Abstract: "The general utility of vacuum evaporated films is discussed. The characteristics that makes this technique most useful are the uniformity of the films, the easy control of their thickness over a large range, and the adaptability of the system to different metals and compounds. The design of a vacuum evaporator should provide adequate pumping speed, cooling of components, filament heater supply, and general flexibility and adaptability of the components to different materials. The design of filaments or boats and the evaporation of Al, Ag, Au, Li, Na, UCl4, ThF4, Be, SiO, Nal (Tl), U, and UO2 are considered. Special attention is given to the problem of obtaining uniform layers of UO2 on a large, flat target relatively close to the source."

The following report describes the high pressure and temperature homogeneous reactor experiment which has been started at Los Alamos, as well as the hazards and safety aspects for the experiments.

Report discussing a study in which "a separation of americum from americum-lanthanum mixtures is obtained by the fractional precipitation of dilanthanum trioxalate from homogeneous solution."

"Hydrodynamic theory predicts that if a shock wave in a metal is not too strong it will separate into two waves." This report discusses a modification of the contactor technique to determine the velocities of the two waves simultaneously for samples of steel and tungsten alloy.

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 new method for the determination of O/sub 2/ in metals is described. The sample is dropped into molten Pt in a graphite crucible. The oxide in the sample reacts with C to form CO, which is swept out by a stream of argon at atmospheric pressure. The CO is oxidized to CO/sub 2/, which is condensed in a capillary trap and measured with a capillary manometer. The apparatus is sensitive to 0.3 mu g of O/sub 2/, and routine 50-mg Pu samples give a standard deviation of 7 ppm or 0.35 mu g. Pu samples with added O/sub 2/ gave a standard deviation of 1.5 mu g or 2% of the total oxygen, with no significant bias. The apparatus is simple and rugged permitting replacement of parts without glassblowing. The speed is superior to vacuum fusion methods, most samples requiring only twelve minutes for analysis.

It has been found that two silver atoms replace one polonium ion during the electrochemical exchange of polonium ion with silver metal. It is believed that the most probable exchange reaction may be described by the equation Po++ + 2Ag = Po + 2Ag+ . From the concentrations of polonium ion and Ag+ ion when the exchange reactions were terminated, calculations indicate Po = Po^ + 2e", E°< - 0.7.

The angular distribution of fission fragments from the neutron-induced fission of several isotopes has been studied. Distributions were observed for thermal neutrons on U233 and U235, Lady Godiva leakage neutrons on U235 and U238, and 14 Mev neutrons on U233, U235, U238, Th232, and Np237. No anisotropy was observed for thermal neutron fission, whereas for Lady Godiva neutrons and 14 Mev neutrons the probability of fission along the axis of the neutron beam was determined to be higher than for fission in the orthogonal direction. Experimental results are given on pages 10 and ll.

The perturbation theory for material replacement experiments is given through second order thus permitting corrections for sample size. Computed flux and adjoint distribution functions are tabulated for the Lady Godiva assembly enabling the observed danger coefficients for U-238 and U-235 to be compared with corresponding predicted values. Consistency of this data is checked by its use in three independent combinations each yielding for the effective fraction of delayed neutrons from fast fission the value L841=0.0068 * 0.0002. Estimation of the reactivity contributions associated with inelastic scattering give the following connection between central danger coefficient ratios and [(%1>~-q~ ratios for the Topsy assembly (oralloy core + 81/2”tuballoy reflector), AK$U-233) A&(U-235) AKO(PU-239) AKJu-235) = 1.71= 1.93 = 1.78. Evaluation of transport cross sections by means of replacement measurements in Godiva is illustrated for the several elements carbon, copper, and gold, the values relative to ~!&(OY) = 1 being ~fi(c) = ().43 f 0.02, ~(CU) = 6.5!5 * 0.02} ~ti(Au) = 0.91 f 0.02.

The procedures used in the complete and permanent disassembly of the Los Alamos Fast Reactor are described.

Semi-empirical modifications of age theory have been made to interpret the critical masses of proton moderated assemblies, which may or may not have reflectors of various substances, in particular, water or steel. Section I shows that critical masses of untamped water moderated systems can be calculated by use of an appropriate age and linear extrapolation length. Assuming that all captures and fissions take place at thermal, a familiar expression can be set up which contains the age and extrapolation length which are not well determined by theory. An age value suggested by theory, (Sec. II) is taken and ORNL criticality data (K343) are used to find the best extrapolation length. With these values the K343 critical mases can be computed to bout +-5%, which is their estimated experimental uncertainty; this for H/U-235 atomic ratios between 43 and 755. Section II contains a theoretical discussion of effects which the simple "theory" of Sec I neglects. It is indicated that several of these effects compensate to make a simple theory more useful than one would believe at first sight. to take into account reflectors of water, water shield by cadmium, or steel of various thicknesses, it proves sufficient to alter the extrapolation …

A device has been designed which will support small spheres and cylinders in a vacuum system during a plating operation. While supporting the object to be plated, the device automatically shifts the position of the supports so that the coating is evenly distributed. This report describes the mechanism by which this motion is achieved.

A criticality equation is derived assuming slowing-down only by hydrogen. The use of criticality experiments as a basis for calculation is described. Approximate methods are given for handling inharmonicities and multi-region reactors. Some criticality data on solutions of U03 dissolved in H3PO4 are listed in Appendix 1, and the Goertzel-Selengut equations are derived in Appendix II.

This report describes the construction, operation, and typical uses of Topsy, the versatile, remotely controlled, critical assembly machine at Pajarito. Section 1 covers the mechanical design of the machine, and the hydraulic and electrical operation of the various components. Section 2 describes how Topsy is used for investigating reacting metal assemblies. Procedures for establishing a delayed critical configuration and operation at delayed critical are illustrated for the oralloy-tuballoy system. Also included are brief descriptions of oralloy-nickel, plutonium-tuballoy, and low density and concentration assemblies that have been made on the machine.

