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Detection of antineutrino by the reaction of the inverse β-decay can be used for an independent monitoring of a nuclear reactor power. DANSS detector is located directly under a commercial WWER-1000 reactor and counts up to 5000 antineutrino per day, providing the accuracy of 1.5% in 2 days of the flux measurement. A powerful system of the passive and active shielding in combination with the fine spatial segmentation of the detector allows to diminish the contribution of the background processes to a level, negligible in comparison to the statistical error. The influence of the nuclear fuel composition on the neutrino flux can be accounted for based on the input from the NPP staff.

The KLL Auger electron spectra of Zr (Z = 40) and Nb (Z = 41) following respectively the electron capture (EC) decay of 90Nb and the de-excitation of the isomeric state of 91mNb were investigated in detail using a combined electrostatic electron spectrometer and radioactive sources prepared by surface sorption on a polycrystalline carbon substrate. For both elements, energies, relative intensities, and natural widths of all the nine well-resolved basic spectrum components were determined and compared with theoretical predictions and with results of previous measurement as well. Results of our ab initio multiconfiguration Dirac-Hartree-Fock calculations are discussed also in relation to the solid-state effect. Indications of an influence of the EC decay on the absolute energy of the KL2L3(1D2) transition (so-called atomic structure effect) in Zr were found. The effect of the retarded current-current interaction on the KL1L2(3P0) transition intensity was observed to be appreciable for the investigated elements in accordance with the prediction.

Effects of the atomic environment on the L 1 , L 2 , L 3 , M 1 , M 2 , M 3 , and N 1 electron binding energies in samarium generated in the electron capture decay of radioactive 149 Eu were investigated by means of the internal conversion electron spectroscopy using the conversion electron spectrum of the 22.5 keV M1 + E2 nuclear transition in the daughter 149 Sm. In this investigation, four pairs of 149 Eu sources prepared by vacuum evaporation deposition and by ion implantation at 30 keV with the use of four different source backing materials, namely polycrystalline carbon, aluminium, gadolinium and platinum foils, were employed. The greatest average difference of (3.1 ± 0.1) eV in the L 1 , L 2 , L 3 , and M 1 subshell electron binding energies was observed between the 149 Eu sources prepared by ion implantation into the aluminium and platinum substrates. On the other hand, minimal differences in the electron binding energies were generally found between samarium generated in the evaporated layer and in the bulk for the individual investigated source backings with the exception of the gadolinium foil. A doublet structure of all investigated conversion electron lines with the average values of 8.1 ± 0.2 eV and 1.5 ± 0.1 for the separation energy and the intensity ratio of the low-energy to high-energy components, respectively, was observed for the 149 Eu sources prepared by ion implantation into the aluminium and carbon foils. This structure was presumably caused by the presence of both the trivalent and divalent Sm ions in the sources. No significant differences in natural widths of the L 1 , L 2 , L 3 , M 1 , M 2 , and M 3 samarium atomic levels among the investigated matrices were observed with the exception of the source prepared by the implantation of the 149 Eu ions into the platinum foil for which the determined values for all investigated subshells were apparently higher.

The KLM+KLN Auger electron spectrum of rubidium (Z=37) emitted in the electron capture decay of radioactive $^{83}$Sr in a polycrystalline platinum matrix and also $^{85}$Sr in polycrystalline platinum and carbon matrices as well as in an evaporated layer onto a carbon backing was experimentally studied in detail for the first time using a combined electrostatic electron spectrometer. Energies, relative intensities, and natural widths of fifteen basic spectrum components were determined and compared with both theoretical predictions and experimental data for krypton (Z=36). Relative spectrum line energies obtained from the semi-empirical calculations in intermediate coupling scheme were found to agree within 3$\sigma$ with the measured values while disagreement with experiment exceeding 3$\sigma$ was often observed for values obtained from our multiconfiguration Dirac-Hartree-Fock calculations. The absolute energy of the dominant spectrum component given by the semi-empirical approach agrees within 1$\sigma$ with the measured value. Shifts of + (0.2$\pm$0.2) and - (1.9$\pm$0.2) eV were measured for the dominant KLM spectrum components between the $^{85}$Sr sources prepared by vacuum evaporation on and implanted into the carbon foil, respectively, relative to $^{85}$Sr implanted into the platinum foil. A value of (713$\pm$2) eV was determined for the energy difference of the dominant components of the KLM+KLN Auger electron spectra of rubidium and krypton generated in the polycrystalline platinum matrix. From the detailed analysis of the measured data and available theoretical results, the general conclusion can be drawn that the proper description of the KLM+KLN Auger electron spectrum for Z around 37 should still be based on intermediate coupling of angular momenta taking into account relativistic effects.

