A. M. Vinodkumar

The heavy-ion magnetic spectrometer PRISMA

Abstract PRISMA is a magnetic spectrometer for heavy ions under construction at Legnaro, with very large solid angle (80 msr), wide momentum acceptance (± 10%) and good mass resolution via TOF measurement; it will be dedicated to the study of nuclear dynamics and nuclear structure with stable and exotic ion beams. This is a review of its main features and of the present status of the project.

A search for deeply bound kaonic nuclear states

Abstract We have measured proton and neutron energy spectra by means of time-of-flight (TOF) from 4He( K stopped − , p / n ) reactions (KEK PS E471 experiment). In the proton spectrum, a clear mono-energetic peak was observed under semi-inclusive condition, which was assigned to the formation of a strange tribaryon S0(3115) with isospin T = 1 . The mass and width of the state were deduced to be 3117.7 −2.0 +3.8 ( syst . ) ± 0.9 ( stat . ) MeV / c 2 and 21.6 MeV / c 2 , respectively, and its main decay mode was Σ N N . In the neutron spectrum, a mono-energetic peak was found as the result of a detailed analysis, which was assigned to the formation of another kind of strange tribaryon S+(3140). The mass and width of the state were deduced to be 3140.5 −0.8 +3.0 ( syst . ) ± 2.3 ( stat . ) MeV / c 2 and 21.6 MeV / c 2 , respectively, and its main decay mode was Σ ± N N . The isospin of the state is assigned to be 0. The results are compared with recent theoretical calculations.

Study of transfer channel coupling and entrance channel effects for the near and sub-barrier fusion of 46Ti+64Ni, 50Ti+60Ni and 19F+93Nb systems

Abstract The fusion excitation functions for the 46 Ti+ 64 Ni , 50 Ti+ 60 Ni and 19 F+ 93 Nb systems have been measured from ∼ 10% below to 15% above the nominal Coulomb barrier, utilizing the recoil mass separator, HIRA at the Nuclear Science Centre, New Delhi. Mean spins have been deduced from the fusion cross sections by two different methods, one using the statistical model and the second by a fit to the fusion cross sections. Good agreement is found between them. It is seen that the simplified coupled-channel calculations, with couplings to the lowest surface inelastic excitations alone, do not explain both the observed fusion cross sections and mean spins in the low energy domain for all the three systems. A systematic comparison is made between the systems 46 Ti+ 64 Ni and 50 Ti+ 60 Ni which have quite different ground-state transfer Q -values ( Q gg ) for the transfer channels. The 46 Ti+ 64 Ni system shows a significant enhancement of the sub-barrier fusion cross section and mean spin as compared with the 50 Ti+ 60 Ni system, indicating the importance of the transfer channel coupling. Fusion cross section and mean spin have been studied for the near and sub-barrier fusion of the highly mass asymmetric system 19 F+ 93 Nb and compared with those for the 48 Ti+ 64 Ni system leading to the same compound nucleus via the nearly symmetric entrance channel. Since the 19 F+ 93 Nb system has a large positive Q gg for one-proton pick-up, the fusion data have been complemented by one-nucleon transfer measurements at energies around the Coulomb barrier. A simultaneous analysis of the fusion excitation functions and mean spin data indicates no significant effects that may be related to the entrance channel mass asymmetry.

Search for pairing-vibration states of even Ca isotopes in 40Ca + 208Pb transfer reactions

Abstract.Multi-nucleon transfer reactions in 40Ca + 208Pb have been studied at several bombarding energies close to the Coulomb barrier. Light reaction products have been identified in mass and charge with a time-of-flight spectrometer. The energy spectra of the inclusive two-neutron pick-up channel show a population in a narrow region of excitation energies which corresponds to the predicted energy of pairing-vibration states in 42Ca.

