Miniaturized circuit improves measurement of radiation dose absorbed in a scintillation crystal. The temperature coefficient of the field-effect transistor gate-source voltage in the isolation amplifier can be readily controlled

Cellier, A.

Hoover, W. M.

English

NASA Technical Reports Server

January 1970	 Brief 70-10096 
NASA TECH BRIE 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Signal Conditioner Circuit for Photomultiplier Tube 
Isolation	 Schmitt Trigger/ 
Amplifier	 Monostable Multivibrator 
Input p	 •	 ,	 I	 •	 Output 
L7AF
	
11') 
1 
1 IFIF 
Charging 
Capacitor	
Electronic 
Switch 
S
Figure 1. Block Diagram of Signal Conditioner Circuit. 
The use of a photomultiplier tube to measure the 
total radiation dose absorbed in a scintillation 
crystal has commonly been performed by pulse-height 
analysis. In this technique a multichannel voltage 
discriminator sorts the phototube output pulses into 
specific amplitude increments, and counts the pulses 
that occur at each amplitude for a specified period. 
The result is a pulse-count rate vs amplitude spectrum 
that is readily adaptable to integration by numerical 
methods, with an accuracy essentially proporfional 
to the number of available channels. 
The simple, miniaturized circuit shown in Figure 
I and a detailed diagram of it in Figure 2 can sig-
nificantly improve the measurement of the total 
radiation dose absorbed. The input is connected 
directly to the anode of a photomultiplier tube that 
is optically coupled to a scintillation crystal. The 
current from the anode is accumulated in the charg-
ing capacitor until the voltage caused by the charge 
reaches the trip-point of the Schmitt Trigger (ST),
as translated through the isolation amplifier. The 
ST has a monostable-multivibrator feature that simul-
taneously supplies an output pulse and a trigger to 
close the shorting switch around the charging capaci-
tor. The capacitor discharges during the period cor-
responding to the output pulse width, and then begins 
to recharge as the trailing edge of the output pulse 
opens the short circuit. The cycle is then repeated, 
resulting in an output pulse rate proportional to the 
current from the phototube. 
The total number of pulses from the circuit during 
a specific time is a measure of the total charge applied 
to the charging capacitor during this time. Since the 
charge per unit time, or current, from the scintilla-
tion detector anode is proportional to the energy 
deposited in the scintillation crystal, the pulse count 
represents the total dose. 
A unique feature of the circuit is that the tempera-
ture coefficient of the field-effect transistor gate-
source voltage in the isolation amplifier can be 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19700000092 2020-03-17T00:23:01+00:00Z
readily controlled. This coefficient has been deter- 	 2. No additional documentation is available. Specific 
mined to be a function of the drain current. questions, however, may be directed to: 
The	 signal	 conditioner	 circuit	 is	 essentially	 a Technology Utilization Officer 
miniature	 charge-measuring	 circuit	 with	 a	 pulse Langley Research Center 
frequency readout. Thus, it can also measure a charge Hampton, Virginia 23365 
supplied in current waveforms that vary randomly in Reference: B70-10096 
amplitude, frequency, and width, such as provided Patent status: 
by photomultiplier tubes in pulse applications. For No patent action is contemplated by NASA. 
example, it is considerably better than the ammeter Source: Alfred Cellier and Wayne M. Hoover of 
for measuring such a current. Texas Instruments Incorporated 
Notes: Subcontractor to The Boeing Company 
1. 'This invention may be of interest to the manu- .	 under contract to 
facturers of electronic equipment. Langley Research Center 
(XLA- 10773) 
Phototube Anode
R19 
51 
R13 
1K	 C4 *I I TT'T2V R R8	 RiO C5 C6 16.8UF 
30K
Qi 62K	 6.2K Q6 
T 1800PF 35V 
2N3085
C2 R14
. N2907A I 100PF 3K R17 
R3* 5.1K CR4 
Ci ______ 11\13595  
220PF C3 CR5 
R4* 47PF 11\191613 
) Q4 
21\12369A
-Wv 
R11 
30K
14
Output 
21\1930 C133 21\12369A 
1N916B - 
Q2 CR2 
2N930 11\191613 S R9 I 
CR1	 . R5* _____  
I N3O70
R2	 R7	 R12 R6* R15	 R16	 R18 
>3K	 7.5K	 82O 56K	 10K	 56K
*Selected 
Figure 2. Detailed diagram of the signal conditioner circuit.
. 
. 
. 
Brief 70-10096	 Category 01 


Signal conditioner circuit for photomultiplier tube

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