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UNITED STATES ATOMIC ENERGY COMMISSION
C J. Borkowski
This document consists of 4 pages.
Date Declassified: June 12, 1947
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Technical Information Division, Oak Ridge Directed Operations
Oak Ridge, Tennessee
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IONIZATION CHAMBER FOR CARBON-14 MEASUREMENTS
By C. J. Borkowski
Measuring C'4 as C~1 0. in an ionization chamber has the following advantages:
I A constant reproducible geometry is always obtained.
2) There are no sell-absorption corrections to apply.
3) increased sensitivity over solid sample counting is obtained Intensities from one disinte-
gration per second to 10 disintegrations per second can be measured.
4) Up to 1000 ml of CO, can be measured. This is equivalent to approximately 8 g BaCO,.
5) The time required to acidify a sample ot BaCO, and introduce it into an ionization chamber
takes no longer than to spread properly an infinitely thick solid sample for G -M counting.
The purpose of this report is primarily to release a design on an ionization chamber, thirty of
which have been used for routine C' and H3 measurement. The ionization currents in all cases were
measured with a dynamic condenser electrometer, although a Lindemann electromeier connected to
this type of chamber could also be used.
In the measuring of ionization currents of the order of 10-s' to 10-16 amperes, .nsulator currents
due to stresses in the insulator begin to manifest themselves. In order to minimize these insulator
currents, the collecting electrode insulator volume should be kept to a minimum, and the insulator
itself should be shielded both from the high voltage electrode and any external fields which might in-
duce charges on the insulator surface when the chamber is remo.'ed from the electrometer.
The insulator current due to stresses on the insulator when the chamber is evacuated is less
The background of the chamber filled witn dead CO, and shielded by 2 inches of lead is 1.5 x 10-6
amperes. About one-half of this background is due to alpha particles present a3 natural radioactive
contamination in the brass.
One disintegration per second of C1" in a chamber of this type having a volume of 300 ml gives a
current of about 1 x 10"'6 amperes, when the diluent gas is dead CO, and is at one atmosphere pres-
The insulator for the collecting electrode may be purchased from the American Phenolic Corp.,
A complete report describing the use of this chamber and associated techniques in acidification
of BaCO, and combustion techniques will be published shortly by C. J. Borkowski and W. Leslie.
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BILL OF MATERIAL
Part Required Description Material
1 1 Stopcock-12/30-straight bore Pyrex
2 1 Chamber end Brass
3 1 Chamber body Brass
4 1 Chamber end Brass
5 1 Insulator Lucite
6 1 Guard ring Brass
7 1 Adapter mounting Brass
8 1 Dust cap Brass
9 1 Collecting electrode Brass
10 1 Gasket Neoprene
11 1 Insert Polystyrene
12 1 Gasket Neoprene
13 1 No. 4-40NC Bristo setscrew 1/8" L Steel
14 1 1/8" Flat washer Brass
15 1 No. 5-40NC hex nut Brass
16 1 Gasket Neoprene
17 1 Wrench ring Brass
18 1 Washer Neoprene
19 1 Plug Brass
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