Feasibility study on an active neutron dosemeter based on carbon activation for the linear collider TESLA

The linear collider TESLA will be operated with a radio frequency (rf) pulse length of almost 1 ms at a repetition rate not higher than 5 Hz. From the point of dosimetry 1 ms of radiation is followed by at least 200 ms rest. The measurement of neutron fluences for radiation protection of persons behind the shielding and that of the electronics inside the tunnel is desirable. The time structure of the radiation opens up the opportunity to use methods where the information is released delayed to the rf-pulse such as activation methods. Therefore an active dosemeter on the basis of a simple plastic scintillator is proposed which uses the activation reaction C-12(n,p)B-12 due to neutrons above 13 MeV. The subsequent beta decay of B-12 with a half-life of 20 ms leads to an exponential signal pattern fight after the rf-pulse. Thermal neutrons also appear in the time spectrum with a lifetime of less than 2 ms; clearly separated from the B-12 decay pattern as well as from the prompt peak. These three indications allow the setting-up of a dose equivalent for persons and a neutron displacement equivalent for electronics. Furthermore the dosemeter could be applied as a beam loss monitor capable of separating dark current and beam.