Determination of Transuranium Elements in a So-Called "bikini Ash" Sample and in Marine Sediment Samples Collected Near Bikini Atoll(Health Physics Article) Health Physics Vol. 35, PP301-307,Aug)

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0 Health Physics Soculy Printed in Great Britais DETERMINATION OF TRANSURANIUM MARINE SEDIMENT SAMPLES COLLECTED NEAR BIKINI ATOLL School of Medicine, Akita University, Hondo 1 - 1 - 1 Akita 010 Faculty of Science, Kanazawa University, Marunouchi 1- I , Kanazawa 920, Japan (Received 3 May 1977; accepfed 9 December 1977) Abstract-The concentrations of 239+uo Pu and 241Am in the debris from the second thermonuclear test detonation of the USA (Bravo) were determined. This debris, called “Bikini Ash”, was collected in 1954 on the deck of t h e Japanese fisherboat “5th Fukuryu-Maru” which was located some I50 krn to the east of Bikini Atoll al the time of the thermonuclear test. A portion of the 1954 sample was subjected to analytical analysis in 1974. Accordingly, the concentrations of 239+w Pu and ’“Am in the sample were determined to be 25.92 1.7 and 12.950.9 djs/min/mg. respectively. From these values. the ratio of w ‘ P u / 2 3 p c ~ uat time zero was calculated to be 26+-3, and this ratio was almost the same as the “Mike” thermonuclear debris. Furthermore. Pu and ’“Am contents of the marine sediment samples collected near Bikini Atoll were also analyz.ed, and i t was found that a significant contamination with these nuclides was found to he stilt remaining ON I MARCH1954, the second thermonuclear test of the USA was carried out at Bikini Fukuryu-Maru” was exposed t o the nuclear debris from this test. T h e highly radioactive debris collected on t h e boat. called “Bikini Ash” in Japan,has become an urgent subject of many investigators (JA54). It was found that this debris was coral reef having a composition of CaO 55.2%, MgO 7.0% and COz 11.8% and contaminated with a large amount of fission products and induced radioactive nucludes, such as 237U. T h e “Bikini Ash” has been subjected t o only a f e w studies on transuranium elements, although the presence of ”vu was supposed from one track on nuclear emulsion exposed for many days to a radiochemically separated w a s to determine the 219’240 Pu and ’“Am contents of both the “Bikini Ash” sample and several marine sediment samples collected near Bikini Atoll, as accurately a s possible by radiochemical techniques. Just recently, the 59.6 keV gamma ray from *41Am i n the “Bikini Ash” has been detected by gamma ray 7hese transuranium elements in the debris might b e produced, a s shown in Fig. la, bythe rapid, successive neutron capture of 23sU exposed to the unusually high neutron flux generated by the thermonuclear explosion and the following hcta-decays. In Fig. l a , the nuclear reaction sequences for the production of heavy nuclides in a reactor are also shown by the broken line. The radiochemical studies (Di60) made soon after the first the rmon uc le arexp Io si o n test fraction: I n ;his present study, the objective (“Mike”) revealed the relative abundance and

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the alpha-activity ratio of these nuclides in the debris, ;IS shown i n Fig. Ib. For mass number 241, the calculated activity of 24'Am is shown ;is a daughter nuclide o f 241Pu. Furthermore, the values o n the upper a b - scissa show the weight ofa sample required t o detect I dis/inin o f other nuclides in the obtained from the 70-mg sample stored in the Institute o f Physical and Chemical Research. Japan. I n this present study, made in 1974 - 1975. 2 rng o f the sample was submitted for the sample was used for low energy photon spectroscopy. I t was found by its spectrum, shown in Fig. 2, that 2Jy+240Pu,241An1.I5'Eu, "'Cs and "'Sb were contained in this sample. was exposed to this explosion debris in 19S4 is plotted in Fig. 3. Marine sediment samples analyzed i n this study were collected i n 1Y73 by a marine research vessel, the "Tokai 11'' of Tokai University. Accurate latitudes a n d longitudes o f these locations are given in Table 1 together with water depths. topographies of sea bottom, arid the characteristics of the sediments. All sediment samples were collected with a dredger. The simple s are identified a s 73105, 73108, 73109 and 731 13 as shown in Table1.One gram of each sample was dried at ll0"C and used for plutonium a n d americium analyses. Sample N o . 731 13 contained manganese nodules, which were removed before analysis. An aliquot of '%Pu and '%d.solution was added t o the samples a s yield tracers for

