Characterization and source term assessments of radioactive particles from Marshall Islands using non-destructive analytical techniques

Abstract

Abstract−A considerable fraction of radioactivity entering the environment from different nuclear events is associated with particles. The impact of these events can only be fully assessed where there is some knowledge about the mobility of particle bound radionuclides entering the environment. The behavior of particulate radionuclides is dependent on several factors, including the physical, chemical and redox state of the environment, the characteristics of the particles (e.g., the chemical composition, crystallinity and particle size) and on the oxidative state of radionuclides contained in the particles. Six plutonium-containing particles stemming from Runit Island soil (Marshall Islands) were characterized using non-destructive analytical and microanalytical methods. By determining the activity of 239,240 Pu and 241 Am isotopes from their gamma peaks structural information related to Pu matrix was obtained, and the source term was revealed. Composition and elemental distribution in the particles were studied with synchrotron radiation based micro X-ray fluorescence (SR-µ-XRF) spectrometry. Scanning electron microscope equipped with energy dispersive X-ray detector (SEM-EDX) and secondary ion mass spectrometer (SIMS) were used to examine particle surfaces. Based on the elemental composition the particles were divided into two groups; particles with plain Pu matrix, and particles where the plutonium is included in Si/O-rich matrix being more heterogenously distributed. All of the particles were identified as fragments of initial weapons material. As containing plutonium with low 240 Pu/ 239 Pu atomic ratio, ~2-6 %, which corresponds to weapons grade plutonium, the source term was identified to be among the safety tests conducted in the history of Runit Island. IntroductionFrom 1946 through 1958 the United States conducted a total of 65 atmospheric nuclear weapons tests on Bikini and Enewetak Atolls within the Republic of the Marshall Islands [UNSCEAR 2000;Hamilton, 2004]. The nuclear test program included air drops (4), barge detonations (35), tower detonations (13), surface detonations (10), and underwater detonations (3). The total yield for all tests conducted on Bikini and Enewetak Atolls was 109 Mt with an estimated fission yield of 53 % [UNSCEAR, 2000;Hamilton 2004]. At Bikini, the total yield was approximately 76.8 Mt with a fission yield of approximately 55 %. At Enewetak, the total and fission yields were 30.2 Mt and 49%, respectively [UNSCEAR, 2000]. A surface safety test and one additional unsuccessful detonation at Enewetak Atoll resulted in little of no fission yield [DOE, 2000].The nuclear test program in the Marshall Islands produced both global and localized forms of fallout contamination. The terrestrial and marine environments of each atoll are contaminated with a range of fission and activation products, and unfissioned nuclear materials [Hamilton, 2004] In general, a considerable fraction of radioactivity entering the environment from nuclear events such as nuclear weapons accidents, auth...

Exploring Actinide Materials Through Synchrotron Radiation Techniques

“…Richard et al also studied fluid inclusions from two quartz samples of uranium deposits by SR‐μ‐XRF and found considerable amounts of U and other elements (mainly transition metals and rare earth elements) in the fluid inclusions, which all distributed homogeneously among the samples. Jernström et al measured plutonium‐containing particles originating from Runit Island soil by SR‐μ‐XRF and found two types of Pu‐rich particles: the first type was with pure Pu matrix, and the other was particles with plutonium heterogenously included in Si/O‐rich matrix. SR‐μ‐XRF has also been used to aid in characterization and quantification of elements of concern in uranium mine tailings .…”

Isotopic analysis of single uranium and plutonium particles by chemical treatment and mass spectrometry

“…Plutonium-containing particles collected from Marshall Islands soil in the northern Marshall Islands were characterized and studied using various non-destructive analytical and microanalytical methods [11]. The results of Pu isotopic ratio measurements, 137 Cs, 241 Am/ 239 Pu and the other matrix elements were used for the conclusions about the source of the particles.…”

The Use of SIMS and SEM for the Characterization of Individual Particles with a Matrix Originating from a Nuclear Weapon

“…Although the main source of exposure to the general population is natural background radiation and the contribution from anthropogenic sources makes up only a fraction of the total radiation dose, areas exist with a significantly increased exposure rate or an enhanced risk for exposure due to releases of radionuclides into the environment. A significant part of such discharges is in the form of so-called hot particles~Eriksson, 2002; Shevchenko, 2004!, which have been released in several known events in the past, for example, the atmospheric tests of nuclear weapons at the Marshall Islands Jernström et al, 2006!, at Semipalatinsk in Kazakhstañ Zheltonozhsky et al, 2000 Maralinga and Emu in Australia, and at the Atolls of Muroroa and Fangataufa in French Polynesia~Danesi, 1998! ; accidents involving nuclear material for military and civilian use, for example, the military aircraft crashes at Palomares in 1966~Jiménez- Ramos et al, 2006!…”