## Abstract

Investigations similar to those described in parts I and II for ordinary water have been made on D$_2$O. For tritium $\beta$-particles the derived yields are $G_{\mathrm{D}} = 3\cdot34\pm0\cdot03, G_{\mathrm{OD}} = 2\cdot26\pm0\cdot1, G_{\mathrm{D}_2\mathrm{O}_2} = 0\cdot81_5\pm 0\cdot02,\\ G_{\mathrm{D}_2} = 0.27_5\pm0.08_5\, \text{and}\, G_{-\mathrm{D}_2\mathrm{O}} = 3\cdot89\pm0\cdot14.$ Observed yields $G(Ce^{3+})^{\mathrm{T}1^+} = 7\cdot50\pm0.5, G(Fe^{3+})^{-\mathrm{O}_2} = 7\cdot15\pm0\cdot15,\\ G(\mathrm{D}_2)^{0\cdot1\mathrm{N}} = 0\cdot61\pm0\cdot02 \text{and} G(\mathrm{D}_2\mathrm{O}_2)^{\mathrm{O}_2}_i = 1\cdot02\pm0\cdot1$ are close to expected values. For polonium $\alpha$-particles of 3$\cdot$0 and 1$\cdot$6 MeV energy respectively the yields are G(Fe$^{3+}$) = 6$\cdot$20 and 4$\cdot$27, G(Ce$^{3+}) = 3\cdot$20 and 2$\cdot$68, G(Ce$^{3+})^{\mathrm{T}1+}$ = 3$\cdot$50 and 2$\cdot$85, and hence G$_{\mathrm{D}}$+G$_{\mathrm{DO}_2}$ = 1$\cdot$35 and 0$\cdot$71, G$_{\mathrm{OD}}$ = 0$\cdot$15 and 0$\cdot$085, G$_{\mathrm{D}_2\mathrm{O}_2}$ = 1$\cdot$0 and 1$\cdot$03; G(D$_2O_2)^\mathrm{O}_2$ for 1$\cdot$6 MeV $\alpha$-particles is 1$\cdot$24. The isotope effect thus extends up to the highest accessible l.e.t. and in fact increases slightly, which is to be expected if it is caused by a more widespread distribution of D as compared with H atoms. Striking confirmation of the more widespread distribution of D is afforded by the fact that in deaerated tritiated solutions almost 100% of the available D atoms react with ferrous ion under conditions where only 60% of the available H atoms react.

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