DANSS is a highly segmented 1 m3 plastic scintillator detector. Its 2500 one meter long scintillator strips have a Gd-loaded reflective cover. The DANSS detector is placed under an industrial 3.1 ...GWth reactor of the Kalinin Nuclear Power Plant 350 km NW from Moscow. The distance to the core is varied on-line from 10.7 m to 12.7 m. The reactor building provides about 50 m water-equivalent shielding against the cosmic background. DANSS detects almost 5000 ν˜e per day at the closest position with the cosmic background less than 3%. The inverse beta decay process is used to detect ν˜e. Sterile neutrinos are searched for assuming the 4ν model (3 active and 1 sterile ν). The exclusion area in the Δm142,sin22θ14 plane is obtained using a ratio of positron energy spectra collected at different distances. Therefore results do not depend on the shape and normalization of the reactor ν˜e spectrum, as well as on the detector efficiency. Results are based on 966 thousand antineutrino events collected at three different distances from the reactor core. The excluded area covers a wide range of the sterile neutrino parameters up to sin22θ14<0.01 in the most sensitive region.
Fluorine abundance determination is of great importance in stellar physics to understand s-elements production and mixing processes in asymptotic giant branch (AGB) stars. Up to now, theoretical ...models overproduce F abundances in AGB stars with respect to the observed values, thus calling for further investigation of the reactions involving fluorine. In particular, the 19F(p, )16O reaction is the main destruction channel of fluorine at the bottom of the convective envelope in AGB stars, an H-rich environment where it can experience temperatures high enough to determine its destruction, owing to additional mixing processes. In this paper the Trojan horse method (THM) was used to extract the 19F(p, 0)16O S-factor in the energy range of astrophysical interest (Ecm 0-1 MeV). This is the most relevant channel at the low temperatures (few 107 K) characterizing the bottom of the convective envelope, according to current knowledge. A previous indirect experiment using the THM has observed three resonances in the energy regions below Ecm 450 keV. These energies correspond to typical AGB temperatures, thus implying a significant increase in the reaction rate. Statistics are scarce for performing an accurate separation between resonances, preventing one from drawing a quantitative conclusion about their total widths and spin parities. Before THM measurement, only extrapolations were available below about 500 keV, showing a non-resonant behavior that sharply contradicts the trend of the astrophysical factor at higher energies. A new experiment has been performed to verify the measured TH astrophysical factor and to perform more accurate spectroscopy of the involved resonances.
The observation of neutrinos emitted in the p − p chain and in the CNO cycle can be employed to test the Standard Solar Model. The 3He(α,γ)7Be reaction is the first reaction of the 2nd and 3rd branch ...of the p − p chain, so the indetermination of its cross section significantly affects the predicted 7Be and 8B neutrino fluxes. Notwithstanding its relevance and the great deal of experimental and theoretical papers, information of the reaction cross section at energies of the core of the Sun (15 keV - 30 keV) is sparse and additional experimental work is necessary to attain the target (~ 3%) accuracy. The precise understanding of the external capture component to the 3He(α,γ)7Be reaction cross section is pivotal for the theoretical assessment of the reaction mechanism. In this work, the indirect measurement of this external capture component using the Asymptotic Normalization Coefficient (ANC) technique is discussed. To extract the ANC, the angular distributions of deuterons yielded in the 6Li(3He,d)7Be α-transfer reaction were detected with high precision at E3He=3.0 MeV and 5.0 MeV. The ANCs were then deduced from the juxtaposition of DWBA and CC calculations with the experimental angular distributions and the zero energy astrophysical S-factor for 3He(α,γ)7Be reaction was calculated to equal 0.534 ± 0.025 keVb. Both our experimental and theoretical approaches were tested through the analysis of the 6Li(p,γ)7Be astrophysical factor, with further interesting astrophysical implications.
The detection of the neutrinos produced in the p−p chain and in the CNO cycle can be used to test the Standard Solar Model. The 3He(α,γ)7Be reaction is the first reaction of the 2nd and 3rd branch of ...the p−p chain, therefore, the uncertainty of its cross section sensitively influences the prediction of the 7Be and 8B neutrino fluxes. Despite its importance and the large number of experimental and theoretical works devoted to this reaction, the knowledge on the reaction cross section at energies characterizing the core of the Sun (15 keV - 30 keV) is limited and further experimental efforts are needed to reach the desired (≈ 3%) accuracy. The precise knowledge on the external capture contribution to the 3He(α,γ)7Be reaction cross section is crucial for the theoretical description of the reaction mechanism. In the present work the indirect measurement of this external capture contribution using the Asymptotic Normalization Coefficient (ANC) technique is reported. To extract the ANC, the angular distributions of deuterons emitted in the 6Li(3He,d)7Be α-transfer reaction were measured with high precision at EH3e = 3.0 MeV and EH3e = 5.0 MeV. The ANCs were then extracted from comparison of DWBA calculations to the measured data and the zero energy astrophysical S-factor for 3He(α,γ)7Be reaction was found to be 0.534 ± 0.025 keVb.
