SWRHL-500r
A SEPARATION TECHNIQUE FOR THE DETERMINATION OF KRYPTON-85 IN THE ENVIRONMENT
by
D,J L. Stevenson and F. B. Johns
Western Environmental Research Laboratory*
ENVIRONMENTAL PROTECTION AGENCY
Presented at the
International Symposium on Rapid Methods
for Measuring Radioactivity in the Environment
Neuherberg, Germany
July 5-9, 1971
This study performed under a Memorandum of
Understanding (No. SF 54 373)
for the
U.S. ATOMIC ENERGY COMMISSION
~Formerly Southwestern Radiological Health Laboratory

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Available from the National Technical Information Service,
U. S. Department of Commerce,
Springfield, Va. 22151
Price: paper copy $3.00; microfiche $.95

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A SEPARATION TECHNICS FOR "HE OETBRMIN.ATIC^ OF K^PTON-SS IH THE fMUCAHENT
D. L. Stevenson and F. B. Johns
Southwestern Radiological health Laboratory
Environmental Protection Agency
P. 0. Box 15027
Las Vegas, Nevada 89114, IJ. S. A.
INTRODUCTION
Krypton-85 is a by-product of nuclear fission. It is being added to the
atmosphere in ever increasing amounts by nuclear reactors, fuel reprocessing
facilities, and to a smaJl extent by nuclear weapons tests [11. Because of
.the low concentration (1.14 ppm) of stable krypton in the atmosphere, and
.its properties as an inert gas, krypton presents special analytical problems.
Early separations of krypton from air involved the use of stable krypton
carrier gas followed by internal gas counting techniques [21. Sax et al
[3] used a series of chemical artel coinbusuon reacLions to purify krypton
which was then counted ir a liquid scintillation countsr with a so'iri
scintillant, Mors recently Shaping ft. al used scintill£tisn solution
to absorb krypton gas prior co coj'itirc in a Jiqufcf scint-:iIeti'op counter.

