Patent Number: 054593662
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gamma radiation field intensity meter, and more particularly to an electroscope-type dosimeter which is supplied a constant current from an energy source to provide rate of radiation dose rather than total accumulated dose. 2. Background of the Related Art Electroscope-type dosimeters have been developed over the years to measure the accumulated or total dose of gamma radiation. Specifically, the prior art electroscope-type dosimeter determines the total gamma radiation exposed to it. Typically, the electroscope-type dosimeter, more commonly known as the Lauritsen electroscope, is precharged by a conventional dosimeter charger. The electroscope-type dosimeter includes a quartz fiber and a metal frame used as a charge acceptor, and during the charging process a potential is applied between the frame and the exterior of the dosimeter. Electrical charges of the same polarity appear on both the fiber and frame, causing the fiber to be repelled from the frame by a distance proportional to the applied voltage. The chamber walls or exterior of the electroscope-type dosimeter provides an electrostatic shield for the electroscope-type dosimeter. If the electroscope-type dosimeter is exposed to additional ionizing gamma radiation, the charge on the quartz fiber decreases and the fiber tends to return to the discharge position which is closer to the frame. An image of the fiber in the new position resulting from the additional gamma radiation is projected onto a reticle scale and viewed through an eyepiece lens of the dosimeter. The scale, typically calibrated in Milliroentgens or Roentgens, indicates total accumulated radiation dose, and may be read by looking through the eyepiece toward a lamp or other light source. Thus, the prior art electroscope-type dosimeters have been unable to measure the radiation dose rate experienced when exposed to an ionizing gamma radiation field. It is, therefore, desirable to reliably measure the radiation dose rate which a meter is exposed to in a radiation field to further indicate whether the ionizing gamma radiation field is dangerous. In addition, it is also desirable that the gamma radiation field intensity meter be compact. SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a gamma radiation field intensity meter which is able to measure the dose rate at which the meter is exposed to the ionizing gamma radiation. It is another object of the present invention to provide a gamma radiation field intensity meter which is compact. To achieve these and other objects, the gamma radiation intensity meter of the present invention includes a current source generating a current which is essentially constant and a dose rate determining unit which determines the dose rate of the radiation field exposed to the gamma radiation intensity meter. The dose rate determining unit includes an ionization chamber having gas, a conductive frame disposed in the ionization chamber conducting the current generated by the tritium battery and a charge accepting fiber connected to the conductive frame. The gamma radiation intensity meter also includes a resistor, connected between the conductive frame and the ionization chamber wall which conducts the current forming a potential across the resistor. When the gamma radiation intensity meter is exposed to a radiation field, the radiation field penetrates the gamma radiation intensity meter and ionizes the gas in the ionization chamber forming ionized gas, and the ionized gas conducts a current proportional to the radiation field intensity from the conductive frame to the wall of the ionization chamber, thereby shunting that amount of current away from the resistor. The reduced current through the resistor proportionally reduces the voltage on the conductive frame and the fiber and the charge accepting fiber moves toward the conductive frame to a new position indicating the dose rate. These, together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, with reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.