The L 1 , L 2 , L 3 , M 1 , M 2 , N 1 , N 3 , O 1 , O 2 , O 3 , and P 1 subshell electron binding energies (related to the Fermi level) in thulium generated by the electron capture decay of radioactive 169 Yb atoms implanted at 30 keV into polycrystalline platinum and aluminum foils and deposited by vacuum evaporation on surfaces of polycrystalline platinum, carbon, and aluminum foils were determined by the internal conversion electron spectroscopy. The greatest differences in the electron binding energies (4.5 ± 0.1 eV in the average without the P 1 shell and 7.0 ± 0.5 eV for the P 1 shell alone) were found between the matrices of the evaporated ytterbium layer on the aluminum foil and the bulk of the high purity polycrystalline platinum. The thulium electron binding energies in the matrices of the evaporated ytterbium layers on both the platinum and carbon foils and in the aluminum bulk were observed to be the same within the experimental uncertainties. The N 1 , N 3 , and O 2,3 electron binding energies most frequently presented in data compilations were found to be higher by about 3 eV. Natural widths of most of the K, L 1 , L 2 , L 3 , M 1 , M 2 , M 3 , N 1 , N 3 , and O 1 subshells in Tm in the investigated matrices were also determined. No significant differences in the natural widths were found among the matrices. The results obtained demonstrate that the physicochemical surrounding of the radioactive atoms should be well defined and understandable for any type of electron calibration source particularly in the case of the super stable calibration 83 Rb/ 83m Kr electron sources for the KATRIN neutrino mass experiment.

The low-energy electron spectra emitted in the radioactive decay of the $^{83}$Rb and $^{83}$Sr isotopes were measured with a combined electrostatic electron spectrometer. Radioactive sources used were prepared by ion implantation of $^{83}$Sr into a high purity polycrystalline platinum foil at 30 keV and by vacuum-evaporation deposition of $^{83}$ Rb on the same type of foil. From the measured conversion electron spectra, the electron binding energies (referenced to the Fermi level) for the K, L$_1$ , L$_2$ , L$_3$ , M$_1$ , M$_2$, and M$_3$ shell/subshells of krypton in the platinum host were determined to be 14 316.4(12), 1 914.3(9), 1 720.3(9), 1 667.6(9), 281.5(9), 209.6(13), and 201.2(15) eV, respectively, and those for the evaporated layer were observed to be lower by 0.7(1) eV. For both host matrices, values of 2.3(2), 4.6(2), 1.7(2), 1.3(2), and 3.2(3) eV were obtained for the krypton K, L$_1$ , L$_2$ , L$_3$ , and M$_1$ natural atomic level widths, respectively. The absolute energies of 10 838.5(9) and 10 839.5(10) eV were measured for the KL$_2$L$_3$ ($^{1}$D$_2$) Auger transition in krypton implanted in Pt and generated in the evaporated rubidium layer, respectively. A value of 601.0(8) eV was measured for the energy difference of the KL$_2$L$_3$ ($^{1}$D$_2$) transitions in Rb and Kr in the Pt host. Multiconfiguration Dirac-Fock calculations of the krypton KLL transition energies and intensities were also performed.

The KLM + KLN Auger electron spectrum of Cu (Z = 29) emitted in the electron capture decay of radioactive 65 Zn in a solid matrix was investigated for the first time using a combined electrostatic electron spectrometer adjusted to the 7 eV instrumental resolution. Energies and relative intensities of nine resolved spectrum components were determined and compared with theoretical expectations. An agreement within 3 σ was found between the semi-empirical predictions for the KLM transition energies by Larkins and the experimental data with the exception of the weak (KL 2 M 4,5 + KL 2 N 1 ) and (KL 3 M 4,5 + KL 3 N 1 ) lines where the differences reached 5 σ . From a comparison of the measured relative KLM transition intensities with available theoretical results a conclusion was derived that calculations of the KLM transition rates at Z = 29 should be based on intermediate coupling of angular momenta and take into account relativistic effects.

