Hashimoto Tetsuo

Komura Kazuhisa

Osawa Masumi

Sakanoue Masanobu

阪上 正信

大沢 真澄

小村 和久

Kanazawa University Repository for Academic Resources

Sci. Rep. l{anazawa Univ吋Vol. 10， No. 2， p. 69-78 December 1965 Observations of the faU-out radionuclides at Kanazawa Masanobu SAKANOUE， Ma呂umiOSAWA， Tet日uoHASHIMOTO and Kazuhisa I(OMURA Radiochemical Laboratory， Department of Chemistry Faαuty of Scie目iGe， Kanazawa University (Received 25 S巴ptemb色r1965) From January 1963 to May 1965， four events in r巴gardto the radioactive fallout were experienced at Kanazawa owing to the nuclear test explosions in foreign coun四tries. 111 these cases， som巴studieswere carried out by the members of the radiochemical laboratory of Kanazawa University and their resu1ts are reported here. 1. RadionucHde fractionation seen in the faUout accompanied with the heavy snow fall in January， 1963. In the middl巴 ofJanuary 1963， there was the heavy snow fal at the Hokuriku Districts of Japan， including our city， Kanazawa. S巴veralraclionuclicles were observed by m巴ansof gammaィay spectrometer in the samples brought with snowfall ancl unusual environmental racliation close of 0.016 mr/h was measurecl at this area by survey meter 011 February 1. These raclionuclicles might be originatecl from the Russian large scale nuclear test aiト burstin th巴autumnof 1962. The relative contents of some raclionuclides in various s乱mp!eswer百 studiedand the fractionation effect for radionu回clid四 proclucedby nuc1ear explosion w乱sobserved in those samples. This fractionation process may be causεd through a whole stage of their history， that is， from their procluction to their fal with snow. Furthermore， when snow thaws and that water passes into the soil of surfac巴 area，th巴 seconclaryfractionation may oCCUl‘ owing to thεdifferent properties of these raclionuclides in solutiol1. These informations for each radionuclide in various samples ar己 usefulto cleal with the health physical pl叶Jlemsrelatecl to radiological hazards. Gamma scintillation counter of Nuclear Corp. with 1 '/φ)， 1" NaI crystal was used to measure th巴 grossactivity and 100 channel pulse height analyzer of Ten AN聞 100type (Kob色 KogyoCorp.) with 13/4吋、く 2"NaI well type crystal was also usecl for gamma spectrometric measurement of various samples. All samples studied were collected at the old campus of the Faculty of Sciεnce in Sengoktトmachiof Kanaz旦wacity. The samples (a) ancl (b)， whose spectrums were shown in Fig. 1， were the snow samples deposited on the same plac巴 atthe play帽grouncl， but the former was sampled from the surfac日 ofdepositecl snow ancl the latter from the layer at 50 cm depth. Both samples were meltecl with heating， respectively - 69ー70 Masanobu SAKANOUE， Masumi OSA W A， Tetsuo HASHIMOTO， and Kazuhisa KOMURA， X 103 counts 2目。0.1 0.5 Mev Fig⑨1. Gamma ray spectra of snow and soil (a) the surfac邑 snowsample (12'50つ(b) the 50cm depth snow sample (46'31") (c) the soil sample (60') (d) th芭 dri出 i時 watersamp!e (20') ) measuring time and one li tre of εach sample was evaporated to dryn巴sin order to measure its gamma radioactivity. The sample (a) had 2.6 x 103 counts pεminut号 radioac“tivity and the sample (b) showed 0，94 x 103 cpm (background count : 0.57 x 103 cpm). From the gamma ray spectrums shown in Fig. 1， itwas found th旦tCト141 (its half 1ifε: 33.1 days) ， Ru目 103(39.8 d) and Zr回95 -Nト95p旦ir(their half lives: 65 d and 35 d respec圃tively) were predominant compon色nts，but the relative activities of these nuclides were different from each other. Ratios of peak heights due to these nuclides are estimated graphically as follows. The Ru阻 103: Zr-95 : Ce町 141ratios are found to be 1 1.1 2.3 in the sample ( a) and 1 0.5 1 . 