on one side of the cylinder and a Geiger-Mueller tube as a probe on the opposite side, readings were taken at 1-inch intervals up the cylinder. From the readings, a diagram of the cylinder was drawn to scale and the positions of the sand and lead layers indicated.

Although the invention has been illustrated by the preceding examples, it is not to be construed as being limited to the materials employed therein, but rather, the invention encompasses the generic area as hereinbefore disclosed. Various modifications and embodiments of this invention can be made without departing from the spirit and scope thereof.

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