M. Salomaa

Sub-barrier fusion ofNi58,64withNi64andGe74

Differential cross sections for evaporation residue formation following complete fusion of /sup 64/Ni and /sup 74/Ge with 171 to 215 MeV /sup 58/Ni and /sup 64/Ni ions were measured with high precision using a velocity selector together with a counter telescope. The resulting excitation functions for complete fusion ranged in magnitude from 10 ..mu..b to 300 mb. The excitation functions exhibited a strong response, at subbarrier energies, to changes in the underlying nuclear structure. We interpreted these variations as evidence that the fusion proceeds through dynamic single-particle/softness-related processes. A phenomenological analysis was performed. In the analysis, we employed the WKB method, constructed a simple interaction potential and introduced a radially-dependent effective mass. The use of the variable effective mass led to a meaningful description of our above-barrier data and to improvements towards describing our subbarrier data.

Velocity selector for heavy-ion separation☆

Abstract A velocity selector with an electric field strength of 0–40 kV/cm and a magnetic field strength of 0–4000 G has been designed for the purpose of separating heavy-ion reaction products, particularly from fusion reactions. The instrument has been installed at the Tandem Facility of the Brookhaven National Laboratory and is being used mostly in conjunction with a magnetic spectrograph to produce an energy-mass spectrograph (EMS) described in full in the preceding paper.

A HIGH INTENSITY NANOSECOND PULSED VAN DE GRAAFF ACCELERATOR

Abstract A description is given of a Van de Graaff generator modified for nanosecond pulsing in the terminal. The beam is chopped by sweeping past a limiting aperture by an RF oscillator. A discussion is given for the choice of design parameters. Pulse widths as low as 2 × 10 −9 seconds have been obtained. Typical operating conditions are 3 × 10 −9 seconds pulse width, 1 40 duty cycle, peak currents 0.8-1 mA, with an average current of 17 μA. Measured gamma ray and neutron time spectra are shown.

In-flight mass separation of 205Rn, 206Rn and 207Rn fusion recoils from the 197Au(14N, xn) reaction using an energy-mass spectrograph

Abstract A recently constructed energy-mass spectrograph has been used to study the in-flight fusion products from the reaction 197Au(14N, xn)211−xnRn. Direct mass separation of the evaporation residues 205Rn, 206Rn, 207Rn have been achieved. They are detected by alpha-disintegration tracks on nuclear emulsions located at the spectrographs focal plane. The velocity spectrum and angular distribution of the recoils is determined directly and compared to predictions of multiple scattering and neutron evaporation predictions. The test of the spectrograph in this study determines practical limits on cross sections and degree of multiple scattering for which in-flight detection of fusion recoils is feasible.

Sub-barrier fusion of /sup 58,64/Ni with /sup 64/Ni and /sup 74/Ge

Differential cross sections for evaporation residue formation following complete fusion of /sup 64/Ni and /sup 74/Ge with 171 to 215 MeV /sup 58/Ni and /sup 64/Ni ions were measured with high precision using a velocity selector together with a counter telescope. The resulting excitation functions for complete fusion ranged in magnitude from 10 ..mu..b to 300 mb. The excitation functions exhibited a strong response, at subbarrier energies, to changes in the underlying nuclear structure. We interpreted these variations as evidence that the fusion proceeds through dynamic single-particle/softness-related processes. A phenomenological analysis was performed. In the analysis, we employed the WKB method, constructed a simple interaction potential and introduced a radially-dependent effective mass. The use of the variable effective mass led to a meaningful description of our above-barrier data and to improvements towards describing our subbarrier data.

Sub-barrier fusion of Ni-58, Ni-64 with Ni-64 and Ge-74

Differential cross sections for evaporation residue formation following complete fusion of /sup 64/Ni and /sup 74/Ge with 171 to 215 MeV /sup 58/Ni and /sup 64/Ni ions were measured with high precision using a velocity selector together with a counter telescope. The resulting excitation functions for complete fusion ranged in magnitude from 10 ..mu..b to 300 mb. The excitation functions exhibited a strong response, at subbarrier energies, to changes in the underlying nuclear structure. We interpreted these variations as evidence that the fusion proceeds through dynamic single-particle/softness-related processes. A phenomenological analysis was performed. In the analysis, we employed the WKB method, constructed a simple interaction potential and introduced a radially-dependent effective mass. The use of the variable effective mass led to a meaningful description of our above-barrier data and to improvements towards describing our subbarrier data.

Automatic liquid nitrogen pumping system for particle accelerators

Abstract A description is given of an automatic liquid nitrogen pumping system. Pumping of liquid nitrogen into cooling traps up to a predetermined level is achieved by an automatically controlled compressed air system. An important feature of the equipment is the ability to switch automatically from an empty liquid nitrogen reservoir to a full one. This allows for a much more flexible operation than in conventional systems where the reservoir has to be replaced manually when empty.