US3733489A

US3733489A - Radiation timing device

Info

Publication number: US3733489A
Application number: US00160287A
Authority: US
Inventors: S Berk
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1971-07-07
Filing date: 1971-07-07
Publication date: 1973-05-15
Anticipated expiration: 1990-05-15

Abstract

Radiation timing device for use in fuzes for bombs, shells, mines and the like. The constant emission of radioactive emanations from a radioactive source is used to measure time. The device consists of a source, a shutter or absorber placed between the source and a radiation detector and counter. When a predetermined number of emanations is counted a switch activates the device.

Description

Unite States Patent 1 Berk [ 1 May 15, 1973 [54] RADIATION TIMING DEVICE [75] Inventor: Sigmund Berk, Philadelphia, Pa. 1

[73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, D.C.

221 Filed: July7, 1971 211 Appl.No.: 160,287

[52] US. Cl. ..250/83.3 R, 250/84, 250/106 R, 250/106 S [51] Int. Cl. ..G01t 1/16 [58] Field of Search ..250/83.3 R, 84, 106 R, 250/106 S [56] References Cited UNITED STATES PATENTS 3,094,622 6/1963 Handel 250/84 X 3,370,414 2/1968 Lazrus et al. ..250/83.3 R 3,443,097 5/1969 Smith ..250/83.3 PD X 3,510,656 5/1970 Hood ..250/84 3,629,582 12/1971 Koehler et al ..250/106 R X Primary ExaminerArchie R. Borchelt Attorney- Harry M. Saragovitz, Edward J. Kelley and Herbert Berl et a1.

[57] ABSTRACT 9 Claims, 4 Drawing Figures 2,967,243 1/1'9'6'1 "wl'ler'..;...f...;;...'..;.L......25b7ibii3 :1 DETECTOR AMPUFIER UNTING SWlTCH DESIRED b SYSTEM FUNCTION H.V. -15 SUPPLY PATENIEDHAHSIUB 3 733,489

lo 4 16 17 p8 DETECTOR AMPUHER COUNT'NG swn-cH oesmw SYSTEM P. Fumcrmgg H 12 H.V. -15 $UPPLY f ELECTROMETER L DETECTOR SYSTEM; 21

4J94 27L I 26, f

. VETEQTOR RATE SWITCH DES\RED SYSTEM METER FUNCTON \NVENTOR SEGMUND BE RK HARRY M. SAGWITLEWARDJKELLY, HERBERT BERL & MORRIS WISE-IMAM ATTORNEY RADIATION TIMING DEVICE The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to a very accurate timing device for measuring fractions of seconds, minutes, hours, days or longer without the use of clock mechanisms. This device is particularly useful in fuzes for use in bombs, shells, mines and the like. The constant emission of alpha or beta particles or gamma radiation from radioactive sources is used to measure time.

There are many advantages to a device utilizing radiation timing. First, the emission from a particular source is uniform and thus the timing may be very accurate. Furthermore, there is no interference from temperature or atmospheric pressure in the operation of the device. The efficiency of radiation detectors is very high, approximating 100 percent for solid state detector. The rate of emission may be controlled by the choice of radioisotopes used and the choice of absorber, if any used. The radiation hazard is negligible because of the shielding which is used. This is particularly true with respect to alpha and beta sources where relatively little shielding is needed to block out all radiation. Finally, certain embodiments of this invention are very inexpensive to produce and as there are very few parts, chances of failure are small.

The invention essentially consists of a radioactive source shielded except in one direction. A shutter or absorber is placed between the source and a radiation detector and counter. When a predetermined number of emanations is counted the device is activated. The detector and counter may be a simple charged capacitor. As the alpha and/or beta particles are collected on the electrodes of opposite polarity, the voltage between the electrodes decreases proportionately. When a certain voltage is achieved, the bomb or the like is activated.

Accordingly, it is an object of this invention to provide a timer for fuze application which does not include a clock mechanism.

It is a further object to provide a timer which is accurate to measure time in seconds, minutes, hours, days or longer.

It is still another object of this invention to provide a timer for fuze application which is not affected by temperature or atmospheric pressure.

These and other objects, features and advantages will become more apparent from the following description and accompanying drawings in which:

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram showing another embodiment of the present invention.

FIG. 3 is a block diagram showing still another embodiment of the present invention.

FIG. 4 is a schematic and block diagram showing yet another embodiment of the present invention in use.

Referring to FIG. 1, radioactive source is shielded in all directions but one by shield 11. In the direction left unshielded by shield 11 is a shutter 12 which may be opened to let the radiation pass or closed to completely contain the radiation. Detector 14 powered by high voltage supply 15 is located on the opposite side of the shutter 12 from the source 11. This detector 14 catches the radiation which passes the open shutter 12.

An amplifier l6 and counting system 17 are aonnected to the detector and when a certain predetermined count is achieved the switch 18 activates the function desired. Absorber 13 may be placed between the source 10 and the detector 14 in order to attenuate the amount of radiation received by detector 14. The radioactive source 10 may be an alpha, beta or gamma source. The type of source used is dependent upon the specific application. For most purposes alpha emitters are preferred because they are the easiest to shield and are the least dangerous. If the device is designed such that the radiation must penetrate an absorber 13 to reach the detector 14, beta or gamma radiation may be preferred. Furthermore, as will be discussed below, the proper combination of radioactivity and half-life must be determined and the source selected which meets the qualifications.

