Repetitive velocity-scan systems

The only other essential equipment in these constant-velocity spectrometers comprises a y-ray detection system, a timer, and a scalar for registering the accumulated count at each successive velocity. 

The advantages offered by a constant-velocity spectrometer include the ability to examine a small velocity range not centred on zero velocity, and to calibrate the instrument direetly in terms of absolute velocity. It is also often considered to be less expensive than the alternative velocity-sweep techniques considered in Section 2.3, but this probably applies only to simple demonstration equipment. A constant-velocity instrument of any precision must involve considerable expense in machine-shop and development time. 

The cumulative result of these disadvantages has been to restrict the continued development of constant-velocity spectrometers. One of the few major developments of recent years has been the description of an instrument which takes readings at a number of velocities pre-programmed on a length of punched tape [14]. The great majority of investigations are now made using repetitive velocity-scan systems. 

Mechanical drives can be very tedious to operate (unless they are very fully automated) because of frequently having to alter the velocity setting. The availability of small, transistorised, multichannel analysers embodying tj pically 400 or 512 individual scalars in a computer-type memory store prompted de Bennedetti to suggest their use for Mossbauer data acquisition 

Several types of command waveform have found favour, and three of these 

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