Neutron Fission Of 235U Research Articles

STRUCTURE IN THE MASS–YIELD DISTRIBUTION FOR U235 FISSION

Recent measurements of the cumulative yields of essentially all the mass chains in the thermal neutron fission of U235 have enabled a detailed examination of the fine structure in the mass–yield curve. It has been found that most of the structure results from a slowly changing neutron yield as a function of the mass of the primary fission fragments.

New measurements of the age of U235 fission neutrons in hydrogenous materials

New measurements of the age of U235 fission neutrons in hydrogenous materials

ON THE PRODUCTION OF Be7, Mg28, AND Ni66 IN THE SLOW NEUTRON FISSION OF U235

The yields of 53-day Be7, 21.3-hour Mg28, and 56.6-hour Ni66 from the slow neutron fission of U235 have been investigated. Upper limits of 3 × 10−7% and 4.2 × 10−9% have been set for the fission yields of Be7 and Mg28 respectively. A fission yield of 2.0 ± 1.0 × 10−8% has been found for the formation of Ni66. These results are compared with the current knowledge of the frequency of triple fission of U235.

Slowing down of fission neutrons by water

In this articie we describe the method and results of measurement ofτfor U235 fission neutrons slowed down by water to energies of 1.46 ev. The value obtained for τ1.46 ev = 294 ± 1.5 cm2

Slowing down of fission neutrons by uranium-Water media

The spatial distribution of resonance neutrons (E = 1.46 ev) which results from the slowing down of U235 fission neutrons emitted by a “point” source is measured for three variations of a uranium-water lattice made of thick slugs (35 mm) of natural uranium enclosed in cadmium tubes. The absence of anisotropies in the distribution of slowed-down neutrons is demonstrated, and the values of τ determined.

A Measurement of the Average Number of Neutrons per Fission from Uranium and Bismuth when Bombarded with 147 MeV Protons

A direct measurement of the average number of neutrons per fission from uranium and bismuth excited by 147 MeV protons has been made by coincidence method. Taking the figure for the average number of neutrons per thermal neutron fission of 235U to be 2.5 ± 0.1, the results obtained are 13.1 ± 1.6 for uranium and 10.0 ± 2.7 for bismuth.

THE YIELD OF Cs138 IN THERMAL NEUTRON FISSION OF U235

The yield of Cs138 in thermal neutron fission of U235 has been investigated using the 4π counting technique. The value obtained for the fission yield is (7.22 ± 0.29)% based on a value of 6.32% for the fission yield of Ba140. The half-life of Cs138 was determined and found to be 32.2 ± 0.1 min.

Slowing Down Distribution of U235 Fission Neutrons from a Point Source in Light Water

The results of a measurement of the slowing down distribution in water of neutrons from a point fission source to indium resonance energy, 1.458 ev, are given. The second, fourth, sixth, and eighth moments of the measured distribution are calculated and have the values, r̄2=184.7 cm2, r̄4=1.222×105 cm4, r̄6=2.27×108 cm6, and r̄8=8.6×1011 cm8.

Slowing Down Distribution to Indium Resonance of U235 Fission Neutrons from a Point Fission Source in Two Aluminum Light Water Mixtures

The mean square slowing down length, r̄2, has been measured for two aluminum light water mixtures, the aluminum-to-water volume ratios being 1:1 and 1:2 by volume. The values of r̄2 obtained are 460.7 cm2 and 297.4 cm2, respectively.

DETERMINATION OF THE ABSOLUTE FISSION YIELD OF Ba140 IN THERMAL NEUTRON FISSION OF U235

The absolute fission yield of Ba140 in the thermal neutron fission of U235 has been determined to be (6.32 ± 0.24)%. The reaction B10(n, α)Li7 was used as a neutron monitor and the B10/B11 ratio determined mass spectrometrically before and after neutron bombardment. The Ba140 disintegration rate was determined using 4π counting techniques. The half-life of La140 has been found to be 40.31 ± 0.06 hr.

THE FISSION YIELDS OF Ba139 AND Ba140 IN NEUTRON FISSION OF U235 AND U238

The fission yields for Ba139 and Ba140 for thermal neutron fission of U235 and fast fission of U238 have been measured using naturally occurring uranium. This was accomplished by comparing the barium fission product activities with the U239 formed in radiative capture. With these data the fission yields were calculated from known values of the cross-sections for thermal fission and capture in uranium and were found to be 6.1% and 5.6% for Ba139 and Ba140, respectively, for thermal fission and 5.1% and 4.2% for Ba139 and Ba140, respectively, for fast fission. The contribution of resonance fission to the thermal neutron effect has been shown to be less than 5% in the irradiation arrangement used.