ACCIDENTAL FAST-NEUTRON DOSIMETRY BY MEANS OF PLASTIC IDENTITY CARDS

Identity cards of high security against falsification are often composed of polymeric compounds and a paper-like inlay, containing the identifying information. This system may be considered as a fast neutron detector when certain boundary conditions, especially concerning the polymer are fulfilled. The track recording properties of the plastic envelop of a widely used identity card was investigated. Recoil tracks induced by fast neutrons could be revealed with electrochemical etching in 5N NaOH in a thin cover, which is mounted on a thick etch-resistant base. The etching parameters (etchant normality, temperature, time, field strength, frequency) were optimized to achieve maximum neutron sensitivity. The response for Cf-neutrons is about one per cent of that of the widely used CR-39 track detector material. A possible use of the investigated identity card as an etch track detector in accidental neutron dosimetry is discussed.