Critical Spheres Research Articles

Asking for Trouble

Asking for Trouble

Proliferation resistance properties of u and Pu isotopes

The present study provides a quantitative basis for assessment of proliferation resistance properties of U and Pu isotopes. Within the large area of issues covered by term of proliferation resistance, the only technical characteristics were chosen as a subject for discussion. The present study concentrates on intrinsic proliferation resistance features focusing the material characteristics associated with bare critical mass (BCM), decay heat (DH) and spontaneous-fission neutrons (SFN), which are treated as the main constituents of isotopic barriers against proliferation. The present study aims at determining major proliferation resistant attributes for U and Pu. This determination is largely based on analysis of their critical bare spheres. The MCNP code coupled with JENDL 3.2 data library is the main tool applied for this study. The other characteristics were summarized from the data available in scientific literature.

Marshak Conditions Applicable in Spherical Geometry to the Simplified Spherical Harmonics Equations

The application of the simplified spherical harmonics (SSH) method for neutron transport calculations of critical homogeneous spheres of aqueous solutions of uranium has been reexamined to estimate the error introduced by the use of the simplified P7 approximation. Recalculation of the critical spheres in the SSH-P7 approximation with modified Marshak boundary conditions showed that no substantial error was introduced in the earlier analysis.

Donor States in Highly Compensated Silicon, as Elucidated by Electron Spin Resonance Experiment

The electron spin resonance experiment was performed on phosphorus donors in compensated n -type silicon in the temperature range of 1.5 K to 4.2 K, using the microwave of 46 GHz. From the comparison of the peak shifts of the central lines in highly compensated samples and in uncompensated ones, the average local density of donor electrons were obtained in highly compensated samples, whose magnitude was rather close to N D than N D - N A . This result is interpreted in terms of a simple model that the donor electrons are mostly located outside the critical spheres centred at each negatively charged acceptor as a result of Coulomb repulsion between the donor electrons and the charged acceptors, as first considered by Mott and Davis. The temperature dependence of the peak shift of the central line and the line broadening are also discussed.

Analysis of a Set of Critical Homogeneous U-H2O Spheres

Analysis of a Set of Critical Homogeneous U-H₂O Spheres

A Direct Comparison of Some Nuclear Properties of U-233 and U-235

Nuclear properties of U233 and U235 are compared using data obtained in a series of critical experiments. Aqueous solutions of uranyl oxyfluoride containing uranium enriched to about 90% in each of the two isotopes have been made critical in water-reflected spherical reactors having diameters of 26.4 and 32.0 cm. Assuming the reported nuclear constants for U235 are reliably known and assuming equality of the neutron leakage spectra of U233 and U235 for the same water-reflected critical sphere, the value of η(U233) at 0.026 ev was determined to be 2.31 ± 0.03. The critical masses for the two isotopes in these systems have been measured over the temperature range from 20°C to 100°C; corresponding values of the reactivity temperature coefficient are reported. Delayed neutron yields for the two isotopes were compared by noting the periods resulting from the withdrawal of a boron poison from the critical spheres. It is shown that the yield from U233 is about one-third that from U235, in agreement with other determinations.