John T. Park

A Heavy‐Ion Energy Loss Spectrometer

A high resolution system for the measurement of the energy loss spectra of 20–250 keV heavy ions incident on gas targets is described. The high resolution is obtained by decelerating the ion beam to a low, well defined energy before performing the energy analysis. The energy loss spectrum is determined by changing the accelerator energy to compensate for energy lost in collisions with the gas atoms. The system is arranged so that normal fluctuations in the accelerators power supply do not affect the energy resolution. The resolving power of the system is 2.5×104. The primary proton beam has a detected WHM of 2 V at 50 kV. An energy loss spectrum is shown for which the collision‐excited 11S‐21P transition in helium is clearly resolved.

System for Data Acquisition from High Voltage Terminals

An inexpensive data acquisition system has been designed to provide high voltage isolation for data acquisition in analog, digital, and pulse modes. The telemetry system uses GaAs light sources, fiber optics, and phototransistors to accomplish the data transmission. Prewired logic boards have been adapted to accomplish the timing and logic functions. Seven decades of digital data are transmitted error free, pulse data can be transmitted at rates up to 1 MHz, and analog data are transmitted with 0.05% full scale accuracy.

Microprocessor‐based pressure controller

A device for automatic control of pressure in an ion‐atom scattering experiment has been constructed. The system was modeled to achieve the minimum time for transition from one pressure to another. The pressure controller ‘‘learns’’ the system response and iterates the parameters used in ‘‘profiling’’ the valve voltage to reduce the transition time. The device has been used with two different scattering chambers and has worked well with both.

Reactive scattering cell for atomic hydrogen and deuterium

A design for a high‐temperature reactive scattering cell for atomic hydrogen and atomic deuterium is described. At approximately 2700 K a dissociation of the molecular target species of over 95% has been obtained. The lifetime of 340 h of operation is sufficient for precision, long‐time, differential cross‐section measurements.

Charge Transfer in Quasi-One-Electron Systems at 'High' Energy

The authors have made absolute and relative measurements of differential cross sections for single-electron transfer in collisions between Mg+ (30-150 keV) and Be+ (56.25 keV) ions and He atoms. The behaviour of transfer probability as a function of impact parameter can be understood qualitatively from recent molecular orbital calculations of quasi-one-electron systems.