Raporty IFJ PAN (IFJ PAN Reports)

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Beryllium neutron activation counter for pulsed D-D fusion sources
(Institute of Nuclear Physics Polish Academy of Sciences, 2013) Bieńkowska, Barbara; Prokopowicz, Rafał; Scholz, Marek
The fusion reaction occurring in DD plasma is followed by emission of 2.45 MeV neutrons, which carry out information about fusion reaction rate and plasma parameters and properties as well. Neutron activation of beryllium has been chosen for detection of DD fusion neutrons. The cross-section for reaction 9Be (n, α) 6He has a useful threshold near 1 MeV, which means that undesirable multiply-scattered neutrons do not undergo that reaction and therefore are not recorded. The product of the reaction, 6He, decays with half-life T1/2 = 0.807 s emitting β– particles which are easy to measure. Large area gas sealed proportional detector has been chosen as a counter of β– particles which leave activated beryllium plate. The plate with optimized dimensions adjoins the proportional counter entrance window. Such set-up is also equipped with appropriate electronic components and forms beryllium neutron activation counter. The density of neutron flux on beryllium plate can be determined from the number of counts. Therefore, a proper calibration procedure needs to be performed to establish such a relation. The measurements with the use of known β– source have been done. In order to determine the detector response function such experiment has been modelled by means of MCNP5 – the Monte Carlo transport code. It has allowed a proper application of results of the transport calculations of β– particles emitted from the radioactive 6He and reaching the proportional detector active volume. In order to test the counter system and measuring procedure a number of experiments have been performed on PF-6, PF-1000 and PF-4 devices. The experimental conditions have been simulated by means of MCNP5. The correctness of simulation outcome have been proved by measurements with known radioactive neutron source. The results of the DD fusion neutrons measurements have been compared with other neutron diagnostics.
Detection of delayed neutrons from neutron activation of fissionable substance samples. Monte Carlo modelling of response of the DET-12 device
(Institute of Nuclear Physics Polish Academy of Sciences, 2013) Tracz, Grzegorz; Bieńkowska, Barbara; Drozdowicz, Krzysztof
Activation of fissionable elements by neutrons has been considered as a possible diagnostics of D-D and D-T fusion plasma. Fission caused by fusion neutrons leads up to emission of secondary neutrons: prompt and delayed. Proper interpretation of the time decay of delayed neutrons enables an assessment of the parameters of the primary neutron flux inducing fission. Monte Carlo calculations have been carried out by means of the MCNP code in order to elaborate the method considered. Three nuclides: pure 235U, 238U and 232Th, and additionally sintered UO2 have been selected as possible materials for the sample to be irradiated. Four energies of neutrons irradiating samples have been chosen: thermal, fast and two high ones. Computations have been accomplished for two variants: pure physical effect and real experimental conditions of neutron registration in the DET-12 device designed and built in IFJ PAN. Decay curves have been obtained for each case. Detection efficiency of DET-12 has been also estimated.
Method of interpretation of measurements of delayed neutrons in the DET-12 device
(Institute of Nuclear Physics Polish Academy of Sciences, 2014) Bieńkowska, Barbara; Prokopowicz, Rafał; Drozdowicz, Krzysztof; Woźnicka, Urszula
DET-12 is a device to measure delayed neutrons from fissions in fissionable material samples which were activated in the primary neutron flux from D-T or D-D reactions in hot plasma of big fusion devices (tokamaks, stellarators). In the paper, a method is outlined how to interpret the registered time decay of delayed neutrons in order to obtain information on intensity of the primary neutron flux. The method combines a restoration of the decay function (multi-exponential) from the data stored in a multiscaler regime and a Monte Carlo calculation of a basic approximation of the neutron energy spectrum.
Monte Carlo simulations of neutron and photon radiation fields at the PF-24 plasma focus device at IFJ PAN in Krakow
(Institute of Nuclear Physics Polish Academy of Sciences, 2016-04) Tracz, Grzegorz; Wiącek, Urszula; Bieńkowska, Barbara
The medium scale PF‐24 facility was installed at the Institute of Nuclear Physics of the Polish Academy of Sciences (IFJ PAN), Poland. The MCNP model of the PF ‐ 24 device in the main hall of the laboratory was elaborated. Two variants of the plasma source emitting particles were considered: a point neutron source and a volume source with photon and neutron emission. Based on presented calculations the influence of the laboratory construction (the walls, the ceiling and the floor) on neutron and photon space distributions in the main hall were assessed. A study of fast uncolided and collided neutrons contributions to the total field of neutrons was performed. The contribution of photons emitted directly from the source and created as the result of neutron scattering was established. Neutron spectra at selected points were calculated.
Physical assumptions for a design of the DET-12 chamber for detection of delayed neutrons
(Institute of Nuclear Physics Polish Academy of Sciences, 2014) Bieńkowska, Barbara; Drozdowicz, Krzysztof; Gabańska, Barbara; Igielski, Andrzej; Prokopowicz, Rafał; Wiącek, Urszula; Woźnicka, Urszula
Physical assumptions have been outlined to design a new device (DET-12) for measurements of delayed neutron emitted from samples of fissionable materials activated with neutrons at big fusion-plasma devices. The aim is to support in this way a classic neutron activation method used as one of the hot plasma diagnostics at tokamaks or stellarators. Physical fundamentals of generation of the delayed neutrons are mentioned and a resulting concept of the measuring chamber is presented. A general size and dimensions of particular constituent material layers, and a number and placement of neutron detectors are optimized by means of Monte Carlo modelling of the neutron transport. Recommendations for a technical design of the measuring chamber are formulated.
Technical design and operation tests of the DET-12 device for detection of delayed neutrons
(Institute of Nuclear Physics Polish Academy of Sciences, 2014) Bieńkowska, Barbara; Drozdowicz, Krzysztof; Gabańska, Barbara; Igielski, Andrzej; Janik, Władysław; Kurowski, Arkadiusz; Tracz, Grzegorz; Wiącek, Urszula; Dankowski, Jan
A technical design of the device for detection of delayed neutrons emitted from neutron-activated fissionable material samples has been performed according to physical assumptions which were earlier elaborated. The DET-12 device was constructed. The detection system was composed, consisting of twelve 3He neutron detectors, related electronics lines, and the data acquisition and recording system. The detectors were adjusted to work in groups by three connected to one preamplifier, considering a weak intensity of emission of the delayed neutrons. Laboratory measurement tests of the device operation were made with use of an isotopic neutron source. A total efficiency of neutron detection in DET-12 was experimentally determined and a relative benchmark calculation was made by means of a Monte Carlo modelling of the neutron transport in the device from the source to detectors.

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