Narrow Results

In order to determine the cross sections of astrophysical reactions at relevant energies the new Felsenkeller underground laboratory, Germany, houses a 5 MV Pelletron accelerator. The accelerator provides stable and high-intensity ion beams which are much-needed in low-background environments. The properties of the two ion sources used in the new accelerator facility are discussed: The external 134 MC-SNICS cesium sputter source providing carbon beams in tandem mode and the internal radio frequency source for hydrogen and helium beams in single-ended mode.

One important component of the ambient background in underground laboratories are neutrons, which cover a wide energy range from thermal up to 100 MeV. After a few meters rock overburden, cosmic-ray neutrons are a negligible contribution underground and the remaining flux is due to neutron production by cosmic-ray muons and by (α,n) reactions from natural radioactivity in the rock.

There are only a few measurements of the full spectral neutron flux available in the literature, a fact which hampers comparisons between laboratories and negatively affects the planning of future experiments.

In an effort to overcome this issue a setup consisting of six moderated and one unmoderated ³He neutron counters that has been used at a depth of 850 m in the Canfranc underground laboratory, Spain [1], was utilized to study the neutron flux in the 48 m deep Dresden Felsenkeller underground laboratory, Germany. At Felsenkeller, an additional counter with a lead liner was used in order to address also the high-energy flux up to several hundreds of MeV.