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The fragment mass and energy distributions have been measured for fission of 213At, zlZPo, 21~ 2~ 2~ 2~ 2~ 2~ and /~in (e,f) and (p,f) reactions.The yield of the asymmetric component has been found to decrease with decreasing Z and N of the fissile nucleus and vanish at 2~ The analysis has shown the two main fission modes (symmetric and asymmetric) to be determined by the two distinct valleys in the deformation potential energy, which had been theoretically predicted by Pashkevich. The boundaries of validity of the hypothesis of two distinct fission modes have been estimated at 200~

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The heights of the symmetric and asymmetric fission barriers have been found to be different for 213At. The difference accounts for the anomalous energy dependence of the symmetric to asymmetric yield ratio and confirms theoretical predictions on the occurrence of distinct valleys in the structure of the fission barrier in the pre-actinide region.