  Thin polypropylene (CH$_2$) fibers have been used for internal experiments in
storage rings as an option for hydrogen targets. The change of the hydrogen
content due to the radiation dose applied by the circulating proton beam has
been investigated in the range $1\cdot10^6$ to $2\cdot10^8$~Gy at beam momenta
of 1.5 to 3 GeV/c by comparing the elastic pp-scattering yield to that from
inelastic p-carbon reactions. It is found that the loss of hydrogen as a
function of applied dose receives contributions from a fast and a slow
component.
