US3056123A - Radiation alarm or the like - Google Patents

Description

Sept. 25, 1962 M. H. SHAMOS 3,056,123

1 RADIATION ALARM OR THE LIKE Filed July 29, 1958 2 Sheets-Sheet 1 I I I Q I I M I L E \f I 3: 2 g I' Y o i /A *28 INVENTOR- QL-EEE MORRIS H.SHAMOS ATTOR N EYS.

Sept. 25, 1962 M. H. SHAMOS 3,056,123

RADIATION ALARM OR THE LIKE Filed July 29, 1958 2 Sheets-Sheet 2 lllllllw INV/Vf0R.. MORRIS H. SHAMOS ii/.4, 211M KM ATTORNEYS.

nited Stats rt 3,056,123 RADIATION AL OR THE LIKE Morris H. Shamos, Riverdale, N.Y., assignor to Tung-Sol Electric Inc., a corporation of Delaware Filed July 29, 1958, Ser. No. 751,715 Claims. (Cl. 340-237) This invention relates to alarm devices and has particular reference to an alarm system which will sound a warning or produce a visual indication when gamma ray radiation level exceeds a predetermined tolerance level.

The large increase in the use of radioactive materials during the past few years, coupled with the threat of radiation hazards resulting from atomic warfare make it desirable to have a simple, automatic radiation alarm which will give a signal when the radiation level exceeds a predetermined value. Since such devices should be on duty twenty-four hours a day, it is advisable to use a simple dependable arrangement which does not require a continuous supply of electrical energy in the standby condition.

The present invention, while primarily directed to the detection of gamma and X-ray radiation, can also be arranged to act as a smoke alarm and as such can be used in the home or in any building where there is danger from fire.

Radiation alarms used at present generally consist of ion chambers or Geiger counters coupled to appropriate amplifier circuits to operate preset relays and alarm sys terns. In any of these devices hot cathode tubes must be used which require a continuous supply of heater or filament current in the standby condition. The level for which these alarms are set is usually the accepted tolerance level, which is 6.25 milliroentgens per hour.

The alarm described herein is an improvement on the alarm described in Us. Patent No. 2,817,768, issued December 24, 1957 to Morris H. Shamos.

One of the objects of this invention is to provide an improved radiation alarm which avoids one or more of the disadvantages and limitations of prior art arrangements.

Another object of the invention is to provide a radiation alarm which consumes almost no electrical energy in the standby condition.

Another object of the invention is to increase the sensitivity of radiation alarms.

. Another object of the invention is to provide a radiation alarm which may be used to detect neutrons or beta radiation as well as gamma radiation.

Another object of the invention is to provide an alarm which detects the presence of smoke.

Briefly the invention comprises two constant current devices connected in series across a source of energy and an electrostatic switch connected in series with a high resistor across one of the devices with its switch arm normally positioned between two electrodes, one of which is connected to the junction between the devices and the other of which is maintained at a substantially fixed potential. Actuation of the switch in response to the electric field existing between the electrodes causes energization of an alarm device. One of the constant current devices may be an ionization chamber having a resistance responsive to penetrating radiation and the other of the constant current devices may be sensitive to the presence of smoke and dust. In one embodiment of the invention the last mentioned electrode of the elec trostatic switch serves as an electrical contact and is connected to the firing electrode of a gaseous discharge device, the discharge device, when triggered, causing energization of the alarm. In another embodiment of the invention a separate contact is provided for engagement by the movable arm of the electrostatic switch, the switch arm in this embodiment completing an energizing circuit for the alarm when the switch is actuated.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

FIG. 1 is a schematic diagram of connections showing one arrangement of the alarm circuit.

FIG. 2 is a schematic diagram of connections showing an alternate arrangement using a photoelectric cell and a self luminous source.

FIG. 3 is a graph showing the characteristics of the two constant current devices.

FIG. 4 is a schematic diagram of connections showing another alternate arrangement using two photoelectric cells.

FIG. 5 is a schematic diagram of connections using an electrostatic switch or relay without a vacuum or gaseous discharge device.

Referring now to FIG. 1 the alarm comprises an ionization chamber 10 connected in series with a constant current device 11 and a source of potential T2. The ionization chamber id is a constant current device within a well defined range of applied voltages. The constant current device 11 includes two electrodes mounted with lead-in conductors which may be sealed to a partial glass envelope. The space between the electrodes, however, must be open to the atmosphere in order to detect the presence of smoke. Any other type of insulation mounting can be used for the two electrodes as long as they are securely mounted and open to the atmosphere. The space between the electrodes is subject to constant ionization by some radioactive material such as radium and this material may be conveniently supported on one of the electrodes as shown in the figure. While the circuit will function without any means of ionization in envelope 10, it has been found advisable to include some radioactive material in this device also.

