The N-Ring array consists of 6 individual detectors. The
detectors replace the 6 most forward elements of the BGO inner ball and therefore
they are placed on a ring at 20o against the beam axis. The distance
from the target to the front face of the neutron detectors is of about 30 cm.
Each detector is filled with 1 liter of BC501A liquid scintillator that is characterized
by good timing properties (~ 3 ns.). The inner walls of the detectors were painted
with reflector paint BC622A. The light produced in the liquid scintillator is
collected by standard 3 in. photomultiplier tubes through a quartz window. The
10 cm. depth of the detectors yields an intrinsic efficiency for evaporation
neutrons of about 25%. Each detector subtends a solid angle of 1%. The resulting
total efficiency of the detector system is of the order of 3-5 % depending on
the reaction kinematics. To reduce the large counting rate produced by the x-rays
emitted XXlarge counting rate produced by the X-rays emitted following the reactions,
in front of each detector were placed composite absorbers made of Pb/Cu/Cd.
The signals from the PMT's are analyzed by CAMAC modules that produced three
output signals: energy, zero crossing (Z/C) and time.
The neutron energy accepted by these modules ranges from 200 keV to 10 MeV.
The Z/C signal is used to discriminate neutrons from gammas. The modules allow
for the multiplexing of both the analogue and digital signals. The programming
and control of the neutron modules could be easily integrated in the GASP's
computer control system. The good suppression of the channels with charged particles
evaporation makes such a device a unique filter for the selection of proton-rich
nuclei close to the N=Z and proton drip-line, populated with extremely low cross
sections. In recent experiments with this detector we have pushed the observational
limit of GASP down to 10-5, as in the case of the N=Z nucleus 88Ru
populated with only ~3 microbarn cross section.