Atmospheric nuclear weapon test sites and cumulative total yields at each site (indicated by symbol size) during 1945–1966²⁷. Four tests in the Pacific Ocean and three in the Atlantic Ocean are not included because of no description of accurate detonation sites²⁷. Their cumulative yields are approximately 0.11 Mt. Background map is created using Adobe Illustrator CS6 (https://www.adobe.com/).
Global fallout plutonium isotopic ratios from the 1960s are important for the use of Pu as environmental tracers. We measured the 240Pu/239Pu and 242Pu/239Pu atomic ratios of monthly atmospheric deposition samples collected in Tokyo and Akita, Japan during March 1963 to May 1966. To our knowledge, our results represent the first data measured for a...
... In another study, soil samples collected from Salzburg, Austria, exhibited 242 Pu/ 239 Pu isotope ratios of about 3.2 × 10 − 3 , which were attributed to global fallout (Steier et al., 2013). Recently, Ohtsuka et al. reported rather comparable 242 Pu/ 239 Pu isotope ratios in monthly atmospheric deposition samples collected in Tokyo (3.7 × 10 − 3 to 6.4 × 10 − 3 )and Akita (3.4 × 10 − 3 to 6.5 × 10 − 3 ), Japan, during March 1963 to May 1966 (Ohtsuka et al., 2019). 242 Pu/ 239 Pu isotope ratios ranging from 0.79 × 10 − 4 and 1.72 × 10 − 3 have been detected in soil samples collected at and near the low yield test site of Semipalatinsk-21, Kazakhstan (Beasley et al., 1998). ...
We present plutonium (Pu) and uranium (U) isotopic fingerprints (or signatures) in environmental samples collected at Bikar Atoll. Bikar is the second –most northern atoll of the Republic of the Marshall Islands, and therefore an important reference point to evaluate the extension of the regional fallout from the Pacific Proving Grounds (PPG) in Bikini and Enewetak Atolls. Previous studies have shown that regional fallout from atmospheric nuclear weapon testing (NWT) in Bikini and Enewetak has resulted in elevated levels of fallout radionuclides in this atoll. In order to optimally interpret the isotopic fingerprints, we compare our results with data obtained in eleven certified reference materials, representing different contamination sources. As well as ²³⁸Pu, ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu, ²³⁸U and ²³⁵U, this study also encompasses less commonly reported radionuclides such as ²⁴²Pu, ²⁴⁴Pu and ²³⁶U. We show the importance of combining numerous fingerprints for improved assessment of the source of a nuclear contamination. In samples from Bikar, Pu and U isotope ratios were found to vary within narrow ranges. Pu and U fingerprints suggest that regional fallout from the Castle Bravo test in March 1954 was the main source of the contamination. This was further confirmed by two different age dating approaches that estimated 1954 as the year of the contamination. We demonstrate that use of an exponential function to approximate the yield of heavy radionuclides in thermonuclear explosions with increasing mass is a valid approach for estimating the age of a contamination. We show that, if sufficient radionuclide activity concentration measurement results with low uncertainties are available, this method is robust.
... This illustrates the absence of a thermal neutron contribution in a fast breeder resulting in a reduced yield of 240 Pu relative to that of a thermal spectrum reactor. It is worthy of note that, while fallout from a detonation would also derive from a neutron spectrum harder than a thermal spectrum fission reactor, it would also have a much higher associated neutron flux, resulting in R 240/239 of a similar order to a thermal spectrum yield 3,41 , and consistent with what is observed in the average of the off-site-far data, i.e., 0.167 ± 0.005. Hence, the lower R 240/239 observed for the on-site samples in this research is consistent with the material comprising a combination of anthropogenic plutonium produced locally by a fast breeder and global fallout, on the basis that less 240 Pu is produced in a fast breeder relative to that of a thermal spectrum reactor 42 or fallout, because of the greater thermal neutron component in the former and the higher neutron flux in the latter. ...
