Excess of 236U in the northwest Mediterranean Sea

233U/236U signature allows to distinguish environmental emissions of civil nuclear industry from weapons fallout

“…In these cases, the 236 U/ 238 U atom ratio serves as tracer for ocean currents 5,17,18 . However, in systems affected by several contamination sources with complex water circulation processes, such as the Mediterranean Sea 19 or the Arctic Ocean 20 , the lack of a second anthropogenic U isotope is a disadvantage compared with plutonium (Pu). Isotopic ratios of two anthropogenic nuclides, such as 240 Pu/ 239 Pu, allow further insight than that provided by a single isotope concentration or its ratio to an also naturally occurring isotope like 238 U. Isotopic ratios strongly depend on the production mechanism and hence, the emission source, which allows discrimination between possible origins of the contamination 21,22 .…”

On the Quality Control for the Determination of Ultratrace-Level 236U and 233U in Environmental Samples by Accelerator Mass Spectrometry

“…For example, Greenland seawater consists of about 30% and 70% of GF-and RP-derived 236 U according to the 233 U/ 236 U atomic ratios, 30 and a relative uncertainty of 30% for 233 U will contribute a relative uncertainty of 13% for RP-derived 236 U. The reported 236 U analyses enabled the precise measurement of 236 U/ 238 U atomic ratios (within 10% of relative uncertainty) in 1 -2 L seawater samples with the lowest value of 10 - 9 17,21,22,27 and 3 -20 L with 10 -10 1,7, 15,17,19,[24][25][26][27]29,33,35,37 . Even though limited experience exists for the 233 U analyses, unavoidably large uncertainties can be expected due to its extremely low concentrations in environmental samples, restricting its application on sources discrimination.…”

“…[1][2][3][4] Besides a minor amount of naturally produced 236 U, 5 the majority of environmental 236 U was released through anthropogenic nuclear activities, including atmospheric nuclear weapon tests, 1,6-8 authorized discharges of nuclear reprocessing plants 9 and nuclear accidents [10][11][12] . The pulse injection of anthropogenic 236 U results in a wide scale of 236 U/ 238 U atomic ratios (10 -13 -10 -6 ) in the global oceanic systems (Figure 1), 1,7,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]29,30 which roughly corresponds to a range of (10 3 -10 9 ) atoms/kg for 236 U concentrations in seawater.This makes 236 U a suitable transient tracer to investigate the oceanic circulation patterns, water masses mixing, and transit time.Recent developments of the AMS technique enable the measurement and tracer application of another long-lived anthropogenic uranium isotope 233 U (t1/2 = 0.16 Myr) in the environment. 3,30,31 Different from 236 U, the only massive emission of anthropogenic 233 U occurred during the global fallout of nuclear weapons testing (GF).…”

“…[1][2][3][4] Besides a minor amount of naturally produced 236 U, 5 the majority of environmental 236 U was released through anthropogenic nuclear activities, including atmospheric nuclear weapon tests, 1,6-8 authorized discharges of nuclear reprocessing plants 9 and nuclear accidents [10][11][12] . The pulse injection of anthropogenic 236 U results in a wide scale of 236 U/ 238 U atomic ratios (10 -13 -10 -6 ) in the global oceanic systems (Figure 1), 1,7,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]29,30 which roughly corresponds to a range of (10 3 -10 9 ) atoms/kg for 236 U concentrations in seawater.…”

Accelerator Mass Spectrometry (AMS) in Radioecology

“…Villa et al 2016, on the other hand, present in these Proceedings results on 236 U in the Equatorial area of the Pacific Ocean.Also based in measurements carried out in the AMS CNA system, López-Lora et al 2016, have measured 236 U in South Atlantic water samples. 236 U/ 238 U ratios of some 10 -10 are obtained lower than those presented by Eigl et al 2016 of 10 -9 for North Atlantic samples which points to an influence in this region of a local contamination coming from the nuclear reprocessing plants.The same CNA group together with that from IAEA-Environment Laboratory at Monaco (Chamizo et al 2016b) have determined 236 U in the Northwestern Mediterranean area. In this case the 236 U/ 238 U atom ratio reached a value of 10 -9 indicating that anthropogenic 236 U dominates the whole water column.…”