AN/PDR-65.- The AN/PDR-65 (fig. 8-11) is designed to detect and measure gamma radiation. The set consists of two primary elements-the detector unit and the radiacmeter.

The detector unit must be located at or near a masthead. Its view of an enveloping base surge cloud and resultant fallout must be relatively unobscured. As a result, if suitable scaling factors are available, gamma dose rates at any location inside the ship can be estimated from the masthead radiation intensity data.

The radiacmeter is to be installed on the bridge. One or more auxiliary readouts are to be located in DCC and other prime locations. The radiacmeter has two types of displays; one is for dose rate and the other is for accumulated dose. The main meter displays the dose rate. The small counter registers the accumulated dose in rads by counting the rad pulses from the detector. Each

Figure 8-11.-AN/PDR-65 radiac set. 8-17

time that a dose of 1 rad is accumulated, the radiacmeter sounds a loud beep. The range of the small counter is 0 to 9,999 rad. Gamma intensity is indicated on one of the following four ranges: 0 to 10 rad/hr, 0 to 100 rad/hr, 0 to 1,000 rad/hr, and 0 to 10,000 rad/hr.

For normal operation, the AN/PDR-65 is powered by the 115 vac ship's power. In an emergency, the radiac operates on four internal, rechargeable, nickel-cadmium, C-cell batteries which are on floating charge. The batteries can power the radiac for approximately 20 hours.

Dosimeters

A number of types of radiation doseindicating devices (dosimeters) are in the Navy radiac system. Dosimeters of interest to the Damage Controlmen are the DT-60/PD, the IM9/PD, and the IM-143/PD.

DT-60/PD.- The DT-60/PD (fig. 8-12) is a gamma radiation dosimeter with a usable range of 10 to 600 R. It is a solid-state package in the form of a locket. It is designed to be worn on a chain around the neck. Inside the black plastic casing is a phosphate glass. When the phosphate glass is exposed to ultraviolet light, it emits an orange light. The intensity of the orange light is proportional to the amount of radiation the glass has received. The DT-60/PD stores the dose information indefinitely and is a permanent record of the amount of exposure to radiation.

The CP-95/PD (fig. 8-13) is a radiac computer-indicator that is used to read the amount of radiation a DT-60/PD has been exposed to. A newer model, the CP-95A/PD (fig. 8-14), is also available. The cover on the DT-60/PD must be removed before the DT-60/PD is inserted into the radiac computer-indicator. Each of these radiac computer-indicators has two scales: 0 to 200 R and 0 to 600 R. However, 10 R is the minimum detectable exposure. These units have an accuracy rate of 20 percent. The radiac computer-indicators operate off of the ship's 115 vac power source.

IM-9/PD.- The IM-9/PD (series E through H) is a pocket dosimeter of the quartz-fiber type. It indicates the gamma radiation dose in the range of 0 to 200 mR. The IM-9/PD is a self-reading dosimeter. By holding the dosimeter up to the

3.177

Figure 8-12.-High range or casualty dosimeter (non-self-reading) DT-60/PD. 8-18

Figure 8-13.-Radiac Computer-Indicator CP-95/PD, front panel controls and receptacles.

Figure 8-14.-Radiac Computer-Indicator CP-95A/PD.

light and looking through the lens (fig. 8-15), you can read the radiation dose received. The reading is obtained by observing the position of the quartz fiber on the scale of the built-in optical system. The IM-9/PD is primarily a health-physics device that is particularly useful in areas of low dose rates.

IM-143/PD.- The IM-143/PD is identical to the IM-9/PD except in range. The IM-143/PD indicates gamma radiation dose in the range of 0 to 600 R. It is used by repair locker personnel that are involved with the survey, monitoring, and the decontamination details during CBR evolutions. It keeps track of the dose they have received up to the time they read the dosimeter.

The PP-4276A/PD dosimeter charger 816) is used to reset the self-reading dosimeters to (fig.

zero. This is accomplished by placing the dosimeter into the charger. The charger provides an adjustable voltage source that is applied between the central wire and the shell (fig. 8-17). Because the quartz fiber and the fixed central wire of the ion chamber are attached, each will receive the same charge. As a result, when the dosimeter is charged, the movable fiber is repelled from the fixed wire. By proper adjustment of the voltage applied by the charger, the fiber can be set exactly on the zero line of the scale. When nuclear radiation enters the chamber, ions are produced and are attracted to the wire and the shell. The charge is thus reduced; the fiber then moves across the scale because it is not as greatly repelled from the fixed wire as it was previously. The power source for the PP-4276A/PD is one alkaline D-cell battery.

When you charge a dosimeter with the PP4276A/PD, use the following procedures:

1. Remove the dust cover from the charger receptacle.

2. Place the electrode end of the dosimeter into the charging receptacle and depress it firmly. This illuminates the dosimeter scale and operates the charger.

Figure 8-15.-Method of reading IM-9/PD dosimeter by looking through it at the light. Insert shows a dose reading of 82 mR.

Figure 8-16.-Dosimeter Charger PP4276A/PD.

3. Rotate the charging knob until the hairline on the meter scale is located on the zero mark.

4. Remove the dosimeter from the charger and check to ensure that it is still on zero.

5. Replace the dust cover on the charger.