The stability of a pinched plasma equilibrium with a longitudinal magnetic field superimposed on the characteristic azimuthal magnetic field of the pinch current is studied theoretically. The linearized solutions are developed as helical perturbations of the plasma surface, and the behavior of these is given for the different cases of uniform longitudinal, longitudinal field zero inside the plasma, and for helices of the same and opposite sense to the helix which describes the total magnetic field. Very approximately, the conclusions are: that the longitudinal field has the effect of stabilizing short-wave perturbations, but that some long-wave perturbations remain unstable no matter how large the externally imposed longitudinal magnetic field.

The reported procedures for the polarographic determination of uranium, vanadium, and titanium in plutonium were investigated to ascertain if they could be used to determine other common metals in plutonium. It was found that the procedure using hydroxylamine hydrochloride to reduce plutonium to the (III) oxidation state could be used to determine bismuth, platinum, rhodium, copper, tin, lead, thallium, iridium, and cadmium. The procedure using zinc and zinc amalgam in hydrochloric acid to reduce the plutonium to the (III) oxidation state is quite limited, but it might be used to determine molybdenum.

It was found that hydrogen is introduced into uranium during process-annealing in a fused salt bath. The increased hydrogen content reduces the tensile elongation and general formability of the metal. The partial removal could be affected by annealing in argon, helium, or nitrogen, and better by annealing in high vacuum at temperatures above 450°C. The effect of the hydrogen content on the tensile properties was confirmed by annealing in hydrogen. Tensile properties, the hydrogen content, and certain X-ray results after each annealing treatment are presented and briefly discussed

By means of measurements with a double ionization chamber, the average fission cross section of U238 for neutrons from the fission of U235 was determined in terms of v, the average number of neutrons per fission of U235. the number of fission of U238 was measured in one of the ionization chambers while the number of fissions from the fission neutron source of U235 was measured in the other chamber. In the nine runs made to determine the cross section, a variety of different methods was used to determine the number of fissions and the mass of U238.

A high-vacuum casting furnace with an internal diameter of 15 inches has been designed, fabricated, and installed at LASL. The furnace was designed to accommodate casting crucibles up to 7 inches OD; however with a larger diameter heating element, casting crucibles up to 9 inches could be accommodated. This report describes the basic features of the furnace and presents engineering drawings of both the furnace and the furnace box.

A theoretical study of the kinetics of a model of the Los Alamos Power Reactor Experiment (LAPRE) was made through integration of the dynamic equations with the IBM 701 computer. The stability is investigated under various conditions of power demand, rod-induced reactivity changes, and other conditions especially applicable to LAPRE. The results are given in graphical form, along with conclusions as to appropriate conditions of operation.

This report is a collection of data which were determined by several safety tests to assure safe procedures during the fabrication of Oy. These tests indicated that a 4 in. ID melting crucible which had become flooded from the cooling coils of the furnace would be critical with about 23.7 kg of Oy. A 5 in. ID crucible under similar conditions would be critical when it contained 21.3 kg. A series of measurements to simulate multiple crucibles in a melting furnace indicates that a flooded array of four charged crucibles with a spacing of 1.6 in. between the graphite heater jackets would have a neutron multiplication of 16.2. It has been shown that a 1 in. thick Oy plate in infinite paraffin tamping has a critical mass of 58 kg, and a 1 1/2-in. thick plate with the same tamping has a critical mass of 41 kg. Another test shows that a flooded Oy hemisphere 10 in. ID would be critical with a wall thickness of 1 in. at 60 kg. Also given in the last section are curves of Oy critical mass for various diameter cylinders with water, paraffin, and graphite tamping.

A method is presented for determining heat transfer rates and thermal stresses from the gamma-ray energy absorption of nuclear reactor shells for plane, cylindrical, and spherical geometries. Criteria for minimizing thermal stresses are developed, along with the corresponding external cooling rates necessary to minimize the thermal stress. Design charts are presented for rapid determination of approximate thermal stresses and heat transfer rates, along with a numerical example illustrating the use of the charts..

The annealing or heat treatment of uranium in any medium other than a good vacuum or purified helium atmosphere, will lower the room temperature properties of ultimate strength, hardness and elongation. In general, the elongation of vacuum annealed uranium exceeds considerably the elongation of air or salt annealed uranium. Any annealing medium which permits contact of the uranium metal with atmospheric gases tends to produce low elongation and ductility and a lowering of the ultimate strength. The above is true for uranium in any solid form, whether it is rolled sheet, cast bars or plates, rolled rod, or extruded shapes. Annealing in the molten salt bath (65% potassium carbonate and 35% lithium carbonate), which is used by Los Alamos and other laboratories concerned with the fabrication of uranium, produces the lowest elongation or ductility and ultimate strength when compared to similar properties of metal annealed in the other media examined. Mass spectrometer analyses of the dissolved gases present in high ductility and low ductility uranium indicate that dissolved hydrogen is probably the chief cause of low physical properties.

A spherical, unreflected U-235 critical assembly (52.6 kg) has been in operation since August, 1951. A remotely controlled mechanical system is used to assemble subcritical components of the sphere, and reactivity is adjusted with U-235 control rods positioned in the sphere. The maximum power level during sustained operation is about 1 kilowatt. In addition to investigations of the neutron spectrum of the assembly, observation of the changes of reactivity produced by inserting foreign materials into the assembly, and the dletermination of parameters such as the temperature coefficient of reactivity, studies have been made of the behavior of the assembly at reactivities above prompt critical.