The Origin of the Survey Meter 

Paul Frame, Oak Ridge Associated Universities

A Very Early, if Not the First, Radiation Survey Meter

It was during 1928, his first year at the NBS, that Lauriston Taylor probably received the bulk of his lifetime dose from radiation. It happened while he was calibrating clinical radiation meters in an x-ray beam. After one instrument change-out, he forgot to replace a two foot by two foot lead panel that was in his direct line of sight of the 200 kV water-cooled tube. Unfortunately he didnít notice that the panel was missing until he had completed several minutes of high intensity measurements.

Reconstructing the exposure, and performing measurements with film and a Fricke-Glasser dosimeter, he estimated that he had received an exposure of 200 R. At the time, he was somewhat relieved because this was substantially lower than what was being used in radiotherapy. Nevertheless, he felt that it was probably best to prevent the recurrence of such an event. His solution was to construct a battery operated instrument which he could carry with him to measure exposure rates. The device employed a string electrometer that was coupled to one of three interchangeable thin-walled aluminum chambers. If not the first, it was certainly a very early portable survey instrument.

Robley Evans Invents the Count Rate Meter

Robley Evans is generally credited with developing the first whole body counter, the purpose of which was to measure the radium burden in the bodies of radium workers. This device employed a geiger-mueller (GM) tube and Evans wanted to improve its sensitivity. To this end, he undertook a series of exhaustive investigations into the role of fill gas pressure and cathode construction (Evans and Mugele 1936). The result was a GM tube that used a copper screen as its cathode. The increase in the cathode surface area gave the detector double the gamma sensitivity of the traditional tubeósomething sufficiently marvelous that Lauriston Taylor (Taylor and Sauer 1984) remarked it was "so nice, itís almost cheating." 

Still, the achieved sensitivity presented a problem: the mechanical registers that were used to count the pulses had a long resolving time (ca. 0.1 second) and couldnít handle the higher count rates. What to do? The solution came to Evans during a particularly good rally with co-worker Newell Gingrich in a ping pong game in Evansí basement (Kathren and Ziemer 1980). Evans shouted, "Iíve got it!," stopped the game and explained the concept to a skeptical Gingrich who didnít think it would work. Perhaps, Gingrich was in a contrary mood because of the interruption to a game he thought he was about to win. In any event, the next morning Evans and Gingrich built a prototype. Lo and behold, it worked: the first direct reading count-rate meter (Gingrich et al 1936). They referred to it as a "speedometer."

Robley Evans and the First Radiation Survey with a Count Rate Meter

However, to my knowledge, the next story has never been written down. It was told to me by Dr. Evans in the summer of 1995. Since then, Bob Gallaghar has added a couple of details. It is the story of the very first radiation survey using a count-rate meter:

The year was 1936, or thereabouts. A radium-containing industrial radiography source had disappeared at a General Electric (GE) facility in Lynn Massachusetts and GEís insurance company, Liberty Mutual, was immediately notified. To head off liability claims, Liberty Mutual contacted Evans at MIT and asked him to help locate the missing source. Evans packed up his count-rate meter, a long extension cord, and a GM detector, and off he went. Surveying the plant with his bulky equipment connected to long cables and running off AC current was a cumbersome process, but eventually Evans located a strong source of radiation coming from an unexpected location: a workerís locker. When the locker was opened, the manís clothes were inside and the radium source was in the pocket of a shirt. The worker was immediately tracked down and found to have a severe skin burn on his chest. And on his back, opposite the burn on the front of his body, was a patch of erythema. As Evans recounted the incident, "It got him right through the heart . . . those were the days of the wild west."

References

Evans, R.D.; Mugele, R.A. Increased gamma-ray sensitivity of tube counters and the measurement of the thorium content of ordinary materials. Rev. Sci. Instr. 7:441-449; 1936.

Gingrich, N. S.; Evans, R.D.; Edgerton, H.E. A direct-reading counting rate meter for random pulses. Rev. Sci. Instr. 7:450-456; 1936.

Kathren, R.L. and Ziemer, P.L. ed., ďHealth Physics: A Backward GlanceĒ  Pergamon Press , New York , 1980;

Taylor, L. S.; Sauer, K.G. Vignettes of early radiation workers (Transcripts of the videotape series): Robley D. Evans. U.S. Dept. Of Health and Human Services; Rockville; 1984.

 

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