Design of array and target chamber

The TaLL experiment demonstrated that good quality spectra can be obtained with an intense radioactive beam. In singles spectra, beam pulsing is required for background subtraction. The pulsed beam also allows the best reduction of the background in coincidence spectra, but the combination of fast timing and an efficient particle detector can also be effective in the absence of pulsing. Indeed, a particle detector with a very high efficiency for detecting at least one evaporated particle would be a useful addition to the experimental trigger requirement and would significantly reduce the unwanted data processed and written to tape.

 

Figure: Array designs: (a) schematic layout incorporating the important factors as learned from experiment [6], and (b) side view of EXOGAM [7].

The 511 keV background in TaLL was equivalent to 0.02% of the beam being stopped in view of the array, which corresponds to a cross section of approximately 10 barns. This demonstrates the need for good beam quality and the removal of elastically scattered beam from the array. The implications for an `ideal' experimental arrangement [6] are summarised in figure 4(a).