An absolute method for performing neutron-activation analysis of large oil samples is presented. Software has been developed for performing a Monte Carlo calculation (based on nuclear-physical data in the ENDF and ENSDF format) of the distribution of the neutron flux and activation of the analyte nuclides in large samples. A method and software have been developed for calculating the detection efficiency for γ-rays from a large sample by a planar detector. The coefficient α of deviation of the epithermal neutron flux from the 1/E law is determined to be α = 0.023. The content of 38 elements in samples of raw oil samples from a deposit in Eastern Siberia in the concentration range from 10–9 to 0.5% is determined.

At present, the possible existence of a sterile neutrino having a significantly smaller cross section of interaction with a substance than, for example, electronic antineutrinos from a reactor is being widely discussed. It has been suggested that, due to reactor antineutrino transition into a sterile state, one can observe both the oscillation effect at short distances (5–15 m) from the reactor and a deficiency of the reactor antineutrino flux at large distances. We have investigated the possibility of performing experiments in search for reactor antineutrino oscillations into a sterile state on research reactors. A model experiment has been carried out on a 16-MW WWR-M reactor at the Petersburg Nuclear Physics Institute with a view to implementing a full-scale experiment using a 100-MW SM-3 reactor at the Research Institute of Atomic Reactors (RIAR). Background conditions of these experiments have been studied for both reactors. It is concluded that the implementation of a full-scale Neutrino-4 experiment on the SM-3 reactor at the RIAR is possible.

This manuscript presents an application of calculation methods in neutron activation analysis (NAA) of a large crude oil sample. Monte-Carlo computer code was developed. The computer code calculates neutron cross sections and neutron flux density distribution in the interior large sample. ENDF/B-VII.0 data files and ENSDF BNL-NCS-51655-01/02-Rev data files were used as nuclear databases in our computer code. HPGe planar detector efficiency registration technique and the software were developed for the absolute NAA technique of the large sample. The concentrations of Na, K, Ca, Sc, Cr, Fe, Co, Ni, Cu, Zn, Ga, As, Br, Sr, Zr, Mo, Ag, Sb, Cs, Ba, Ce, Nd, Sm, Eu, Tb, Dy, Ho, Tm, Yb, Lu, Hf, Ta, W, Pt, Au, Hg, Th and U in the crude oil samples of Eastern Siberia oilfield were determined using calculation and relative techniques in the concentration range from 10-9 to 0.5%.

The half-lives of the isomers 161 m 1 Dy and 161 m 2 Dy ( E = 25.6 keV and T 1/2 ∼ 30 ns for the former and E = 74.6 keV and T 1/2 ∼ 3 ns for the latter) placed in a 160 Gd 2 O 3 crystal lattice at T = 300 K and surrounded by stable 161 Dy nuclei in the composition of 161 Dy 2 O 3 were measured by the method of ( β-γ ) coincidences in the beta-decay process 161 Tb → 161 Dy. Nuclei of 161 m 1, m 2 Dy were obtained according to the chain 160 Gd( n, γ ) 161 Gd → 161 Tb → 161 Dy from 160 Dy 2 O 3 weighted portions irradiated at the PWR-M reactor of the Petersburg Nuclear Physics Institute (PNPI, Gatchina, Russia). The T 1/2 value observed for the isomer 161 m 1 Dy was found to be correlated with the number of surrounding 161 Dy nuclei. The presence of this correlation in 161 m 1 Dy can be explained by the multiple resonance scattering of photons from isomer decay within the sample used. No such correlation was observed for 161 m 2 Dy. The half-lives measured for the isomers 161 m 1 Dy and 161 m 2 Dy in the absence of the above environment are 29.2(1) and 3.50(1) ns, respectively.

The “Neutrino-4” experiment for the 100-MW SM-3 reactor has been developed with the aim of testing the reactor antineutrino anomaly at Petersburg Nuclear Physics Institute. The advantages of this reactor for studying the antineutrino anomaly are (i) a low background level and (ii) small dimensions (35 × 42 × 42 cm) of the active zone. Operation of a position-sensitive antineutrino detector comprising five working sections and moving so as to cover a region of distances within 6–13 m from the active zone has been simulated by the Monte-Carlo method. The range of experimental sensitivity with respect to the oscillation parameters Δm 2 and sin22θ is determined, which will make it possible to confirm the hypothesis of antineutrino oscillations into a sterile state.

