Outlook

The MUST array [22] developed in France is an example of a high solid angle silicon strip system that is suitable for this type of experiment, and it has been used successfully to study inelastic scattering in inverse kinematics and for the ¹⁰Li experiment described in section 5. This array is particularly well adapted to studies of inelastic scattering and of reactions leading to unbound nuclei, using Method 2.

  

Figure 5: Preliminary design for TIARA (Transfer and Inelastic All-angle Reaction Array) which is being developed in the UK, specifically to use particle-gamma coincidences to study transfer reactions induced by radioactive beams.

The TIARA array [23] has recently commenced development in the UK, and is planned to be installed at GANIL for experiments using both secondary fragmentation beams and reaccelerated beams from the SPIRAL facility. The preliminary design for the silicon array at the heart of TIARA is shown in fig. 5. This is designed to be mounted inside of the EXOGAM gamma-ray array [15] in its most compact geometry with the germanium detectors approximately 50 mm from the target. The paramount criterion was to fit a high resolution, $\sim 4\pi$ array within this small space. The adopted solution includes an octagonal barrel of silicon detectors with resistive strips oriented parallel to the beam direction. One face of the octagonal barrel is omitted, to allow the target to be inserted via a vacuum interlock, and oriented at a suitable angle on its frame. The most forward and backward reaction angles are instrumented using annular non-resistive strip detectors that are placed further from the reaction region and can be shielded from the EXOGAM detectors. The vacuum vessel away from the interaction region is large enough to allow additional beam tracking detectors. At angles close to zero degrees, the beam-like particles emerge and are detected using either a pixellated particle telescope or, ideally, a magnetic spectrometer that can discard the actual un-reacted beam particles. The TIARA design has been made to allow the coupling of the array to the VAMOS spectrometer [15] which is designed with large angular and momentum acceptances, specifically for radioactive beam experiments, and is being built at GANIL. Fig. 5 shows the back plate of the TIARA assembly, which mounts directly on to the front of the entrance quadrupole of VAMOS. Transfer reactions induced by radioactive beams have already been established as a useful spectroscopic tool. The first generation of specialised transfer arrays, of which TIARA is an example, is under construction. Their use is poised to escalate with the imminent availability, at several facilities worldwide, of a wide range of reaccelerated radioactive beams at Coulomb barrier energies. This will reveal new information about shell structure near exotic magic numbers, and also new information about low-lying levels in deformed nuclei far from stability.