Fission, spontaneous

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Property of very heavy atomic nuclei to fission without external excitation; mostly superimposed by other decay types. The half-life for spontaneous fission in the case of U-238 amounts to 8·10¹⁵ years, i.e. one nucleus per gram U-238 converts by spontaneous fission about every 2.5 minutes . (The half-life of U-238 for alpha decay, in comparison, amounts to „only“ 4.5·10⁹ years, therefore about 750,000 uranium atoms per gram U-238 convert by alpha decay per minute.) Cf-254 and Fm-256 convert almost exclusively by spontaneous fission.

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