Storage and retrieval of waste 133Xe

0.662 MeV photopeaks in the spectra of standard sources of 13’Ce and “‘Cs, introducing the necessary corrections. The impurities (‘4’Ce. 13’I. 9”Nb. ‘%Zr. etc.) were detcrmined using gamma spectra. measured after a period of 36 days to allow for 99Mo decay. The ““Ba + i4”La was measured in fresh solutions, usmg the 1.6 MeV peak in the spectrum of 14’La. Before measuring the activity of 13’Te and i3’1, the ‘9Mo was extracted with I-benroin oxime solution in chloroform. For the determination of ~-emitters, lanthanum carriei was added to the solution and precipitated as lanthanum fluoride (after reduction if necessary). The precipitate was mixed with a solid scintillator and its activity was measured with a photomultiplier using a known T-source as a standard. The results of the analysis of some “‘MO preparations are given in Table I ; these show that the proposed method produces ““MO preparations with a radionuclidic purity of more than 99.8% and practically carrier free.

Storage and Retrieval of Waste

’ 33Xe*

Introduction

WITH THI- increased use of the radioactive isotope ‘.‘JXe for clmical applications. a safe and simple management and disposal of the radioactive waste is necessary. Disposal can be accomplished by adding the expired iA3Xe to an externally directed airstream. According to National Dutch Regulations. the concentration of ’ '"Xe leaving the exhaust should not exceed 100pCi/mJ. Usmg IOmCi “JXe and blowing the radioactive waste into the open air, a displacement of about IO* m3 air is required. Because this is impractical. the expired ‘33Xe should be collected. in such a way that the Maximum Permissible Concentration (MPC)(IO-’ HCi/cm3) in the room where the investigation takes place is not exceeded. In clinical investigations, as used by us.“’ about lot)1 v. 1. LtVlN are collected. ‘To our knowledge. two L. S. KOZYREVA-ALEXANDKOVA expired gas/patient methods are in use to reduce these quantities to more T. N. S~KOLOVA manageable sizes. Klein et al.‘*’ disposed of the expired T. D. TITKOVA i”‘Xe by compressing it into steel congas containing N. M. VOLKOVA have to be stored during several V. G. ZAL~:~.~KY tamers. These containers half lives (rt = 5.3 days for “‘Xe). Another method is L. P. MWAVIWA separating the la3Xe from the non-radioactive gases (HzO, CO,, N, and 0,) and storing only the ‘j3Xe. This is pcrInstitute of Biophysics, formed by adsorption on active charcoal. From published Health Ministry @‘the U.S.S.R.. data on the adsorption of xenon.‘3’ it follows that adsorpJivopeesnaya 46, tion of xenon/g charcoal increases exponentially with dcMoscow 123182. creasing absolute temperature. Therefore the active charU.S.S.R. coal and the gas-mixture should be cooled. Since the amount of “‘Xe is very small (the partial pressure of xenon in the expired gas is about 10-s mm Hg). it should be possible m this way to trap all the i.r3Xc present in the expired gas. An apparatus based on this References principle has been used by us, using solid CO, as cooling agent. 14i Similar techniques have been used by others.‘< ‘I BOYD R. E. In dadiopharmaceuticals jrom Generatorat various temperatures. Since the adsorbed “3Xe can be Produced Radionuclides, p, 53. IAEA, Vienna (1971). eluted by heating the active charcoal. it should be possible BoYD R. E. In Radiopharmaceuticals and Labelled Comto use the iaaXe again, A problem arising with the propounds, Vol. 1, p. 3. IAEA, Vienna (1973). longed use of such a trap in a routine environment is the CONSTANTR. E., FALLAIS C.. CHARLIEKR. and Bw.vrcontamination of the connectmg tubing and the pump by LEZ P. In Radiopharmaceuticals and Labelled Comcharcoal dust. pounds, Vol. I, p. 17. IAEA, Vienna (1972). Also frequent replacing of the active charcoal should 4. MANI R. S. and NARAMSIMHAND. V. S. In Rudiopharbc avoided. To meet these requirements a new apparatus maceuticals and Lahelled Compounds, Vol. 1. p. 135. was designed. IAEA, Vienna (1973). 5. Section 4: Radioisotopes derived from generators. In Methods Radioisotope Production and Quality Conrrol. p. 657. IAEA Techn. Rep. Ser. No. 128 (1971). A schematic diagram of the apparatus+ is shown in Fig. 6. LEVIN V. I., KOZYREVA-ALEXANDROVAL. S.. TITKOVA I. After removal of CO, and Hz0 the expired gas IS T. D., ‘ZALESSKYV. G. and IVANOV Yv F. USSR Patenr pumped through a column filled with active charcoal at No. 435724 (14 March 1974). a pumping speed of 4l/min. The column is cooled to I. LEVIN V. I. and TITKOVA T. D. Radiokhimiya 17, 55 -3O’C by a conventional one-stage refrigerator. Uniform (1975). temperature distribution is assured by immersing the column and the cooling spiral in ethylene glycol. The dust filters are standard automobile oil filters. adapted to fit the tubing. These filters have a mesh of *This investigation has been supported by the Nether30 pm and do not significantly reduce the pumping speed. lands Organization for Pure Scientific Research (ZWO). By applying these filters and filling the column with active t Manufactured by Lode Instrumenten N.V. Groningen. charcoal so that the charcoal level is situated well hclow The Netherlands.