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EE sci pe peak plutonium isotopes and "'Am, respectively. pha-emitter, was prepared by the reaction o f the Gd/Arn ratio did not change during the same radiochemical procedure as used in t h e present work. Details of the carrier-free '"Gd preparation (Ko76) and the usefulness of '"Gd as tracer were previously reported elsewhere the 2'6Pu tracer was calibrated with a standard 239Pu solution supplied from the Radioactivity Centre, Amersham. England. Each sample was treated with 8 M hot hydrochloric acid. R y adding aqueous ammonia to the supernatant. the coprecipitation of plutonium and other elements with hydroxide precipitates (iron hydroxide. etc.) was carried out. When only a little amount o f precipitate was obtained, i t was spiked with about 5 mg Fe" carrier. The precipitate was open circles indicate sampling points and the bold line, set by the U S. Navy, was the hound n ry o f the area prohibited f o r navigation at the time of the nuclear homh tect in 1954.

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304 ' I ' K ANSU KANI UM ELEMENTS IN SAMPLES COIALEC'I'EL>N EAR UI Kl NI ATOLL then dissolved with hydrochloric acid and the coprecipitation was repeated by adding a sodium hydro x ide so I ut ic)ri. After re movi ng iron by the solvent extraction with di-isobutylketone. plutonium w a s extracted with organic phitse w a s washed successively with 8 M nitric a i d to rernove the uranium, and with 10 M hydrochloric acid t o remove the thorium. Plutonium was stripped with 6 M hydrochloric acid containing 0.2 M hydrofluoric contain ing ;mi er ic i u ni and gad oIi 11i um ,was evaporated to dryness. The americium was then extracled, together with ''"Gd. into 50% chloric acid solution adjusted to pH 1.2, and stripped with 8 M hydrochloric acid. For alpha spectrometry, americium and pluto niumf rac t io n s were s u bje c ted , re s pe ct ive Iy, to electrodeposition o n 18-8 stainless steel disks having diameters of 2.7 cm.The electrolytic solution containing 0.5 ml of 0.1 M hydrochloric acid, 0.5 ml of 0.5 M oxalic acid, 0.75 ml of 2 M ammonium formate, 5 ml o f sodium chloride and 3 ml of distilled water. T h e electrodepohition was carried out for 2 hr at 500mA, using a platinum wire as a n anode. Americium a n d plutonium were determined barrier detector and a 200-channel pulse Concurrent with these analyses, the intercalibration sample, plutonium standard soil N o . 3 , prepared by the US Energy Kesearch Service Laboratory in Idaho was also analyzed by the above-mentioned method. The validity of our calibration o f 2'6Pu tracer w a s confirnied by the agreement of our data with those from the Health Service LaboraDe v e 1o pment Ad m in is t r at io n s RESULTS AND DISCUSSION The alpha-spectra of plutonium and americium fractions of all samples are shown i n Figs. 4a and b, respectively. In the alphaspectra of t h e americium fraction of the sample 731 13, the contamination with '"Ac, the daughter nuclide of 2'JU, is shown by the rxistance of the alpha-emitting daughter nuclides of 227Ac. Since actinium in a 3+ oxidation state is the most stable in a n aqueous solution and the chemical properties of actinium resemble americium and lanthanides, actinium may behave a s similarly a s americium a n d lanthanide in the present analytical procedure f o r americium. As the energies of alpha rays f r o m the daughters of 2 2 1 A ~a r e higher than that from 241An1,the peaks d u e to these nuclides did not interfere with the determination of "'Am in samples which had n o high '*'Ac content. Pu and 241An1a r eT h e contents of 239+24a shown in Table 2and Fig. 3. The overall chemical yields of Z'P~ and '"Gd varied from 12 t o 42%. The '"Am in the "Bikini Ash" sample was found to b e 12.9 5 0.9 dis/niin/nig. Ash" sample and the sediment samples were found to be nearly the s a m e , within the statistical counting error of the samples. contamination of deep sea sediments due Io the worldwide fallout. Noshkin a n d Bowen analyzed six sediment profiles collected from the Atlantic Ocean and the Mediterranean Sea in 1%9- 1971 (No73). Among these samples three had been collected in the northern hemisphere. The contents o f P u in ocean floor sediment samples, collected from about IO00 and 5000 m depths, were around 0.02 a n d 0.005 dis/min/crn' of bulk sediment, respectively. Livingston rt ol. reported the value of 0.16 dis/min/g f o r the top-of-core samples collected from the 1000m depth in the Atlantic Ocean in 1972 (Li75). The present values for samples 73108 and There are afew reports onthe 239+24uPu

