  A new type of radiation detector based on a spherical geometry is presented.
The detector consists of a large spherical gas volume with a central electrode
forming a radial electric field. Charges deposited in the conversion volume
drift to the central sensor where they are amplified and collected. We
introduce a small spherical sensor located at the center acting as a
proportional amplification structure. It allows high gas gains to be reached
and operates in a wide range of gas pressures. Signal development and the
absolute amplitude of the response are consistent with predictions. Sub-keV
energy threshold with good energy resolution is achieved. This new concept has
been proven to operate in a simple and robust way and allows reading large
volumes with a single read-out channel. The detector performance presently
achieved is already close to fulfill the demands of many challenging projects
from low energy neutrino physics to dark matter detection with applications in
neutron, alpha and gamma spectroscopy.
