US3711705A - Alarm radiation dosimeter with improved integrating pulse ionization chamber and high voltage supply - Google Patents

Alarm radiation dosimeter with improved integrating pulse ionization chamber and high voltage supply Download PDF

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Publication number
US3711705A
US3711705A US00196893A US3711705DA US3711705A US 3711705 A US3711705 A US 3711705A US 00196893 A US00196893 A US 00196893A US 3711705D A US3711705D A US 3711705DA US 3711705 A US3711705 A US 3711705A
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chamber
output
voltage
storage means
multivibrator
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US00196893A
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English (en)
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C Borkowski
J Rochelle
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US Atomic Energy Commission (AEC)
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US Atomic Energy Commission (AEC)
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T7/00—Details of radiation-measuring instruments
    • G01T7/12—Provision for actuation of an alarm

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  • ABSTRACT An alarm dosimeter has been provided which features an improved integrating pulse ionization chamber of the type containing an hermetically sealed gas diode. Improved operation and miniaturization of the chamber are made possible by a ringing choke converter high voltage supply having a ripple-type output that insures discharge of the gas diode.
  • PATENTEDJAH 16 I975 ALARM RADIATION DOSIMETER WITH IMPROVED INTEGRATING PULSE IONIZATION CHAMBER AND IIIGll-I VOLTAGE SUIILY BACKGROUND OF THE INVENTION The present invention was made during the course of, or under, a contract with the U. S. Atomic Energy Commission.
  • This invention relates generally to ionization chamber radiation detectors and more particularly to improvements in integrating pulse ionization chamber dosimeters.
  • a gas discharge ionization chamber can be miniaturized and remain an accurate and reliable detector by the addition of a strobe pulse modulated bias voltage which periodically raises the chamber voltage above a critical voltage level at which a gas diode connected in series with the charge collecting electrode of the chamber fires, rapidly discharging the chamber.
  • the rate at which the gas diode fires is proportional to the intensity of the radiation field in which the chamber is placed.
  • Yet another object of this invention is to provide a miniaturized alarm radiation dosimeter utilizing an integrating pulse ionization chamber.
  • this invention comprises an oscillator in the form of an astable multivibrator, the output of which is formed into pulses in a driver circuit and presented to a ringing choke converter to thereby provide a high DC voltage from a low voltage cell connected to the choke.
  • Strobe pulses in the form of ripple on the high DC bias voltage are provided by means of a novel filter and pulse shaping circuit connected to the output of the choke.
  • the detection of a predetermined accumulated radiation dose in the chamber activates a solid state relay which, in turn, latches in a speaker alarm.
  • the chamber output also increases the frequency of the multivibrator into the audio range which through an output to the speaker maintains the audible alarm until the relay is manually reset.
  • FIGURE is a schematic diagram of an alarm dosimeter according to the present invention.
  • a free-running astable multivibrator 5 that has an input for increasing the frequency has a first output connected to the base of a transistor 7 and a second output connected to the base of another transistor 9.
  • the emitter of transistor 9 is biased with a negative 1.5 V DC.
  • the collector of transistor 9 is connected through a biasing resistor 11 to the emitter of a grounded collector driver transistor 13 and through a pull-up capacitor 15 to the base of transistor 13.
  • the base of transistor 13 is further connected through a biasing resistor 12 to ground and its emitter is further connected jointly to ground through a biasing resistor 19 and to the base of a grounded emitter high voltage switching transistor 21.
  • the collector of transistor 21 is connected jointly to a negative 1.5 V through a miniature choke 23 and to the cathode of a rectifier diode 25.
  • the anode of diode 25 is connected to ground through a filter capacitor 27, to a filter resistor 29, and to the cathode of a first pulseforming zener diode 31.
  • the anode of diode 31 is connected to the other lead of resistor 29, to ground through a filter capacitor 33, and to one lead of a filter resistor 35.
  • the other lead of resistor 35 is connected jointly to ground through a filter capacitor 37 and to the electrically conductive housing 43 (cathode) of an ionization chamber 41.
  • the ionization chamber 41 is identical to that disclosed in the above-referenced copending application. Briefly, the chamber 41 consists of an outer'electrically conductive gas-tight housing 43 forming the cathode which is filled with an ionizable gas.
  • the electrically conductive anode 45 is co-axially disposed within the housing 43 and held in position by means of insulators 47.
  • a hermetically sealed gas diode 49 is preferably disposed within the chamber environment and may conveniently be placed within a copper tube forming the anode 45.
  • One lead of the gas diode 49 is connected to the chamber anode and the other lead connects jointly to ground through a load resistor 511 and to the base of an amplifying transistor 53.
  • the emitter of transistor 53 is connected to the negative 1.5 V supply and the collector of transistor 53 is connected to the emitter of a switching transistor 55.
  • the collector of transistor 55 is connected jointly to ground through the biasing resistor 57 and to the base of another switching transistor 59.
  • the base of transistor 55 is connected through a biasing resistor 61 to one lead of a biasing resistor 63, a noise suppression capacitor 65 and to the normally open contacts of a switch 67 that is connected to ground.
  • the emitter of transistor 59 is connected to the negative 1.5 V supply and the collector is connected jointly to resistor 63, capacitor 65, grounded resistor 69 and an electrical lead 71.
  • Lead 71 is connected jointly to the frequency increase input of multivibrator 5 and to the emitter of a gating transistor 73 and is further connected to the negative 1.5 V through normally open contacts of a switch 7 5.
  • Switches 67 and 75 are mechanically ganged so that they close or open together.
  • the base of transistor 73 is connected jointly to ground through a biasing resistor 77 and to the collector of transistor 7.
  • Transistor 7 is connected to the negative 1.5 V supply at its emitter.
  • the collector of transistor 73 is connected through a biasing resistor 79' to the base of a grounded emitter speaker driver transistor 81.
  • a small PM speaker 83 connected between the negative 1.5 V supply and the collector of transistor 81 completes the circuit connection.
  • circuit may be broken down into specific functions or parts as depicted by the dotted line enclosed portions. These specific parts will now be pointed out in conjunction with the explanation of the operation of the circuit.
  • the circuit is activated by the insertion of a 1.5 V battery (not shown) causing the multivibrator 5 to oscillate at a very low frequency below the audio range.
  • These low frequency pulses are applied to a choke switch driver 85 comprised of transistors 9 and 13.
  • the choke switch driver 35 transforms the multivibrator output into a train of 0.15 msec. duration, 0.6 V negative-going pulses that are applied to the base of transistor 21 included in a ringing choke DC-to-DC converter circuit 87.
  • Transistor 21 is turned On for the duration of the driver pulses allowing energy to be stored in the ringing choke 23.