Weak Interaction Studies Using a Paul Trap

New developments in ion cooling and ion bunching allow the trapping of radioactive ions from a low energy beam, in a very short time scale and with very good efficiency. The performances of Radio Frequency Quadrupole (RFQ) coolers, recently developed in several laboratories in Europe and USA, are now better known. In the present study, a RFQ device will be used to inject 6He+ ions in a transparent Paul trap. The ion beam will be delivered by the SPIRAL facility at GANIL. The careful measurement of the β-recoil ion coincidence spectrum is sensitive to the angular correlation parameter a, which depends on the coupling constants of the weak hamiltonian. It should be equal to −1/3 if the interaction is only of axial vector type (V-A theory). Deviation from this value would imply a new tensor-like interaction involving a new exchange boson thus introducing new physics beyond the Standard Model.

Search for low lying dipole strength in the neutron rich nucleus 26Ne

Coulomb excitation of the exotic neutron-rich nucleus 26Ne on a natPb target was measured at 58 A.MeV in order to search for low-lying E1 strength above the neutron emission threshold. Data were also taken on an natAl target to estimate the nuclear contribution. The radioactive beam was produced by fragmentation of a 95 A.MeV 40Ar beam delivered by the RIKEN Research Facility. The set-up included a NaI gamma-ray array, a charged fragment hodoscope and a neutron wall. Using the invariant mass method in the 25Ne+n channel, we observe a sizable amount of E1 strength between 6 and 10 MeV. The reconstructed 26Ne angular distribution confirms its E1 nature. A reduced dipole transition probability of B ( E 1 ) = 0.49 ± 0.16 e2fm2 is deduced. For the first time, the decay pattern of low-lying strength in a neutron-rich nucleus is obtained. The results are discussed in terms of a pygmy resonance centered around 9 MeV.

Gas amplification in isobutane and P10 filled gas counters

Abstract Gas amplification factors have been measured for isobutane and P10 gases in single wire proportional counter and parallel plate avalanche counter geometries for reduced field strength value ranging from 140 to 1000 V cm −1 Torr −1 . Data using the SWPC were found to satisfy the Aoyama formula for gas amplification with m = 0 and also the Diethorn formula. The PPAC data are satisfactorily described again, by the Aoyama formula with m = 0 as well as by the Zastawny formula. The values of the relevant parameters in the formulae used have also been extracted from the fits.

Production of neutron-rich nuclei by multinucleon transfer reactions

Abstract Some aspects of multinucleon transfer reactions relevant for the production of neutron-rich nuclei are discussed. A short overview is given of representative results obtained in thick target experiments and in recent high-resolution studies done at LNL with a time-of-flight spectrometer.

A modular focal plane detector system for the heavy ion reaction analyzer at NSC, New Delhi

Abstract A detector system has been developed for the focal plane of the HIRA. It consists of two independent detectors, a low-pressure multiwire proportional counter (LP-MWPC) followed by a split-anode ionization detector. Details of the design and test results are presented. Using slow preamplifiers, the position resolution is 21 mm and the time resolution is estimated to be 1.5 ns for the LP-MWPC. The ionization detector gives 2.4% energy resolution for 150 MeV “Si scattered off a gold target and the AZ/Z obtained for 28Si+27A1 is l/42 for Z= 14. Some results for fusion and transfer studies for the 48Ti+58Ni and 28Si+68Zn systems, respectively, at energies around the Coulomb barrier, are presented to highlight the performance of the detector system. 1. Introduction Recoil mass spectrometers (RMS) are versatile tools for heavy ion reaction studies [ 1,2]. Coupled to a high rejection for beam-like particles is the excellent mass resolution with large solid angle, and space and energy focusing. They are ideally suited for studying reactions which are forward peaked and have found good application in the study of fusion and transfer reactions around the Coulomb barrier, spectroscopy by residue tagging, etc. The heavy ion reaction analyzer (HIRA) at the Nuclear Science Centre is a large solid angle RMS, details of which are presented elsewhere [3]. An important part of such spec- trometers is the focal plane detector system (see Refs. [4,5] and references therein). At the focal plane, the HlRA brings to focus particles of varying values of

Fusion measurements for the

Evaporation residue (ER) and fission cross sections were measured for the reaction 18 O+ Pt 194 forming the compound nucleus 212 Rn. Fission fragment angular distributions and anisotropies are consistent with the saddle point model predictions. Measured ER cross sections were fitted with statistical model calculations assuming shell-corrected free energy fission barrier height.