[en] A transient absorption spectrum was measured in single crystals of KAl(SO₄)₂x12H₂O by means of pulse radiolysis at ambient temperature. The decay can be described by two exponentials with half-lives of about 100 μs and 2 ms. The transient is attributed to excess-electrons, as it is suppressed in crystals doped with Cd²⁺ ions. (author)