Abstract. The cumulative yields for 13 short-lived neutron rich nuclei in the mass range A = 99 to A = 118, produced via the 23~Th (~,f) reaction were determined at four incident beam energies covering the range from 28 to 72 MeV using y-spectroscopy of fission products. The charge distribution parameter Zp was determined for the A = 99 mass chain at all the four incident beam energies of 28.5, 39.7, 50.8 and 71.4 MeV and was found to fit into a description of fission process with unchanged charge division (UCD). The measured cumulative yields were converted into chain yields assuming UCD and the yieldmass distribution was obtained at all the above energies. The mass distribution remains asymmetric even at 71.4 MeV, the highest energy studied in this work. The excitation energy dependence of the mass and the charge distribution and of the cumulative yields indirectly suggests that the fission has predominantly proceeded from a relatively low level of excitation allowing most of the excitation energy to be carried away by light particles prior to scission.

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A four-rod type heavy-ion radio frequency quadrupole (RFQ) linac has been designed, constructed, and tested for the rare ion beam (RIB) facility project at VECC. Designed for cw operation, this RFQ is the first postaccelerator in the RIB beam line. It will accelerate A/q < or = 14 heavy ions coming from the ion source to the energy of around 100 keV/u for subsequent acceleration in a number of Interdigital H-Linac. Operating at a resonance frequency of 37.83 MHz, maximum intervane voltage of around 54 kV will be needed to achieve the final energy over a vane length of 3.12 m for a power loss of 35 kW. In the first beam tests, transmission efficiency of about 90% was measured at the QQ focus after the RFQ for O(5+) beam. In this article the design of the RFQ including the effect of vane modulation on the rf characteristics and results of beam tests will be presented.

A 33.7 MHz heavy-ion radio frequency quadrupole (RFQ) linear accelerator has been designed, built, and tested. It is a four-rod-type RFQ designed for acceleration of 1.38 keVu, qA> or =116 ions to about 29 keVu. Transmission efficiencies of about 85% and 80% have been measured for the unanalyzed and analyzed beams, respectively, of oxygen ((16)O(2+), (16)O(3+), (16)O(4+)), nitrogen ((14)N(3+), (14)N(4+)), and argon ((40)Ar(4+)). The system design and measurements along with results of beam acceleration test will be presented.

A novel experimental approach has been employed for the measurement of ␤-delayed protons from 24 Si produced via the fragmentation of a 28 Si beam with an energy of 100 MeV/nucleon. The secondary beam of 24 Si was separated by the projectile fragment separator RIPS at RIKEN and was implanted in a 2.6 m aluminum foil placed parallel to a gas-⌬E and silicon-E detector telescope for the measurement of delayed protons. The above arrangement has led to a very clean, ␤-ray background free delayed proton energy spectra and a few new proton peaks could be identified from the decay of 24 Si.