Technical updates from the TNA operations program

The operation of the Thermal Neutron Analysis (TNA) Explosive Detection Systems in a number of airports throughout the world has yielded a wealth of information. These devices have been deployed to detect explosives in checked luggage before they reach the aircraft. Data from over 1 million bags have been collected, and the TNA operation has resulted in one arrest and the apprehension of illicit materials. Distributions of unusual elements, elemental and physical densities of suitcases for various sites are given. These data are critical to the estimation of the performance of new systems based on advanced X-ray or neutron techniques. Several cases of particular importance to TNA were studied. A sample application of this distribution data to the evaluation of proposed changes to the TNA is described. Optimization of the cavity structure and the neutron moderator design to reduce hydrogen backgrounds was performed via computer modeling. ((orig.))