For the first time, the KLL Auger spectrum of La (Z = 57) following the electron capture decay of radioactive 139,141Ce in a solid source was measured. The all nine basic spectrum components were resolved and their energies and relative intensities were determined and compared with theoretical expectations. The absolute energy of 27 383.8 ± 2.2 eV derived for the dominant KL2L3(1D2) transition was found to be higher by 7.7 ± 2.2 eV (i.e. more than 3σ) than a value predicted by the widely used relativistic semi-empirical calculations by Larkins. The possible reasons for this discrepancy are discussed. Despite of less accuracy of some measured data, the predicted strong influence of the relativistic effects on the KL1L2(3P0) transition intensity was nevertheless proved.

The absolute energies of the KL2L3(1D2), KL3M2,3(3P0,2), and L3M4M5(1G4) transitions in Zn 30 67 from the EC decay of Ga 31 67 and from the β− decay of Cu 29 67 and those of the KL2L3(1D2) and L3M4M5(1G4) transitions in Gd generated in the EC decay of 153,155,156Tb fraction and the β− decay of 152,154,155Eu fraction as well were measured with use of the combined electrostatic electron spectrometer. The absolute energies of the KL2L3(1D2) and L3M4M5(1G4) transitions in Gd following the EC decay were found to be higher by 13.9 ± 0.9 and 16.3 ± 0.3 eV, respectively, than those measured for the transitions initiated by the β− decay. Much lower differences of 2.1 ± 0.2, 2.4 ± 0.2 and 1.6 ± 0.2 eV between the EC and the β− decay modes for the above mentioned transitions, respectively, were observed for Zn 30 67 . Due to the uncertainties in the assumed chemical state of the studied isotopes generated by β− decay and EC decay in different sources, contributions from the induced chemical shifts of the electron binding energies to the observed differences can be significant especially in the latter case. Despite this fact the finding corresponds to the results obtained in the X-ray studies of the “atomic structure effect” that the effect is the most pronounced for the 4f and 5f element groups. A comparison of the measured and calculated absolute Auger transition energies indicates that the electron configuration of Gd just after the EC decay can differ from that one supposed in the calculations.

The KLL Auger spectrum of Sm ( Z = 62) following the electron capture decay of radioactive 147,148,149 Eu atoms in a solid state source was measured with the instrumental resolution of 14 eV. Energies and relative intensities of all the nine basic spectrum components were determined and compared with those of the previous measurement and theoretical predictions. Our absolute Auger transition energy 32627.3 ± 1.4 eV for the dominant KL 2 L 3 ( 1 D 2 ) transition was found to be higher by 16.0 ± 1.4 eV than that one of the widely used relativistic semi-empirical calculations by Larkins. Taking into account results of our measurements of the L 3 M 4 M 5 ( 1 G 4 ), L 3 M 5 M 5 ( 3 F 4 ), and KL 2 L 3 ( 1 D 2 ) Auger lines from both the EC decay and the β − decay for atomic numbers Z = 62 and 64 and also previous experimental data a conclusion is made that the discrepancy found is caused by the “atomic structure effect”. The measured value for the KL 1 L 2 ( 3 P 0 / 1 P 1 ) transition intensity ratio proved strong influence of the relativistic effects on the intensity distribution between the 3 P 0 and 1 P 1 doublet components.

The KLL Auger electron spectrum of 65 Cu following the EC decay of 65 Zn has been analyzed at the instrumental resolution of 4.5 and 7 eV using a combined electrostatic spectrometer. Energies and relative intensities of the all nine spectrum components were determined and compared with data obtained from X-ray induced spectra for metallic copper and with results of theories as well. Our value of 7041.8(1.3) eV measured for the absolute energy of the dominant KL 2 L 3 ( 1 D 2 ) spectrum line was found to be higher by 4 eV than those ones obtained in experiments with the use of X-ray photon excitation and by 11 eV (8 σ ) than a prediction of the semi-empirical calculations by Larkins. This discrepancy indicates an influence of the “atomic structure effect” on absolute energies of the KLL Auger transitions in 65 Cu. Its value was estimated to be from 8 to 15 eV. Good agreement of the measured value of 0.08(2) and that one of 0.066 predicted by relativistic calculation for the KL 1 L 2 ( 3 P 0 / 1 P 1 ) transition intensity ratio indicates appreciable influence of the relativistic effects on the KLL Auger spectrum even for copper ( Z = 29).

