Chronology of Milestone Events in Particle Physics - UREY 1932B
Chronology of Milestone Events in Particle Physics

UREY 1932B

Urey, H.C.; Brickwedde, F.G.; Murphy, G.M.;
A Hydrogen Isotope of Mass 2 and its Concentration
Phys. Rev. 40 (1932) 1;

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Reprinted in
The Physical Review - the First Hundred Years, AIP Press (1995) 75.

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In a recent paper Birge and Menzel pointed out that if hydrogen had an isotope with mass number two present to the extent of one part in 4500, it would explain the discrepancy which exists between the atomic weights of hydrogen as determined chemically and with the mass spectrograph, when reduced to the same standard. Systematic arrangements of atomic nuclei require the existence of isotopes of hydrogen H2 and H3 and helium He5 to give them a completed appearance when they are extrapolated to the limit of nuclei with small proton and electron numbers. An isotope of hydrogen with mass number two has been found present to the extent of one part in about 4000 in ordinary hydrogen; no evidence for H3 was obtained. The vapor pressures of pure crystals containing only a single species of the isotopic molecules H1H1, H1H2, H1H3 were calculated after postulating:
1. that the rotational and vibrational energies of the molecules are the same in the solid and gaseous states;
2. that in the Debye theory of the solid state, the 's are inversely proportional to the square roots of the molecular masses;
3. that the free energy of the gas is given by the free energy equation of an ideal monatomic gas; and
4. that there is a zero point lattice energy equal to (9/8)R per mole.
The calculated vapor pressures of the three isotopic molecules in equilibrium with their solids at the triple point for ordinary hydrogen are in the ratio p11:p12:p13 = 1:0.37:0.29. The isotope was concentrated in three samples of gas by evaporating large quantities of liquid hydrogen and collecting the gas which evaporated from the last two or three cc. Sample I was collected from the end portion of six liters evaporated at atmospheric pressure and samples II and III from four liters, each, evaporated at a pressure only a few millimeters above the triple point.
These samples and ordinary hydrogen were investigated for the visible, atomic Balmer series spectra of H2 and H3 from a hydrogen discharge tube run in the condition favorable for the enhancement of the atomic spectrum and for the repression of the molecular spectrum, using the second order of a 21 foot grating with a dispersion of 1.31 per mm. When with ordinary hydrogen, the times of exposure required to just record the strong H1 lines were increased 4000 times, very faint lines appeared at the calculated positions for the H2 lines accompanying H1, H1 and H1 on the short wavelength side and separated from them by between 1 and 2 . These lines do not agree in wave-length with any known molecular lines and they do not appear on the plates taken with the discharge tube operating under conditions favorable for the production of a strong molecular spectrum and the repression of the atomic spectrum. With ordinary hydrogen they were so weak that it was difficult to be sure that they were not irregular ghosts of the strongly overexposed atomic lines. Samples II and III evaporated near the triple point show these lines and another near H1 greatly enhanced relative to the H1 lines over those with ordinary hydrogen showing that these new lines are not ghosts, and that a considerable increase in the concentration of the isotope had been effected. With sample I, evaporated at the boiling point, no appreciable increase in concentration was detected. The new lines agree in wave-length with those calculated for an H2 isotope.
The H2 lines are broad as is to be expected for close unresolved doublets, but they are not as broad and diffuse as the H1 lines, probably due to the smaller Doppler broadening. The H2 line is resolved into a close doublet with a separation that agrees within the accuracy of the measurements with the observed separation for H1.
Relative abundances were estimated by comparing the times required to just record photographically the corresponding H1 and H2 lines. The relative abundance of H2 and H1 in natural hydrogen is estimated to be about 1:4000 and in the concentrated samples about five times as great.

Related references
See also
R. T. Birge and D. H. Menzel, Phys. Rev. 37 (1931) 1669;
W. H. Keesom and H. van Dijk, Proc. Acad. Sci. Amsterdam 34 (1931) 42;
F. W. Aston, Proc. Roy. Soc. A115 (1927) 487;
F. A. Lindemann, Phil. Mag. 38 (1919) 173;
H. A. Barton, Phys. Rev. 35 (1930) 408;
F. A. Lindemann and A. W. Aston, Phil. Mag. 37 (1919) 523;
G. Beck, Z. Phys. 47 (1928) 407;

Particles studied
  deuteron ex, mass, qn

Record comments
Discovery of the deuteron.
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