Analytical Counting Instruments Proportional Counters

These instruments, mid-range in price, are most frequently used for gross alpha/beta testing. They are gas-filled detectors that operate on the principle that gas ionization by radiation can, with the proper circuitry, produce an electrical signal proportional to the amount of radiation that caused the ionization. P-10 gas, a methane-containing mixture, is used as the counting gas. Three types of counters are routinely used: internal, end window, and thin window. Internal counters are especially suited for low-level environmental samples (Greenberg, Clesceri & Eaton 1992). End window and thin window counters are more suitable for moderate to high level radioactivity samples. These are easier to maintain and less prone to contamination than internal counters. All proportional counters require a calibration curve be run to quantify results (Figure 11.24.1).

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