  • Transistor 21 is quickly turned of with the active pull-up of transistor 13 resulting in the production of a large negative going pulse -225 V) at the collector of transistor 21.
  • diode 25 Assume the reverse breakdown of diode 25 is 200 volts, the reverse breakdown of diode 31 is 25 volts, and the sequence beginning with the eutoff of transistor 21 causing the fast rising negative pulse applied to the cathode of diode 25 to forward bias diode 25 allowing it to conduct the pulse.
  • diode 31 When the pulse voltage exceeds the voltages on capacitors 27 and 33, diode 31 also becomes forward biased and the energy stored in choke 23 is transferred to the capacitors raising their voltage to a non-critical maximum which must exceed 225 volts. Now when the collector voltage returns to zero, both diodes break down in the reverse direction and the voltage on capacitor 27 quickly recovers to -200 volts and the voltage on capacitor 33 to 225 volts.
  • Capacitors 27 and 33 are equal in capacitance and are connected by the resistor 29 thereby causing their voltages to come to an equilibrium of -212.5 volts with a time constant of 1 msec. determined by the resistor 29 and capacitors 27 and 33.
  • the voltage across capacitor 33 thus has the appearance of 2l2.5 V DC with an additional -12.5 V slowly decaying pulses superimposed (strobe pulses).
  • the final RC filter consisting of resistor 35 and capacitor 37 acts to slowdown the pulse rise times and suppress the switching spike.
  • the nominal strobe pulse frequency is 25 to 50 Hz.
  • This strobed bias supply is applied to the cathode 43 of the gas discharge ionization chamber 41.'When the chamber is placed in a radiation field, the gas diode 49 breaks down or fires at a rate depending upon the intensity of the radiation field as pointed out in the abovereferenced copending application. As pointed out therein, the additional strobe pulses insure that the diode 49 fires even though the radiation field intensity is not sufficient to provide an ionization current large enough to deposit charge on the chamber anode to fire the diode 49. It will be appreciated from a study of the referenced application that the system could come to a point of equilibrium in low strength radiation fields of interest due to miniaturization of the active gas volume of the chamber 41.
  • the ionization current or chamber charging current would be equal to the diode current preventing the diode from firing.
  • the strobe pulses periodically raise the voltage to a level that will insure a discharge even under these conditions, thereby making it possible to provide a miniatu rized gas discharge ionization chamber which-is accurate and reliable for use as a fallout shelter or pocket dosimeter, for example.
  • Lead 71 is normally at zero volts but the negative 1.5 V potential initiates two actions. First, the voltage is applied to the frequency increase input of multivibrator 5 causing it to be raised to a higher frequency, into the audio range. Second, the -1.5 V gates transistor 73 On allowing it to pass the increased frequency via transistor 7 connected to the first output of multivibrator 5. Transistor 81 is turned on and drives speaker 83 at the audio frequency. An audible alarm is sounded until the switches (67 and are manually actuated to the test/reset position and returned to the operating position to deactivate relay 89. This procedure does not reset the chamber itself, and therefore, an operating cycle can only begin immediately following the completion of the previous cycle (discharge of the chamber). Normally, the chamber would be calibrated to produce a pulse every 50 mR.
  • the chamber output pulse rate is directly proportional to the dose rate and is equivalent to the repetition rate of the sound bursts, an individual would simply search for the quietest location in a given radiation fallout shelter in order to find the safest location in that shelter. Also, a wrist watch with a sweep second hand can be used to determine the absolute dose rate.
  • a strobe pulse modulated DC voltage biasing means comprising:
  • an astable multivibrator for producing fixed amplitude pulses at an output thereof having a predetermined repetition rate
  • a switching means connected to the output of said multivibrator and switched On and Off in response to the output of said multivibrator;
  • an inductive energy storage means connected in series with said DC voltage source and said switching means for storing energy from said DC source each time said switching means is On and providing a voltage surge greater than said chamber bias voltage each time said switching means turns Off',
  • a capacitance storage means having a time constant substantially larger than that of said inductive storage means; diode connected between said inductive storage means and said capacitive storage means for conducting said inductive voltage surge into said capacitive storage means and having a predetermined reverse breakdown voltage so that a predetermined voltage is stored by said capacitive storage means each time said inductive voltage surge is applied to said capacitance storage means; circuit means connecting said capacitive storage means to said ionization chamber; and, a strobe pulse modulating means responsive to said inductive voltage surge applied to said capacitive storage means for providing a predetermined amplitude strobe pulse superimposed on said DC bias voltage each time said inductive device charges said capacitive storage means.
  • said capacitive storage means, said strobe pulse modulating means and said circuit means include a first capacitor connected between ground potential and said diode, a second capacitor having one lead connected to ground potential, a first resistor connected between the ungrounded leads of said first and second capacitors; a zener diode connected in parallel with said first resistor, havinga predetermined reverse breakdown voltage value so ha said second capacitor is held at a voltage greater than that of said first capacitor following each of said inductive voltage surges so that when said zener diode is nonconductive current flows through said first resistor to equalize the voltages across said first and second capacitors, thereby generating a strobe pulse; and a second resistor connected between the ungrounded lead of said second capacitor and said chamber.
  • said astable multivibrator is operable in at least two frequency states, the first state being below the audio frequency range and the other within the audio range and having an output connected to said audio signaling means and a frequency input coupled to the output of said chamber for switching said multivibrator from said first state into a second state in the audio frequency range in response to an output pulse from said chamber, thereby providing an audio frequency signal to said audio signaling means.
  • said audio signaling means includes a solid state relay connected to the output of said chamber and having an output connected to the frequency increase input of said multivibrator for applying a signal thereto following a pulse from the output of said chamber, said relay having a manual reset means for resetting said relay;
  • a transistor switching means connected in series with the output of said multivibrator and said speaker and having a control input connected to the output of said relay, whereby each time said chamber generates a pulse indicating a predetermined radiation dose accumulated in said chamber, said speaker is activated at said audio frequency of said multivibrator until said relay is reset.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Molecular Biology (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Measurement Of Radiation (AREA)
US00196893A 1971-11-09 1971-11-09 Alarm radiation dosimeter with improved integrating pulse ionization chamber and high voltage supply Expired - Lifetime US3711705A (en)

