Wednesday, March 12, 2008

As for me, I'm unbound
A recent article in Physical Review Letters (see the citation below) published by a group of researchers at GANIL reports the detection of "the most neutron-proton unbalanced system presently found." Hydrogen-7. Wow.
I won't pick at the details - the experimental group has done an excellent job, despite having used SRIM for their energy loss calculations (SRIM and I don't get along... 30% is not an acceptable error). Seven events is nothing to be sneezed at, nor is the use of a helium-8 beam or a cross section (the probability, if you will, of the reaction occurring) in the microbarn range (though, with such low statistics, errors are always appreciable). It should be noted that the researchers didn't actually detect the 7H, since it lives such a short time, but they instead detected the telltale remnants of the reaction from which the hydrogen would emerge (namely, the 13N and tritium from the reaction 8He + 12C -> 13N + 7H -> 13N + 3H + 4 neutrons), and reconstructed the reaction kinematics from there. I can't say that I've ever attempted to fit seven data points with a curve that requires two free parameters... it almost doesn't seem fair. It does amuse me, however, to wonder at what point we must acknowledge that it's not really hydrogen anymore. It's really more like a proton with six neutrons in its general vicinity, and with a lifetime of less than 10^-21 seconds (that's a decimal place, 20 zeros and then a 1 at the end), it almost doesn't count as a resonance. It's one of the most unbound resonances I've ever encountered. But, still, physics at the edge is great physics, even if the error bars remind me of my freshman-year introductory physics labs. As a brilliant man told me today, "7H is almost a neutron star, I think."

Caamaño, M., Cortina-Gil, D., Mittig, W., Savajols, H., Chartier, M., Demonchy, C.E., Fernández, B., Gómez Hornillos, M.B., Gillibert, A., Jurado, B., Kiselev, O., Lemmon, R., Obertelli, A., Rejmund, F., Rejmund, M., Roussel-Chomaz, P., Wolski, R. (2007). Resonance State in ^{7}H. Physical Review Letters, 99(6) DOI: 10.1103/PhysRevLett.99.062502


  1. I like the witty analysis, despite my physics handicap. ~brandon

  2. Even better is the witty (if uncouth) use of physics metaphors in poetry.


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