Neutron Beam Spectrometer Studies of Boron, Cadmium, and the Energy Distribution from Paraffin

James Rainwater; William W. Havens, Jr

doi:10.1103/PhysRev.70.136

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Neutron Beam Spectrometer Studies of Boron, Cadmium, and the Energy Distribution from Paraffin

James Rainwater and William W. Havens, Jr.

Columbia University, New York, New York

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Phys. Rev. 70, 136 – Published 1 August, 1946

DOI: https://doi.org/10.1103/PhysRev.70.136

Abstract

A slow neutron velocity selector has been developed for use with the Columbia University cyclotron. By the method of arc modulation, neutron production is usually confined to intervals of (10-200) microseconds out of a (1000-10,000) microsecond cycle. Neutrons slowed down in paraffin are detected by B $F_{3}$ proportional counters. Excellent collimation is obtained by using an extensive $B_{4}$ C and Cd collimating system. Experiments were conducted principally at a 5.4-meter source detector distance. A special selector system counts all the neutrons detected and also selectively counts those detected in an adjustable timed interval after the cyclotron burst. The slow neutron energy distributions from paraffin "source" slabs were shown to be of a modified Maxwellian form with an asymmetrical high energy "tail." Data for the resonance absorption by Cd were well matched by a one-level Breit-Wigner formula having $E_{0} = (0.180 \pm 0.008)$ ev, $Γ = (0.112 \pm 0.006)$ ev, $σ_{0} = (7, 800 \pm 800) \times 10^{- 24}$ ${cm}^{2}$ /atom. The results of measurements with several boron filters over the range of 0.01 ev to over 100 ev were well matched by the $\frac{1}{v}$ relation, $σ_{B} = (118 \pm 4) E^{- \frac{1}{2}} \times 10^{- 24}$ ${cm}^{2}$ /atom.

References (13)

Submitted by James Rainwater in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Faculty of Pure Science, Columbia University, New York, New York
H. A. Bethe, Rev. Mod. Phys. 9, 113-161 (1937)
H. B. Hanstein, Phys. Rev. 59, 489 (1941)
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H. Feeny, C. Lapointe, and F. Rasetti, Phys. Rev. 61, 469 (1942)
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G. A. Fink, Phys. Rev. 50, 738 (1936)
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Fertel, Gibbs, Moon, Thompson, and Wynn-Williams, Proc. Roy. Soc. 175, 316 (1940)
J. H. Manley, L. J. Haworth, and E. A. Luebke, Phys. Rev. 61, 152 (1942)
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Henry Carroll, Phys. Rev. 60, 702 (1941)
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[c1] Submitted by James Rainwater in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Faculty of Pure Science, Columbia University, New York, New York

[c2] H. A. Bethe, Rev. Mod. Phys. 9, 113-161 (1937)

[c3] H. B. Hanstein, Phys. Rev. 59, 489 (1941)

[c4] W. J. Horvath and E. O. Salant, Phys. Rev. 59, 154 (1941)

[c5] H. Feeny, C. Lapointe, and F. Rasetti, Phys. Rev. 61, 469 (1942)

[c6] Dunning, Pegram, Fink, Mitchell, and Segré, Phys. Rev. 48, 704 (1935)

[c7] G. A. Fink, Phys. Rev. 50, 738 (1936)

[c8] L. W. Alvarez, Phys. Rev. 54, 609 (1938)

[c9] Fertel, Gibbs, Moon, Thompson, and Wynn-Williams, Proc. Roy. Soc. 175, 316 (1940)

[c10] J. H. Manley, L. J. Haworth, and E. A. Luebke, Phys. Rev. 61, 152 (1942)

[c11] C. P. Baker and R. F. Bacher, Phys. Rev. 59, 332 (1941)

[c12] Henry Carroll, Phys. Rev. 60, 702 (1941)

[c13] Whitaker, Bright, and Murphy, Phys. Rev. 57, 551 (1940)

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Neutron Beam Spectrometer Studies of Boron, Cadmium, and the Energy Distribution from Paraffin

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