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US19689371A 1971-11-09 1971-11-09

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US (1) US3711705A (enExample)
JP (1) JPS4859885A (enExample)
CA (1) CA961177A (enExample)
DE (1) DE2254894A1 (enExample)
FR (1) FR2159385B3 (enExample)
GB (1) GB1383614A (enExample)
SE (1) SE384741B (enExample)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4605858A (en) * 1984-11-09 1986-08-12 General Electric Company Personal radiation dosimeter

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2752508A (en) * 1950-11-22 1956-06-26 George V Zito Counting-rate meter
US2883551A (en) * 1954-08-20 1959-04-21 George V Zito High voltage generator
US3675116A (en) * 1971-03-15 1972-07-04 Raytheon Co Improvement in resonant charging circuit

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2752508A (en) * 1950-11-22 1956-06-26 George V Zito Counting-rate meter
US2883551A (en) * 1954-08-20 1959-04-21 George V Zito High voltage generator
US3675116A (en) * 1971-03-15 1972-07-04 Raytheon Co Improvement in resonant charging circuit

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
High Voltage Supplies by Thomas Electronics, December 1948, pages 100 103. *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4605858A (en) * 1984-11-09 1986-08-12 General Electric Company Personal radiation dosimeter

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Publication number Publication date
GB1383614A (en) 1974-02-12
AU4845972A (en) 1974-05-02
CA961177A (en) 1975-01-14
JPS4859885A (enExample) 1973-08-22
SE384741B (sv) 1976-05-17
DE2254894A1 (de) 1973-05-17
FR2159385B3 (enExample) 1975-11-28
FR2159385A1 (enExample) 1973-06-22

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