b. Calculation of information required by the experimenter during the experiment, for example, kinematics tables and particle energies corresponding to field strengths in analyzer magnets.
c. Process-control operations, in which the computer directs or regulates a sequence of events in an experiment. Under program control the computer monitors the course of the experiment and supplies signals that cause automatic changes in experimental conditions, such as starting and stopping times of event counting, angles of observation of scattered particles, and accelerator energies. Such applications are designed to relieve the experimenter of unnecessary labor and to reduce the probability of error in routine operations.
Our final class involves even more complex calculations.
Class 3 operations:
a. Complicated treatment of reduced data, including least squares and curve fitting.
b. Large-scale calculations such as those required for the evaluation of theoretical nuclear scattering and reaction cross sections, e.g., DWBA calculations, which may each require running times of the order of minutes, even at a modern computing center.
Apparently Class 3 operations do not always have to be done during the course of the experiment; in fact, they can in most cases be carried out later, leisurely, at the local computing center. Nonetheless, calculations of the first type, and to a lesser extent the second, are currently being done at laboratories having large, powerful computers in their on-line data-acquisition systems.
C. THE COMPUTERS
1. Introduction
Because computers have proved useful in so many fields, many varieties are now on the market, quite a few of them having properties highly suitable for nuclear-data acquisition. The properties particularly useful are, first, the ease with which a great variety of external input and output devices can be attached (interfaced to the computer); second, provisions for rapid, efficient response to interrupt signals from external devices; and third, usually a means of transferring data from external devices directly into blocks of memory without use of the central processor, the transfer possibly requiring only a single memory cycle per word. (This is referred to as direct memory access through a direct data channel.)