RADIAC SET CIRCUIT ANALYSIS

TM 11-6665-209-40

1-10. RADIAC SET CIRCUIT ANALYSIS

a. Detector Circuit. The detector circuit consists of G-M tubes V201 and V 2 0 2

anode load resistors R113 and R114, coupling capacitors C106 and C107, range switch

S102 and connectors.

(1) The two G-M tubes are used as radiation detectors. In the low sensitivity (high-

intensity) ranges, detector V202 is disconnected from the high voltage.

(2) When switch S102 is in the 500 or 50 (mR/hr) position, regulated +700 volt DC

is applied through resistor R113 to V201 alone. When S102 is in the 5 or 0.5

(mR/hr) position, V202 is also energized through R114. When the G-M tubes

conduct under the influence of an ionizing event, a negative voltage pulse is

developed across resistor R113 or R114. This pulse is capacitively coupled to

the circuit through C106 or C107.

The output of the G-M, tubes

consist of a series of

negative-going pulses, one

f o r each ionizing event that

o c c u r s within the tube. G-M

tubes pulses having an

average duration of 80

microseconds and an average

amplitude of 100 volts are oc-

casionally encountered.

P u l s e s of reduced amplitude

and increased width occur at

the input to the circuit

because of capacitive loading

b y the cable connecting the

G-M tubes to the circuit.

Because of the low values of

C106 and C107, input pulses

a r e differentiated into very

short duration pulses. The

o v e r s h o o t associated with a

d i f f e r e n t i a t e d pulse does not

occur since the discharge

t i m e constant for the coupl-

i n g circuit is much shorter

than the charging time cons-

t a n t in the G-M tube circuit.

These negative pulses are

then coupled by V103

through C 1 0 8

1-7