Measurement of dose components in an n-γ field

The classical method for the measurement of the neutron and γ-ray dose components in a mixed n-γ field involves the comparison of the response of a hydrogenous ionization chamber with that of a non-hydrogenous one. A knowledge of the neutron and γ-ray sensitivities of the two chambers then allows the solution of two simultaneous linear equations to obtain separately the neutron and γ-rays absorbed doses. In practice the major source of error in the application of this method has been our inability to determine an accurate value of the neutron sensitivity of the γ-ray detector. We have originated a procedure for the precise measurement of the n/γ sensitivity ratio for any gamma-ray dosimeter, making use of the neutron beam of interest. The γ-ray dose component in the beam is simultaneously determined with greater accuracy than formerly achievable. The key feature of the technique is the use of a lead filter to remove most of the γ rays from the beam while passing the neutrons. The technique as demonstrated involves six measurements made at a single point in the beam; three with a TE-gas filled TE plastic chamber, and three with an air-filled graphite chamber. With each of the two chambers a measurement is made in the unfiltered beam, in the beam filtered by a suitable thickness of lead, and in the residual field at the same point with the beam port completely plugged. It is then possible to write six simultaneous linear equations which can be simply solved to obtain the quantities of interest