Narrow Results

Coupled first order IVPs are frequently used in many parts of engineering and sciences. In this article, we presented a code including three computer programs which are joint with the Matlab software to solve and plot the solutions of the first order coupled stiff or non-stiff IVPs. Some engineering and scientific problems related to IVPs are given and fuel depletion (production of the ²³⁹Pu isotope) in a Pressurized Water Nuclear Reactor (PWR) are computed by the present code.

An appropriately placed array of new generation neutrino detectors, in conjunction with the use of nuclear devices as a source of intense flux of neutrinos, can serve as a powerful precision probe of neutrino–oscillation parameters. If such detectors are made mobile by placing them on a criss-crossing grid of railway tracks, one may under certain hostile circumstances use them to locate nuclear powered vehicles like submarines, aircraft carriers and any other strong neutrino sources. Since neutrinos cannot be shielded, it may not be possible to escape detection.

We present new results of the DANSS experiment on the searches for sterile neutrinos. They are based on more than 2 million of inverse beta decay events collected at 10.7 m, 11.7 m and 12.7 m from the reactor core of the 3.1 GW Kalinin Nuclear Power Plant in Russia. This data sample is 2.4 times larger than the data sample in the previous DANSS publication. The search for the sterile neutrinos is performed using the ratio of ${\tilde{\nu }}_e$ spectra at two distances. This method is very robust against systematic uncertainties in the ${\tilde{\nu }}_e$ spectrum and the detector efficiency. We do not see any statistically significant sign for the ${\tilde{\nu }}_e$ oscillations. This allows us to exclude further a large and interesting part of the sterile neutrino parameter space. A Gaussian CL${}_s$ method was used to obtain exclusion areas. This method is more conservative than a Raster Scan method.

We present new results from the DANSS experiment on the searches for sterile neutrinos. They are based on approximately 5 million inverse beta decay events collected at 10.9, 11.9 and 12.9m from the reactor core of the 3.1GW Kalinin Nuclear Power Plant in Russia. We do not see any statistically significant sign for the $\widetilde{{\nu }_e}$ oscillations. The exclusion area in the $\mathrm{\Delta }{m}_{41}^2$, ${sin}^{2}2{\theta }_{ee}$ parameter space goes up to ${sin}^{2}2{\theta }_{ee}<0.008$ in the most sensitive region. Plans for DANSS upgrade are presented. This upgrade should allow DANSS to test Neutrino-4 claim of observation of sterile neutrinos.

Recent results from the DANSS experiment on the searches for sterile neutrinos are presented. They are based on approximately 5.5 million inverse beta decay events collected at 10.9, 11.9 and 12.9m from the reactor core of the 3.1 GW Kalinin Nuclear Power Plant in Russia. We do not see any statistically significant sign for the ${\bar{\nu }}_e$ oscillations. The exclusion area in the sterile neutrino oscillation parameters $\mathrm{\Delta }{m}_{41}^2$, ${sin}^{2}2{\theta }_{ee}$ goes up to ${sin}^{2}2{\theta }_{ee}<0.005$ in the most sensitive region in the reactor model independent study. A comparison of the absolute neutrino event rate and reactor models predictions allowed to exclude practically the whole sterile neutrino parameter space preferred by the BEST experiment as well as the best fit point of the Neutrino-4 experiment. Studies of the positron energy spectrum in the antineutrino inverse beta decay reaction and its dependence on the fuel composition are also presented. The ratio of the cross sections for ${}^{235}$U and ${}^{239}$Pu was measured. Reactor power was measured remotely using antineutrinos with $1.3\%$ accuracy in 3 days during 6.5 years.

This paper presents an optimality condition for the optimization problem of the assembly distribution in a nuclear reactor, by using the homogenization method. In this paper the reactivity of the reactor core is measured by the critical eigenvalue for both continuous and multigroup neutron transport models. In particular, we extend the spectral theory of the critical eigenvalue and prove the differentiability of the latter with respect to the design parameter, the configuration of the fuels.

Mono-energetic $\gamma$-beams ($\mathrm{\Delta }\sim 10$eV) based on thermal neutron capture, in a nuclear reactor, using the Mn($n,\gamma$) reaction were utilized for generating a fast neutron source from Zinc, via the ${}^{67}$Zn($\gamma ,n$) reaction. One of the incident $\gamma$-lines of the Mn source at $E_{\gamma }=7244$keV, photoexcites by chance a resonance level in ${}^{67}$Zn, with subsequent emission of neutrons at an energy of 191keV. The cross-section for this process was measured and found to be $\sigma (\gamma ,n)=252\pm 41$mb with an intensity of the order of 10⁴n/s. The angular distribution of the 191keV neutron group was also measured.

The measurement procedure based on the continuous thermal neutron beam modulation with a mechanical chopper was developed for delayed neutron yield measurement of the thermal neutron induced fission of ${}^{237}$Np. The idea of the procedure is similar to that widely used in modern computer communications to prevent unauthorized data access. The data is modulated with a predefined pattern before transmission to the public network, and only the recipient that has the modulation pattern is able to demodulate it upon receipt. For thermal neutron induced reaction applications, the thermal neutron beam modulation pattern was used to demodulate the measured delayed neutron intensity signals on the detector output, resulting in nonzero output only for the detector signals correlated with the beam modulation. The comparison of the method with the conventional measurement procedure was provided, and it was demonstrated that the cross-correlation procedure has special features making it superior to the conventional one, especially when the measured value is extremely small in comparison with the background. Due to the strong sensitivity of the measurement procedure on the modulation pattern of the neutron beam, one can implement the modulation pattern of a specific shape to separate the effect of the thermal part of the beam from the higher energy part in the most confident way in the particular experiment. The remarkable property of our method is related to the unique possibility of separation of the effects caused exclusively by thermal neutrons using the neutron time-of-flight measurement available on the IBR-2 pulsed reactor.

The Double Chooz experiment is going to measure the value of sin²2θ₁₃ of great interest at the moment for neutrino physics. Two identical detectors will be installed at CHOOZ nuclear power plant at a distances of 280 and 1050 m from the reactor cores to overcome the existing limit coming from the early CHOOZ experiment. This setup will allow to decrease systematic error down to the level of a percent.