J o h n J. Griffin' a n d Ronald L. S t e v e n s Hull High School Hull. M A 02045 Alexander A. P. P s z e n n y a n d Irving J. Russell Boston College Chestnut Hill. M A 02167
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A P a ~ i Nuclear ~e Debris Collector
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T h e proliferation of nuclear weapons of different designs has placed a n increased responsibility on educators t o provide meaningful information when discussing t h e fallout of atmosoheric nuclear debris. An e x ~ e r i m e nin t the collection and anaiysis of nuclear debris can hk used quite effectively t o enhance related textual information. T h e 15 March 1978 open atmospheric explosion of a relatively small nuclear fission device (less than 25 kilotons T N T equivalent yield) by t h e People's Republic of China provided the opportunity t o test the sensitivity of a novel nuclear debris collector. T h e collector takes advantage of t h e ability of rain t o remove trace substances from the lower atmosphere (1,2). T h e removal or washout ( W )of nuclear debris from the atmosphere can be expressed a s Concentration in Rain (DPMIg Rain) W= (1) Concentration in Air (DPMIg Air) W values obtained bv different researchers in t h e United States and Europe havebeen compiled by Engelmann (3)and indicate rains have heen enriched 1004000 fold in radioactive fission products compared t o equal masses of air. In the event t h a t t h e fallout of nuclear debris does not coincide with rainfall, subsequent rains will wash rooftop depositions of nuclear debris into t h e collector. Experimental The collector, illustrated in Figure 1, consists of a coffee can (content capacity 454 g) with both metal ends removed, itssnap cap plastic lid perforated with eighty 4 mm holes, and a piece of Schleicher & Sehuell #410 filter paper cut to fit the plastic lid. In operation, the collector was placed under a drainspout, and after an appropirate collection time, the filter paper was removed, air dried, and monitored far its radioactive content by a 3.5 em' end window GM tuhe connected to a Tracerlah Scaler. An autoradiograph (visual image) of the radioactivity imbedded in the filter paper was obtained by placing the filter paper in contact with Kodak X-Ray NoScreen film for 95 hr (empirically determined). The film was developed in standard Kodak solutions. A 30 emW4Li) high resolution gamma ray spectrometer at the Nuclear and Radiochemistry Laboratories at Boston College was used to establish the identity of the gamma emitting components of the nuclear dehris. Results The rnllertor'n to remove nuclear - ~ . ~ ~ .nhilitv ~ ~ ~ the - insoluble ~ ~ debris ~ r o duced by a small nuclear explosion in the open atmosphere can be confirmed by an examination of the X-ray film imagery shown in ~
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Figure 2.
Autoradograph lmagery of the 26-27 March 1978 rain filter
Figure 3.
Ge(Li)gamma ray spectrum of 26-27
March 1978 rain filter.
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CAN
FILTER PAPER CAP
Figure 1. Nuclear debris collector (exploded view).
Figure 2, and the GdLi) gamma ray spectrum shown in Figure 3. The half lives of the eamma emittine nuclides found bv the Ge(Li) de-
The absence in the spectrum of naturally occurring gamma emitting radioisotopes such as 'Be and 2'ZPbmay be due to several factors, including the following: non-retention on the filter paper due to particle size, solubility in rainwster, andlor low activity levels relative to the fission products. The decay rate of the beta emitting radioactivity found in the nuclear dehrison the filter paper of 22 March 1978is illustrated in Figure 4. The experimental slope of -1.26 is in good agreement with the experimental slopes ( 4 ) of -1.09 and -1.18 for beta decay of fresh fission products in the same time period after the explosion considering the nuclear dehris fractionation possibilities with respect to the original fission yield distributions. Peak quantities of radioactivity were found in the filter papers of
' Address correspondence to this author. Volume 56, Number 7, July 1979 1 475
nuclear debris heeame available for worldwide fallout within a short time after the explosion. Conclusions ACTIVITY CPM
The sensitivity of the collector described above has been demonstrated by its ability to collect fallout from a relatively small nuclear explosion during the first and second passage of the radioactive cloud around the earth. The time for passage of the nuclear debris from Lop Nor, China, t o Eastern Massachusetts and for s complete circuit of the earth is fairly consistent with earlier findings of 8-9 days and 18 days, respectively (67). In addition, the collector has removed fallout pwduced in a thermonuclear explosion which occurred sixteen months earlier. The collector has the advantages of being efficient for filtering particles associated with nuclear debris, inexpensive, consuming no energy, and requiring minimal attention. The collector lends itself to implementation a t secondary and post fiecondary levels of education. A regular program in filtering rain samples and monitoring the associated filters by beta or gamma ray detectors would establish the background levels for the insoluble fraction of radioactivity found in rain. Any significant washout of radioactive debris from the atmopohere would thus be readilv dis~~~~~~~~
u 50
20
100
200
DAYS
Figure 4. Experimentally observed decay of the beta emitting radioactivity collected from the rain of 22 March 1978. Radionuclides Identified by Ge(Li) High Resolution Gamma Ray Spectroscopy from 12-hr Rain Filtration Sample of 26-27 March -
1978
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Radionuclide 133Xe 1311
99mT~ 14'Ce l4OEa
132Te 239Np lroLa fo3R" 132)
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Half Life
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Gamma Energy-(KEV) ~
5.27 d 8.06 d 6.0 hr 32.5 d 12.8 d 3.25 d 2.35 d 1.67 d 140 d 2.29hr
81 283,364 140 145 162,537 228 228,278 329.487 497 673,780
the 22 and the 2 6 2 7 March 1978 rains. The quantity of radioactivity in the rain filters collected after these dates decreased to background levels until the rains of 11-12April1978. A Ge(Li) gamma ray analysis of the 11-12 April 1978 filter paper indicated the existence of many of the radionuclides found in the gamma ray spectrum of the 26-27 March 1978 filter paper, although a t much smaller activity levels. The 11-12 April filter paper also revealed the presence ofthe long lived radioisotope Ia4Ce (tin = 285 days) present in alarger thanexpeeted quantity relative to the radioisotope 14'Ce. The most probable source of the excess 14"Ce was the powerful Chinese thermonuclear explosion of 17 November 1976 estimated a t 4 Megatons T N T equivalent yield. A characteristic of such high energy explosions with megaton ranges is the injection of most nuclear debris high into the stratomhere. thus resultine in delaved worldwide fallout (5).The low energy'nuelear explosion of 15 ~ & c 1978 h produced a cloud of insuffic~entbuoyancy to penetrate the stratosphere, thus its associated
476 1 Journal of Chemical Educafion
compared t o that expected from fresh fission products; however, positive confirmation of fresh fission products should be established Ih gnmnln ray spectrmnvlry or, allcrnnurrly, hy ht.laanalyrriof the inrlwrlunl radi,f lx.~l,U.4,1970, 1, 8' \ l,ra~l.sA ,8"d5t,,k,",F 11 ,"l'"~~;~rn".,,~",,,:~ 1, < 1 1 1 4 , ~ ,r