1 in the sample (b). For compar回ison， gamma ray spectrums of drinking waters litre) in Kanazawa city and soi1s collected at ground surface are shown旦lsoin Fig¥1. It should be noticed that the peak h巴ightdue to Zr四95is more conspicuous than that duεto Rlト103in the soil sample. To examine the fractionation effects of these radio-nuclides in various materials， the column bed was pre-pared with sands of different partic1e size and cation and anion ion exchangεrs， and the thawed snow waters was passεd into that column bed continuously from the tiled roof of the wooden laboratory building through the polyethylenεtube. As shown in the left part of Fig. 2， the column bed was made by the following way. An acryl r巴sincolumn (4 cm in diameter and 23cm long) was fiUed successively from the upper part to the lower part with coarse sands of about 30咽 60mesh partic1e size， fine sands of under 60 mesh， cation ion exchanger (Amber1ite IR-120 of 30-40 mesh) and finally anion ion exchanger (Dowex 1 x 8 of200凶400mesh). The upper and lower ends of the column wεre sealed wIth nylon of fine net structure and the same net was used at the boundary betw巴endifferent bed fractions. After passing about 100 litres of thawed snow w品terinto the column， the column bed was slic吋 toevery one cm thick layer. Then， the m間 su民mentof gross gamma activities and gamma ray spectrometry were carried out for each sliced layer. The results are shown in Fig. 2 and Fig. 3。Along with these experiments， one litre of the original thawed snow water and the effluent solution from the column (filtratε) were evaporated to dryn巴s and the radioactivity of each was measured respεctively. Besid色sthese s 71 cpm 200 Observatlons of the fall-ozd radionuclides at Kanazawa 150 園 F100 50 二二コ一山10 ?????????? ????? ? ?。 、 ， 、 。 ??》?? ? ? ? ????? ??????????? ? ? ?????? ???? 、??。?? ?? ? ? ?〈?????? ?????》? ????????? ? ?????(layer No) Fig. 2. Column beds and the radioactivity found in each slice of the experiment。十，mblack dust fragment floating on th乱wedsnow water (dust F) was sampled and measured in similar way. These results are shown also in Fig. 3. It is noteworthy that the relative peak heights due to Zト9.5and C←141 to tha t of Ru -103 are much higher in the dust sample (F) having the net gamma activity of 85 cpm as compared with al other samples examined. From the gamma radioactivity distribution shown in Fig. 2， itis clearly found that the upper layεrs of each four differ己ntbed fraction have relative1y high concen-trations of radionuclides compared to the lower layers of the same fractiol1. In the analysis of these results， the following observation should be remarked. After the experiment， the lowεst fraction of the column bed， Dowex 1， had b巴encovered with gray fine powders from its upper to middle layer. Such condition might be caused by the migration of fine sands of the upp巴rfraction of the column bed to the anion exchanger fraction through the coarse cation exchanger p司rticles.So， the contribution of fine sands to the upper layer of the anion巴xchangerfraction must be considered. Radionuclides observed in the gamma ray spectrums of al sampl日sare mainly the following nuc1ides: Zr-95 (gamma energy， 0.726 and 0圃760MeV) and Nb-9.5 (0.768 72 Masanobu SAKANOUE， Masumi OSA W A， Tetsuo HASHIMOTO， and Kazuhisa KOMURA， X 103 counts 2.5 に吋てHむがJ lj il !i 1 2.0ト !I1.5r 門t 一一'-'--0.1 0.5 1.0 ?Vh~\ Fig. 3. Gamma ray sp邑ctraof each slice (1) No. 1 slice (4'1勺 (19) No.lヲslice(2'28") ( 6) No. 6 slice (8'5勺 (23) No.23 slice (20') (E) (13) No.13 slice (7'30勺 (F) the dust sample (3'40つ(S) the snow water (20') (E) the filtrate (40') ) measuring time MeV)， Rlト103(0.498 MeV) and仁e-141(0.145 MeV). The relative activities of these nuclides in問 chsample are estimated by