A sphere of LiD 2 feet in diameter was irradiated by 2 x 10<sup>15 14 Mev neutrons. Samples of Li<sup>7 metal were positioned at various radii for the irradiation. An analysis of these samples for tritium led to a determination of the number of tritons produced by 14 Mev neutrons acting on Li<sup>7 in a LiD system.

Recent measurements on the long counter efficiency in which comparisons were made with the (n, p) scattering cross section, additional variations in efficiency were found which varied slowly with neutron energy but were still correlated with the total neutron cross section of carbon. Because of these variations in efficiency there are errors in the fission cross sections reported in LA-1714. Corrections to these data have been given here.

By use of small magnetic probes inserted into the discharge, the magnetic field distributions in the interior of a high-power pinched discharge have been measured as a function of time. From these data the current distributions can be deduced. By applying a static pressure calculation, in the cases when the radical pinch accelerations are small, the plasma pressure nkT in the pinch has been determined, with superimposed axial magnetic fields, and for stable and unstable configurations.

The use of quartz tubing for sampling molten plutonium and for casting rods is described. These procedures offer cheap and easy-to-use methods for obtaining molten samples and for casting long rods with small diameters.

A measurement of the [Lithium-7] reaction cross section by absolute counting of the tritium betas is described. The cross section was measured at several neutron energies between 4 Mev and 15 Mev. A comparison with results by emulsion techniques is given.

The results of a series of neutron diffusion calculations relating to an untamped Orally sphere are presented in detail in this report. The three-velocity neutron transport theory was taken as the basis for the analytical work preceding the computations. This particular theory, also known as the transport approximation, is defined in LA-1271 and known to be quite accurate for assemblies primarily involving materials of large atomic weight. For a sphere of uniform density and atomic composition the transport theory has another advantage. It can readily be formulated in terms of simultaneous integral equations (in our case three), relatively simple in form, involving the collision densities [formula] and a set of parameter values describing the materials. Nb(r) is , as indicated, a function of the radial distance [formula] and the velocity index g, g - 1, 2, 3. The parameters, fifteen in number for the three-velocity theory, are comprised of the velocities, the inverse mean free paths, and the transfer coefficients.

Exponential rise times, T, of neutron flux in an Oy-Tu assembly have been measured for a set of points essentially equally spaced reactivity-wise in the interval between delayed and prompt critical corresponding to [infinity] > T > 5 seconds. The relationship between positive period and reactivity thus obtained is used to decide (preferentially) between two currently used but divergent collections of delayed neutron data, specifically with respect to the relative abundances of delayed neutrons in the different decay periods. Results of other reactivity measurements supplementing the positive period data are also given.

An accidental burst of radiation occurred at the laboratory on 1 February 1951 during remote control operation of a critical experiment. There was no personnel hazard. Normal operations were resumed within 24 hr, and the active material involved in the burst returned to service within three weeks. An unforeseen brief excursion into the prompt critical region was engendered in the act of scramming the assembly at the end of a series of measurements. This report describes the effects of the burst and analyzes the probable causes in some detail.

The total cross sections of the reactions DDp, DDn, TD at 10 kev to 10 Mev are estimated from a review of the experimental data up to January 1951. Maxwell averages for DDp and TD computed from these estimates are given, together with some fitted analytic expressions provided for machine use. A collection of the identifiable earlier estimates is also included for reference and for comparison with the new figures. For relative order of magnitude purposes, cross sections and the derived Maxwell averages are given down to 50 ev using the theoretical Gamow slopes for the extrapolation. Gamow plots for the derived cross sections above l0 kev arc also given. Much of the primary experimental data exists in the form of thick target yields and we find the most uncertain factor in converting these thick targets yields into cross sections is the magnitude of the D/sub 2/O stopping cross section. The particular D/sub 2/O stopping cross section relation used in this derivation together with some of the earlier stopping cross sections are given. Thick target yields are included for both DD and TD on D/sub 2/ targets, at 0.01 to 1 Mev, experimental values being supplemented by calculated values.

This technical report presents results of nuclear plate work carried out to determine the neutron energy distribution inside the Los Alamos fast reactor. Most of the distributions which were investigated are valid over the energy region from 0.4 to 6 Mev. The results show that at the center of the reactor pot about 65% of the neutrons are located below 1 Mev in a rather narrow energy region which has a maximum in the neighborhood of 0.5 to 0.6 Mev. Above 2 Mev the energy distribution is similar to that of a plutonium fission neutron spectrum, i.e. the spectrum decreases exponentially, diminishing by a factor of 10 in intensity over an energy range of about 4 Mev. The leading geometry of the reactor pot does not seem to appreciably affect the spectrum at the center of the pot. However, spectra determined outside the pot can be significantly altered by the particular viewing geometry employed to examine the neutrons coming from the center of the reactor.

Most books on the subject of gas discharges describe the multiple banded structure which appears in the flow between two electrodes. This structure is actually due to the difficulty in getting electrons out of the cathode to support the discharge. These electrons are obtained by having a large enough potential drop near the cathode so that the positive ions may strike it hard enough to product secondary electrons. If one substitutes a hot cathode to produce a copious quantity of electrons, the banded structure will be radially changed. Hence the banding is not a pure property of the discharge, but is a complication brought on by the presence of electrodes.

Certain types of neutron diffusion calculations were considerably simplified when the Serber.Wilson Method was introduced about eight years ago. This method, semi-empirical In nature and named after its co-discoverers, was first formulated for the one-velocity isotropic theory and applied to spherical geometries. Within these limits it has in general proved to be a fairly accurate method. If restricted source-free case it has, in addition, turned out to be quite manageable both analytically and numerically.

