There were two sources of ionizing irradiation after the atomic bombings of Hiroshima and Nagasaki: (1) initial gamma-neutron irradiation at the moment of detonation and (2) residual radioactivity. Residual radioactivity consisted of two components: radioactive fallout containing fission products, including radioactive fissile materials from nuclear device, and neutron-activated radioisotopes from materials on the ground. The dosimetry systems DS86 and DS02 were mainly devoted to the assessment of initial radiation exposure to neutrons and gamma rays, while only brief considerations were given for the estimation of doses caused by residual radiation exposure. Currently, estimation of internal exposure of atomic bomb survivors due to dispersed radioactivity and neutron-activated radioisotopes from materials on the ground is a matter of some interest, in Japan. The main neutron-activated radionuclides in soil dust were Na,Al, Si,P, Cl,K, Ca,Sc, Mn,Fe, Co, andCs. The radionuclide Mn (T = 2.58 h) is known as one of the dominant beta- and gamma emitters during the first few hours after neutron irradiation of soil and other materials on ground, dispersed in the form of dust after a nuclear explosion in the atmosphere. To investigate the peculiarities of biological effects of internal exposure to Mn in comparison with external gamma irradiation, a dedicated experiment with Wistar rats exposed to neutron-activatedMn dioxide powder was performed recently by Shichijo and coworkers. The dosimetry required for this experiment is described here. Assessment of internal radiation doses was performed on the basis of measured Mn activity in the organs and tissues of the rats and of absorbed fractions of internal exposure to photons and electrons calculated with the MCNP-4C Monte Carlo using a mathematical rat phantom. The first results of this international multicenter study show that the internal irradiation due to incorporatedMn powder is highly inhomogeneous, and that the most irradiated organs of the experimental animals are: large intestine, small intestine, stomach, and lungs. Accumulated absorbed organ doses were 1.65, 1.33, 0.24, 0.10 Gy for large intestine, small intestine, stomach, and lungs, respectively. Other organs were irradiated at lower dose levels. These results will be useful for interpretation of the biological effects of internal exposure of experimental rats to powdered Mn as observed by Shichijo and coworkers.

No abstract

При ядерных испытаниях в нижних слоях атмосферы, а также при атомной бомбардировке, в результате нейтронной активации химических элементов в составе почвы образуются бета-и гамма-излучающие радионуклиды. Радионуклид 56 Mn (T1/2=2,58 ч) -один из основных ней-тронно-активированных бета-излучателей в течение первых часов после нейтронной актива-ции частиц почвенной пыли, поднявшейся в момент ядерного взрыва. Эффекты облучения остаточной радиоактивностью, образовавшейся в результате ядерных взрывов, являются предметом обсуждения и исследований последствий ядерных испытаний и атомных бомбар-дировок. Экспериментальное моделирование облучения лабораторных животных остаточной радиоактивностью в пылевых частицах почвы можно осуществить с использованием ней-тронно-активированного 56 Mn в виде порошка. Нейтронная активация порошкообразного MnO2 проведена на ядерном реакторе ИВГ.1М (экспериментальная установка «Байкал-1», Курчатов, Казахстан) при флюенсе нейтронов 410 14 н/см 2 . Полученный активированный по-рошок с 56 Mn был распылён пневматической системой над экспериментальными животными (крысы линии Вистар), которые находились в специальном боксе. Начальная активность рас-пылённого порошка была равна 2,7410 8 Бк. Облучение проведено в двух вариантах -в пер-вом из них в боксе имелся только воздушный фильтр для обеспечения дыхания животных. Во втором варианте была осуществлена принудительная вентиляция бокса. После распыле-ния порошка было выполнено измерение активности

No abstract

Changes in the structure and the tungsten surface erosion by hydrogen plasma irradiation are studied in the article. It is shown that the change in the surface topography as a result of the development of the non-homogeneous surface etching is observed after surface irradiation. Metallographic analysis showed that the degree of relief is low in comparison with tungsten sample irradiated at T=700°C by tungsten samples irradiation at T=1000°C and 1500°C. However, these samples have small cracks, while the temperature increases the size and number of cracks also increases. It is determined, that the surface roughness varies depending on the irradiation temperature after hydrogen plasma exposure. The greatest increase in the roughness occurs in samples irradiated at T=1500°C, which is associated with the formation of small cracks in the surface layer. It is shown that a degree of surface erosion is increased with increase of the target temperature and the ion energy. Appreciable tungsten erosion due to irradiation of the plasma flow, plasma simulating stationary mode occurs only at relatively high temperatures of the target.