Present status of the development of superconducting tunnel junctions for t
he detection of X-ra? photons and heavy ions is reported. The energy resolu
tion fur 5.9 keV X-rays was measured to be 41 eV. 58 eV. 65 eV and 129 eV:
with STJs of 20 x 20 mum(2); 100 x 100 mum(2). 200 x 200 mum(2) and 500 x 5
00 mum(2). respectively, and a model to describe the phonon-mediated ed X-r
ay signals is discussed. Direct voltage switching induced hy heavy lolls wa
s successfully observed.