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The procedure described here utilizes a carrier free, chromatographic
technique for separating krypton from an atmospheric sample. The krypton
is then dissolved and counted in liquid scintillation solution. The method
is comparatively simple, reproducible, and sensitive enough to routinely detect
environmental levels of krypton-85.
APPARATUS & REAGENTS
The cryogenic-vacuum apparatus (Fig. 1) consists of an all-glass system
containing a vacuum manifold and an interconnecting series of traps. The
system is designed so that a gas flow can be established from any one trap
to another. Inserted in the flow path is a thermal conductivity detector
(Gow-Mac model 10-454) with a power supply feeding a strip-chart recorder.
Vacuum is supplied by a 130 liter/minute mechanical pump connected to a
thermocouple vacuum gauge. A regulated source of helium is used as carrier.
The large charcoal trap (C-l) is filled with lOOg of 8-12 mesh activated
coconut charcoal. The miniature trap (C-2) contains 0.3g of 30-50 mesh
activated charcoal. The three molecular sieve columns (MS-1, MS-2, and MS-3)
are made from 150-cm lengths of 9 mm I. D. glass tubing folded to0fit inside
a one-liter vacuum jar. The columns are filled with Linde type 5A molecular
sieve of 30-6C mesh size.
Tube furnaces are made from cylindrical heating elements wrapped with
asbestos and mounted vertically on movable support clamps. The cold baths
are 1000-ml vacuum jars mounted like the furnaces. The coolants used in the
baths are liquid' nitrogen, dry ice-acetone, and ethylene glycol.
The scintillator solution is 5 g of 2,5-diphenyloxazole (PPO) plus 300 mg
of 1,4 bis-2-(4 methyl-5-phenyloxazolyl)-benzene (Dimethyl P0P0P) dissolved
in one liter of scintillation grade toluene (1). The counting vials were
fabricated by Don Lillie Inc., Smyrna, Georgia, from borosilicate glass fused
to luer fittings. Each vial has an internal volume of about 20 cm*. Valves,
connectors, and caps for luer taper fittings were obtained from the Hamilton
Co., Whittier, California. The samples are counted in a Beckman LS-100
liquid scintillation spectrometer operated at room temperature.
PROCEDURE
A sample is collected in the field by using a compressor to fill an
evacuated air cylinder. A prefilter and a molecular sieve dryer are inserted
on the inlet side of the compressor to remove particulate matter, moisture,
and some carbon dioxide from the sample.
(1) Dimethyl P0P0P was substituted for the suggested solute bis-MSB[A].
The performance of the two is equally satisfactory in this procedure.
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In the laboratory, the cylinder is weighed and then connected to the
inlet of the cryogenic-vacuum apparatus. The total sample is leaked into
the system using vacuum to maintain a constant differential pressure of
one-half atmosphere in the system (2). The gas flow is passed through a
calcium sulfate desiccant trap, a trap containing 13x molecular sieve, a
cooling coil at liquid nitrogen temperature, and finally to a charcoal
trap (C-l) immersed in liquid nitrogen. Vacuum is maintained at the outlet
of the charcoal trap until the sample cylinder is evacuated to less than 10
mm Hg. The empty cylinder is then reweighed and the sample size determined.
Oxygen, nitrogen, and argon are removed from C-l by raising the trap
temperature with a dry ice-acetone bath and purging it with" helium at a
flow rate of 1 liter/minute and 1 atm pressure. The exhaust stream is
directed through the thermal conductivity cell which is used to monitor
the elution. When the removal is complete, the exhaust flow from C-l is
redirected through the first molecular sieve column (at liquid nitrogen
temperature) and finally to vent. Once the flow has been established,
the remainder of the sample is transferred to MS-1 by heating C-l with a
tube furnace to 100°C.
The residual components of the sample are selectively eluted from the
molecular sieve column by establishing a helium flow rate of about 700cm3/
minute through the column and then raising the column temperature with an
ethylene glycol bath precooled to - 15°C. The appearance of individual
fractions (Fig. 2) is again monitored by the thermal conductivity detector
on a strip-chart recorder. Within two or three minutes after raising the
temperature with the glycol bath, the first fraction containing the remaining
oxygen and argon is eluted from the column and discarded. The next fraction
to appear (6-8 minutes) is krypton which is transferred to a second molecular
sieve column held at liquid nitrogen temperature (MS-2). Closely following
the krypton is a fraction containirg nitrogen and methane which is discarded.
The sample is eluted from MS-2 to a third molecular sieve column (MS-3), in
exactly the same fashion, with any residues of the undesired oxygen, nitrogen,
methane, etc. again being vented {Fig. 3).
The final elution of the purified krypton from MS-3 is directed to a
miniature charcoal trap (C-2) immersed in liquid nitrogen. When the transfer
is complete, the trap is isolated and the helium carrier gas pumped off the
trap by means of vacuum. The trap is then opened to a previously evacuated
liquid scintillation vial, and the krypton gas is allowed to expand into the
vial by warming C-2 to room temperature. Pressure inside the vial (20-40 mm
Hg.) is read from the manometer, the valve is closed, and the vial removed
and filled with scintillation solution via a 50-ml luer type syringe. When
all of the krypton is dissolved and the vial is full of solution, it is capped
and counted along with previously prepared standard and background samples [4],
The volume of krypton in the vial is calculated using the vial volume, manometer
pressure, and room temperature. The specific activity of this krypton in
(2) reduced pressure prevents the condensation of liquid air in the trap. A
combination of charcoal and liquid oxygen presents a potential explosion
hazard [2].
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pCi/cm3 multiplied by the known concentration of krypton in the atmosphere
(1.14 cm3/m3) yields the activity of krypton-85 per cubic meter of air.
The scintillation solution must be refluxed for 15 or 20 minutes prior
to its use to remove dissolved air which prevents absorption of the krypton
[4]. The solution should also be slightly warmer than the room or counter
temperature when introduced into the vial. Cooler solution will expand
causing the vial to leak or break.
To prepare the cryogenic-vacuum system for reuse, the traps are evacuated
while being heated to 250-300°C. If samples of high activity are analyzed,
the system can be more efficiently decontaminated by alternately flushing the
hot traps with helium and then evacuating them.
The procedure requires about four hours per analysis excluding counting
time. Environmental samples are routinely counted for 100 minutes each.
RESULTS
Krypton recoveries range from 50 to 70 percent. This yield is based on
the volumetric measurement of the recovered krypton compared to the theoretical
amount of krypton in the original sample. The purity of 3 typical krypton
fractions is shown in table I. Results for the analysis of aliquots from a
single, large air sample are given in table II.
The counting efficiency for krypton-85 is 89 percent with a background
of 28 counts per minute. Using a sample size of one cubic meter, the sensi-
tivity or minimum detectable activity [5] for this method is less than
2 pCi/m3 of air.
DISCUSSION
The selection of sample size is primarily a matter of convenience and the
sensitivity required. Samples larger than one cubic meter will yield greater
sensitivity but are difficult to collect. Very small samples are easy to
obtain but may require the addition of stable krypton carrier to facilitate
the separation. Nearly all commercially available krypton now contains some
krypton-85 contamination. When used as a carrier, this contamination serves
to raise the background count rate and consequently reduces the sensitivity
of the analysis. For carrier free analysis, the sample size should be at
least 0.25m3 or larger.
The greatest source of error in this method is in the determination of
the volume of the purified krypton. If the separation is incomplete, some
oxygen and nitrogen may be transferred to the miniature charcoal trap (C-2)
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and their volumes mea: ' ' ' T" " helium carrier is not
The presence of these „	he apparent specific
activity of the krypton-85.
Other radionuclides do not interfere in the analysis of environmental
air samples. If the sample is taken near a reactor site and analyzed within
a matter of hours, it may contain krypton-85m (4.4h) and krypton-88 (2.8h)
which can be identified by subsequent decay counts.
CONCLUSION
This procedure eliminates the need for krypton carrier, chemical
reactions and combustion furances. It is comparatively simple and yet
readily detects background levels of atmospheric krypton-85. With minor
changes in the conditions, this method can also be used for the separation
and counting of atmospheric argon, xenon, and methane.
completely evacuated
measured as krypton.
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TABLE I	Mass spectrometryc analysis (a) of krypton separated from
three atmospheric samples


