Facilities

The device, which has been in operation since 1994 for lifetime measurements (nanoseconds - picoseconds), was initially designed and fabricated by the Delhi University group. The RDD is routinely used in the GDA system along with the 14 element BGO multiplicity filter.

The array, which covers nearly 4π solid angle, has been fabricated for using in conjunction with GDA. It has large efficiency for detecting protons and α particles evaporated from neutron deficient nuclei in a nuclear reaction. The array consists of fourteen charged particle detectors (phoswich detector, optical guide, PMT base) along with required cables and electronics (buffer module and amplifier cum attenuator module). The scattering chamber include target ladder, collimator support and current feedthrough.

This device is designed and fabricated by the Punjab University group. The spectrometer consists of five wedge shaped magnets with a thick lead absorber. For detecting the electrons, a Si(Li) detector is used. A facility test with the reaction ¹¹B(¹²⁴Sn, 5n)¹³⁰Cs at 55 MeV beam energy was carried out in the GDA beamline with six Compton-suppressed germanium detectors. The conversion electrons from ¹³⁰Cs were identified by gating with γs from the multiplicity filter. Now the facility is open for nuclear structure work at IUAC.

Ensemble of excited and aligned (perpendicular to the beam direction) nuclei is formed in nuclear reactions. The resulting anisotropic intensity distribution of γ-rays can be perturbed due to the extra-nuclear electromagnetic fields (through hyperfine interactions) depending on the lifetime of the excited state. The extracted perturbation factor, observed in the integral or differential mode with respect to time, is proportional to the product of the nuclear parameter (magnetic and quadrupole moments) and the atomic environment (magnetic field and electric field gradient due to electronic spin and charge distribution). The PAD technique is well established technique in most of the accelerator laboratories because of the following reasons:

(i) The static electromagnetic moments (crucial for the unambiguous nuclear structure information) of the excited states can be measured only through this technique.

(ii) As compared to the Mossbauer and the NMR techniques this is a very sensitive technique. For the problems in condensed matter physics, one can have very low concentration (to reduce the impurity – impurity interaction) of probe atoms of most of the elements with no limitation of the temperature.

The PAD facility at IUAC consists of angular correlation table, target chamber and a C-type electromagnet (to provide maximum 1.8 T magnetic field between the 1” pole gap). Both type of detectors, scintillator and semiconductor, can be mounted in the plane perpendicular to the magnetic field. In the past, main interest has been for the systematic investigations of the nuclear structure (configuration and the quadrupole deformation) and the decay mechanism of the K-isomers in Hf-Ta region. Now the PAD setup is redesigned and the experiments are planned for the nuclear moment measurements using the transient magnetic fields and the ionic state of the transitional impurities in dilute magnetic semiconductors.