One has investigated possibility of performing NEUTRINO-4 experiment on search for reactor neutrino oscillations into a sterile state at research reactors. The simulated experiment has been conducted at 16 MW reactor WWR-M in PNPI with the purpose of implementing a full scale experiment with the help of 100 MW reactor SM-3 in RIAR. Background conditions for making such an experiment have been examined at both reactors. The conclusion has been made on possible implementation of a full scale experiment NEUTRINO-4 at the reactor SM-3 in RIAR.

The half-lives of the isomers Dy and Dy (E = 25.6 keV and T1/2 ∼ 30 ns for the former and E = 74.6 keV and T1/2 ∼ 3 ns for the latter) placed in a Gd2O3 crystal lattice at T = 300 К and surrounded by stable Dy nuclei in the composition of Dy2O3 were measured by the method of (β–γ) coincidences in the beta-decay process Tb →Dy. Nuclei of Dy were obtained according to the chain Gd(n, γ)Gd → Tb →Dy from Dy2O3 weighted portions irradiated at the PWR-M reactor of the Petersburg Nuclear Physics Institute (PNPI, Gatchina, Russia). The T1/2 value observed for the isomer Dy was found to be correlated with the number of surrounding Dy nuclei. The presence of this correlation in Dy can be explained by the multiple resonance scattering of photons from isomer decay within the sample used. No such correlation was observed for Dy. The half-lives measured for the isomers Dy and Dy in the absence of the above environment are 29.2(1) and 3.50(1) ns, respectively. DOI: 10.1134/S1063778813060100 Previously, a change in the value observed for the half-life of the 119m1Sn isomer (E = 23.8 keV, T1/2 ∼ 18 ns) under conditions of a resonance environment was discovered experimentally in [1], and a model description of the resulting effect was given in [2]. In this way, the statement of Vysotskii [3] that, in the case where the radiating nucleus is surrounded by similar nuclei occurring their ground states and appearing as final-state nuclei in the respective transition, the half-life value observed for this nucleus may change (increase) in relation to the case where there is no environment. This is so if the energy of the emitted photon coincides with the energy of the first excited state of nuclei in the environment. Yet another possibility of experimentally observing this effect is provided by the decay of isomeric states of the 161Dy nucleus: 161m1Dy (E = 25.6 keV, T1/2 ∼ 30 ns) and 161m2Dy (E = 74.6 keV, T1/2 ∼ 3 ns). These states are formed in the chain of decays from 160Gd irradiated with reactor neutrons: 160Gd(n, γ)161Gd →161 Tb →161Dy. A fragment of the scheme of low-lying excited states of 161Dy is given in Fig. 1. In order to obtain 161Dy, use is made of Gd2О3 oxide; in its crystal lattice, 161Dy nuclei are formed after irradiation with neutrons. From [4], we know E-mail: yurlo@pnpi.spb.ru that, for the 161m1Dy nucleus, the probability for the recoilless emission, f (Lamb–Mössbauer factor), of a Eγ = 25.6 keV photon at T = 300 K is 0.24. The value of f for a Eγ = 74.6 keV transition is unknown. According to various data, the respective value for 119m1Sn falls within the range of 0.4–0.5 [5]. DESCRIPTION OF THE EXPERIMENT As samples for irradiation, we took 1.5to 2mg weighed portions of Gd2О3 oxide enriched in 160Gd to 98.2%. Each weighed portion was irradiated

