Digital Signal Processing for Complete Spectroscopy of Rotating Nuclei

High resolution gamma ray spectroscopy using large array of high
purity germanium detectors is extremely effective to probe the nuclear
shapes at varying angular momentum and isospin. Improved sensitivity of
such array continues to provide new insight on the shell structure and
residual interactions among the nucleons which determine the nuclear
shape. The Indian National Gamma ray detector Array (INGA) is recently
commissioned at the TIFR-BARC accelerator facility. INGA is designed for
24 Compton suppressed clover detectors. For optimum utilization of the
detector array the associated data acquisition (DAQ) system needs to
satisfy a variety of requirements some of which are conflicting with each
other. The requirement of the DAQ of the array is to provide the energy
and timing information for all the 96 channels for 24 clovers vetoed with
the Compton suppressed BGO shields even at high count rate. Coupling the
clover detector data acquisition system with other ancillary detectors is
also required. A digital data acquisition system based on PCI-PXI based
architecture meets the aforementioned requirements. In this DAQ, each
pre-amplifier signal is digitized at 100 MHz sampling speed separately and
further processed digitally to extract required information about the
incident radiation. One such digital DAQ is implemented at TIFR for the
ongoing experiments using the array. Compared to our conventional systems
with analog shaping, the new digital system provides higher throughput,
better energy resolution and better stability. Recent results obtained
from the array will be compared to the conventional systems with analog
shaping. Its scope for future nuclear structure experiments and medical
imaging will be discussed.