Improved electrical circuit determines the amount of light detected by a photomultiplier tube when its output signal is in the dark-current range of the tube. The low-intensity light to which the tube responds arises from a thermo-luminescent ionized dosimeter

Baker, B. R.

Cashion, K. D.

English

NASA Technical Reports Server

November 1968	 Brief 68-10501 
NASA TECH BRIEF	
I& 
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. 
Readout System for Radiation Detector 
An improved electrical circuit, which has been de-
signed, will determine the amount of light detected by 
a photomultiplier tube when its output signal is in 
the dark-current range of the tube. The low-intensity 
light to which the tube responds arises from a thermo-
luminescent dosimeter which has received ionizing 
radiation (e.g., X-rays or nuclear radiation) in the 
range of 10 to 500 milliroentgens. (A thermolumi-
nescent dosimeter emits visible light when it is heated 
after exposure to the ionizing radiation.) To enable 
the detection and reliable measurement of very weak 
sources of light, it is necessary to reduce the dark 
current and thereby improve the signal-to--noise ratio 
of the resultant output signal. Previous methods of 
improving the signal-to-noise ratio, although effective, 
are relatively complex and often unreliable. 
The new circuit utilizes a highly stable variable 
current source which, when combined with the dark 
current signal (no light signal fed into the photomulti-
plier tube), causes the resultant output signal of the 
circuit to be zero. Thus, when an input light signal 
is fed into the photomultiplier tube, with the current
source equal in magnitude but opposite in polarity to 
the dark current, the resultant output signal is pro-
portional to the input signal. In this way, low-intensity 
light signals from a thermoluminescent dosimeter may 
be readily measured by the circuit. 
Note: 
Documentation is available from: 
Clearinghouse for Federal Scientific 
and Technical Information 
Springfield, Virginia 22151 
Price $3.00 
Reference: B68-10501 
Patent status: 
This invention has been patented by NASA (U.S. 
Patent No. 3,358,145), and royalty-free license rights 
will be granted for its commercial development. In-
quiries about obtaining a license should be addressed 
to NASA, Code GP, Washington, D.C. 20546. 
Source: K. D. Cashion 
and B. R. Baker 
(MSC-90180) 
Category 01 
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.
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Readout system for radiation detector

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