Component

Volume percent


1
2
3
Krypton
97.7
98.1
98.1
Oxygen
0.98
0.54
0.53
Ni trogen
0.85
0.77
1.06
Helium
0.23
0.54
-
Hydrogen
0.09
-
-
Methane
0.07
-
-
Carbon Dioxide
'0.05
0.07
-
Argon
0.04
-
0.04
C4+ Hydrocarbons
-
-
0.30
(a) Analyses performed by the Chemistry Department of the
Lawrence Radiation Laboratory, Livermore, California
TABLE II Replicate analyses of a Homogeneous air sample
quot
Aliquot
size(m3)
Krypton-85
(pCi/m3)
2-Sigma counting
error (pCi/m3)
.1
0.54
12.1
± 2.9
2
0.58
12.0
± 2.3
3
0.41
13.0
± 2.9
4
0.37
12.1
± 3.0
5
0.31
13.4
± 5.4
6
0.37
13.6
± 2.9
7
0.23
11.6
±12.1
8
0.26
12.1
± 4.3
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FIGURES
1.	Cryogenic vacuum apparatus
2.	Elution chromatogram from the first molecular
sieve column showing residual air components
3.	Elution chromatogram from the second molecular
sieve column indicates the removal of unwanted
fractions
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03
CRYOGENIC-VACUUM APPARATUS
DETECTOR
VENT
SAMPLE
h2o co2 pre-
TRAP TRAP COOLER

VAC.

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MS-1 MS-2 MS-3
SCINT. VIAL
5
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C-2
MANOMETER

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MINUTES
FIGURE 2. Elution chromatogram from the first molecular
sieve column showing residual air components.
MINUTES
FIGURE 3. Elution chromatogram from the second molecular
sieve column indicates the removal of unwanted fractions
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REFERENCES
[1]	EHHALT, D.,K. 0. MUNNICH, W. ROETHER, J. SCHOLCH, and W. SUCH.
Krypton-85 in the atmosphere. Proc. of the 3rd International Conf.
on Peaceful Uses of Atomic Energy 14:45-47 (1965)
[2]	MOMYER, F. F. The Radiochemistry of the Rare Gases National
Academy of Sciences-National Research Council Publication NAS-NS
3025 (1960)
[3]	SAX, N.I., R.R. REEVES, and ¦].C. DENNY. Surveillance for krypton-85
in the atmosphere. Radiol health '\ita Rep 10:99-101 (March 1969)
[4]	SHUPING, R.E., C.R. PHILLIPS, and A.A. MQGHISSI. Low-level count-
ing of environmental krypton-85 by liquid scintillation. Anal.
Chem., 41,2082 (1969)
[5]	National Bureau of Standards. A Manual of Radioactivity Procedures,
NBS Handbook No. 80 U. S. Dept. of Commerce. 27-28 (1961)
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