Table 11. Results (Counts/Gram at to) Obtained for Irradiations of Teflon Disks in “C” Configuration Sample A B C D E Mean values for disk positions
1,795,139 1,780,039 1,785,347 1,789,938 1,795,082
2 1,789,340 1,780,487 1,781,633 1,781,237 1 ,771 ,291
Disk position 3 1,787,169 1,795,936 1,787,399 1,782,322 1,775,712
4 1,795,579 1,793,509 1,784,355 1,783,152 1,799,226
5 1,801,852 1,805,095 1,787,875 1,789,427 1,788,919
Mean values for samples 1,793,815 1,791,013 1,785,599 1,785,215 1,782,046
1,789,109
1,780,797
1,785,708
1,787,164
1,794,633
1,787,482
1
both homogeneous and inhomogeneous samples can be precisely controlled. Homogeneous samples can be irradiated with the rotator in any configuration if the samples to be compared are placed in corresponding positions in the rotator. Long ( 5 / 8 inch) and/or inhomogeneous samples must be irradiated in the C configuration if they are to be uniformly activated. The sample rotator in its present form is primarily useful for activation analysis of elements that produce radionuclides with half-lives of several minutes or hours. It would not, for example, be useful for measuring trace amounts of oxygen which forms 7.4-second *6N. For such analyses sample transfer by a pneumatic system to and from the rotator would be required. Although the rotator might be designed for pneumatic sample transfer, there would be little advantage in irradiating more than two samples simultaneously when short-lived radionuclides are measured. Some increase in sensitivity would be achieved by enlarging the rotator for increased sample size. Measurements have
shown that a sample in the rotator (configuration C) is exposed to w 1 / 8 of the fast neutron flux value it receives when taped to the generator face plate. A further decrease in flux exposure would be obtained in a larger rotator. Calculations, based on the inverse square law, indicate that for samples longer than inch to be uniformly activated, the rotation angle in the C configuration would have to be altered. There are, of course, sources of error in fast neutron activation analysis -e.g., neutron self-shadowing and gamma-ray self-absorption by the sample-not caused by irradiation configuration. Although the rotator does not eliminate the effect of neutron self-shadowing, the well known technique of irradiating standards and unknowns of similar matrix (composition and density) can be fully exploited to reduce self-shadowing, errors in activation analysis.
RECEIVED for review July 27, 1967. Accepted September 5, 1967.
Device for Transfer and Dilution of Radioactive Gases Lawrence A. Elfers and Mark Herman1 National Center for Air Pollution Control, 1055 Laidlaw Avenue, Cincinnati, Ohio 45237
THE MOST
COMMON applications of radionuclides in tracer studies involve their use in liquid media. Their transfer and dilution present little or no contamination problem (1). Radioactive gases are being employed as tracers in air pollution studies in this laboratory, and others (2) have applied them in studies of analytical methods and instruments. The tracer gas must often be transferred from a glass ampoule into an appropriate cylinder so that the gas can be diluted under high pressure. T o accomplish this task, an inexpensive device was designed, which, in one operation, breaks the glass ampoule, transfers the tracer gas into a steel cylinder, and dilutes it under high pressure with inert gas. The device, shown in Figure 1, consists of a series of No. 316 stainless steel pipe sections and fittings, joined in such a
Present address, Chemical Engineering Department, University of California, Berkeley, Calif. (1) R. T. Overman and H. N. Clark, “Radioisotope Techniques,”
McGraw-Hill,New York, 1960. (2) P. Urone, J. B. Evans, and C. M. Noyes, ANAL.CHEM., 37,1104 (1965).
fashion as to provide a barrel for the guidance of a projectile and a larger compartment for the glass ampoule. The projectile, a stainless steel ball, is propelled by the pressure of the diluent gas. One-way check valves must withstand pressures higher than the maximum diluent gas pressure. Prior to use, the receiving cylinder is evacuated. The apparatus is divided at the 11/4inch union (No. 9). The steel ball is then inserted into the appropriate half of the system; and the glass ampoule, containing the radioactive gas is placed in the other half. The two are then reconnected by means of the stainless steel union. After valve No. 22 is closed, valves No. 3 and No. 26 are opened. The shutoff valve on the high pressure diluent gas cylinder (No. 1) is then opened with a brisk twist, and the pressurized gas causes the steel ball to shoot forward and break the glass ampoule. A sintered stainless steel filter (No. 15) (pore diameter 60 p ) prevents broken glass from entering the receiving cylinder. After the pressure in the two cylinders has reached equilibrium (about 1000 psi), the cylinder valves are closed and the pipe system is slowly vented through the vent valve (No. 22) into an appropriate scrubber system before the gas in the pipe is released to a fume hood. VOL. 39, NO. 14, DECEMBER 1967
e
1909
d
d A L L SCREWED J O I N T S SEALED WITH TEFLON TAPE AND TESTED AT 2200 p s i g BEFORE USE. ALL F I T T I N G S MADE OF 316 STAINLESS STEEL.
Figure 1. Schematic diagram of apparatus to dilute %02 with nitrogen
NO.
1
2 3
8 9 10
11 12 13 a
Inlet connection
Table I. Description of Apparatus (Numerals Refer to Figure I) Outlet Inlet connection Comments No. Name connection CGA 580 F 14 Nipple inch M 15 Filter '14 inch F
Name 1A cylinder, Prepurified N2 @ 2200 psi Adapter CGA 580 M CGA 350M Needed for regulator available High-pressure CGA 350 F in. M 0-4OoO psi inlet regulator and outlet Elbow 'I4 inch F 'I4 inch M Check valve inch F inch F Arrow indicates flow Reducer 'I4 inch M "4 inch F Nipple 3/4 inch M "4 inch M Length 12 in. O.D. in. Contains SS ball Reducer inch F 1 1 / 4 inch M Union 1 inch F 1'14 inch F l1I4 inch M 1'/a inch M Length 12 in. Nipple Contains vial of 35S02 Coupling 1 inch F 1'14 inch F Reducer 1'14 inch M inch F Reducer a/4 inch M inch F
Iron bars.
Clamps.
c
Support strap.
d
ANALYTICAL CHEMISTRY
Check valve
17
Tee
18 Nipple 19 Union 20 Nipple 21 Nipple 22 High-pressure
inch M '14
inch F
'I4 inch M inch F
'I4inch M inch M inch F
F
inch M inch F 'I4 inch M inch M inch F '14
valve Hose connec- '/4 inch M Connected to tion vacuum 24 High-pressure '14 inch F '14 inch F Made of stainless hose Steel 25 Adapter '14 inch M CGA 580 M 26 1A cylinder, CGA 580 F Previously used evacuated for N2
23
Cylinder retaining straps.
Soft iron, as used for the manufacture of the 1A cylinder, reacts to some extent with chemically reactive gases such as SOz. Storage of low concentrations of these gases, (less than 10 ppm) should be avoided. Preconditioning of the soft iron tank with nonradioactive gas of the same concentration was found to minimize these wall losses. A stainless steel tank could be employed as the receiving vessel to further reduce this problem. 0
16
Outlet connection Comments ' 1 4 inch M '14 inch F Sintered Stainless Steel, 60 pores Arrow indicates flow 'I4 inch M Arrow indicates flow '/a inch F Tee is also inch
Experience with this apparatus for transfer of %Q2 gas has proved it to be a safe, efficient, and economical solution to the problem of transferring and diluting radioactive gases into steel cylinders.
RECEIVED for review September 1 1 , 1967. Accepted October 6,1967.
