Automatic calibration of the spectrometric channels in a device for detecting explosives

Abstract

The calibration of the energy scale of a device which is a spectrometer and is to be used for detecting explosives in various objects (baggage of airline passengers, mail, briefcases, cases, and others) is examined. The work is based on the method of neutron-radiation analysis. In the present case the calibration is of fundmental importance because the nitrogen sensitivity of the device is low. A brief description of a working model, the basic characteristics, the background spectrum of capture radiation with a sample of nitrogen-containing substance, and an example of a calibration curve are presented. The method of check sums and its advantages are examined. It is shown that it can be used in setups for detecting explosives.Today there are various methods for detecting explosives. Operational systems have been developed in our country and abroad on the basis of these methods [4][5][6][7]. Specifically, neutron-radiation analysis is used to detect explosives according to the elemental composition. This method is well known and is used successfully in various branches of science and technology [1-3], including searching for explosives. Analysis of the operation of the setups using various methods of detection [6][7][8] shows that in most cases it is difficult to satisfy all requirements which a real setup must satisfy. We note that from the standpoint of use in practice, irrespective of the method of detection, the reliability of the setup, simplicity of operation, and accessibility for repair are important. Application of the Method of Neutron-Radiation Analysis for Detecting Explosives.It is well known that the method of neutron-radiation analysis is based on irradiation of an object by a flux of thermal neutrons and detecting the spectrum of the capture γ radiation using spectrometric detectors. Since the nitrogen content in most explosives widely used today is 25% [7], the detection of a high nitrogen concentration in an object being inspected could indicate the presence of explosives in it. The difference of the spectrum of capture radiation of nitrogen from the spectra of other elements is that nitrogen contains a 10.83 MeV γ-ray line [1], which makes it possible to avoid the difficulties associated with complete interpretation of the spectrum of the object being inspected. The main requirement for the setup is detection with a prescribed probability of a definite amount of explosive in the shortest possible time time. The procedure should be conducted automatically to avoid any influence of a subjective factor on decision making. Given the presence of modern personal computers, the time required to process the information and make a decision is negligible compared with the total inspection time. Consequently, complicating the algorithm in exchange for increasing the size of the instrumental part of the system is justified, since doing so does not increase the inspection time and, aside from decreasing the cost of the system, makes it possible to satisfy the requirement of higher reliability.