.
The depletion of
18
O via the
(
p
,
γ
)
capture competes with the
(
p
,
α
)
capture during the CNO cycles in AGB stars. Despite the fact that the
(
p
,
α
)
capture is dominant, the
(
p
,
γ
)
can ...play an important role in mixing stages of the AGB star evolution. Here, we attempt to determine the astrophysical
S
-factor of the direct part of the
18
O(p,
γ
)
19
F capture by the indirect method of asymptotic normalization coefficients (ANC). We measure the differential cross section of the transfer reaction
18
O(
3
He, d)
19
F at a
3
He energy of 24.6 MeV. The measurement was performed on the cyclotron of the CANAM infrastructure of NPI in Řež, Czech Republic, with the gas target consisting of the high-purity
18
O (99.9%). The reaction products were measured by eight
Δ
E
-
E
telescopes composed of thin and thick silicon surface-barrier detectors. The parameters of the optical model for the input channel were deduced by means of the code ECIS and the analysis of transfer reactions to 12 levels of the
19
F nucleus up to 8.014 MeV was made by the code FRESCO. The deduced ANCs were then used to specify the direct contribution to the
18
O(p,
γ
)
19
F capture process and were compared with the mutually different results of two works.
The bare nucleus S(E) factors for the H2(d,p)H3 and H2(d,n)He3 reactions have been measured for the first time via the Trojan Horse Method off the proton in 3He from 1.5 MeV down to 2 keV. This range ...overlaps with the relevant region for Standard Big Bang Nucleosynthesis as well as with the thermal energies of future fusion reactors and deuterium burning in the Pre-Main-Sequence phase of stellar evolution. This is the first pioneering experiment in quasi free regime where the charged spectator is detected. Both the energy dependence and the absolute value of the S(E) factors deviate by more than 15% from available direct data with new S(0) values of 57.4±1.8 MeVb for H3+p and 60.1±1.9 MeVb for He3+n. None of the existing fitting curves is able to provide the correct slope of the new data in the full range, thus calling for a revision of the theoretical description. This has consequences in the calculation of the reaction rates with more than a 25% increase at the temperatures of future fusion reactors.
A detector of the reactor antineutrino based on a cubic meter of plastic scintillator is installed below 3.1 GW industrial reactor. The detector is placed on a movable platform which allows to change ...the distance to the reactor core center in the range 10.7-12.7 m. 2500 scintillator strips are read out individually by SiPMs and in groups of 50 by PMTs. In addition to the overburden by the reactor (50 m w.e.) the detector has multilayer passive shielding and active muon veto. Inverse beta-decay count rate of about 5000 events per day in the fiducial volume (78% of the detector) with about 5% of cosmic background has been reached. DANSS is sensitive to sterile neutrino in the most interesting region of mixing parameter space. The article covers the detector status and performance, as well as the first results.
The results of the research in the field of neutrino physics obtained at Kalinin nuclear power plant during 15 years are presented. The investigations were performed in two directions. The first one ...includes GEMMA I and GEMMA II experiments for the search of the neutrino magnetic moment, where the best result in the world on the value of the upper limit of this quantity was obtained. The second direction is tied with the measurements by a solid scintillator detector DANSS designed for remote on-line diagnostics of nuclear reactor parameters and search for short range neutrino oscillations. DANSS is now installed at the Kalinin Nuclear Power Plant under the 4-th unit on a movable platform. Measurements of the antineutrino flux demonstrated that the detector is capable to reflect the reactor thermal power with an accuracy of about 1.5% in one day. Investigations of the neutrino flux and their energy spectrum at different distances allowed to study a large fraction of a sterile neutrino parameter space indicated by recent experiments and perform the reanalysis of the reactor neutrino fluxes. Status of the short range oscillation experiment is presented together with some preliminary results based on about 170 days of active data taking during the first year of operation.
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