TEPC MEASUREMENTS WITH THE VARIANCE COVARIANCE METHOD ON BOARD AIRCRAFT

A portable instrument based on the variance-covariance method is descr ibed. It consists of two TEPC detectors, which are connected to electr ometers. The electric current and its variance as well as the covarian ce between the two currents are used to determine the dose and the qua lity factor. The paper gives the essential relations from which the qu antities are calculated and presents the main sources of uncertainties . The instrument has been used on board an aircraft at 11 km height fo r measurement of the ambient dose equivalent rate and the average qual ity factor. After normalisation to a reference neutron field at CERN t he ambient dose equivalent rate became (4.5 +/- 1.0) mu Sv.h(-1). For the normalisation it wits important to have an accurate estimate of th e low LET dose fraction.