Plutonium isotopes and 241Am in the atmosphere of Lithuania: A comparison of different source terms

Sources of plutonium in the atmosphere and stratosphere-troposphere mixing

“…Plutonium isotopes released from these accidents were characterized by higher 238 Pu/ 239,240 Pu, 241 Pu/ 239,240 Pu activity ratios and higher 240 Pu/ 239 Pu atom ratios than those ratios derived from nuclear tests6. The 238 Pu/ 239,240 Pu, 241 Pu/ 239,240 Pu activity ratios and 240 Pu/ 239 Pu atom ratio for the Chernobyl accident were 0.5, 85, and 0.41, respectively173031, while for the Fukushima accident these ratios were 1.2, 108, and 0.30–33, respectively3233.…”

“…The 239,240 Pu levels observed in the lower stratosphere during 2007–2008 were by about two orders of magnitude larger than those observed in surface air61631. The 239,240 Pu concentrations are expressed per standard cubic meter (15 °C, 101.325 kPa), however, the pressure at 10 km of altitude is about one order of magnitude lower than that in ground-level air.…”

“…Further, plutonium isotopes results obtained for surface air at mid-latitude region of the Northern Hemisphere were also included in Fig. 1: New York (USA, 40° 45′N, 74° 00′W), Beaverton Oregon (USA, 45° 32′N, 122° 53′W)34, Tsukuba (Japan, 36° 03′N, 140° 08′E)3637, Prague (Czech Republic, 50° 04′N, 14° 26′E)7, Braunschweig (Germany, 52° 17′N, 10° 33′E)38, Vilnius (Lithuania, 54° 42′N, 25° 30′E)6 and Milford Haven (UK, 51° 43′N, 5° 02′W)39. All plutonium isotope concentrations in surface air were determined at monthly or quarterly basis.…”

“…The plutonium concentrations in surface air were as follows: <2.5 to 9.5 nBq m −3 during the period from 1986 to 1989 (as quarterly means) at Milford Haven39; 0.53 to 8.1 nBq m −3 during the period from 1987 to 1998 (as annual means) at Neuherberg41; 0.39 to 4.5 nBq m −3 during the period from 1990 to 2003 (as quarterly means) at Braunschweig38; 0.53 to 217 nBq m −3 during the period from 1997 to 2006 (as quarterly means) at Prague7; 2.2 to 49 nBq m −3 during the period from 2005 to 2006 (as monthly means) at Vilnius (54° 42′N, 25° 30′E)6; and 1.7 to 15 nBq m −3 during the period from 2001 to 2002 (as monthly means) at Seville (37° 22′N, 5° 59′W)42. The results suggest that most of the 239,240 Pu concentrations in surface air during the period from 1986 to 2006 were in the range of 1 to 10 nBq m −3 in the mid-latitude region of the Northern Hemisphere, except of specific events such as a local contamination7, Chernobyl accident6, and dust events45. The 239,240 Pu concentrations in surface air did not show decreasing rates, and similar trends were observed for the 239,240 Pu deposition441.…”

“…The typical spring maxima in the ground-level air caused by the stratosphere-troposphere inputs were observed till the 1990s. Later, the observed radionuclide variations have been mostly due to their resuspension from soil245678. It has been believed therefore that there have not been significant amounts of these radionuclides left in the stratosphere because most of the radionuclides derived from the atmospheric nuclear testing conducted from 1945 to 1980 had already been transported to the lower troposphere and deposited on land and ocean surface29.…”