Patent Number: 
Section: description

FIG. 1 shows extremely schematically an analysis system 1 which essentially comprises four components: a neutron source 3, a xcex3 radiation detector 4 with evaluation electronics 5, shielding devices 9 and 10. Retaining and adjusting devices 6, 7, 12, and 13 have been left out of FIG. 1 for simplicity""s sake. Neutron source 3 is designed as a neutron generator in which a deuteron beam hits a deuterium-containing target 8, where it releases neutrons which are emitted from the target, essentially isotropically, with an energy of approx. 2.5 MeV. Due to the use of deuterium instead of the otherwise usual tritium, neutron source 3 contains no radioactive material. The emitted neutrons penetrate case 22 of an object 2 and are scattered inelastically by the atomic nuclei inside object 2 or, possibly after several scattering processes, absorbed. In both cases the atomic nuclei concerned emit characteristic xcex3 radiation in the range between 100 keV and approx. 11 MeV, which is detected by a xcex3 detector 4 (e.g. HPGe). Detector 4 is thermally coupled to a cooling system 11, which keeps it at approximately the temperature of liquid nitrogen. To keep direct xcex3 radiation or neutron radiation away from detector 4, shields 9 and 10 are positioned between source 3 and detector 4. They are made of tungsten blocks 9, which surround cadmium plates 10. Downline of detector 4 there is an electronic measurement and evaluation unit 5, which processes the signal received from detector 4 by energy dispersion turning them into a spectrum. Due to the use of fast amplifiers and ADC, counting losses are kept to a minimum. Electronic unit 5 can also include an evaluation computer which can then also control the pulse sequences of neutron generator 3. However, as an alternative, a portable (laptop) computer can be used at some distance from analyzer 1. FIG. 2 shows a schematic diagram of the geometric arrangement of the components of analyzer 1. Neutron generator 3, detector 4 and a holder 7 for test object 2 are attached to a common frame 6. Adjusting devices 12 and 13 ensure that neutron source 3 and the detector 4 can be moved along several axes relative to object 2. This adjustment option permits optimization of the geometry of the arrangement with regard to signal strength and stray radiation. In addition, it can be adapted to different objects 2. Optionally, parts of shields 9 and 10 can also be adjustable or can be replaceable. Apart from the preferred materials tungsten and cadmium, lead and 6Li or a combination of polyethylene and boron can be used, for instance. Parts of the common frame 6, electronics unit 5 and cooling system 11 are accommodated in a housing 14. The number of nuclear reactions of an element depends on the neutron flux, the interaction cross sections of the element atomic nuclei and the concentrations in the substance being investigated. The interaction cross sections differ very much, not only from element to element, they also depend considerably on the neutron energy. Due to the large number of different interactions, mutual influencing and disturbances occur. A solution to the problem is the pulsed operation of the neutron generator and the recording of the xcex3 spectra in measurement windows during and after pulsed excitation. FIG. 3 shows a schematic representation of the measuring principle. The upper part shows a neutron pulse 100 between relative times 0 and t1, which is repeated periodically. Typical pulse lengths are in the region of several microseconds and the repetition times are a few milliseconds. The lower part shows the measurement windows 101 and 102, during which signals from the detector can be recorded. The first detection window 101 in the illustrated cycle coincides temporally with neutron pulse 100 in each case. Generally speaking, there is at least one temporal overlap range between time windows 100 and 101. The first measurement interval 101 is followed by one or more further measurement windows 102, which do not overlap temporally with neutron pulse 100. In the first measurement interval 101 it is chiefly xcex3 quanta which are detected due to inelastic neutron scattering. During the subsequent one 102 they are essentially detected by neutron capture when the neutron concerned has already been scattered inelastically. The energy windows for the respective xcex3 radiation to be detected can be selected accordingly, particularly if the presence of certain substances has to be specifically confirmed. FIG. 4 shows the spectrum of the mustard gas simulation substance obtained in this way and the characteristic xcex3 lines of hydrogen, sulfur and chlorine (2) which are identified by the identification software stored in the computer. The upper spectrum stems from the first measurement window 101 and is based on inelastic neutron scattering on sulfur nuclei and the lower one is from a further one 102. It is based on neutron capture by chlorine nuclei with subsequent emission of two characteristic lines. The wall thickness of the iron container 22 was 15 mm. In FIGS. 5 and 6, the characteristic peaks of arsenic (2) for lewisite (simulation mixture) and phosphor and fluorine (2) from sarin (simulation mixture) were identified, each in the first detection window 101. Here the wall thickness of the container was 10 mm steel in each case. These examples demonstrate in which way substance detection takes place. The presence or absence of key elements leads to typical patterns in the xcex3 spectrum. By analyzing certain energy regions of the xcex3 spectra the software can decide which substance is in the container. On the PC monitor, a graph shows the result of measurement and analytical calculations (FIG. 7). For each key element a bar is displayed which, when a threshold is exceeded, indicates that the element was detected. These identified elements are indicated on the top lines of the graph. At the same time, the substance determined thereby is stated. A special symbol at the top right-hand corner gives a warning if a chemical warfare agent was detected. Evaluation of the xcex3 spectra and indication of the results takes place during measurement. The data can be saved and therefore analysis can also be performed at any time after the current measurement.