603 COPPER

I

TUBING

8 25 mm

XENON

UMP

I

I

ACTIVE CHARCOAL R=0.8 mm

BRdSS CONTAINER AND LEAD SHIELDING

----------------

L

FIG. 1. Schematic

Na I (T II .,

DkAlN

COOLING

HEATER

I ) detector

diagram

I -I

of the apparatus.

X I

1

I

1

1

No I ( T

I ) detector l”X 1”

cl

rl HV

HV

/

douglas

{cl--/

1

bag\

window

H

digital

tape

/dough

bag\

read-out

punch

FIG. 2. Block diagram

system

of the test set-up. Detectors and electronics have been taken from the 12-detector The expired gas is pumped from the left Douglas bag into the right Douglas bag for adsorption and in the opposite direction for retrieval.

used in this laboratory.

the inlet and outlet, the contamination of charcoal dust has been minimized. The inspiratory concentrations normally used with ventilation studies can easily be regained by heating the column to 60°C and eluting the ‘s3Xe by a gas flow in the opposite direction. Heating is performed with an electrical heater wrapped around the charcoal column, The

gas flow is reversed by means of a triple three-way valve. An oil-free rubber membrane pump is used to assure that the gas coming from the pump is not contaminated and can therefore be inhaled. The reversed gas flow can be mixed with O2 so that a gas-mixture is obtained containing 0,. air and the previously adsorbed ‘j3Xe. This procedure makes it possible to use the ‘s’Xe in following patients.

604

Technical notes

I

Gxnts/min. ( detector

adsorption

I

Counts/min. (detector

;Ij

.DETECTOR

0

1,

20

oDETECTOR 2

1

,

40

60 time

FIG. 3. Results

2

of a test with the set-up

0

20

40 time

(min.)

shown

in Fig. 2. showing

complete

recovery

60 (min.)

of r3’Xe.

Results

Conclusion

The performance of the apparatus has been tested in a set-up shown in Fig. 2. Detectors and electronics have been taken from the standard 12-detector system”’ used in this laboratory. The result is shown in Fig. 3. The Douglas bags monitored by detector I contained initially 5 mCi *ssXe in a volume of SO I. The Douglas bag monitored by detector 2 has been connected to the exhaust of the recovery apparatus. From Fig. 3. it is clear that no increase in count rate has been observed in detector 2 while pumping out the first Douglas bag. This means that all the IsaXe had been trapped in the active charcoal. The differences m count rate when both bags are empty can be explained by the fact that the first bag had been in use for the collection of ‘33Xe for long time. Therefore the material of the bag had been saturated with 13-‘Xe (xenon has a high solubility in rubber”‘). The other bag had never been used for the collection of “3Xe. so that the count rate in that bag is completely due to background radiation. The peak appearmg in the count rate of detector I after heating to 60°C can be explained by the fact that the xenon IS totally released after heating, and is led back into the Douglas bag in the first 20 min. giving rise to a higher mItta! concentration. After further intlatron of the Douglas bag. the count rate reaches a value equal to the value prior to processing. From the analysis of the experimental errors we conclude that more than 99.5% of the initial amount of ‘-‘sXe had been led back into the first Douglas bag after processing. The rise in concentration of ‘33Xe in the room (volume 100 m3) where the investrgation takes place, is consequently less than 0.01 MPC. A similar test has been made after processing 10.0001. of expired gas, without replacing the active charcoal. No deterioration of the performance of the apparatus has been observed.

The apparatus described in this note IS a complete. selfcontained unit capable of storing waste ’ 33Xe making use of adsorption of xenon on active charcoal at -30‘C. The stored ‘-‘jXe can also be reused, thereby eliminating the need for storage of waste radioactivity during several half lives. The umt is very easy to operate. is mobile and can be used anywhere without an expensive or bulky system for disposal of 133Xe. Lung Functiotl Laboratory and Isotope Laboratory. University fiospital. Groningen, The Netherlands

TH. W.

VAN

DER

R.

MARK &SET

w. VAALRIJHG H. BEEKHUIS A. E. C. RO~KMAKEK M. G. WOLDRING

References I PESET R., BEEKH~JISH.. TAMMELINC G. J., VAAL.IIIJR~: W. and WOLDRING M. G. Radioactive Isotope in K111lrk und Forschung, IO. Urban & Schwarzenberg. Muncher1 (1972). KLEIN R. C., NEL~QN J. A. and PUGH N. 0. Atn. Kcr, Resp. Dis. 103, 118 (1971). DLJSHMAN S. Scientific Foundations oj Vacuum Techrlryue. Chapter VI. Wiley. New York (1949). VAALB~JRG W.. PES~T R.. BEEKHUIS H., WOLDRI~C~ M. G. and TAMMELING G. J. Itlr. J. appl. Radial. 1.wtopc.s 22, 785 (1971). H. H. and MANTEL .I. 5. CORRIGAN K. E., CORREAN Radiology 106, 615 (1973). 6. Lruzz~ A.. KEAKY J. and FREEDMAN G. J. nuci. Med. 13. 673 (1973). 7. MURPHY P. H. HIth Phys. 29. 779 (1975).