Vertical profiles of Cs-137 in soil of the Matua Island ( the Central Kuril Islands, Russia) in 2017
Authors: Alexander Borisov , Ivanov Andrey , Linnik Vitaly 
Published: March 2020

&lt;p&gt;The 2011 Fukushima-Daiichi nuclear power plant (FDNNP) accident resulted in the atmospheric releases of large quantities of man-made radionuclides. According to [1], Matua Island, located at a distance of more than 1000 km from FDNPP, was also subjected to minor radioactive contamination. Matua Island, 52.6 sq.km, a recent volcano with the highest point of 1446 m a.s.l. is located in the center of the Kuril Islands Arc. Volcanic soils are formed on stratified gravelly-stony tephra more than 60 cm thick, underlain by thin layers of volcanic slags. The latest catastrophic eruption which changed the landscape of the island occurred in 2009.&lt;/p&gt;&lt;p&gt;Studies of the vertical distribution of the Cs-137 in soils were carried out on four landscape catenas. The length of the catenas from the sea shore deep into the island ranged from 700 m (maximum height a.s.l. &amp;#160;70 m) to 3.3 km (height a.s.l. &amp;#160;450 m).&lt;/p&gt;&lt;p&gt;Soil core samples were taken in &amp;#160;summer 2017 at a depth of tephra, which was located at a depth of 10 to 25 cm. Soil was sliced into separate layers with a step of 2 to 5 cm.&lt;/p&gt;&lt;p&gt;The measurement activity concentrations of the Cs-137 in the soil samples were carried out on a low-background gamma spectrometer Canberra Industries. &amp;#160;The counting time&amp;#160; was fixed not less than 24 h to ensure that the statistical measurement error is small.&lt;/p&gt;&lt;p&gt;Cs-134, the &amp;#171;Fukushima&amp;#8221; fallout marker, due to the decay, was not detected. Therefore, it is difficult to accurately assess the Cs-137 contribution from the FDNNP accident from a global fallout.&lt;/p&gt;&lt;p&gt;The vertical distribution of Cs-137 is characterized by extreme heterogeneity, which reflects both the primary fallout conditions and the landscape conditions of the likely lateral redistribution. For &amp;#1089;atena 1 with a length of 1 km and an altitude&amp;#160; of 400 m, the number of pickets (P0, P1, etc. &amp;#8211; the numbering of pickets goes downhill), the specific activity of Cs-137 (Bq/kg) and the depth of the layer (cm) are given as follows: P0-27 Bq/kg (2-4 cm); P1 - 64 Bq/kg (6-8 cm); P2 &amp;#8211; 70 Bq/kg (8-10 cm); P3 - 53 Bq/kg (4-6 cm); P4 - 15 Bq/kg (0-5 cm).&amp;#160; Similar spatial&amp;#160; heterogeneity of the specific activity of Cs-137 and its depth penetration was also found for catena 3 with a length of 1250 m and a height of 75 m (the numbering of pickets goes up the slope): P1-137 Bq/kg (17-20 cm); P2-76 Bq/kg (0-5 cm); P3 - 35 Bq/kg (0-4 cm); P4 - 43 Bq/kg (3-6 cm); P6 &amp;#8211; 24 Bq/kg (5-10 cm).&lt;/p&gt;&lt;p&gt;The distribution of Cs-137 in individual soil layers was used to evaluate the empirically found shapes of the vertical profiles of radionuclide concentration. Cs-137 is believed here to be a&amp;#160; very valuable tracer&amp;#160; that&amp;#160; can be used to test&amp;#160; variability of vertical geochemical migration in Matua&amp;#160; landscapes.&lt;/p&gt;&lt;p&gt;[1]. Ramzaev V.P., Barkovsky A.N., Gromov A.V., Ivanov S.A., Kaduka M.V. Fukushima fallout in Sakhalin Region, Russia, part 1: &lt;sup&gt;137&lt;/sup&gt;Cs and &lt;sup&gt;134&lt;/sup&gt;Cs in grassland soils. Radiation Hygiene, 2018, Vol. 11, No. 1, pp. 25-42.&lt;/p&gt;