comparing the peak heights of three peaks corresponding to Zト 95(Nb-95)， Ru同 103and Cか 141activities in gamma spectrums. Having many different chemical forms in solution， Ru-l03 was retain吋 inal samples at different degrees and observed even in the filtratεsampl告.Th色 pres巴nceof Rlト103in the low radioactive filtrate may be derived from the deficiency of whole exchange capaci ty of Dowex 1 x 8 resin used or the norトionicstate of this nuclide. Activities due to Zr-95 (Nト95)was not found in the fitrate， but巴nrichedin the fine sands fraction including the contaminated portion to anion exchanger. Especially， Zト 95(Nb姻95) was much enriched in the dust sample (F). It is notice在blethat the activity of 。bservalionsof the fatl-ozll radionuclides at Kanctzama 73 C巴回141is retained obviously in the upper part of the coarse sands fraction and also in the dust sarnple (F). From the results mentionecl above， the fractionation of 丘dionuc1idesin clifferent rnaterials is fairly weli r巴cognized.Therefor日， if considerab1e rnasses of snows have thawed and resulting waters pass into ground， the fractionation of the radionuc1ides wilI occur and sorne nuclides wiU be captured by soil cornponents. As one exarnple of this case， itis interesting to observe the migratiol1 process of radionuclide from S110WS to ground at the p1ayground wher巴 remarkableamounts of S110WS were dumped. When the thawing of dumped snow had come， two soil samples of ground were collected from the different sites of this area on May 1. These two samp1es were cut Into every one cm fraction from the surface to th己 deeperpart. By the radioactivity m巴asurementof each fraction， it was found that the surface fraction was more radioactive than the other fraction， and Zr-95 (Nb町 95) and Ce-141 were clearly enriched compared to Ru-l03. Thus， the more effective fractionation had occurrecl in the soi1 samples than in thεsnow samples. The environmental radiation dose showecl somewhat high values arouncl the play-grouncl even in Ju1y， 1963. The three or four holds higher raclioactivities than that of backgrouncl wer巴 measureclby survey metεr at the places where appreciab1e dusts accumulatecl after the thawing of clumpecl snows. 2. Radionuclides in the faHout from the first Chinese nuclem.' test explo呂ionResulting from the first Chinese nuclear explosion carriecl out on October 16， 1964， the highly raclioactive fallout fel on Kanazawa city two cl旦ysafter this exp1cトsion. 1n order to examine the radionuclides in this fallout， the sample was collεcted on the roof of the builcling belonging to the Faculty of Science by sweeping that floor 乱tabout 10 o'clock a. 111. 01 October 20. The raclioactivity measurement of this sample by well type scIntillation counter showecl about 75x103 cpm as for 5g of this sample on that day. The gamma ray spectra of this sample w巴rerecorclecl by 100 channe1 PHA at various 1i1己aramplifier conclition. 11 each case， thεchannel凶energycalibration curve was macle by using several raclionuclicles (Ce-144， Pa皿233，Cs-137， ZI1-65乱ndCo圃60)as the standarcl g乱mmael1ergy sources. The spectra of the fallout sample at various gamma energy region are showecl in Fig. 4 (a)， (b)， (c)， (d). The same sample hacl the gamma activity of 38 x 103 cpm 01 October 23 and its spectrum is shown in Fig. 4 (a) as th巴dottedline f01" comparison with the spectrum on October 20. From these spectra， the existences of the following raclionuclicles are confirmed: Np帽239(2.35 cl.)， Ba-140 ancl La-140 pair (12.8 d. ancl 40.2 h. respec-tively)， and 1-132 (2.26 h.