Measurement of the color intensity of the uranium thiocyanate complex is discussed as a method for the quantitative determination of uranium. Two procedures for amounts from 1 microgram to 1 milligram are described, and standard curves are shown. The effects of numerous foreign ions are shown, and methods of removal for some of these are discussed.

The coefficient of linear expansion of alpha plutonium has been determined for the range -180 to +100 degree C by the silicon-tube and dial-indicator method. The value of the expansion coefficient is reported as [formula]. Included are a detailed description of the apparatus and a discussion of the method.

The pressure and temperature cycles developed during the bomb reduction of uranium tetrafluoride by calcium have been determined. Data for the 250, 500, and 1000 gram scale reductions are given, and the apparatus used is described.

The coefficient of linear expansion of alpha plutonium has been determined for the range -180 to +100 degree C by the silicon-tube and dial-indicator method. The value of the expansion coefficient is reported as [formula]. Included are a detailed description of the apparatus and a discussion of the method.

The oxidation of uranium metal has been studied from the standpoint of the oxygen dependence of the reaction rate in an effort to establish the mechanism. The experimental data of Perkins agree with the theoretical dependence of the oxygen pressure derived this report. This agreement supports the hypothesis that the rate-controlling step in the migration of cations in the DO2 lattice, although the observed time dependence is not necessarily in agreement with this conclusion. Experimental entropies of activation are corrected for the observed pressure dependence. No firm conclusion could be reached as to whether the rate of diffusion or adsorption is rate-controlling.

High purity, homogeneous uranium-molybdenum alloys have been made successfully in the reduction bomb. The preparation of the alloys and some of their properties are described.

A method for determining zirconium in plutonium-zirconium alloys was required as part of an investigation of alloys containing fissionable material, with possible use in nuclear reactors. Alloys of these two elements were brought into solution with a bisulfate fusion and the zirconium was separated by precipitation with p-bromomandelic acid. Determinations were completed by weighing the zirconium oxide obtained after ignition of the precipitate at 925 degree C. The precision of this recommended procedure was estimated in terms of the standard deviation for quadruplicate determinations, made with weight aliquots from dissolved alloy samples. The range for the standard deviation was 0.5 to 1.7 parts per thousand for samples from which aliquots each containing 9 to 15 mg of zirconium were selected. The complete recovery of zirconium from solutions of pure zirconyl chloride and plutonium trichloride was shown by the 95 percent confidence limits of 99.9 +- 0.3 percent for the average of four determinations, observed with samples containing 5 to12 mg of zirconium in the presence of 10 to 20 mg of plutonium. It was found the Mo, La, PU(III), and K2Cr2O7 do not interfere with zirconium determinations made according to the recommended procedures, but Pu(IV) does interfere slightly. It was …

A method using photographic emulsions for the study of neutron distributions is described. The construction of a simple machine for producing experimental critical assemblies in which the method has been used is reported. Sources of error are discussed. Curves of the perturbations when small spheres of various materials are placed in the center of the assembly are shown.

The total neutron cross sections for normal uranium, U235, and Pu239 are reported as a continuous function of energy for neutron energies between 40 and 7500 Kev. Three additional measurements were made between 17 and 20 Mev. The data were obtained from a good geometry transmission experiment in which 1-in.-diameter cylindrical samples were interposed midway between a neutron source and a neutron counter spaced at about 20 in. separation. In general, the statistical errors were within +- 0.2 barn. Measurements on normal uranium were in agreement with those made at Wisconsin in 1950 (LA-1060). The total cross section curves are almost identical for the three materials and very similar to those of other heavy elements. This suggests that the total neutron cross section for other heavy elements can be predicted with some accuracy.

The usual method of removing surface oxide from plutonium metal samples, by electrolytic cleaning in a mixture of ethylene glycol and phosphoric acid, is not satisfactory for preparing samples for oxygen determination. Samples prepared in this way give erratic oxygen values. This report describes a new method of electrolytic cleaning, using a 20 ~ aqueous potassium carbonate solution as the electrolyte. The sample is placed in a rotating tantalum cup which is made the anode. Electrolysis for two minutes at 4.5 volts is usually sufficient. Samples cleaned by the new method give lower and more consistent oxygen results than those prepared in the old way. The new method is also neater and more convenient.

A tentative nickel-plutonium constitutional diagram was based on data obtained by thermal analysis, metallography, and x-ray-diffraction techniques. The systema is a complex one with the following important features. Nickel is soluble in epsilon plutonium, extending the epsilon field to 4.3 at.% nickel at 465 deg C. Nickel and plutonium form six intermetallic compounds, PuNi, EnNi/sub 2/, PuNi/sub 3/, PuNi/sub 4/, PuNi/sub 5/, and PuNi/sub 9/. The compound PuNi/ sub 5/ forms congruently from the melt at approximately l300 deg C, whereas the other compounds form peritectoidally. The extended epsilon field terminates in a eutectoid reaction at 415 deg C and l.5 at.% nickel. Epsilon plutonium and the compound PuNi form a eutectic system at 465 deg C with a eutectic composition of l2.5 at,% nickel. Nickel and the compound PuNi/sub 9/ form a eutectic system at l2l0 deg C with a eutectic composition of 92 at.% nickel. Plutonium forms a limited solid solution with nickel.

Critical mass of an Oy (93.9%) sphere in graphite is given as a function of graphite tamper thickness. It was shown that approximately 20(in) of graphite is effectively infinite and that the approximately 17(in) used herein is approximately 98% infinite. Critical mass measurements of Oy (93.9%) spheres and cylinders of different diameters are given for approximately 17(in) graphite tamper, for effectively infinite paraffin tamper, and for effectively infinite water tamper. From these measurements cylindrical shape factors were computed. Both shape factors and critical masses are shown in Figs. 22 and 23 as function of the critical height to diameter rate of the cylinders.