Today, nuclear reactors are widely used as a source of high-density neutron flux in physical research, production of radioactive isotopes, radiation chemistry, and testing of electronic products. This requires the development of tools and methods that would ensure accurate and reliable measurement of neutron field characteristics directly in the core of nuclear reactors. At present, activation detectors made of various metals are most commonly used for such measurements. These methods are labor-intensive, require complex equipment, and do not cover the required range of fast neutron flux density monitoring.
Scientists at Tomsk Polytechnic University have proposed a simple method for measuring the fluence of fast and thermal neutrons using detectors made of monocrystalline silicon. It was developed based on the technology of nuclear doping of silicon used at TPU Research Nuclear Reactor, a process that allows to obtain semiconductor silicon with tailored electrophysical properties. The principle of operation of such detectors is based on monitoring the changes in the electrophysical parameters of silicon under the influence of neutrons.
The detectors developed at TPU are on a par with conventional activation methods in terms of measurement accuracy. They make it possible to determine the absolute values of thermal neutron flux density in nuclear facilities operating in the 1014-1018 cm-2 range. In addition, such detectors are capable of infinite data storage, making the obtained measurements available at any time.Fast neutrons cause complex radiation defects in silicon, reducing its conductivity. The change in conductivity is linearly related to the fluence of fast neutrons. This is the basis of fast neutron detection. A single silicon crystal is used to change the fluence of thermal neutrons. In this case thermal neutrons affect the electrical resistivity of silicon, i.e. the effect of its doping occurs. Under the influence of thermal neutrons, a stable isotope phosphorus-31, which is a donor impurity, is formed in monocrystalline silicon from the atoms of the natural isotope silicon-30. The concentration of phosphorus is proportional to fluence and thermal neutron flux density,
"Silicon detectors can also serve as tracking detectors. They are currently used at the TPU Research Nuclear Reactor to monitor technological processes for producing radiopharmaceuticals, radioisotopes, nuclear silicon doping, as well as for research purposes. The detectors are protected by four patents of the Russian Federation," Valery Varlachev notes.
At this stage of the research, scientists are studying the changes in the electrophysical characteristics of time under the influence of neutrons of different energies. The resulting data will make it possible to implement the detectors to monitor the fast neutron field during cyclotron radiotherapy.