The effects of the atomic bombs at Hiroshima and Nagasaki : report of the British mission to Japan.

Date:
1946
Catalogue details

Licence: Public Domain Mark

Credit: The effects of the atomic bombs at Hiroshima and Nagasaki : report of the British mission to Japan. Source: Wellcome Collection.

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    50. The Japanese commonly employed two kinds of roof tiles, on both of which the heat flash raised characteristic bubbles. These were largest where the radiation was most intense, that is, either where the tile was closest to the explosion or, as in photograph 24, where it faced the radiation squarely. This effect will serve to give independent estimates of ground temperatures. It extended nearly 14 times as far in Nagasaki as in Hiroshima. 51. Among miscellaneous materials affected by heat radiation were the bronze of the ceremonial animals guarding a Shinto temple, immediately below the explosion in Hiroshima ; the asphalt surface of roads, which retained the “* shadows ”’ of those who had walked there at the instant of the explosion, objects of macabre interest and pilgrimage for visitors ; and concrete and mortar ' renderings of buildings, which had flushed to various shades of pink. 52. As photograph 22 shows, unpainted wood displayed the most striking flashburns. These ranged from a just perceptible deepening of the natural colour, which could be observed on telegraph poles at nearly two miles from the centre of damage, through progressive scorching to complete superficial charring at small distances, where isolated timbers had sometimes been fired. Painted wood was also scorched, with no discernible selection of colours. In all timbers, the soft portions of the annual rings were most deeply charred. 53. Some paints were also directly affected, the most sensitive being the black coating on gas holders, where, as photograph 23 shows, exposure to heat radiation gave a polished appearance to the original dull and sooty finish. 54. In all these cases, “‘ shadows ’’ were cast by intervening objects where they shielded a part of the otherwise exposed surface from the direct heat radiation. In the shadow, the surface retained its original state ; outside it, across a more or less sharply defined boundary, it was scorched. When neither the shielding object nor the scorched surface had moved, as in photograph 23, it was therefore possible to determine the direction from which the radiation had come. A number of such determinations then served to fix the position of the explosion. This procedure had already been used by the Japanese and others, and there was reasonable agreement between the determinations. 55. Where shadows were susceptible to precise measurement, for example the shadows of vertical or horizontal bars, they were usually found to be narrower than the shielding obstruction. In particular, there could be observed the striking phenomenon of the complete disappearance of the shadows of narrow objects at sufficient distances from the scorched surface. For example, on a bridge in Hiroshima the lowest of three equal and parallel sets of bars had cast a well-defined shadow, and the middle a perceptible one, but the highest none. The main cause of this effect was probably the finite size of the radiating fire ball. 56. There were cases where a clump of grass or the leaf of a tree had cast a sharp shadow on otherwise scorched wood. Therefore the most intense flash from the ball of fire had ended in a time less than that required to shrivel vegetation. On the other hand, since direct injuries to the eye-ball were not common, the heat radiation may be presumed to have required a perceptible time to build up to its maximum intensity, during which some people had closed their eyes.