"^ J>.At'7'^'f^ /AA^'^c.-/^9f MDDC - 1099 UNITED STATES ATOMIC ENERGY COMMISSION IONIZATION CHAMBER for CARBON-14 MEASUREMENTS by C. J. Borkowski .ijroiNEERINa SCIENCES LfBRARy This document consists of 4 pages. Date Declassified: June 12, 1947 This document is for official use. Its issuance does not constitute authority for declassification of classified copies of the same or similar content and title and by the same author (s). Technical Information Division, Oak Ridge Directed Operations Oak Ridge, Tennessee ^JUNIV. OF FL UB .DOCUMENTS DEPT. U.S. DEPOSITORY Digitized by tine Internet Arclnive in 2011 witln funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/ionizationchambeOOusat IONIZATION CHAMBER FOR CARBON-14 MEASUREMENTS By C. J. Borkowski Measuring C" as C^* O^ in an ionization chamber has the following advantages: 1) A constant reproducible geometry is always obtained. 2) There are no self -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 COj can be measured. This is equivalent to approximately 8 g BaCOj. 5) The time required to acidify a sample of BaC03 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 H' measurement. The ionization currents in all cases were measured with a dynamic condenser electrometer, although a Lindemann electrometer connected to this type of chamber could also be used. In the measuring of ionization currents of the order of 10'" to 10"'° amperes, insulator currents due to stresses in the insulator begin to manifest themselves. In order to minimize these insulato.r 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 removed from the electrometer. The insulator current due to stresses on the insulator when the chamber is evacuated is less than — 10"" amperes. The background of the chamber filled with dead CO^ and shielded by 2 inches of lead is 1.5 x 10"" amperes. About one-half of this background is due to alpha particles present as natural radioactive contamination in the brass. One disintegration per second of C'^ in a chamber of this type having a volume of 300 ml gives a current of about 1 x 10"'° amperes, when the diluent gas is dead COj and is at one atmosphere pres- sure. The insulator for the collecting electrode may be purchased from the American Phenolic Corp., Chicago, Illinois. A complete report describing the use of this chamber and associated techniques in acidification of BaCOj and combustion techniques will be published shortly by C. J. Borkowski and W. Leslie. MDDC - 1099 [ 1 2] MDDC-1099 •iiHS q: 0= ©in — — la -^ o — 5 lio ©CD MDDC-1099 [3 -I* -1 .^ - \ f -1^ / o UJ a: I Q_ to o 3 IT ^ © a o 111 a: — _j < lTt«» a 4] MDDC - 1099 BILL OF MATERIAL Part 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 Required Description Material Stopcock-12/30-straight bore Pyrex Chamber end Brass Chamber body Brass Chamber end Brass Insulator Lucite Guard ring Brass Adapter mounting Brass Dust cap Brass Collecting electrode Brass Gasket Neoprene Insert Polystyrene Gasket Neoprene No. 4-40NC Bristo setscrew 1/8" L Steel 1/8" Flat washer Brass No. 5-40NC hex nut Brass Gasket Neoprene Wrench ring Brass Washer Neoprene Plug Brass uniVbKtiM Y OF FLORIDA 3 1262 08907 9676