ABSTRACT
There is a defined level of ionizing radiation (effective dose of 50mSv in any single year) that radiation workers are allowed to be exposed to, according to the International Committee on Radiation Protection (I.C.R.P) proposal which is duly adopted by International Atomic Energy Agency. Gas detectors are commonly used for radiation monitoring because of their ease of operation. In principle, a gas detector can be operated as an Ionization chamber, a Proportional counter, or a Geiger- Mueller tube, depending on the level of high voltage bias supply it is subjected to. Geiger - Mueller detectors are preferred for radiation monitoring because of their ability to detect nearly all kinds of ionizing radiation and they provide a very strong signal that a pre-amplifier is not necessary. This work has utilized the characteristics of G-M tubes to design and construct a Radiation alarm device capable of detecting unsafe radiation level in its vicinity. The device is intended for both indoor and outdoor use. This has therefore necessitated the use of a 9 volts alkaline battery for the device. Complementary Metal Oxide Semiconductor (CMOS) integrated circuit(IC) low power consumption and its ability to operate satisfactorily on a wide range of supply voltage made it a choice for this project. High efficiency performance of Switched Mode Power Supplies (SMPS) has been harnessed to provide high voltage (HV) bias for the G-M tube. In order to further decrease the power consumption of the unit, the high voltage circuit was gated such that it operates for a very short period, and a buffer capacitor used to supply the tube continuously during the inactive period of the high voltage circuit. The radiation alarm device developed is capable of alerting personnel once exposed to radiation dose of 27�Sv/hour (Twenty seven microSeivert per hour) or higher. This threshold was found to be the maximum allowable radiation a personnel is allowed to be exposed to. Beside the cost advantage that the Radiation Alarm Device has over existing similar devices, it is also difficult to acquire ionizing radiation related instruments due to restrictions imposed on them globally. The cost of the device is put at about twenty seven thousand naira (N27,000), a price much less than the price for GM-90 Geiger Counter Radiation Detector, a product of Black cat system, whose price is three hundred and fifty dollars ($350).