The half-lives of the isomers Dy-161m1 and Dy-161m2 (E = 25.6 keV and T (1/2) similar to 30 ns for the former and E = 74.6 keV and T (1/2) similar to 3 ns for the latter) placed in a (Gd2O3)-Gd-160 crystal lattice at T = 300 K and surrounded by stable Dy-161 nuclei in the composition of (Dy2O3)-Dy-161 were measured by the method of (beta-gamma) coincidences in the beta-decay process Tb-161 -> Dy-161. Nuclei of Dy-161m1,Dy-m2 were obtained according to the chain Gd-160(n, gamma)Gd-161 -> Tb-161 -> Dy-161 from (Dy2O3)-Dy-160 weighted portions irradiated at the PWR-M reactor of the Petersburg Nuclear Physics Institute (PNPI, Gatchina, Russia). The T (1/2) value observed for the isomer Dy-161m1 was found to be correlated with the number of surrounding Dy-161 nuclei. The presence of this correlation in Dy-161m1 can be explained by the multiple resonance scattering of photons from isomer decay within the sample used. No such correlation was observed for Dy-161m2. The half-lives measured for the isomers Dy-161m1 and Dy-161m2 in the absence of the above environment are 29.2(1) and 3.50(1) ns, respectively.

There has been designed an experimental project "Neutrino-4" for 100 MW reactor SM-3 to test the hypothesis of the "reactor antineutrino anomaly". Advantages of the reactor SM-3 for such an experiment are low background conditions as well as small dimensions of a reactor core - 35x42x42 cm3. One has carried on the Monte-Carlo modeling of a position sensitive antineutrino detector consisting of 5 operation sections, which as a result of displacement, covers the distance from 6 to 13 meters from the reactor core. One has succeeded in obtaining an experimental area of sensitivity to oscillation parameters, which enables to verify the hypothesis of reactor antineutrino oscillations into a sterile state.

A model description of the increase in the observed value of the half-life of isomeric nuclei 119 m 1 Sn ( E = 23.8 keV, T 1/2 ∼ 18 ns) in a resonance environment created by stable nuclei of 119 Sn is proposed. According to the model used, the observed effect is due to gamma radiation from isomeric nuclei 119 m 1 Sn newly produced upon the resonance capture of gamma rays emitted in 119 m 1 Sn decay by stable nuclei of 119 Sn. On the basis of T 1/2 values that were measured previously, the radiative shift of the position of an excited nuclear state (nuclear analog of the Lamb shift in an atom), Δ ω 0 , was estimated at 1.5(2) × 10 11 s −1 for the isomer 119 m 1 Sn.

In order to analyze the effect of resonant environment on the γ decay of excited nuclei, the half-life of the 119 m 1 Sn isomer ( E = 23.8 keV, T 1/2 ∼ 18 ns), which appears from the decay of the 119 m 2 Sn state ( E = 89 keV, T 1/2 ∼ 293 d), has been measured by the e -γ coincidence method on samples consisting of the mixture of tin oxides containing the 119 Sn stable nucleus and 119 m 2 Sn radioactive nuclei with various values of the 119 SnO 2 / 119 m 2 SnO 2 ratio. For the samples, where this ratio is equal to 6.2 × 10 4 , 1.2 × 10 6 , 6.5 × 10 6 , and 1.7 × 10 7 , the half-life T 1/2 is equal to 18.69(2), 18.71(2), 18.91(5), and 19.43(4) ns, respectively. For the reference sample (a metal with a 119 Sn/ 119 m 2 Sn ratio of 1.5 × 10 5 ), the value T 1/2 = 18.68(6) ns is obtained.

The previously unknown absolute intensities of 28 prompt γ-rays from the thermal neutron capture in 91Zr, 143Nd, 177Hf and 116,118–120,122,124Sn were measured by an in-beam γ-spectroscopy method at the WWR-M reactor (PNPI, Gatchina). Cross sections of the production of isomers 123m,125mSn were also measured.

