SOLITAIRE detector

SOLITAIRE, which has recently been installed in the Department of Nuclear Physics, is an innovative detector system for making precise measurements of the probabilities of fusion of atomic nuclei. The main features of the system are: a 6.5 T superconducting solenoid for separation of fusion products, an iron shield to minimize the magnetic field at the target and detector positions, and two position sensitive multi-wire proportional counters for detection of fusion products.

Fusion of atomic nuclei, initiated by energetic beams of nuclei from our accelerator, produces new unstable nuclei. These fused nuclei must be physically separated from the beam particles, so that the detectors used to identify the fusion products are not swamped by the extremely high rate of direct beam (up to 1000 billion particles/second) and scattered beam particles (1 million/second). Spatial separation between the fused products and elastically scattered particles is achieved using the 6.5 Tesla superconducting solenoid. The solenoid acts as a lens, generating an image of the target downstream, but with a different focal length for beam particles and fusion products (evaporation residues), as shown in the figure below. The beam particles are stopped, whilst the evaporation residues, focused to a point further along the beam axis, enter a position sensitive multiwire proportional counter. They are identified by their time-of-flight with respect to the beam pulse, and their energy-loss signal in the detector.

SOLITAIRE will be used to carry out sensitive studies of the influence of nuclear rotations and vibrations on the fusion process, which can give thousand-fold enhancements of fusion probabilities. This will impact on understanding fusion reactions leading to the formation of new heavy elements. Other applications of SOLITAIRE will be in gamma-ray spectroscopy, studying the structure of new nuclei, and in advanced materials characterization.