Thresholds for Fast Neutron Fission in Thorium and Uranium

Shoupp, W. E.; Hill, J.E.

doi:10.1103/physrev.75.785

Cited by 8 publications

(1 citation statement)

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“…The fission cross section rose rap idly with neutron energy up to about 1.0 Mev and stayed essentially con stant at 1,45 barns from 1.0 to 3.0 Mev. Shoupp & Hill (2) found that U2 a 8 and ThZ3Z fissioned with neutrons above 1.0 Mev, and Grosse, Booth & Dunning (3) fixed the threshold for neutron fission of Pa231 as being higher than thermal energy and less than 2.0 Mev.…”

Section: Fissionability Of Nuclidesmentioning

confidence: 97%

High Energy Fission

Spence¹,

Ford²

1953

Annu. Rev. Nucl. Sci.

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INTRODUCTIONShortly after the discovery that UZ36 readily underwent fission with thermal neutrons, investigations were begun to determine what other nuclides could be made to fission. Neutrons of energy higher than thermal energy were used as well as ')'-rays. As more intense sources of high energy particles were developed, fissionability studies were extended, until at the present time, par ticles with hundreds of million electron volts energy have been used to induce fission in elements as light as copper. In this article we survey the work done on fission using bombarding particles above thermal energies. The first sec tion covers those experimental results which indicate at what energies neu trons, photons, and charged particles have been observed to induce fission in the elemen ts so far studied; some idea of the fission cross sections is also gi ven although in many cases only approximate values have been measured. For convenience, this first section on the fissionability of nuclides has been divided into two parts: the first part deals with heavy elements from thorium on up, while the second part deals with medium elements from bismuth on down. No fission studies have been reported as yet on elements between bismuth and thorium, and from the standpoint of ease of fissionability, the gap be tween the two groups is large. The second section of this article is concerned with the observed changes in modes of fission as the target element and the energy of the bombarding particle are changed. FISSIONABILITY OF NUCLIDESHEAVIEST ELEMENTS (Z >89) Neutron induced fission.-Aside from nuclides such as PUZ39, UZ35, and U233, which undergo " fission with thermal neutrons, Npz37, U2a8, PaZ3t, and Th232 have all been observed to fission with somewhat more energetic neu trons. Klema (1) measured the N p237 fission cross section using neutrons from thermal energy to 3.0 Mev and observed the fission fragment pulses in an ionization chamber. The thermal cross section was apparently zero, but fis sions were observed for 350-kev neutrons. The fission cross section rose rap idly with neutron energy up to about 1.0 Mev and stayed essentially con stant at 1,45 barns from 1.0 to 3.0 Mev. Shoupp & Hill (2) found that U2 a 8 and ThZ3Z fissioned with neutrons above 1.0 Mev, and Grosse, Booth & 1 The survey of the literature pertaining to this review was concluded in June, 1952. 399 Annu. Rev. Nucl. Sci. 1953.2:399-410. Downloaded from www.annualreviews.org Access provided by University of California -San Diego on 06/21/16. For personal use only. Quick links to online content Further ANNUAL REVIEWS 400 SPENCE AND FORD Dunning (3) fixed the threshold for neutron fission of Pa231 as being higher than thermal energy and less than 2.0 Mev. Photon induced fission.-For the five nuclides PU23 9 , U238, U23., U233, and Th232, the photofission thresholds are all 5.3 Mev within a few tenths of a million electron volt [Koch, McElhinney & Gasteiger (4)]. This result is not in accord with the predicted values calculated from the liquid drop model ...

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Section: Fissionability Of Nuclidesmentioning

confidence: 97%