[Neutron pollution in roentgen beams from electron accelerators]

The neutron dose was measured in X-ray beams with a limiting energy of 8 to 45 MeV and in 42 MeV electrons (10 X 10 cm2) from several electron accelerators (betatrons, linear accelerators, microtron). The measurements were taken with activation probes and nuclear films of polycarbonate coated with 0,5 mm Cd. On a 42 MeV betatron, the neutron spectrum, the density of neutron flow and the neutron dose of the central ray were evaluated in a paraffin phantom by means of seven threshold value reactions. The neutron spectrum showed only a small dependence on depth. The neutron equivalent dose (with Q approximately equal to 10) was 13 mSv at the surface per Gy of the absorbed dose of 42 MeV X-rays in the dose maximum. The neutron dose contribution to the dose maximum was only a little higher and showed a curve resembling to the depth dose curve of X-radiation. In case of 42 MeV electrons, the neutron equivalent dose was 0,8 mSv per Gy of the electron dose at the surface of the phantom. The measurements taken by means of nuclear films showed a monotonous increase of the equivalent dose contribution of fast neutrons from 0,8 mSv in case of 8 MeV to 15 mSv in case of 45 MeV X-rays per Gy of the primary radiation dose in the dose maximum. The increase became lower above 25 MeV and was not dependent on the field size or on measurements with or without phantom.