Proton-induced degradation of VUV transmission of LiF and MgF(2).

Proton-induced degradation of vacuum ultraviolet (VUV) transmittance of LiF and MgF(2) was measured for 85- and 600-MeV protons for a fluence up to 2.8 x 10(13)p/cm(2). Transmittances were measured from 105 to 210 nm. When the irradiation level for a given material is expressed in terms of absorbed energy per unit of volume of crystal, 85- and 600-MeV protons produce the same degradation. MgF(2) is substantially more radiation resistant than LiF in the VUV. Irradiation of LiF with 1.8 x 10(13)p/cm(2) at 85 MeV changed the transmittance of the hydrogen Lyman-alpha line at 121.6 nm from 55 to 23%. The corresponding change for MgF(2) was from 52 to 42% for 2.8 x 10(13)p/cm(2).