The detector 14 may be of any known design or of any design which may hereinafter be devised. It may be of the Geiger-Meuller type, the scintillation type or solid state. The type of amplifier, counting system and means of actuating the function desired will of course depend on the detector used and they are well-known to persons skilled in the art.

FIG. 2 shows a simplified variation of the device of FIG. 1. Again there is source 10, shield 11, shutter 12 and if desired, absorber 13, but in place of detector 14 is an electrometer 19. This electrometer may be a simple ion chamber which becomes discharged as radiation enters. When it becomes discharged to a certain extent the desired function is actuated. The advantage of this embodiment is that it is very simple and devoid of complex electronics. The electrometer could be charged at the last minute, a required decrease in charge for functioning set, and the shutter opened. This could easily be miniaturized.

FIG. 3 shows still another embodiment of the present invention. Rather than reading the amount of radiation emitted directly, the device could be set up such that the detector system 21, reads the radiation backscatter from a reflector 20. The amount of reflection of radiation is a function of the average atomic number and the thickness of the reflector. Thus another variable is added to the system so that there are more possibilities of arriving at a desirable radiation count reaching the detector.

FIG. 4 shows a variation of the backscatter technique shown in FIG. 3 as it may be used in a simple application. The device is placed on a roadside with source 10 and shield 11 arranged such that the radiation is directed across the road 25 and away from detector system 22. The detector system 22 reads the radiation backscattered normally from the air or the environment. When a vehicle 26 passes, the backscattered radiation increases above the normal backscattered radiation level. The rate meter 23 is preset so that when the radiation count rate received from the detector system 22 increases above a certain limit, switch 24 activates the function desired. The count rate limit which has been set is predetermined from known standards of backscatter for various metals in vehicles. Thus, for instance, a rate could be preset such that the backscatter from an animal would not be great enough to activate the device, and only a tank would provide the preset backscatter count rate.

As has been stated heretofore, selection of the proper source depends upon the radioactivity and half-life of the source. Table I shows the half-life and particle energy of certain preferred isotope sources.

Table I Isotope Half-life Energy (Mev) Type Radiation 14 5,570 y 0.15s 13 35 87.1 d 0.168 B 147p, 2.5 y 0.223 B 3 12.6 y 0.018 B 60 5.27y 0.31 B

1.33, 1.17 y 241 458 y 5.31, 5.48, 5.53 a 63 125 y 0.067 [3 85, 10.6 y 0.69 [-3 0.54 'y 204 4.1 y 0.77 B

for the radioactivity to be predicted over a period of time, it is necessary to known the half-life of the material. l-Ialf-life is defined as that time required for an initial statistically large number of atoms to be reduced by radioactive decay to half that number. In other words it is that length of time required for the activity of a given mass of material to decrease by half. The longer the half-life, the more constant will be the radioactivity of a source. Thus it can be seen that if the radioactivity and the half-life of a given source are known, the number of emissions in a given time can be determined. When this number of emissions or the equivalent count on a detector, is set on the present invention, the device will activate when this number of emissions is reached. The accuracy of this method of timing is great because the rate of radioactive decay is not alterable by chemical or physical means. If one desires to set a time twice as long as that mentioned above on the timer of the present invention, it could be done in one of several ways. The capacity of the counter could be increased and the timer set to activate upon receipt of approximately double the emissions. A less active source could be used which will take twice as long to have the same number of emissions. Or an absorber could be inserted with the same source and counter. The absorber would be chosen with the characteristics that it would shield one-half of the emissions from the counter. Thus it would take twice as long to reach the set count.

These simple examples show the versatility of the present invention. Variations in the basic device to accomodate these and other advantages include the following. The source could be permanently set or removable so that the type and activity of source could be varied in the same timer. An absorber could be insertable so that absorbers of different thickness and shielding ability could be inserted between the source and the detector if desired. The source could be a liquid or a gas in a glass ampule which could be broken to begin the operation of the timer. In the backscatter embodiment, the reflector could be removable to insert materials with various degrees of scattering ability.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

1 claim:

1. A radiation timing device comprising a radioactive source selectable to radiate any one of alpha, beta or gamma radiation,

detector means arranged to receive radiation from a selected said source for accumulating a count of the number of particles of said radiation,

said detector means comprising a charged ion chamber detector which discharges in a direct relation with the number of particles of radiation received from said selected source,

an amplifier connected to said detector for amplifying the response of said detector to the receipt of said radiation; and

a counter connected to said amplifier for keeping a cumulative count of said detected and amplified radiation, which count is directly related to the number of total radiations emanating from said radioactive source;

shield means partially surrounding said source for allowing radiation therefrom only in the direction of said detector means;

shutter means between said source and said detector means for shielding said detector means from said radiation when closed and permitting said radiation to reach said detector means when open; and

absorber means between said source and said detector means for attenuating the amount of said radiation reaching said detector means when said shutter is open.

