THE MATHEMATICAL MODEL FOR DECAY CURVE OF THE NUCLEI-DELAYED NEUTRON PRECURSORS IN EXPERIMENT AT A PULSED ELECTRON LINEAR ACCELERATOR

The importance of the use of delayed neutrons in applied nuclear physics is widely recognized [1]. Among the applications are the control and determination of small amounts of fissile elements (uranium and transuranium elements) in solid and liquid radioactive wastes, in spent fuel elements, and also the measurements of nuclear constants used in reactor engineering (relative yield and half-life period of certain groups of delayed neutrons). To determine the nuclear-physical constants, the world practice makes use of the fission processes of uranium, plutonium and other nuclei in neutron/gamma-ray beams. The beams may be both pulsed and continuous. The neutron/gamma-ray beams can be generated in different machines, including electron accelerators, through the use of targets-converters. Work [2] can serve an example of the use of a accelerator of continuous action . The electrostatic accelerator was used there to obtain some nuclear-physical constants necessary for the development of nuclear reactor engineering. The research techniques for investigating the composition of transuranium wastes with the use of pulsed reactors are well developed in France [3]. Though the pulse techniques are more complicated as compared to the continuous methods, yet they have certain advantages. In the pulse technique, delayed neutrons can be registered by two methods during one measuring run. In the first method, delayed neutrons are registered between the machine pulses in a certain time window chosen so as to reduce the background. In the second method, the sample is saturated with nuclei-delayed neutron precursors. Then the beam is switched off and the decay curve is measured. With machines of continuous action, only the measurement of the decay curve is possible. Since the delayed neutron yield registered between the pulses and the decay curve are described by the same parameters, the pulse technique is more informative, because it provides a joint analysis of the data obtained by the two measuring methods. In our papers [4-9], we have developed the methods for determining fissile elements with the use of the pulsed electron accelerator. These methods can find their application in different countries (e.g., France, Russia, etc.), where nuclear engineering is developing. Paper [8] was concerned with the first method of delayed neutron registration (between the accelerator pulses). The present work is devoted to the second method (decay curve measurement).