A discharge circuit is also connected across the source of potential 12 and includes a three electrode gaseous discharge device 13 containing a cathode, an anode, and a firing electrode. The discharge device 13 is connected in series with a high resistor 14, and an alarm 15. A capacitor 16 is connected between the anode and the negative terminal of the potential source 12 and aids in the dis charge of the device 13 by furnishing a quantity of electricity which flows through the discharge device 13 and the alarm 15 whenever the firing electrode renders the device conductive. The firing electrode is connected to the negative terminal of source 12 by a high resistor 17.

An electrostatic switch 18 is employed in this circuit to make the device more sensitive and more reliable. The switch is enclosed in an air-tight envelope and is a single pole, single throw switch having a movable element 29, which may be a metalized quartz fiber, and two electrodes 22 and 23, the latter also serving as the switch contact. The switch is normally open, as shown in the figures, and under normal conditions of no penetrating radiation, there is practically no force exerted on the movable member to be actuated. Both electrodes 22 and 23 are at about zero potential and there is no electrostatic field between them. When this switch is operated, the movable member 29 is moved to the position indicated by the dotted line and makes contact with a conductor connected to the firin electrode of the discharge device 13.

Both constant current devices 10 and 11 possess a constant current feature Within their range which extends from about 15 volts to about 200 volts, the upper limit depending upon the spacing and area of the electrodes. At values between 0 and 15 volts the devices act as normal resistors, and above 200 volts secondary electronic processes cause the current to increase sharply. When no ambient ionizing radiation is being received the ionization chamber passes only a small current and this current is below the normal constant current of the device 11, which because of its constant source of ionization can conduct a larger current. It the voltage of the potential source is 200 volts, then substantially all of this voltage under these conditions is across the ionization chamber 10 and only a few volts, less than the critical volts, is applied across the constant current device 11.

The division of voltages across devices 10 and 11 may be better explained by reference to the graph shown in FIG. 3. Here the characteristic curve of the ionization chamber 10 is shown at A. The chamber passes a small current I because of the small amount of radioactive material deposited within its envelope. The characteristic curve B for the constant current device 11 is plotted in a reverse direction. That device is adapted to pass about three times as much current (1 because it contains considerably more radioactive material. When no ambient ionizing radiation is being received, the voltages are represented by the intersection 2t; of curves A and B applying about 6 volts across device 11 and about 200 less 6 or 194 volts across chamber 10.

When penetrating radiation is incident upon the ionization chamber 19, causing it to be more conductive than device 11 (curve D), the potential ditIerences across each component shift; the drop across chamber 10 becomes lower while the drop across device 11 becomes higher. This action changes the potential of contact 22 abruptly, raising it to a value which may be as high as 180 volts (with 200 volts supplied by source 12). This condition is represented in the graph in FIG. 3 by intersection 30. Since contact 23 is at zero potential an electrostatic field is set up between electrodes 22 and 23 and since member is at 200 volts, it is attracted toward the zero potential electrode 23 While being repulsed by the positive potential electrode 22. When member 20 moves to its actuated position as shown by the dotted line in the figures, the potential of the firing electrode in triode 13 is raised and the triode conducts. Capacitor 16 now discharges through the alarm 15, operating it and giving notification that the penetrating radiation applied to chamber 10 is above a predetermined value.

Curve C represents the characteristic of chamber 10 when an intermediate amount of radiation is being received by the chamber (less than the predetermined value).

FIG. 1 shows device 11 open to the atmosphere because of the cut-away portion 31 of its envelope. Small changes in atmospheric pressure have very little efiect on discharge device 11 and this device generally operates well at this pressure. Since the electrodes and the space between them are open to the atmosphere, smoke particles which might be the result of a fire can enter the space between the electrodes and reduce the current between the electrodes either by masking the alpha rays and thereby reducing ionization or else by causing recombination of the ionized gas molecules. In either case the current through device 11 is lowered causing a large change of voltage similar to the operation described above and the alarm is again operated.

The circuit shown in FIG. 2 is the same as FIG. 1 except that a photoelectric cell 24 is used as a circuit component instead of the constant current device 11. The photoelectric cell 24 is enclosed in a light tight shield 25 having access to the atmosphere through a series of bafile plates 26. A small quantity of luminescent material 27 is positioned adjacent to the cell 24 and causes a constant current to flow through the cell. Under such conditions, photoelectric cells possess constant current characteristics similar to device 11. The operation of this circuit is similar to the operation of the circuit shown in FIG. 1. When smoke passes through the shield baflle plates it cuts off the light from material 27 and causes an abrupt shift in voltage across chamber 10 and cell 24.

