Zero-degree telescope

Beam particles that do not react in the target, and also in many cases the beam-like products from transfer reactions, will pass through the centre of the forward annular detector. In many applications, it will be sufficient to record these particles and to identify the atomic number. In other cases, it will be necessary to record the angle at which the particle left the target, for example in a transfer experiment that produces an unbound state that sequentially decays. The detailed design of the zero-degree telescope could be changed for different experiments. The basic design included with the array uses one or two single-sided resistive strip detectors, backed by a CsI(Tl) scintillator. The strip detectors can both be used as as passing detectors, or the beam could be stopped in the second detector. In either case, the strips would be arranged at right-angles so that a position measurement was made in each direction. Particle identification will be achieved using the $\Delta E.E$ method. The complete kinematics of the binary transfer reactions will then allow the mass to be inferred. The use of strip detectors is also advantageous in terms of splitting the zero-degree counting rate between essentially independent detectors. By placing the zero-degree detector at a greater distance from the target, the angular divergence of the beam (say, one degree in the case of SPIRAL) can be exploited to spread the beam particles across the strips. For more-energetic beams such as those obtained from LISE rather than SPIRAL, it is not practical to use silicon detectors to stop the beam. In these cases, the beam intensity is likely to be reduced relative to SPIRAL intensities, for the reactions of interest, and 10⁴ pps would be a typical intensity. In these cases, the CsI(Tl) detector provides an excellent choice for the stopping detector.