The new Felsenkeller 5 MV underground accelerator

Abstract

The field of nuclear astrophysics is devoted to the study of the creation of the chemical elements. By nature, it is deeply intertwined with the physics of the Sun. The nuclear reactions of the proton-proton cycle of hydrogen burning, including the 3 He(α,γ) 7 Be reaction, provide the necessary nuclear energy to prevent the gravitational collapse of the Sun and give rise to the by now wellstudied pp, 7 Be, and 8 B solar neutrinos. The not yet measured flux of 13 N, 15 O, and 17 F neutrinos from the carbon-nitrogen-oxygen cycle is affected in rate by the 14 N(p,γ) 15 O reaction and in emission profile by the 12 C(p,γ) 13 N reaction. The nucleosynthetic output of the subsequent phase in stellar evolution, helium burning, is controlled by the 12 C(α,γ) 16 O reaction.In order to properly interpret the existing and upcoming solar neutrino data, precise nuclear physics information is needed. For nuclear reactions between light, stable nuclei, the best available technique are experiments with small ion accelerators in underground, low-background settings. The pioneering work in this regard has been done by the LUNA collaboration at Gran Sasso/Italy, using a 0.4 MV accelerator.The present contribution reports on a higher-energy, 5.0 MV, underground accelerator in the Felsenkeller underground site in Dresden/Germany. Results from γ-ray, neutron, and muon background measurements in the Felsenkeller underground site in Dresden, Germany, show that the background conditions are satisfactory for nuclear astrophysics purposes. The accelerator is in the commissioning phase and will provide intense, up to 50 µA, beams of 1 H + , 4 He + , and 12 C + ions, enabling research on astrophysically relevant nuclear reactions with unprecedented sensitivity.

Neutron flux and spectrum in the Dresden Felsenkeller underground facility studied by moderated He3 counters

“…The present study was initially motivated by a project to install an ion accelerator and a second low background activity-counting facility [33] in tunnels VIII and IX ( Fig. 1) of Felsenkeller [30,31].…”

Impact ofO16(γ,α)C12measurements on theFilippone1, Pieper2 2019Phys. Rev. C

“…The collision matrix for the OSGA reaction will be given in terms of the Hamiltonian H L which electromagnetically couples the photon of multipolarity L to the nucleus. We introduce the wave function E (J ) that describes the α- 12 C system in total spin state J and an initial-state wave function ψ i(J i ) which describes the nucleus ( 16 O) in its ground state. Then, the collision matrix is given by…”

“…To do this, we perform fits to the existing data using the R-matrix approach [4] and study the impact of including new data on the inverse reaction. This is achieved by starting with a reasonable R-matrix fit that can be used as a basis for comparison to fits with and without projected 16 O(γ , α) 12 C data. For the inverse capture data, we start with a proposed Jefferson Laboratory (JLab) experiment [5] in order to assess the possible role of new measurements in reducing the overall uncertainty in the cross section [6].…”

“…Measurements of the S factor as a function of energy are often reported in the literature. For the 12 C(α, γ ) 16 O reaction, the value of S at E = 300 keV is typically quoted as the most probable energy for stellar helium burning. Of course, the cross section is so small at 300 keV that it cannot be directly measured.…”

“…Thus, extrapolations to 300 keV must be performed to study the impact of data on the extrapolation. Of course, efforts aimed at improving the data and extrapolation are under way [5,[7][8][9][10][11][12][13][14] at a number of laboratories worldwide. The new inverse reaction (OSGA) experiments [5,7,8,13,14] bring a different set of systematic errors than previous experiments and thus provide an additional check on systematics.…”