A Personal Radiation Alarm Dosimeter

A personal alarm dosimeter for X- and gamma-rays based on new principle of charge detection has been developed. Ion current of an ionization chamber is accumulated on a “vibrating” capacitor, whose output is fed to its driving coil through an a.c. amplifier so that, if the charge on the capacitor exceeds a certain critical amount, the system produces “howling oscillation”, a part of the oscillation signal being amplified to provide audible alarm and visible indication. The prototype instrument is alI transistorized and encapsuled in an aluminum case of 21 × 26 × 155 mm. The weight is about 110 g. The alarm level is adjustable in the range 0–20 mR, and the dose accumulated is readable by simple procedure at any desired time. The natural leakage is about 0.8 mR per 24 hr. The power is supplied from a 15 V battery, and the current consumption is about 0.4 mA in quiescent state (1–1.2 mA during oscillation) at 20°C.