a. The U.S. Army has recently replaced several instruments used for measuring the gamma radiation dose rate and total gamma radiation dose to include:

     (1) The radiac set, AN/PDR-27 (Geiger counter), a dose rate instrument used for measuring low intensity (zero to 500 milliroentgens per hour) gamma radiation and detecting beta radiation, and

     (2) The radiacmeter, IM-174/A, a dose rate instrument used for detecting and measuring high level (up to 500 roentgens per hour) gamma radiation only.

b. Both the AN/PDR-27 and the IM-l74/A were replaced by the AN/VDR-2 (see Figure 1-9). The AN/VDR-2 detects, measures and displays gamma dose rate from background to 100 Gy/hr; detects and displays beta particle radiation from background to 5 cGy/hr; and measures, stores, and displays accumulated dose from 0.01 uGy to 9.99 Gy. This device is autoranging (that is, the readout is digital and requires no input from the operator to read from the lowest to highest dose/dose rate).

Figure 1-9
. Radiac Set, AN/VDR-2

c. The radiacmeter, IM-93/UD (Tactical Dosimeter—0 to 600 roentgens) or pocket dosimeter (see Figure 1-10) measures total gamma radiation dose and utilizes a variation of the electrical collection of ions principle of operation with immediate information capability. The U.S. Army currently has three standard pocket dosimeters with different operating ranges:

     (1) Radiacmeter, IM-9/PD (Clinical Dosimeter)—zero to 200 milliroentgens.

     (2) Radiacmeter, IM-147/PD (NBC Defense Team Dosimeter)—zero to 50 roentgens.

     (3) Radiacmeter, IM-93/UD (Clinical Dosimeter)—zero to 600 roentgens. The choice of dosimeter depends on the radiation environment and is based on the dose range to be encountered. As mentioned before, this instrument is used as a personal device to indicate the total exposure to the individual wearing it.

Figure 1-10. Radiacmeter, IM-93/UD (Clinical Dosimeter)

d. The pocket dosimeters mentioned above are being replaced by the AN/UDR-13 Pocket Radiac (see Figure 1-11). The new Pocket Radiac is a radiation
dosimeter that measures initial and residual gamma radiation and prompt neutron radiation. It can measure dose from 1 to 999 cGy (neutrons/gamma-prompt initial and fallout) and dose rate from 0.1 to 999 cGy/hr (gamma fallout).

Figure 1-11. Pocket Radiac – AN/UDR-13

e. The Thermoluminescent Dosimeter (TLD) (see Figures 1-12 and 1-13) is a total dose device, which measures beta, x-ray, gamma, and neutron radiation. It utilizes the thermoluminescent principle of operation. Energy or radiation is absorbed by the detector molecules and raises them to an excited or metastable state. They remain in this excited state until they are heated to a temperature high enough to cause the molecules to return to a normal or ground state. When these molecules return to their normal state, they give off the excess energy they contain, in the form of light. The amount of light is proportional to the energy or radiation absorbed. The emitted light is measured with a photomultiplier tube that serves to convert the light photons into an electrical signal that can be quantified. The TLD is worn by an individual as a personnel-monitoring instrument. The TLD, however, is not self-reading. It requires a sensitive reader to quantify the dose. For peace-time use, the TLDs are shipped to the Test, Measurement, and Diagnostic Equipment facility at Redstone Arsenal, Alabama for analysis. During battlefield operations, the AN/PDR-75 Reader (see Figure 1-14) is used for analysis of the DT-236 Dosimeter. Variations of the TLD are used quite extensively in both military and civilian practices involving the use of radiation.

Figure 1-12. Thermoluminescent Dosimeter.

Figure 1-13. Thermoluminescent Dosimeter components.

Figure 1-14. The AN/PDR-75 Reader with DT-236 (Wrist Watch/Tactical) Dosimeters.

f. The instruments discussed in the preceding paragraphs are by no means all that exist in the U.S. Army inventory. Additional instrumentation is often necessary for special cases, such as low level alpha radiation monitoring or determining neutron emission from certain types of nuclear reactions. There are a number of instruments, which are designed specifically for these purposes, and will be found wherever the need for such devices exists.

g. Occasionally, the preventive medicine specialist may assist in the use of such instruments or devices and will at that time have the opportunity to evaluate the particular radiation environment and monitoring program in detail.

X-ray Schools | X-ray and Radiation Safety
For Informational Purposes Only - Based On US Army Radiation Safety Training