New Automation Technique for Constant Velocity Mössbauer Spectrometers
1.E. Kankeleit, Rev. Sci. Instr. 35, 195 (1964). This work describes a popular “speaker” type system and gives references to earlier work along these lines.
2.P. A. Flinn, Rev. Sci. Instr. 34, 1422 (1963). This paper describes one example of a constant velocity, automated mechanical system.
3.J. G. Mullen, Phys. Rev. 131, 1410 (1963). This gives an example of a “rapid scan,” time mode mechanical system.
4.R. H. Nussbaum, F. Gerstenfeld, and J. K. Richardson, Am. J. Phys., 34, 45 (1966).
5.G. K. Wertheim, Phys. Today, 20, 31 (1967). The strong objections to mechanical systems raised in this article are not inherent in the present system or in the crank system described3 in 1963.
6.O. C. Kistner (private communication) has developed a system of the electromechanical type which permits programming of data similar to the one which we describe, and in fact is the “speaker” analog of our mechanical system. These two systems complement each other and both have distinct advantages for particular types of experiments. The mechanical system has the inherent advantage of allowing the motion of heavy Dewars and furnaces, thereby permitting independent control of the source and absorber temperatures. The speaker system, on the other hand, permits a short scan time for sampling of all velocities, which minimizes effects due to count rate drift. Another noteworthy point of comparison is that the credibility of the mechanical system is more easily established, because absolute velocities instead of relative velocities are measured, and because it is difficult to demonstrate convincingly that signals from secondary transducer coils have a one‐to‐one correspondence with velocity to better than a few percent. Despite this difficulty, however, the trend in the field appears to be towards electromechanical systems, perhaps because these systems can be purchased commercially.
7.A Gaertner model M‐301 microscope slide was used to convert rotary motion to linear motion. Bushings made from Kel‐F, a plastic bearing material which does not suffer from “cold flow,” were substituted for the metal ones used in the Gaertner leadscrew, to minimize vibrations. In addition, the leaf springs used to tension the slide were removed to eliminate another possible source of vibration. The direct reading feature of the microscope slide permits quick and accurate measurement of the displacement of the slide.
8.Hamner AEC standard modular electronics were used for most of the commercial electronics such as scalers, amplifier, etc. Each scaler has provision for remote control operation such as start, stop, inhibit, and reset.
9.Teletype printer model 33, equipped with tape perforator.
10.It should be noted that noise from external components, such as the drive motor and mechanical relays can produce unwanted signals in the automation electronics. This effect was eliminated by careful shielding of interconnecting cables, and by operating the drive motor from an ac line separate from the line used for the power supply to the electronics. Also all relays were run on a power supply different from the one used for the automation electronics to insure that relay noise did not initiate false commands.
11.Metron variable ratio changer, DVR‐650‐F1. Metron Instruments, Denver, Colo.
12.For those who have not built mechanical spectrometers we give the following suggestions, which hint at some of the inherent difficulties. (a) Ball bearings on the final drive should be avoided as they are notorious sources of vibration. (b) The final drive table should be shock mounted from floor vibrations. (c) Vibrations from motors and speed reducers must be isolated from the final drive table. Tilton elastic belts were used for this purpose in our apparatus. (d) Very stable speed reducers must be used to avoid velocity drift. Direct measurements of the long term drift for the custom Metron speed reducer used in the present apparatus indicate a maximum drift of less than 0.1% at all speed ratio settings.
13.R. M. Housley, J. G. Dash, and R. H. Nussbaum, Phys. Rev. 136, A464 (1964).While our linewidth is better than that generally measured, it is not as narrow as that described in this article. We believe that our system would show equally narrow lines if a more dilute source had been used, although this point was not experimentally verified.
14.Texas Instruments optical sensor such as H 35, or 1N2175.
15.The Hamner data scanner which is used in our apparatus supplies a level during printout. This level is inverted through G1 so as to give a level upon completion of printout.
16.A. H. Muir, Jr., K. J. Ando, and H. M. Coogan, Mossbauer Effect Data Index (John Wiley & Sons, Inc., New York, 1966), p. 24.
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