Trace-level plutonium in the environment often comprises local and global contributions, and is usually anthropogenic in origin. Here, we report estimates of local and global contributions to trace-level plutonium in soil from a former, fast-breeder reactor site. The measured ²⁴⁰Pu/²³⁹Pu ratio is anomalously low, as per the reduced ²⁴⁰Pu yield expected in plutonium bred with fast neutrons. Anomalies in plutonium concentration and isotopic ratio suggest forensic insight into specific activities on site, such as clean-up or structural change. Local and global ²³⁹Pu contributions on-site are estimated at (34 ± 1)% and (66 ± 3)%, respectively, with mass concentrations of (183 ± 6) fg g⁻¹ and (362 ± 13) fg g⁻¹. The latter is consistent with levels at undisturbed and distant sites, (384 ± 44) fg g⁻¹, where no local contribution is expected. The ²⁴⁰Pu/²³⁹Pu ratio for site-derived material is estimated at 0.05 ± 0.04. Our study demonstrates the multi-faceted potential of trace plutonium assay to inform clean-up strategies of fast breeder legacies.
Radionuclides in the environment originating from natural (cosmogenic, primordial, and radiogenic) and anthropogenic sources are shortly reviewed. The main focus is on anthropogenic radionuclides of global fallout and from the Chernobyl accident with emphasis on pre-Fukushima ¹³⁷Cs, ⁹⁰Sr, ¹²⁹I, ³H, and ¹⁴C levels in the terrestrial and marine environments.
Plutonium (Pu) has been released in Japan by two very different types of nuclear events – the 2011 Fukushima accident and the 1945 detonation of a Pu-core weapon at Nagasaki. Here we report on the use of Accelerator Mass Spectrometry (AMS) methods to distinguish the FDNPP-accident and Nagasaki-detonation Pu from worldwide fallout in soils and biota. The FDNPP-Pu was distinct in local environmental samples through the use of highly sensitive ²⁴¹Pu/²³⁹Pu atom ratios. In contrast, other typically-used Pu measures (²⁴⁰Pu/²³⁹Pu atom ratios, activity concentrations) did not distinguish the FDNPP Pu from background in most 2016 environmental samples. Results indicate the accident contributed new Pu of ~0.4%–2% in the 0–5 cm soils, ~0.3%–3% in earthworms, and ~1%–10% in wild boar near the FDNPP. The uptake of Pu in the boar appears to be relatively uninfluenced by the glassy particle forms of fallout near the FDNPP, whereas the 134,137Cs uptake appears to be highly influenced. Near Nagasaki, the lasting legacy of Pu is greater with high percentages of Pu sourced from the 1945 detonation (~93% soils, ~88% earthworm, ~96% boar). The Pu at Nagasaki contrasts with that from the FDNPP in having proportionately higher ²³⁹Pu and was distinguished by both ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu atom ratios. However, compared with the contamination near the Chernobyl accident site, the Pu amounts at all study sites in Japan are orders of magnitude lower. The dose rates from Pu to organisms in the FDNPP and Nagasaki areas, as well as to human consumers of wild boar meat, have been only slightly elevated above background. Our data demonstrate the greater sensitivity of ²⁴¹Pu/²³⁹Pu atom ratios in tracing Pu from nuclear releases and suggest that the Nagasaki-detonation Pu will be distinguishable in the environment for much longer than the FDNPP-accident Pu.
Reference materials (RMs) are very important for method development and validation. In order to quickly and reliably select the suitable RM for validating the determination of plutonium (Pu), we reviewed the RMs of Pu and prepared extensive Pu datasets in this study. After data treatment and a series of statistical analyses, we obtained the statistical values of 238−241Pu activity and Pu isotopic ratio for RMs. The statistical value of 239+240Pu activity is consistent with the certified value, indicating these measured values are highly reliable. We anticipate that, after further independent work at different laboratories, the statistical values of the Pu isotopic ratios are very important to validate analysis methods and calibrate the mass bias for environmental Pu analysis.