Abstract: A new process for marking currency to permit easy and positive authentication at a later date comprising exposing a small region of the currency to bombardment by high energy neutrons for a short period, treating the exposed small region with a chemical reagent which reacts with the treated area to form tiny holes which can later be used for authentication. Also provide is a method for authentication which comprises exposing the marked currency to monochromatic X-rays, allowing the transmitted beam to impinge upon a fluorescent screen which will show shiny dots where the beam has reached the screen, said dots corresponding to the tiny holes in the marked currency.

Abstract: Structural failures, as in metal aircraft structures, are rapidly detected and measured by use of a new detection system comprising a thin film adhesively bonded to the metal structural surface to be monitored, said film containing a plurality of thin continuous strips which are adapted to be broken when a crack appears under the strips, said strips being substantially parallel but insulated from each other and the metal structural surface and arranged in a pattern such that there is frequent change in direction of the strips as in a zig-zag or rectangular pattern, each of said strips constituting a separate circuit joined to an electric power source and a sensing and recording means capable of detecting and recording any circuit failure caused by disruption of the metal strip, said disruption being caused by the formation of a crack under the said strip.