Determination of photodisintegration cross sections independent of detector efficiency and photon spectrum

Abstract

For a nucleus of mass number A whose binding energy for a particle of mass X exceeds that of the nucleus with mass S≈2 X, the differential cross section σ A(γ, X) can be obtained at one photon energy when neither the detector efficiency nor the photon energy spectrum is known, provided that the cross section σ S(γ, X) is known. For example, if X is a nucleon, S is the deuteron, and if X is a triton, S is 6Li. At one specific energy the detector efficiencies and photon fluxes will cancel in the ration of the counting rates. If the relative detector efficiency and spectral shape of the photon beam are known, the comparison sets the absolute cross section scale over an extended energy region. Where efficiency and number of photons per interval are both thought to be known absolutely, the comparison point allows a check on self-consistency. When the spectral shape has been obtained from deuteron photodisintegration, secondary standards can be used if the detector efficiency is known. Alternatively the efficiency function can be checked by comparing several different nuclei. The method is applicable to photoneutron time-of-flight measurements.