The production and distribution of H atoms under UV photolysis of HI in a Xe matrix is studied. Our experiments indicate that H atoms do not migrate extensive distances during primary photolysis and the resulting spatial distribution is quite local. After the primary photolysis, H atoms can be further distributed to larger distances via radiation-induced secondary (hidden) processes, HXeI and Xe2H+ being possible intermediates in these processes. The amount of H atoms produced in the photolysis is comparable to the amount of I atoms, and the loss channels are minor.