APS News

April 2013 (Volume 22, Number 4)

Letters to the Editor

Centrifuges, not Lasers, the Real Proliferation Danger


Regarding the January Back Page on “The Benefits and Risks of Laser Isotope Separation”: It seems strange that you should pick on an inefficient method that had already been tried for years at Livermore. Centrifugal separation is much more efficient and is the reason we are worried about Iran’s program. 

In the 1970s, Livermore had a large program for isotope separation using copper lasers. At the same time, TRW had a large program using ion cyclotron acceleration of uranium in a magnetized plasma, based on the theory and impetus of John Dawson. It was headed by Don Arnush, who reported to Peter Staudhammer, and the theoretical group was headed by Burt Fried. I am the only survivor. The method made clever use of the fact that a minority species could be accelerated to much larger orbits than the majority species. The experiment was a success, and palpable quantities of U235 could be obtained. Nonetheless, the politicians canceled the program to protect Livermore’s status as a national lab. (You can tell I’m incensed about this.)

Years later, the Dawson scheme was revived in several places for the purpose of making medical isotopes, but they all ran out of money. Most recently, Alfred Wong, after retiring from UCLA, formed the company Nonlinear Ion Dynamics LLC, in which he had a new Dawson Separation machine built with superconducting coils. I don’t know what became of that. On Wong's website, I see that in 2011 he was working on “charged-fluid centrifuges for separation of large quantities of isotopes.”

I wrote up a summary of the Dawson Separation project as a chapter entitled “The Double Helix: The Dawson Separation Process” in the book From Fusion to Light Surfing, Lectures on Plasma Physics Honoring John M. Dawson by Thomas Katsouleas (now Engineering Dean at Duke). This paper is No. 136 in my website below. As far as I know, I am the only one with copies of all the previously classified memos produced in the project.

It would be more fruitful to develop the Dawson scheme for medical isotopes rather than using lasers, which are more glamorous and more attractive to the ill-informed. Furthermore, one cannot discuss proliferation without emphasizing centrifuges.

Frank Chen
Los Angeles, CA


Nothing Wrong with Fewer Women Physicists


I was shocked by the quote from Kate Kirby in the February APS News in which she says, “Encouraging women to pursue physics is a top priority for us.” If you believe that physicists “should” be 50% men, 50% women, and then try to achieve that goal by “encouraging” girls to pursue physics, you are deciding ahead of time what you believe the percentage should be, and then trying to make that happen. This would be the same as if you believed that physicists “should” be 100% men, 0% women, and then tried to achieve that goal by discouraging girls to pursue physics. It is morally wrong to believe that the percentage of physicists who are women should have any specific value. If you believe that in a perfect ideal world, physicists would be 50% men, 50% women, do you also believe that in a perfect ideal world, nurses, elementary school teachers, and secretaries would also be 50% men, 50% women? Nurses, elementary school teachers, and secretaries are 90% women, 10% men. Nobody thinks that’s a problem. Nobody says we should encourage boys to enter those professions. If boys are less interested in those professions, what’s wrong with that? If physicists are 80% men, 20% women, why would that be a problem? If girls are less interested in being physicists, what's wrong with that?

Jeffery Winkler
Hanford, CA

Solution to Pioneer Anomaly is Premature

Michael Lucibella’s “Top Physics Newsmakers of 2012” in the February APS News listed the culprit for the Pioneer Anomaly as having been found. I think this is premature. Turyshev’s paper dealt with only the Pioneer 10 (P10). Much of the data used to calculate the forces are less well known or are unsupported by other data. A lower anomaly occurred during the Saturn encounter of P11. Also, the P11 values were slightly different from the P10 data. The P10 data at the furthest distance flattened and increased which is inconsistent with a declining thermal cause. Although this increase is within error limits, several readings showed the trend. Turyshev et al.’s 2011 paper suggested the Pioneer anomaly may be Earth directed which is inconsistent with a declining thermal cause. The cosmological connection is unexplained by the thermal model. The solar and sidereal diurnal periodicities are unexplained by a thermal model. Anderson 2002 overreaches the uncertainty of the JPL’s Horizons data. At the very least we should wait until Turyshev’s model is compared to P11 data.
Although Turyshev’s paper is probably the last possibility for traditional physics, a new physics cause may still be possible.

John C. Hodge
Flat Rock, NC


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Editor: Alan Chodos
Staff Science Writer: Michael Lucibella