Disintegration of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">N</mml:mi></mml:mrow><mml:mrow><mml:mn>14</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math>by Thermal Neutrons

Coon, J. H.; Nobles, R. A.

doi:10.1103/physrev.75.1358

Cited by 39 publications

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“…More accurate measurements of the abundance of aHe in 4He have subsequently been made, notably by Aldrich and Nier (1946) and by Coon (1949). Aldrich and Nier used a mass spectrograph of high resolution in which the ~He peak was clearly resolved from the HD peak, a necessary requirement in the measurement of such very small abundances of 3He.…”

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confidence: 98%

“…The more recent measurements of Coon involved the observation of the rate of nuclear reaction of 3He when the gas was placed in a known slow neutron flux. aHe has a large cross section for thermal neutrons (5000 barns for 293 ° neutrons (Coon and Nobles 1949, King and Go]dstein 1949, Batchelor, Epstein, Flowers and Whittaker 1949), yielding the reaction 3He (n, p) 3H. The experiment therefore consisted in putting the helium gas under test in a proportional counter locate d in a region containing thermal neutrons and counting the rate of the 3He disintegrations.…”

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“…Another mechanism has been suggested by Libby (]946), namely the transformation of laN in the air by fast neutron bombardment from cosmic rays in the reactions I~N (n, 12C) aH and 14N (n, 3~) SH, after which the SH decays to SHe. Libby estimated that although the reactions require high energy neutrons (see Cornog and Libby 1941) they would be sufficiently frequent to account for the SHe content of the air. Downloaded by [University of California Santa Barbara] at 03:39 18 June 2016…”

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Properties of helium three at low temperatures

Daunt

1952

Advances in Physics

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Properties of helium three at low temperatures

Daunt

1952

Advances in Physics

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“…Such an investigation has been carried out using techniques similar to those previously described. 2 A proportional counter having a known sensitive volume was filled with a 31.4-cc sample of pure He 3 to which was added Kr at suitable pressure. Nearly monenergetic neutrons were produced at various energies in the range from 0.4 to 3.0 Mev by use of the two reactions: T(/>,w)He 3 and D((/,w)He 3 .…”

Section: University Of California Los Alamos Scientific Laboratory mentioning

confidence: 99%

Disintegration ofHe3by Fast Neutrons

Coon

1950

Phys. Rev.

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with the annihilation of B\ and after the fermion has emitted B 2i the Fermi particles are annihilated with the emission of B z . A second way in which this process can take place is obtained if the antifermion emits B 2 . The triangles in the two cases differ only in the directions of the Feynman arrows.The only difference in the matrix elements for the two transitions is that the first one contains the trace of the matrix X~X 1 (p l -m)-l X 2 (p2-m)-iXs(p z -m)-\ while the second contains the trace of the matrixwhere pi are appropriate functions of the energy-momentum fourvectors of bosons and Fermi particles combined with -y M according to Feynman. The minus signs of pi in X f occur in the usual way when the behavior of fermions is contrasted with that of antifermions. By Eq.(1) x ,T =(-ycxc-\where r of the matrices Xi satisfy Eq. (1) with the minus sign.Taking the traces of the matrices makes it at once evident that the contributions of the two processes cancel each other if r is odd.Other contributions to the total matrix element are obtained by permuting the processes involving 5», which means orienting the triangle in different ways with respect to the time direction. These contributions can similarly be grouped into pairs.For the sake of simplicity we have considered a triangular loop, but it is obvious that the above argument can be generalized for any closed loop. Hence, we have Furry's theorem for transitions between neutral bosons: processes associated with closed loops which can be traversed in opposite directions are forbidden if an odd number of odd Dirac matrices are associated with that closed loop.Analogous selection rules can be formulated for the case where the bosons in Eq. (2) are neutral and charged mesons. In this case, to every way in which a transition can take place, there corresponds a second way which is obtained by replacing in the Feynman triangle, protons (neutrons) by antineutrons (antiprotons) or vice versa.Let the contribution of the first process depend on the trace of where n (*=1, 2, 3) are the isotopic spin matrices. The contribution from the second process then containswhere the introduction of ri effects the above replacements. SinceT\Ti T -TiTl (*=1, 2),where r denotes the number of odd matrices among Xi (i-1, 2, 3), and ^ the number of neutral mesons. This result can be generalized as follows for transitions between neutral and charged mesons via nucleons: Transitions between charged and neutral mesons associated with reversible closed nucleon loops are forbidden if the sum of the number of odd Dirac interaction matrices and the number of neutral mesons is odd.The first theorem plays a fundamental role in a process like vacuum polarization. The second theorem will apply in cases where, for instance, a heavy charged meson decays into a lighter charged meson and a neutral one. Thus far no such decay process has been observed. i R. P. Feynman, Phys. Rev. 76, 769 (1949). 2\V. H. Furry, Phys. Rev. 51, 125 (1937). 3\V. Pauli, Rev. Mod. Phys. 13, 203 (1941). Our C equals Pauli'...

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“…Consider the transition 01-*02+03 (2) between three neutral bosons (photons or neutral mesons), the process taking place by means of the virtual creation and annihilation of fermions. According to reference 1, the Feynman diagram will be a closed triangle of fermion and antifermion lines with boson lines at the vertices.…”

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Selection Rules for Closed Loop Processes

Wyk¹

1950

Phys. Rev.

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I N an earlier note, 1 we described a method of measuring the cyclotron frequency of ions with an instrument which we called the omegatron. In illustration of the promise of this method, w r e presented a preliminary value of the ratio of the cyclotron frequency of the proton v e to its precessional frequency v n in the same magnetic field. Because this preliminary value has been used by others in several publications, we feel that our most recent results should be made available, although further work will probably improve the accuracy.A careful study made it apparent that the resonant frequency could be shifted by more than 1 part in 5000 by sufficiently varied operating conditions. A consistent method of correcting for these shifts, which are attributable largely to space charge, has now been developed. Since the frequency shift is proportional to the mass, the true cyclotron frequency can be determined by using the isotopic weights of the ions. The frequency shift can thus be determined by making measurements under identical experimental conditions on several masses. Consistent results for the proton have been obtained by correcting with H 2 + , D 2 + , and H 2 0 + . A detailed description will be presented later. Our result is now ir"Ac=2.79268=fc0.00006,where v n was measured in water. This ratio is MP> the proton moment in nuclear magnetons 2 (without diamagnetic correction). Using the gyromagnetic ratio of the proton, 3 T P = (2.67523db0.00006)X10 4 sec." 1 gauss" 1 (no diamagnetic correction), and the isotopic weight of the proton, 4 A p = 1.007580, the faraday is F=9652.03 ±0.3 e.m.u./g (physical scale).Combining our result on the frequency ratio with the measurement of Gardner and Purcell 5 one obtains J/ p /w,= 1836.12±0.05.

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Disintegration ofHe3andN14by Thermal Neutrons

Cited by 39 publications

References 8 publications

Properties of helium three at low temperatures

Properties of helium three at low temperatures

Disintegration ofHe3by Fast Neutrons

Selection Rules for Closed Loop Processes

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