2. A radiation timing device as described in claim 1, wherein: said radioactive source is selected from the group of isotopes consisting of C, S, "Pm, H, Co, Ni, Kr, T1 and Am.

3. A radiation timing device as described in claim 2, wherein: said radioactive source is Am.

4. A radiation timing device as described in claim 1, further including: a frangible capsule containing said radioactive source, wherein said radioactive source is in a gaseous state.

5. A radiation timing device comprising:

a support;

a radioactive source connected to said support and selectable to radiate any one of alpha, beta or gamma radiation;

a reflector connected to said support and in a position relative to said source to receive and reflect radiation therefrom;

' detector means connected to said support and in a position relative to said reflector to receive reflected radiation backscatter therefrom for accumulating a count of the number of particles of said radiation backscatter; and

activating means connected to said detector means for activating said device when a predetermined number of said radiation backscatter particles have been detected by said detector.

6. A radiation timing device as described in claim 5,

wherein said detector means comprises:

a detector arranged to receive the backscatter from said reflector;

an amplifier connected to said detector for amplifying the response of said detector to the receipt of said backscatter; and

a counter connected to said amplifier for keeping a cumulative count of said detected and amplified backscatter, which count is directly related to the number of total radiations emanating from said radioactive source.

7. A radiation timing device as described in claim 5,

wherein:

said detector means comprises a charged electrometer whereby said electrometer discharges in a direct relation with the amount of backscatter received from said reflector.

8. A radiation timing device as described in claim 5,

wherein:

said radioactive source is selected from the group of isotopes consisting of "C, 'C, Pm, H, Co, Ni, Kr, Tl and Am.

9. A radiation timing device comprising:

a support;

shield means partially surrounding said source for allowing radiation therefrom only in one general direction;

a vehicle movable into the path of said radiation;

detector means connected to said support and positioned with respect to said source so as to receive no direct radiation therefrom but in such a position that backscatter radiation may be detected from said vehicle when it is in the path of said radiation;

a rate meter connected to said detector for counting the rate of radiation received therefrom;

activating means connected to said rate meter for activating said device when a predetermined count rate is measured by said rate meter.

Claims

1. A radiation timing device comprising a radioactive source selectable to radiate any one of alpha, beta or gamma radiation, detector means arranged to receive radiation from a selected said source for accumulating a count of the number of particles of said radiation, said detector means comprising a charged ion chamber detector which discharges in a direct relation with the number of particles of radiation received from saId selected source, an amplifier connected to said detector for amplifying the response of said detector to the receipt of said radiation; and a counter connected to said amplifier for keeping a cumulative count of said detected and amplified radiation, which count is directly related to the number of total radiations emanating from said radioactive source; shield means partially surrounding said source for allowing radiation therefrom only in the direction of said detector means; shutter means between said source and said detector means for shielding said detector means from said radiation when closed and permitting said radiation to reach said detector means when open; and absorber means between said source and said detector means for attenuating the amount of said radiation reaching said detector means when said shutter is open.

2. A radiation timing device as described in claim 1, wherein: said radioactive source is selected from the group of isotopes consisting of 14C, 35S, 147Pm, 3H, 60Co, 63Ni, 85Kr, 204Tl and 241Am.

3. A radiation timing device as described in claim 2, wherein: said radioactive source is 241Am.

5. A radiation timing device comprising: a support; a radioactive source connected to said support and selectable to radiate any one of alpha, beta or gamma radiation; a reflector connected to said support and in a position relative to said source to receive and reflect radiation therefrom; detector means connected to said support and in a position relative to said reflector to receive reflected radiation backscatter therefrom for accumulating a count of the number of particles of said radiation backscatter; and activating means connected to said detector means for activating said device when a predetermined number of said radiation backscatter particles have been detected by said detector.

6. A radiation timing device as described in claim 5, wherein said detector means comprises: a detector arranged to receive the backscatter from said reflector; an amplifier connected to said detector for amplifying the response of said detector to the receipt of said backscatter; and a counter connected to said amplifier for keeping a cumulative count of said detected and amplified backscatter, which count is directly related to the number of total radiations emanating from said radioactive source.

7. A radiation timing device as described in claim 5, wherein: said detector means comprises a charged electrometer whereby said electrometer discharges in a direct relation with the amount of backscatter received from said reflector.

8. A radiation timing device as described in claim 5, wherein: said radioactive source is selected from the group of isotopes consisting of 14C, 35C, 147Pm, 3H, 60Co, 63Ni, 85Kr, 204Tl and 241Am.

9. A radiation timing device comprising: a support; a radioactive source connected to said support and selectable to radiate any one of alpha, beta or gamma radiation; shield means partially surrounding said source for allowing radiation therefrom only in one general direction; a vehicle movable into the path of said radiation; detector means connected to said support and positioned with respect to said source so as to receive no direct radiation therefrom but in such a position that backscatter radiation may be detected from said vehicle when it is in the path of said radiation; a rate meter connected to said detector for counting the rate of radiation received therefrom; activating means connected to said rate meter for activating said device when a predetermined count rate is measured by said rAte meter.