The KLL Auger electron spectrum of 88 Sr generated in the EC-decay of 88 Y has been analyzed at the instrumental resolution of 11 eV using a combined electrostatic spectrometer. Energies and relative intensities of the all nine transitions were determined and compared with theoretical predictions. Our value of 12067.3(12) eV measured for the absolute energy of the dominant KL 2 L 3 ( 1 D 2 ) transition was found to be higher by 7.4 eV (i.e., more than 3 σ ) than that one obtained in a measurement with external excitation. The discrepancy indicates substantial influence of the “atomic structure effect” on absolute transition energies in our experiment. Very good agreement of the measured 0.14(3) and predicted 0.12 values for the KL 1 L 2 ( 3 P 0 / 1 P 1 ) Auger transition intensity ratio clearly proved the predicted strong influence of the relativistic effects on the KL 1 L 2 ( 3 P 0 ) transition rate even at Z = 38.

The low energy KLL Auger electrons of neon emitted after EC-decay of 22Na have been investigated with a 4 eV instrumental resolution using an electrostatic spectrometer and a solid state radioactive source. This is the first experimental investigation of the KLL Auger spectrum of neon from the solid state. Relative intensities and energies of all resolved spectrum components were determined. Measured absolute energy of the dominant KL2L3(1D) transition was found to be 824.5(19) eV, i.e. about 20 eV higher than that obtained in experiments with free Ne atoms. Within the experimental uncertainties, no influence of solid state effects on relative intensities of the KLL transitions was found.

KMM, KMN and KNN Auger electron spectra of 111 Cd emitted in EC-decay of 111 In were analyzed at instrumental resolutions of 14 and 21 eV using a combined electrostatic spectrometer. Energies and relative intensities of 26 resolved components were determined and compared with theoretical predictions. For the first time, the predicted intermediate coupling structure of some KMM Auger lines was observed. A structure of the KNN Auger group for Z

A spectrum of the low energy electrons from the electron capture decay of 67Ga has been analyzed at the instrumental resolution 4, 7, and 14 eV in the region 570–10 400 eV using an electrostatic spectrometer. Energies and relative intensities of the LMM + LMN, KLL, KLM + KLN, and KMM + KMN Auger transitions have been determined with high accuracy and compared with results of available calculations. The measured absolute energies of the dominant KLL and KLM Auger lines have been found to be significantly higher than the semi-empirical values. Generally, worse agreement has been found between measured and calculated transition intensities. Relative intensities of the main spectrum components have been also determined to be: (LMM+LMN)/KLL/(KLM+KLN)/(KMM+KMN)=(27.5±2.3)/(60.1±4.6)/(14.5±1.0)/(1.00±0.07).

The KLL Auger spectrum of 73 Ge from the electron capture decay of 73 As was measured with 7 eV instrumental resolution using a combined electrostatic spectrometer and a source prepared by a gas-chemical method. The energies and relative intensities of all the nine resolved KLL lines were precisely determined. A rather poor agreement was found between the measured KLL transition energies and predictions of the widely used semiempirical calculations. Our relative KLL transition intensities agree only with results of the relativistic calculations in intermediate coupling with configuration interaction. The predicted influence of the relativistic effects on the KL 1 L 2 ( 3 P 0 ) transition rate was also proven.

The KL1L2 Auger doublet of 14059Pr and the KLL Auger spectrum of 14561Pm from the electron capture decay of 140Nd and 145Sm, respectively, have been measured with high instrumental resolutions using a combined electrostatic spectrometer and sources prepared by a modified Langmuir–Blodgett method. An exceptional agreement of the determined KL1L2(3P0)/(1P1) intensity ratios of 0.42(2) and 0.45(1) for 140Pr and 145Pm, respectively, with the respective calculated values of 0.419 and 0.450 has proved the predicted strong influence of the relativistic effects on the KL1L2(3P0) transition intensity. While the measured relative intensities of the KLL transitions in 145Pm were found to agree well with the relativistic intermediate coupling calculations, the measured relative energies deviate from results of the widely used semi-empirical calculations. A doublet structure of the KL2L3(1D2) line of 145Pm with a splitting of 18.3(6) eV has been observed. We made an assumption that this structure originates in two different K shell excitation processes. The measured absolute energies of 28 397(3), 29 423.1(26), and 31 542.9(15) eV for the KL2L3 transition in 140Ce, 140Pr, and 145Pm, respectively, were found to be higher by about 20 eV than the semi-empirical values. The most intense L3MM line groups of 145Pm have also been measured but not evaluated. The absolute energy of the L3M4M5(1G4) transition has been determined to be 4342.6(16) eV. The energy of the M1 61.2 keV nuclear transition in 145Pm has been improved to be 61 226.5(17) eV using the measured energy of 16 042.5(15) eV of the K-61.2 conversion line. Values of 19.2(5) and 25.3(9) eV were determined for natural widths of the K shell and KL2L3 transition of 145Pm, respectively.

