SHARC (Silicon Highly-segmented Array for Reactions and Coulex) is a charged particle detector, used in conjunction with TIGRESS, that detects the direction and energy of light charged particles, particularly protons, emit during nuclear reactions.
Although it can be used for Coulomb excitation experiments as well, it has proven to be the key element of the transfer-reaction program, and it is for these experiments that it is best suited.
For instance, the strontium experiments described in the TIGRESS section use SHARC. The 95Sr beam was directed upon a target containing deuterium (one proton and one neutron). After the reaction, if the outgoing particle was a proton, then the neutron had to have been transferred into the beam, forming 96Sr. If the outgoing particle was tritium (one proton and two neutrons), then a neutron was stripped from the beam, forming 94Sr. SHARC measures not only the direction and energy of the outgoing particle, but it can also determine whether or not it was a proton, deuterium nucleus, or tritium nucleus.
TRIUMF scientists learn about the orbit of the transferred neutron, and other nearby neutrons, by measuring the overall strength of the reaction as measured by TIGRESS via gamma ray detection, and the scattering direction of the proton. SHARC measures the scatter distribution of protons relative to the beam axis, a pattern that reveals how the outermost nucleon in the beam ion orbits the rest of the nucleus, its angular momentum.
Transfer reactions can reach ground and excited states of nuclei, so SHARC experiments can reveal the orbital structure of many different states in the nucleus and is thus a powerful tool for exploring shape coexistence.
The development of SHARC was led by scientists from the University of York and funded by a major grant from the UK Science and Technology Facilities Council. SHARC research involves a TRIUMF research collaboration with scientists from eight universities in the UK, USA, France, and Canada.
How it Works
SHARC’s silicon detectors are located inside the central focus in the TIGRESS target chamber. Eight square detectors, each approximately five-centimeters on a side and less than a millimetre thick, form a box around the beamline, and the ends of the box are closed by four pie-shaped detectors each.
To enable the accurate measurement of the angle at which a charged particle is detected, the detectors are divided into 16-to-32 electrical segments, perpendicular to one another.