Physical launch of the WWR-M reactor in the branch of Physical-Technical Institute of AS of the USSR in Gatchina took place on the 29th of December in 1959. However the first work on nuclear spectroscopy was carried out before the reactor was launched; namely, gamma-radiation was measured of short-lived isomeric nucleus with lifetime of some tens of minutes produced by irradiation in the reactor mock-up processed at a power of 1-2 Wt. The internal conversion coefficient measured from Xand γ-ray intensity ratio coincided with the one measured earlier and L.I. Rusinov delivered a report about the beginning of scientific activities at the WWR-M reactor [1]. This was a new level of work with short-lived isotopes, as earlier the most short-lived nucleus investigated in the laboratory of L.I. Rusinov was Hf with T1/2=5.5 h. Earlier this isotope irradiated in the reactor of Kurchatov Institute in Moscow was brought to PhysicalTechnical Institute in Leningrad by plane. That work was undertaken in order to bring a contribution in a study of K-forbiddenness. Indeed, it was wonderful that the 57.6 keV transition of E1 type determines such a large half-life [2]. Launch of a new reactor in Gatchina has given a possibility to deal with very short-lived isotopes using various pneumatic and other posts in which the minimal time of delivery of sample to measuring installation amounted to 40 ms [3]. Generally speaking, the works on nuclear spectroscopy in Physical-Technical Institute began as early as in 1934, when an investigation of properties of Br decay was carried out with participation of L.I. Rusinov [4]. That work was a push for development of studies about nuclear isomerism. So, all the following works of Laboratory of nuclear isomerism in PhTI in some way or other were connected with this interesting phenomenon. The first works in this direction made at the WWR-M reactor under the leadership of D.M. Kaminker were developed to the measurements of lifetimes of nuclear levels of doubly odd nuclei after radiative capture of neutron. It should be noted that the excited states of doubly odd nuclei are excited in the decay of radioactive nuclei very seldom, therefore, one nucleon transfer reaction are nearly the only source of information about such nuclear states. In these works carried out by A.M. Berestovoj and Yu.E. Loginov eight new nuclear isomers were found and investigated [5, 6].

From the comparison of absolute intensities of the two-step gamma-cascades and known intensities of their primary and secondary transitions, the cascade and total population of about  100 levels of 181Hf and 184,185,187W excited in thermal neutron capture was determined. These experimental results and intensities of two-step cascades to the low-lying levels of mentioned nuclei were reproduced in calculation using level densities with clearly expressed step-like structure. Radiative strength functions of the primary transitions following gamma-decay of these compound nuclei to the levels in the region of pointed structure are considerably enhanced. Moreover, population of levels below 3 MeV can be reproduced only with accounting for local and rather considerable increase in radiative strength functions of the secondary transitions to the levels in vicinities of break points in energy dependence of level density and significant decrease of that to lower-lying states. Simultaneous change in both level density and strength functions in the same excitation region of a nucleus corresponds to the definition of the second-order phase transition.

The formally T -odd triple correlation between the directions of the momenta of α particle and γ quantum and the polarization pseudovector of a thermal neutron was examined for the 10 B+ n = 7 Li+ 4 He+γ reaction. Such T -odd correlations can be directly used for checking time reversal invariance in the elastic scattering of particles. In more complex reactions, this correlation can occur as a result of particle interactions in the entrance and exit channels of the reaction and, being a background effect, requires correct theoretical or direct experimental estimation. Our experiments gave an upper limit of 3.2×10 −4 (90% confidence level) for the possible T -odd asymmetry parameter in the reaction under study.

The formally T-odd triple correlation between the directions of the momenta of alpha particle and gamma quantum and the polarization pseudovector of a thermal neutron was examined for the B-10 + n = Li-7 + He-4 + gamma reaction. Such T-odd correlations can be directly used for checking time reversal invariance in the elastic scattering of particles. In more complex reactions, this correlation can occur as a result of particle interactions in the entrance and exit channels of the reaction and, being a background effect, requires correct theoretical or direct experimental estimation. Our experiments gave an upper limit of 3.2 x 10(-4) (90% confidence level) for the possible T-odd asymmetry parameter in the reaction under study. (C) 2000 MAIK "Nauka / Interperiodica".

A procedure for energy calibration using a priori information is employed to determine the binding energy of neutrons in the 118 Sn nucleus: E=9326.18 (6) keV from the 117 Sn(n, γ) reaction. The effect of energy correlations and their errors on the results is indicated.