Parkins replies: Henry F. Ivey asserts that the pinch effect in electron beams due to residual gas ionization was well known to many researchers including us at Cornell University. He states that it differs only in the trivial change of polarity, but there are other significant differences:
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▸ The pinch effect is localized.
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▸ It contains many small fields.
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▸ A mass spectrometer cannot tolerate even slight space-charge repulsion.
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▸ In the calutron’s final design, the entire tank fills with a uniform equipotential plasma except for a thin sheath only a few volts positive relative to the tank wall.
This surprising natural process was totally unexpected. The Japanese gave up on even trying mass spectrometry, as did the Germans, because they did not believe that the space-charge fields, even minor ones, could be overcome. Ernest Lawrence and his small team at Berkeley had no idea of this phenomenon. They were surprised, and Lawrence enthusiastically welcomed our research and invited us to Berkeley. This was no pinch that created partial ionization in a limited region; this was total homogeneous plasma but, as stated in box 2 of my article, apparently perfect and with no upper limit on beam intensity.
The calutron succeeded in producing the fissionable material for the Hiroshima bomb during World War II. The same apparatus has been used to manufacture isotopes of great benefit to science, technology, industry, and medicine.
Ned Rasor’s letter displays a grand vista of natural processes, which all must have at least two cooperating steps that lead to a beneficial result. As implied in box 2 of my article, there are countless millions of natural processes in the life sciences, particularly in biology, and only a handful in the physical sciences. Evolution created the discrepancy. A few natural processes over which humankind has no control include magnetopause, the ozone layer, favorable winds, ocean gyres, the precipitation cycle, and fusion within the Sun.
Nature may also be capable of creating and sustaining physical processes that can be initiated and sustained by humans. Those are a limited number of countable processes that include automatic neutralization in the calutron and electric discharges such as cold cathodes, arcs, and the elegant example Rasor describes. Physical scientists as well as life scientists may find this great discrepancy between the two fields a challenging problem.
Woodlief Thomas Jr says that the Tennessee Eastman branch of Eastman Kodak was chosen to manage the Manhattan Project. However, that branch’s only assignment was managing the electromagnetic Y-12 plant. With this one modification, Thomas’s statement at the end of his letter is entirely correct.
[Editor’s Note: After a period of failing health, Bill Parkins died on 30 September 2005. We are honored that, as his daughter told us, he was driven in his last days to complete this reply for our readers.]