， the claughter of Te-132 having half life of 77.7 h.). Th巴existence of C←141 (33.1 cl.) having the gamma energy of 0.14 MeV is also revea1ed by comparing the dotted line spεctrum with the former 0日e.In Fig. 5， another gamma ray spectrum of the rain-out samples are shown. These Masanobu SAKANOtJE， Masumi OSA W A， l'etsuo HASHIMOTO， and Kazuhisa KOMURA， (b) (0.5~1. 1 Mev) ??? ? ? ?? ? ? ? ???(a) ???????〈??〉? ?? ????? ?????74 一一一二(0.3-'0.7 Mev) 0.3 Mev Fig.4島 Gammaray spectra of the dry fallout sample in various energy r巴glOns0.2 i 0.1 samples were collected on th巴 roofof the Ishikawa hygienic laboratory in the diffεrent period of October， 1964. The sample (註)is the total rain咽outfrom 1st to 16th of this month and the sample (b) from 17th to 29th. Both samples were made one 1i tre of the original sample， r巴spectivelyand subjected to the gamma ray me走路『urement. The gross gamma activities were 750 cpm (B.G. 530 cpm) for the sample ( a) and 26 x 103 cpm for the sample (b). From th巴sedata and the gamma ray spectr昌 ofthese samples， itis obvious that the first Chinese nuclear test explosion has a great effect on the radioactivity of the rain司outsamples. As these spectra were record色don October 30， the peaks due to Np-239 which had been seen overwhelmingly in the spectra of October 20， diminished to its fairly short half life and the pe呂.ksdue to Ce-141， La凶 140and Zr-95 (Nb-95) wεre identified in this spεctrum. B色sidesthe gamma ray spectrometric study， the radiochemical analysis was carried out as for th巴abovementioned sample by the following procedure in order to examine mainly th邑 existenceand abundance of various uranium isotopes. The sample was evaporating 75 Obse，'vatiωS 01 the fall-oul radionuclides at Karu:tzarna Fig咽 5.Gamrna ray spectra of the rain-out samples (a) the sample from 1st to 16th，October， 1964 (b) the sample frorn 17th to 29th， Octo-ber， 1964; 212 counts ful sc昌lere-corcling (b') the same sampl巴 210 counts ful scale recorcling (c) the back grouncl radioactivity (All spectra were recorclecl after the raclioactivity rneasurements for 20 rnin utes.) decompos巴dby aqua regia and evapo-rated up to near1y dryness. Then， this residue was taken up by concentrated nitric acid and the solution was sepa-rated from the residue by filtratiol1. The chemical separation procedure with ethyl acetate solvent extraction and anion exchange was applied to this solution and the main scheme of this procedure is shown in Fig. 6. Th巴 finalsolution leached from Dowex 1 anion巴xchangerby 0.1 N HCl was convertεd to the electrolytic solution which contained 0.25 M formic acid and had the definite pH value suitable for effecti ve electrodeposition of uranium. The electrodeposition was carried out on the stainless steel plate (3.5 cm diam己t巴1・)as cathode for two hours by electric current of 400 mA. The counting source obtained by ? ? ?〉? ? ? ? ?↑ 恥1evSample l……ー」出忠告，eby aqua regia; evaporate up HNO匂呂印凶仙山lu凶1Residue (σfi江lt甘r.) Fi江lt位ra訓叫te1一一」:::;::21;Ml〉ora…HN03soln. adcl Ag20z伽warm Residue (filtr.) Filtrate I clilute with water add NH生OHPr日cipitate(centrifug.) Supernatant 1dis山 ein 7:93 HN03; aclcl AI(NO)3州shake vdth ethyl acetat巴Org. (solvent extr.) Aq. i一一一 I7:93 !立2?Org. (washing) Aq. i---L旦20Org. (stripping) Aq. I evaporate to dryness ↓8N HCl 。owex1 x8 column 一一一一-r市立賢市[elelution Electrodeposi tion The chemical separation scheme Fig.6. The Masumi Tetsuo I-IASHIMOTO， and Kazuhisa KOMURA， ? ? ? ?} ?????5C 20l-....A. o 2 Mas呂田bu76 rers Fig. 7幽 Uranium-237decay curv巴( 訟や、。¥0， αコふ3N ド司、-" 、7 ドトロ之三主? ???〉????「? ????????「〕CQunts ?????? ??? ? ???、??????? ? ???????、〈?? ? 、??? ??700 500 300 this procedure was subjected to the beta and alpha radioactivity m四 surements.beta activity was 115.4 cpm at the time immediately after the above mentionedpr配 e-dure and decayed exponentially by the half life nearly equal to that of U聞237as shown in Fig. 7. 