HYBALL Charged-Particle Detector System

Construction of a small, Hybrid-4-pi (HYBALL) array of charged-particle detectors to operate as an inner ball inside the CLARION array of clover Ge detectors, is in progress. The first phase of the project, which consists of an array of 95 CsI(Tl)-crystals coupled to photodiodes has been completed and is being commissioned with beams from the HRIBF. Preliminary results indicate that its use with CLARION and RMS will allow excellent channel selection by simultaneous detection of light-charged particles emitted in heavy-ion fusion-evaporation reactions. In addition, it will allow kinematic reconstruction of the recoil momenta and, thus, event-by-event correction of the gamma-ray spectra for the Doppler broadening introduced by particle emission.

Fig 1. - A view of the CsI portion of the HYBALL as seen from the beam direction.

The requirements to minimize the attenuation of gamma-rays prohibits the use of massive detectors. The combination of CsI(Tl) coupled to large area photodiodes provides a thin compact detector Fig. 1. This technology has been successfully used with the 8-pi-Miniball [1] and the Gammasphere-Microball [2]. Particle identification will be achieved by pulse shape discrimination with electronic gates on CsI(Tl) output pulses. The detector consists of a 95-element CsI(Tl) array mounted in 9 concentric rings shown in Fig. 2. and described in Table 1. In the second phase, 79 of the CsI detectors will be used to cover angles greater than 25 degrees and will be complemented, without loss of efficiency, with large-area, segmented, silicon microstrip detectors in the forward direction. Proton-alpha discrimination in the Si-detectors may be achieved using either a single layer in the transmission mode, or two layers of Si-detectors in a dE-E configuration.

Fig. 2 - The CsI portion of HYBALL mounted in the target chamber. Note the preamplifier section is mounted directly inside the overhead support structure. The CLARION array and first quadrupole of the RMS is also observed.

The Hyball array is housed in an aluminum target chamber with a forward funnel that will accommodate the microstrip-Si-detectors Fig. 3. The geometry of this chamber minimizes the exposure of the Ge- and CsI-detectors to the gamma-rays and positrons resulting from the decay of the scattered radioactive ions.

Fig. 3 - The CsI portion of HYBALL mounted in the target chamber. The support structure inside the vacuum system can be seen as well as the open construction of the target chamber. The target and charge reset foil vacuum ports which allow changing of targets without letting the entire target chamber up to air can be seen below the chamber.

More images of hyball and other experimental equipment may be found in our picture gallery. The people and institutions involved in this project are A. Galindo-Uribarri, C. Baktash, W. Barnett, J. W. McConnell, D. C. Radford, ORNL, C. J. Gross, J. W. Johnson, ORISE J. Mas, JIHIR and E. Padilla, S. Pascual, Mexico City.


[1] A. Galindo-Uribarri, Prog. Part. Nucl. Phys. 28, 463 (1992).
[2] D.G. Sarantites et al., Nucl. Instr. and Meth. A 381, 418 (1996).

This information was last updated on July 21, 2000.
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