The KLL and KLX Auger spectra of Cd from the EC-decay of 111 In have been analyzed with the 7 eV instrumental resolution using a combined electrostatic spectrometer and a source prepared by a modified Langmuir–Blodgett method. Energies and relative intensities of all the nine well resolved KLL lines have been precisely determined. While the latter quantities were found to be in very good agreement with the relativistic intermediate coupling calculations, the former ones deviate from results of the widely used semi-empirical calculations especially in the case of the absolute energies. The predicted strong influence of the relativistic effects on the KL 1 L 2 ( 3 P 0 ) transition intensity has been proved. Most of the main KLX Auger lines have been well separated and their complex structures have been observed. Accurate energies and intensities obtained for these lines have been compared with results of calculations. The intermediate coupling splitting of the KL 2 L 2 and KL 3 L 3 lines have been revealed. The KLX/KLL, KLN(O)/KLM, and KXY/KLL group intensity ratios have also been determined. A conclusion is made that further finer theoretical investigation on the complex interaction mechanism for two inner-shell vacancies is still very much needed.

The low-energy electron spectrum from the 57Co decay has been examined in the region from 0 up to 15 keV at instrumental resolution ranging from 2 to 15 eV. Two electrostatic spectrometers and radioactive sources prepared by vacuum evaporation of 57Co onto Al foils were utilized. Relative intensities of the main spectrum components have been obtained as follows: (TSE+LLX+Shake-off)/LMM/KLL/KLM/KMM/K−14.4/L−14.4/MN−14.4=116±12/51±4/59.7±1.8/15.2±0.4/1.15±0.07/49.6±1.5/5.05±0.15/0.79±0.02 where TSE means “true secondary electrons”. Absolute and relative energies of the LMM, KLL, KLM, and KMM Auger transitions in Fe have also been determined, as well as their relative intensities with the exception of the LMM lines, the shapes of which were strongly distorted due to the inelastic electron scattering and probably also chemical effects. From the measured conversion electron lines of the 14.4 keV M1 transition in 57Fe, a transition energy of 14412.8±0.8 eV and the E2 admixture less than 8×10−6 were derived. Relative intensities of both the KL2,3(M4,5N1) Auger line group and the M4,5N1−14.4 conversion line were found to be lower by about 30% for the “oxide” state of decaying 57Co atoms than for the “metallic” state. Pronounced broadenings of narrow spectrum lines have been observed as a consequence of the oxidation of the 57Co sources in the laboratory atmosphere. Natural widths for most of the KLL, KLM, and KMM Auger lines and those of the K, L1, L2, L3, M1, M2, M3 and N1 atomic levels in 57Fe were also determined.

The KLL Auger spectrum of Ni generated in the electron capture decay of radioactive 64Cu in a solid state matrix was measured for the first time using a combined electrostatic electron spectrometer adjusted to a 7 eV instrumental resolution. Energies and relative intensities of the all nine basic spectrum components were determined and compared with data obtained from X-ray induced spectra of metallic Ni and with theoretical results as well. Absolute energy of 6562.5 ± 1.3 eV (related to the Fermi level) measured for the dominant KL2L3(1D2) than a value obtained from the X-ray induced spectra which is probably caused by the effects of chemical bonding and physico-chemical environment. Moreover, it is higher by 20.4 eV (16σ) than a prediction of the semi-empirical calculations by Larkins which indicates an influence of the “atomic structure effect” on absolute energies of the Auger transitions following the electron capture decay and, possibly, some imperfections in the calculations. Good agreement of the measured and predicted KL1L2(3P0/1P1) transition intensity ratios indicates perceptible influence of the relativistic effects on the KLL Auger spectrum even at Z = 28.

The KMM + KMN Auger spectrum of Cu emitted in the electron capture decay of radioactive 65Zn in a solid state matrix was investigated for the first time at the instrumental energy resolution of 14 eV. Energies and relative intensities of twelve resolved spectrum components were determined and compared with theoretical predictions. A reasonable agreement of the semi-empirical calculations of transition energies by Larkins with experiment was observed. A comparison of theoretical and the measured transition rates indicates the important role of a coupling scheme applied. A more detailed analysis was hampered by absence of theoretical intensities for the individual intermediate coupling spectrum components. A slight indication of the influence of the source backing material on the absolute energies was found for the L3M4, 5M4, 5 and L2M4, 5M4, 5 Auger lines.