Detector monitors gamma dose rate at particular position in a radiation facility where a mixed neutron-gamma environment exists, thus determining reactor power level changes. Device also maps gamma intensity profile across a neutron-gamma beam

Been, J. F.

English

NASA Technical Reports Server

May 1972	 B72-10227 
NASA TECH BRIEF 
Lewis Research Center 	
_4V 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
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be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Simple Dynamic Electromagnetic . Radiation Detector 
Cabling
Measuring
	
Radiation - -	 Power Diode 
Gamma	 p	 Semiconductor	
Instrument* 
Ammeter or A.C. 
Capacitance Bridge 
A very simple but reliable detector has been developed 
for dynamically monitoring gamma dose rates such as are 
associated with nuclear reactors. Its size and simplicity 
make it attractive for use in instances where the relatively 
elaborate ion chamber system may not be needed. For 
example, this detector can be used to monitor the 
gamma dose rate at a particular position in a radiation 
facility where a mixed neutron-gamma environment 
exists, in order to determine reactor power level changes. 
In another application, it can be used to map the gamma 
intensity profile across a neutron-gamma beam. 
The entire detector is shown in the figure and con-
sists of a commercial power diode, a measuring instru-
ment, and connecting cabling. Two electrical character-
istics of the diode can be measured as a function of 
gamma dose rate: the short circuit photo current and 
the diode junction capacitance. The photo current pro-
vides considerably greater measurement range since, at 
zero gamma intensity, the photo current is zero but 
there is an initial junction capacitance. At higher dose 
rates, however, the change in photo current and junction 
capacitance show comparable sensitivities. The detector 
tested used a 1N1189 silicon power diode. In a gamma 
radiation environment of approximately 106 rads per 
hour, the photo current from this diode was approxi-
mately 10 microamperes and the capacitance increased 
ten times. 
There are several advantages of a detector of this type 
when compared to a conventional ion chamber system: 
(1) there is no need for the ion chamber high voltage 
power supply' and its associated cabling, (2) the sensor 
can be one-hundredth the size of even miniature ion 
chambers with comparable output signals, (3) it can be 
constructed from standard stock items, (4) the response 
time of the system will be limited generally to the re-
sponse time of the measuring equipment, and (5) cable 
leakage and noise problems are considerably reduced. 
Notes: 
1. In mixed neutron-gamma environments, high neutron 
fluences may damage the silicon crystal and therefore 
change the electrical characteristics of the diode. Thus, 
more frequent calibration and/or replacement will be 
required if the diode is left in a neutron field for long 
periods of time. 
2. There are many other possible applications of 'this 
detector in the measurement of electromagnetic 
radiations. One such application would be the moni-
toring of X-ray intensities where the very small size 
and fast response of the diode would be advantageous. 
(continued overleaf) 
This document was prepared under the sponsorship of the National	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19720000227 2020-03-17T03:33:19+00:00Z
No additional documentation is available. Technical 	 Patent status: 
questions, however, may be directed to:
	
No patent action is contemplated by NASA. 
Technology Utilization Officer 
Lewis Research Center 	 Source: J. F. Been 
21000 Brookpark Road	 Lewis Research Center 
Cleveland, Ohio 44135	 (LEW-1 1159)
Reference: B72-10227 
B72-10227	 Category 03	 41


Simple dynamic electromagnetic radiation detector

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