New neutrino source for the study of solar neutrino physics in the vacuum-matter transition region

Production of a neutrino source through a proton-induced reaction is studied by using the particle transport code geant4. Unstable isotopes such as ${}^{27}\mathrm{Si}$ can be produced when the ${}^{27}\mathrm{Al}$ target is bombarded by 15-MeV energetic proton beams. Through the $\beta$-decay process of the unstable isotope, a new electron-neutrino source in the 0–5.0 MeV energy range is obtained. Proton-induced reactions are simulated with JENDL-4.0 High Energy File (JENDL-4.0/HE). For radioactive decay processes, we use the G4 radioactive decay model based on the Evaluated Nuclear Structure Data File (ENSDF). We suggest detailed target systems required for future solar neutrino experiments, in particular for the vacuum-matter transition region. As for a detection system of the new neutrino source, we evaluate reaction or event rates for available radiochemical detectors and Low Energy Neutrino Astronomy (LENA)–type scintillator detector and discuss effects due to possible sterile neutrinos as an application.

Figure 1

Cross section for ${}^{27}\mathrm{Al}(p,n){}^{27}\mathrm{Si}$ by various data sets. The symbols in the legend denote various experimental data taken from the EXFOR database [27], which are compared with the calculated cross sections using the hadronic models of geant4 and the nuclear data model in panels (a) and (b), respectively.

Figure 2

Schematic diagram of the simulation for ${}^{27}\mathrm{Si}$ production target geometry drawn using the OpenGL library.

Figure 3

Upper panel (a) represents the energy levels (in the right-hand side) and their decay scheme with the branching ratio (BR) (in the left-hand side) of ${}^{27}\mathrm{Si}$. Values in parentheses with G4 denote those used in geant4. Lower panel (b) notes the normalized energy distribution of electron-neutrinos through the decay of ${}^{27}\mathrm{Si}$. $E_{\mathrm{ex}}$ means the excitation level (MeV) of the daughter ${}^{27}\mathrm{Al}$ reached after the decay. ${\nu }_0$ means the electron-neutrinos with the residual ${}^{27}\mathrm{Al}$ in the ground state. ${\nu }_1, {\nu }_2, {\nu }_3, {\nu }_4, {\nu }_5$, and ${\nu }_6$ denote the electron-neutrinos leaving ${}^{27}\mathrm{Al}$ with the excitation levels 0.84376, 1.01456, 2.21201, 2.73490, 2.98200, and 3.00420 MeV, respectively. ${\nu }_{\mathrm{tot}}$ is the sum of ${\nu }_0$ to ${\nu }_6$. It should be noted that the large difference between ${\nu }_0$ and others comes from the multiplied BRs in panel (a).

Figure 4

Simulation geometry for Low Energy Neutrino Astronomy (LENA)–type detector.

Figure 5

Panels (a) and (b) show a simulation snapshot and expected event rates for a LENA-type detector, respectively. The neutrinos are generated from the decay of ${}^{27}\mathrm{Si}$ produced by the 15-MeV and 10-mA proton beams on a ${}^{27}\mathrm{Al}$ target. The distance between the ${}^{27}\mathrm{Si}$ source and the center of the LENA detector is assumed to be 50 m.

Figure 6

Generated neutrino spectrum. The black solid lines represent the expected electron-neutrino energy spectrum at a distance of 10 m from the ${}^{27}\mathrm{Al}$ target. The neutrinos are generated from decay of ${}^{27}\mathrm{Si}$ produced by the 15-MeV and 10-mA proton beam on a ${}^{27}\mathrm{Al}$ target. For further discussions, we show theoretical cross section for ${}^{37}\mathrm{Cl}\left({\nu }_e,e^{-}\right){}^{37}\mathrm{Ar}$ [64], ${}^{71}\mathrm{Ga}\left({\nu }_e,e^{-}\right){}^{71}\mathrm{Ge}$ [65], ${}^2\mathrm{H}({\nu }_e,e^{-}pp$) [66], and ${}^2\mathrm{H}({\nu }_e,{\nu }_{e}pp$) reactions [66].

Figure 7

Electron-neutrino induced reaction rates via ${}^{37}\mathrm{Cl}\left({\nu }_e,e^{-}\right){}^{37}\mathrm{Ar}, {}^{71}\mathrm{Ga}\left({\nu }_e,e^{-}\right){}^{71}\mathrm{Ge}, {}^2\mathrm{H}({\nu }_e,e^{-}pp$), and ${}^2\mathrm{H}({\nu }_e,{\nu }_{e}np$) reactions. The neutrinos are generated from decay of ${}^{27}\mathrm{Si}$ which are produced by the 15-MeV and 10-mA proton beam on a ${}^{27}\mathrm{Al}$ target. Results of the cross sections in Fig. 6 are exploited for these reaction rate calculations.

Figure 8

Expected event rates and their ratios for LENA-type detector. The neutrinos are generated from decay of ${}^{27}\mathrm{Si}$ produced by the 15-MeV and 10-mA proton beams on a ${}^{27}\mathrm{Al}$ target. $R_3, R_{3+1}$, and $R_{3+2}$ are mean the reaction rates with electron-neutrino survival probabilities $P_3, P_{3+1},$ and $P_{3+2}$ in Eqs. (5), (6), and (7), respectively. $L$ is the distance between the ${}^{27}\mathrm{Si}$ source and the center of the LENA detector.