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

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 ≥1 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 28Si scattered off a gold target and the ΔZ/Z obtained for 28Si+27Al is 1/42 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

Transfer measurements for the Ti plus Ni systems at near barrier energies

Large enhancements have been observed in the sub-barrier fusion cross sections for Ti + Ni systems in our previous studies. Coupled channel calculations incorporating couplings to 2(+) and 3(-) states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer were carried out for Ti-46,Ti-48 + Ni-64 systems. The present paper gives the results of these studies

Ionospheric photoelectrons at Venus: Initial observations by ASPERA-4

Abstract We report the detection of electrons due to photo-ionization of atomic oxygen and carbon dioxide in the Venus atmosphere by solar helium 30.4 nm photons. The detection was by the Analyzer of Space Plasma and Energetic Atoms (ASPERA-4) Electron Spectrometer (ELS) on the Venus Express (VEx) European Space Agency (ESA) mission. Characteristic peaks in energy for such photoelectrons have been predicted by Venus atmosphere/ionosphere models. The ELS energy resolution (DE/E$7%) means that these are the first detailed measurements of such electrons. Considerations of ion production and transport in the atmosphere of Venus suggest that the observed photoelectron peaks are due primarily to ionization of atomic oxygen.

Transfer and higher-order phonon coupling effects in the sub-barrier fusion of {sup 28}Si and {sup 93}Nb

Measurements have been carried out for the fusion excitation function and one and two nucleon transfer probabilities at energies near and below the Coulomb barrier for the system 28 Si 93 Nb. The recoil mass separator HIRA at the Nuclear Science Center, New Delhi, has been used for these measurements. A coupledchannels formalism has been employed for explaining the observed enhancement in the sub-barrier fusion cross section. Present results support the significance of positive Q-value transfer channel in the sub-barrier enhancement. The possible role of higher-order multiphonon coupling effects in the reaction mechanism have also been investigated. S0556-28139703910-

The effect of spacecraft radiation sources on electron moments from the Cassini CAPS electron spectrometer

Data from the Cassini plasma spectrometer (CAPS) electron spectrometer (ELS) have been found to be contaminated with an energy-independent background count rate which has been associated with radiation sources on Cassini. In this paper we describe this background radiation and quantitatively assess its impact on numerically integrated electron moments. The general properties of such a background and its effects on numerical moments are derived. The properties of the ELS background are described and a model for the background presented. A model to generate synthetic ELS spectra is presented and used to evaluate the density and temperature of pure noise and then extended to include ambient distributions. It is shown that the presence of noise produces a saturation of the electron density and temperature at quasi-constant values when the instrument is at background, but that these noise level moments are dependent on the floating spacecraft potential and the orientation of the ELS instrument with respect to the spacecraft. When the ambient distribution has a poor signal-to-noise ratio (SNR) the noise determines the density and temperature; however, as the SNR increases (increasing primarily with density) the density and temperature tend to those of the ambient distribution. It is also shown that these noise effects produce highly artificial density–temperature inverse correlations. A method to subtract this noise is presented and shown to correct for the presence of the noise. Simulated error estimates for the density and temperature are also presented. The analysis described in this paper not only applies to weak background noise, but also to more significant penetrating backgrounds such as those in radiation belt regions of planetary magnetospheres

Transfer and higher-order phonon coupling effects in the sub-barrier fusion of 28Si and 93Nb

Measurements have been carried out for the fusion excitation function and one and two nucléon transfer probabilities at energies near and below the Coulomb barrier for the system 28Si+93Nb. The recoil mass separator HIRA at the Nuclear Science Center, New Delhi, has been used for these measurements. A coupled-channels formalism has been employed for explaining the observed enhancement in the sub-barrier fusion cross section. Present results support the significance of positive Q-value transfer channel in the sub-barrier enhancement. The possible role of higher-order multiphonon coupling effects in the reaction mechanism have also been investigated

Sub-barrier few-nucleon transfer reaction and channel coupling effects in heavy ion fusion

Measurements of sub-barrier transfer reactions are reported for the systems 28Si + 64Ni, 32Si + 64Ni and 28Si + 144Nd using the recoil mass spectrometer HIRA in kinematic coincidence mode. The problem related to M/Q-ambiguity in measurements with mass separators has been resolved. Excellent mass resultion with a large solid angle is obtained by correction of the aberrations. Simplified coupled-channels calculations are carried out for these systems with transfer form factors extracted from the measured transfer probabilities. The surface vibration coupling is treated up to two phonon states with second-order coupling terms