CHAPTER 2 FUNCTIONING OF EQUIPMENT - TM-11-6665-245-340009

TM 11-6665-245-34

CHAPTER 2

FUNCTIONING OF EQUIPMENT

2-1. Introduction

connects the main and auxiliary probes to the

radiacmeter body.

The radiac set is composed of a Radiacmeter lM-

d. Discriminator. This block represents two

160F/PDR-56 (radiacmeter), three probes: DT-

transistors connected to discriminate between

224B/PDR-56 (main probe), DT-228A/PDR-56 (aux-

low level random noise and actual signals. The

iliary probe), and DT-590A/PDR-56F (X-ray probe), a

discriminator allows signals to pass to the next

set of earphones, an extension handle, a carrying

block, but eliminates the noise signal. The output

strap, an operator's technical manual, and a case

signal from this block is a constant amplitude

to contain the components. The radiac set is used

pulse which coincides with the light pulse to the

to detect and measure alpha radiation which

photomultiplier (PM) for the beta probes. With the

penetrates the detecting screen of the main probe

x-ray probe, which has an amplifier-discriminator

(or auxiliary probe) and to detect and measure low

circuit integral to the probe (self-contained with a

energy gamma radiation with the x-ray probe con-

s c i n t i l l a t o r - p h o t o m u l t i p l i e r combination), the

nected to the radiacmeter. The functioning of the

resulting signal i s c o u p l e d t o t h e m a i n

equipment will be explained first on a block

discriminator as shown in the block diagram at

diagram and then on a detailed analysis of the cir-

Figure 2-2.

cuitry.

e. Buffer-Inverter. In this block, the signal is

2-2. Block Diagram Analysis

inverted and sent to the count rate circuit.

f. Count Rate. The count rate block provides a

(Fig. 2-1)

changeable timing circuit so that scales can be

The operating portion of the radiac set includes

changed. Part of the circuit is the scale change

the radiacmeter and the main, auxiliary, and x-ray

switch which selects the proper timing com-

probes. These items and their circuitry are laid out

ponents for changing scale.

on the block diagram (fig. 2-1) with the direction of

g. Indicating Meter. This block represents the

signal flow from left to right. The signal starts in

meter on which the counts per minute (CPM) are

the probe (main, auxiliary, or x-ray) and ends up as

read.

both a meter indication and a sound indication in

h. Headset Connector. Provides an output

the headset.

connection for listening to the signal (clicks).

a. Reg Power. This block supplies power and

various voltages to operate the radiacmeter. The

2-3. Probe Operation

power is taken from two dry cells that are in-

Both the main probe and the auxiliary probe

stalled in the radiacmeter. The relatively low

operate on the same general principle. They both

voltage of the dry cells is stepped up through an

convert alpha particles to pulses of light and then

oscillator-transformer-rectifier

arrangement

convert those light pulses to an electrical signal

w h i c h supplies the different voltages. The

(electrical pulses). The. x-ray probe converts gam-

regulator portion of this block is used to maintain

ma radiation incident to its scintillator-

output voltage constant as the dry cell voltage

photomultiplier from light pulses to an electrical

changes slightly over the battery life.

signal.

b. Probes. The main and auxiliary probes con-

a. Main Probe. Figure 2-3 shows a cut away

vert low energy alpha particles into pulses of light

view of the inside of the main probe. The base and

for the photomultiplier tube. The x-ray probe

cover form a light tight covering for the

senses low energy gamma radiation and pro-

photomultiplier tube. Slots cut into the metal

duces voltages of sufficient amplitude, which are

base bottom form the area (window) where alpha

passed by the discriminator and fed to the count

particles are detected. The window area is also

rate meter, which shapes and displays the events

sealed to keep light from entering by a sandwich

per unit of time in the meter circuit.

formed of a piece of clear Iucite and a piece of

c. P h o t o m u l t i p l i e r and Emitter Follower.

very thin aluminum foil bonded to clear plastic

These items are contained in the handle of the

(aluminized mylar). Directly above the aluminized

main (and auxiliary) probes. The photomultiplier

mylar is a layer of phosphor, a chemical

changes the light pulses from these probes into

substance that gives off light when activated by

electrical signals. The emitter follower provides

radiation. Above the Iucite are pieces of clear

impedance matching to the coiled cable which

Change 1

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