50， the existence of U-237 (6.7 d.) is unquestiorトable and it should be remarked that the nuclear reaction， U開238 (n， 2n) U岨237，by fast neutron had occured in th巴firstChinese test explosion together with the reaction， U醐238(n， r) U-239→Np-239， by thermal n巴utron.To study th巴 alphaemit幽in the electrodeposi ted source， the alpha pulse spec回乱ifev.---1...一一一一一-'--一一一」一一一一一一i4.6 4.8 Alpha ray spectrum Fig. 8. 1 4.2 4.0 77 trometry was carried out by the combination of Frish grid ionization chamber (Osaka Denpa Corp.) wi th the rise time converter and 100 channel PHA. From the alpha spectrum shown in Fig. 8.， itis found that the ratio of U-234 to U-238 is nearly unity in activity unit ratio and therefore the natural uranium had been contained in fairly large amount in the first Chinese nuc1ear bomb. This fact was proofed also by the existence of conspicuous gamma energy peaks due to Np~239 in the early gamma ray spectrum of the same sample. The small p巴akin the about 5.1 Mev region of the alpha sp巴ctrumis considered to be attributable to Pu-239， but it could not be con-firmed wheth巴rthis nuc1id巴 producedas the decay product of Np-239 found in the fallout or the original nuc1ear bomb had contained PU・239in some quantity before that explosion. Observations of the fall-oui radionuclides at Kanaz仰 aRadionuclides in the fallout from the underground nuclear test explosion in U.S.S.R.. 3. The rain蝿outsample collected at Kanazawa in the middle of January， 1965， showed the radioactivity due to the fission products probably originated from the underground nuc1ear test explosion which was reported to be carried out in U .S.S.R. some days ago. The gamma spectrum of this sample recorded on January 22， showed obviously the existences of Te-132 (1-132) and Ba-140 (La・140)as shown in Fig. 9' Furth巴rmore，it was confirmed from the spectrum recorded on February 23 that this same sample had contained such radionuc1ides as Ce-141， Ru-103 and Zr-95 (Nb圃95)as shown in ????、? ?〈? ? ?? ? ?『? ?????〉?? ?? ?????〈????? 。 ， 。 ????????1.5 Mev Fig. 10. Gamma ray spectrum of the falout sample recorded on Feb. 23， 1965. _..~-~~， 1.0 0.5 0.5 Mev Fig. 9. Gamma ray spectrum of the falout sample recorded on Jan. 22， 1965. 0.4 0.3 0.2 0.1 78 Masanobu SAKANOUE， Masumi SAWA， Tetsuo HASHI:MOTO， and Kazuhisa KOMURA， Fig. 10. As contrast with the first Chinese nuclear test explosion， itwas notic泡ablethat the gamma activity peak of Np・239had not come out clear in the spectrum of the energy region up to 500 keV which was recorded few days after the nuclear explosion and shown in Fig. 9. 4. The radioactive fallout from the second Chinese nuclear test explosion X10' counts 10.。1.0 1.5 Mev Fig. 11. Gamma ray spectra of the fallout samples (a) the sample collected on May 17; measured on that day for 34 minutes (b) the sample collected on May 22; measured on May 24 for 26 minutes ¥ It was reported that the second Chinese nucle泊rexplosion was carried out on May 14， 1965. The radioactive fal10ut was collected on the roof of the building belonging to the Faculty of Science of our University on 17th of this month. And the other sample was col1ected on 22th of this month. The gamma spectrums of these samples were shown in Fig. 11. The absence of the peak due to Np・239in these spectrum should be remarked in contrast with the spectrum of the fa110ut from the first Chinese nuclear test explosion. The gross gamma acti vi ties of these samples were 1. 26 x 103 cpmj 4. 8gram and 2.3 x 103 cpmj9. 5gram respectively on May 24. 

Observations of the Fall-out Radionuclides at Kanazawa

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Observations of the Fall-out Radionuclides at Kanazawa

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