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S. HIS A MATSU and M. SAKA NO UE I I73113 High energy region 174 4hrl sediment samples. h. Alpha spectra of americium fraction from "RikiniAsh" sample and marine zediment samples.

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73 I09 are one-to-two orders o f magnitude higher than those quoted above. T h e 230'2u)Pu detected in sample 73105 is the same level a s that of worldwide fallout. I t is notable that I'u was not detected in sample 731 13. I t may b e caused by the water depth o f the sampling site. since this sample w a s collected from the deepest site among the four samples. along with the effects o f the winds and current at the lime of the nucleiii- testing. Recently, Nevisse and Shell reported Pu and 241Am contents in sediments collected in Bikini Atoll lagoon (Ne75). They det er inin ed the 241A 111 contents by gam m a- ray spectrometry. According to their data, the contents of plutoniunl and americium i n 3 1 samples, including t w o samples collected outside t h e atoll, varied from 0.9 to ratio o f 2 4 1 A m / 2 3 Y t 2 w P ~varied from 0.2 to 0.8, and the 'average value was 0.53. Compared with those values, the results of marine sediments in this study have reasonable Since 24'Am is a daughter nuclide o f 2 4 1 1 ~ u , i t seemed interesting to calculate the 241Pu content in the "Bikini Ash" sample b y assuming the '41Am originally present in t h e bomb was negligible. By considering the growth of 2"Am f r o m "'Pu in the sample during the 20yr,the content of 241Puin the "Bikini Ash" is estimated to have the value of 666 t 49 dislminlrng just after the time of Pu and 45Ryr for U'Ain a r e used in these estimates. The ratio of 241Pu/239*240Puw a s calculated to be 26t3atthe time of nuclear testing. According to the data reported by debris is 2 7 2 3, almost t h e same as the present value. For sediment samples, t h e above-mentioned calculations may not b e valid because the sediments were contaminated with various debris from many other explosion tests carried out since 1946. I t is important from the environmental point of view that the growth of 2"Arii f r o m 2 4 1 P ~ should be taken into account to evaluate t h e future radioactive contamination of the environment with long life alpha-emitting By using o u r new radiochemical determination technique with '"Gd a n d %Pu tracers, the americium and plutonium were accurately determined together with the contents of these nuclides in several marine sediment samples collected near Bikini Atoll. This new technique may b e applied to the environmental americium determination in the future, and this information o n the e n - vironmental contamination with transuranium elements i n this region may be useful for the estimation of local environmental radioactivity d u e to alpha-emitting radionuclides. Ash" sample at time zero was calculated to b e 26* 3, and was almost the same with that in the "Mike" thermonuclear debris. i n 'Mike' thermonuclear device", Phys. Rev. 119, JAS4 'The Japan Society of Analytical Chemistry,

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vironment by a radiochemical procedure", Earfh Planet. Sci. Letf. 25, 361. tribution of plutonium and americium in Bikini Atoll Lagoon," Health Phys. 28, 539. fallout radionuclides in open ocean sei-...nents". Proc. IAEA Symp. Inferarfion o/ Radioarfioe Confanrinanfs wifh the Consfifuonts of [ h e mental samples". Proc. IAEA Syrtrp. Rapid methods for Measuring Radioacfiuity in the analysis of alpha radioactive actinide nuclides