The circuit shown in FIG. 4 is the same as that shown in FIG. 2 except that a second photoelectric cell 32 is substituted for the ionization chamber 10. This second cell 32 i mounted in a light tight case 33 which may be made of thin aluminum and which is also gas tight.

A scintillation crystal 34 is mounted within the case 33 and lights up whenever bombarded by ionizing radiation. A small portion of radio-active material 35 such as a radium salt, is placed adjacent to the crystal to provide the background current necessary to produce the current indicated by curve A in FIG. 3. The operation of the circuit is as described above.

For certain installations where a more rugged form of electrostatic switch may be used, the gaseous triode 13 may be omitted and the circuit shown in FIG. 5 be employed. This circuit includes two constant current devices 4G and 41 in series connection, one of the devices being controlled by bombarding penetrating radiation. Either one of the devices, It 11, 24, or 32, a illustrated in FIGS. 1, 2 and 4, may be used in these positions. Source of potential 12 is connected across both of the components 49 and 41, and the positive terminal is connected in series with a high resistor 21 to the movable blade 2% of the switch 18A. This form of switch includes tWo electrodes 22 and 42 which are used exclusively for setting up an electrostatic field. Switch 18A also includes a contact 23, as before, but in this circuit it is connected directly to the alarm 15. The storage capacitor 16 is connected between the negative terminal of the source 12 and the movable switch blade 20. Electrode 42 is connected to the negative terminal of source 12 through a protective resistor 4-3.

The operation of this circuit (FIG. 5) is similar to the circuits described above except that when the voltage shifts and the switch is operated, the current from the charged capacitor 16 flows through the blade 20, through contact 23, and through the alarm 15, back to the other side of the capacitor 16. Since all the above described circuits are not designed to be operated at fast repetition rates, the capacitor may be charged slowly with resistor 14 in FIGS. 1, 2 and 4, and resistor 21 in FIG. 5 having a value of about 10 megohms.

It will be obvious that the above described circuits provide an efiicient and dependable radiation alarm while using negligible electrical power in the standby condition. Details of the alarm 15 have not been shown but it will be understood that besides including a structure which produces a visual or audible signal, the alarm assembly may include a relay with a holding circuit or a mechanical lock so that once tripped the alarm will continue to operate after capacitor 16 has been discharged.

The foregoing disclosure and drawings are merely illustrative of the principles of the radiation alarm as disclosed and are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

What is claimed is:

1. A radiation alarm for indicating the presence of penetrating radiation above a predetermined value comprising; an ionization chamber having an anode and a cathode within a permeable envelope; said chamber arranged to pass current which is proportional to the intensity of the penetrating radiation incident thereon but passing constant current in response to a wide range of applied voltages; a constant current device in series with the ionization chamber and a source of potential; said constant current device including an anode, a cathode,

and a source of constant ionization within an envelope; an electrostatic switch having a movable switch blade positioned adjacent to a stationary plate and a switch contact; a connection between the stationary plate and the junction between the ionization chamber and the constant current device; said movable blade connected to the anode of the ionization chamber in series with a resistor; a gaseous discharge device having an anode, a cold cathode, and a control electrode positioned within an envelope containing an ionizable gas at reduced pressure; said control electrode connected to said switch contact; an alarm connected in series between the cathode of said discharge device and the negative terminal of the source of potential; and a connection between the anode of said discharge device and the positive terminal of the source of potential in series with a resistor.

2. A radiation alarm as set forth in claim 1 wherein said control electrode is connected to the negative terminal of the source of potential in series with a resistor.

3. A radiation alarm as set forth in claim 2. wherein said ionization chamber contains a source of ionizing radiation.

4. An alarm circuit according to claim 2 wherein said constant current device includes two electrodes and is 6 open to the atmosphere, the resistance between said electrodes changing when smoke particles enter the space between the electrodes.

5. An alarm circuit according to claim 2 wherein said alarm is adjusted to operate when the gaseous discharge is rendered conductive and to be non-operative when the discharge device is not conductive.

References Cited in the file of this patent UNITED STATES PATENTS 1,605,911 Banneitz Nov. 9, 1926 1,962,849 Tour June 12, 1934 2,408,051 Donelian Sept. 24, 1946 2,702,898 Meili Feb. 22, 1955 2,817,768 Shamos Dec. 24, 1957

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