Liquid scintillation counting technique is applied to the direct measurement of carbon-14 in carbon dioxide. This method has high counting efficiency and eliminates many of the basic problems encountered with previous techniques. The technique can be used to achieve a percent substitution reaction and is of interest as an analytical technique

Horrocks, D. L.

English

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April 1969.	 Brief 69-10092 
•	
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AEC-NASA TECH BRIEF	
L it 
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Direct Measurement of 14 Ø 2 by Liquid
Scintillation Counting 
The problem: 
To develop a technique for the direct measurement 
of carbon-14 in carbon dioxide. Previous methods 
suffered from such drawbacks as nonquantitative ab-
sorption or reaction of the CO 2 , quenching from the 
addition of absorbents or reactants, and isotope ef-
fects during successive reactions. 
The solution: 
A liquid scintillation counting technique for meas-
urement of 14C activity. The carbonaceous sample is 
first converted into CO 2 , and the ' 4CO 2 is then meas-
ured by a liquid scintillation counter. This method has 
high counting efficiency and eliminates many of the 
basic problems encountered with previous measuring 
techniques. 
How it's done: 
• Three different counting systems have been used 
with equal success: a room temperature single-multi-
plier phototube (RCA-8575) system; a - 20°C single-
multiplier phototube (DuMont-6292) system; and a 
0°C coincidence liquid scintillation counter. 
Two scintillator solutions were used to match emis-
sion from the solution with response of the multiplier 
phototubes. With the RCA-8575 multiplier phototube, 
a solution of 3 g of PPO in a liter of toluene was used; 
with the DuMont-6292 multiplier phototube, a solu-
tion of 7 g of PPO and 0.5 g of M 2 -POPOP in a liter 
of toluene was used. 
The CO2 gas samples were prepared by normal vac-
uum line manipulations. The CO 2 was condensed with 
liquid nitrogen onto a previously degassed and frozen 
volume of the scintillator solution. The sample tubes 
were then sealed by flame, minimizing the volume of 
space above the scintillator solution.
The solubility of CO2 in toluene base scintillator 
solution is sufficient to allow the . 14C measurement 
at room temperature. By the use of a special type of 
sample container, the space above the solution was 
minimized to the extent that greater than 99% of the 
CO 2
 was dissolved in the solution. 
To determine the concentration quenching of CO2, 
samples were prepared with varying concentrations of 
CO2 . The relative scintillation yields were determined 
by the Compton edge technique. There was no detect-
able quenching up to 5 cc (STP) per ml of liquid scm-
tillator solution. 
To determine the counting efficiency, several sam-
ples of known volume of 14C containing CO2 were 
dissolved in 2 ml of scintillator solution and counted 
in a room temperature single-multiplier phototube 
system. The counting rates were determined by the 
integral counting technique. Aliquots of the same gas 
were counted in a gas counter. The extrapolated in-
tegral counting rates of samples in the liquid scintil-
lators agreed with ±2% of the absolute disintegra-
tion rate obtained with the gas counter. 
This method can be useful for either assay or abso-
lute measurement of 14C radioactivities in samples 
converted into CO2. Counting efficiencies of greater 
than 90% are obtained with low backgrounds. With 
an integral counting technique, a counting efficiency 
of (100 ± 2) % was obtained. The lower level of de-
tection of ' 4 C by this method is 10 7 Ci per cc (STP) 
Of CO2 for a 10 cc sample (about 2 disintegrations per 
minute). 
Notes: 
1. The use of scintillation counters is not new, but 
this particular measurement is a novel application. 
(continued overleaf) 
This document was prepared under the sponsorship of the Atomic 
Energy Commission and/or the National Aeronautics and Space 
Administration. Neither the United States Government nor any per-
son 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 the use of any information, apparatus, 
method, or process disclosed in this document may not infringe pri-
vately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000092 2020-03-16T17:52:09+00:00Z
2. The technique can be used to achieve a percent 
substitution reaction, and may be of interest to 
university and hospital laboratories as an analyti-
cal technique. 
3. Inquiries concerning this report may be directed 
to:
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B69-10092 
Source: D. L. Horrocks
Chemistry Division
(ARG- 10237)
Patent status: 
Inquiries 'about obtaining rights for commercial use 
of this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U. S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439
. 
Brief 69-10092	 Category 03


Direct measurement of carbon-14 in carbon dioxide by liquid scintillation counting

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