C. V. K. Baba

Semiclassical description of one- and two-nucleon transder reactions at large distances in heavy ion collisions

Abstract It is shown that the variation of the one- and two-nucleon transfer probability with distance can be understood on the basis of semiclassical models if the contributions from the nuclear and Coulomb branches of the classical deflection function are considered. A shallow potential, with a diffuseness parameter a = 0.8–0.9 fm for the real part of the heavy ion optical potential, was found necessary to understand the data.

Search for a light neutral particle in the decay of the 3.68 MeV state in 13C

A search is made for a short lived neutral particle, o, in the decay of the 3.68 MeV (32-) state in 13C. No evidence for such a particle with a rest mass in the region of 1.7–2.0 MeV/c2 is found with a limit on the branching ratio Γ o/Γγ⩽7×10 −5. An upper limit of 10−6 is placed for the coupling of such a particle to proton/neutron.

A multi NaI(Tl) detector array for medium energyγ-ray spectroscopy

An array of seven hexagonal NaI(Tl) detectors has been set up for measuringγ-ray spectra in the energy region 5 MeV ≤Eγ ≤ 40 MeV with good accuracy. This is in contrast to earlier set ups which mostly used one large sized (about 10 inchesφ × 15 inches long)NaI(Tl) detector. This set up has been made for the study ofγ decay of GDR based on high spin states and ultra-dipole radiations.The array has been provided with the following features: a) TOF discrimination against neutrons, b) pile up detection and elimination, c) active and passive shielding to cut down background and d) an array of trigger counters for multiplicity dependence measurements. The well known program EGS4 has been used to determine the response of the array forγ-rays in the energy region 5–40 MeV and several test measurements have been carried out to confirm the validity of the calculated response functions. Some typicalγ-ray spectra fromα and16O induced reactions measured at VECC, Calcutta and Pelletron accelerator at TIFR are also shown.

A search for colour van der Waals interaction

It is suggested that the strength of nuclear colour van der Waals interaction, if present, can be determined by measuring deviations from Rutherford scattering of charged hadrons from nuclei, at energies well below the Coulomb barrier. Experimental limit on the strength of such a potential is obtained asλ<50, when the colour van der Waals potential is given byV(r)=λ(hc/r0)(r0/r)7, withr0, the scaling length, taken as 1 fm. This limit is obtained from an analysis of existing experiments and by performing scattering experiments of 3–4.6 MeV protons from a208Pb target.

Four quasi-particle level at 2256 keV in182Re

In-beam nuclear spectroscopic studies of182Re, following the reaction181Ta(α, 3n)182Re have been made using gamma-ray and internal conversion electron techniques.K-conversion coefficients for several transitions have been measured and the multi-polarities of the various transitions assigned. In particular, the spin and parity of the four-quasi-particle isomeric level at 2256 keV were determined to be 16−. Theg-factor of this level has been measured to beg = 0·32 ± 0·05. On the basis of theg-factor and the decay pattern of this level, a configuration {v9/2+ [624↑]v7/2− [514↓]v7/2− [503↑]π9/2− [514↑]}kx = 16− has been assigned to this level. The nature of the retardation of the gamma transitions deexciting this level is discussed. It is argued that the measured retardation factors can be explained if the nucleus has a triaxial shape.

An experimental limit on the coupling of a light neutral pseudoscalar particle to hadrons

Detailed results of an experiment, looking for a short-lived neutral particle decaying by ane+e− pair in the decay of the 3.68 MeV (3/2) state in13C, whose decay is predominantly M1, are presented. An upper limit of 7 × 10−5 has been placed on the branching ratio for decay through such a particle with a mass in the range 1.7 to 1.9 MeV/c2. This leads to an upper limit of 10−6 for the coupling of such a particle to nucleons. Such a limit rules out the explanation of thee+ ande− peaks recently observed in heavy ion collisions, as due to the decay of a neutral particle.