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Metallurgical Laboratory, Physics and Metallurgy Division, Report for the Month of February 1946: Technical report with short reports from the (A) Crystal Structure Section ; (B) Mass Spectroscopy Section ; and (C) Metallurgy Section.
Effect of Routing Upon Temperature of Cooling Stream: With discussion under way concerning power production by chain reacting piles, it becomes pertinent to consider the ration of the temperature of the hottest spot in the pile to the average exit temperature of the cooling stream. This is important because the temperature of the hottest spot in the pile is one of the limiting factors in determining the maximum power at which a pile can be operated. However, the higher the temperature of the emerging cooling stream, the more efficient can be the thermal engine operated by it. Thus the ideal situation is to have the average exit temperature of the cooling stream as near as possible to the hottest temperature of the hottest spot in the pile.
A Note on the Kinetics of Homogeneous Piles: Abstract. In investigating stability of a homogeneous pile it has been customary to assume that the production of bubbles follows the production of power instantaneously. Here we investigate the implications of introduction of an intermediate dissolved gas stage under two hypotheses on the formation of bubbles from this dissolved gas. It is seen that this additional stage tends to make the pile unstable.
The Laplacian for a Beryllium Metal Lattice of Volume Ratio 17.2: Abstract. the Laplacian of a beryllium metal lattice with 3.3 kg of uranium metal per cell and a volume ratio of 17.2 was measured in the removable region of the CP-2 machine. the sandwich effect with different moderators made interpretation of the observations very uncertain. The best result found was Be = 407 x 10(-6) cm(-2).
The Stopping Power of Metals: Summary. The effect of the conduction electrons on the stopping power of metals has been considered from two essentially different points of view. No numerical calculations have been carried out, because we have found no completely satisfactory was of computing Z'e, the effective charge on the moving ion. A rather crude estimate made on the basis of the Thomas-Fermi atomic model indicates that Z'2/E is roughly constant. Using this relation one finds that the stopping power of the conduction electrons is of the same order of magnitude as the stopping power due to bound electron excitation, and is important for the greater part of the range of the particle.
The Hall Effect in Neutron Irradiated and Annealed Graphite: Abstract. Irradiated Whiting graphite possesses a small negative or a positive Hall constant, depending upon the dosage. Annealing at 500 degrees C for 1 hour in helium results in a Hall constant which is large in magnitude and negative in sign. The properties of the annealed graphite are presumably close to those of the original unirradiated material. Unirradiated AGOT-K graphite has a large, negative Hall constant. A mechanism is suggested which accounts for the change in sign of the Hall constant as a result of neutron bombardment.
Theory of Oscillating Absorber in a Chain Reacting Pile: Abstract. the fluctuation in pile intensity caused by an oscillating point absorber is calculation. It is found that the nature of the response depends on the frequency of the impressed oscillation. If the frequency is high compared to the decay rate of the high harmonics, the response consists of a wave which is propagated away from the oscillator. If the frequency is low, the propagated wave character of the response disappears and the intensity of the whole pile tends to oscillate with the same phase. The amplitude of the response decreases with increasing frequency.
Solubility and Diffusion Constants for Gases: The solubility constants are presented for He , Kr , Xe , O2 , N2 , and air in H20 . Inter-diffusion constants for gases and the diffusion of gases in water are given.
The Effect of Thermal Cycling on the Thermal Transfer from a Sand Blasted Slug to an Unbonded Jacket: Abstract. Measurements were made to determine the effect of thermal cycling on heat transfer from slug to jack using a slug with a sand blasted surface. The value of the transfer coefficient h decreased from initial values ranging from 10 to [formula], to values and [formula] after 1700 cycles, and to a range of 0.15 to 0.45 [formula] after 3200 cycles. Comparisons are made with the results found for slugs with different surfaces.
Metallurgical Laboratory, Physics Section, Report for the Month Ending May 31, 1945: Technical report with short reports from the (1) Physics Section I; (2) Physics Section II ; and (3) Physics Section III.
Final Report on Swell Detection by Pusher Method: Experiments wee performed to evaluate the feasibility of detecting swelled slug elements in Hanford reactors by measuring the force necessary to push the slug column in its tube. These experiments are described. The results indicate the method presents no unsolvable problems.
Pile Heat Exchanger Calculations: Abstract. Some idealized calculations (CP-807) relating to the design of heat exchangers for minimum holdup of pile liquid are presented in compact form to facilitate quick estimates. Their use is illustrated by application to a falling film type exchanger.
The Digging-in of a Warped Rod Into a Rib: Abstract. Some rather idealized considerations are given regarding the depth a warped rod presses into the ribs at the places of contact. It appears that this distance may, under some conditions, be of the order of 70 times greater than for a straight rod resting uniformly on the ribs.
On the Statistics of Rod Warping: Abstract. The probability of exceeding assigned values of displacements or forces in simple rod models assembled from slugs picked at random is discussed, and some estimate for the statistical gain resulting from use of shorter slugs is obtained. The probability that a rod with self-warping will touch the top of the tube appears great enough to justify a recommendation of the use of top ribs.
Metallurgical Laboratory, Physics Section, Report for the Month Ending February 25, 1945: Technical report with short reports from the (1) Physics Section I; (2) Physics Section II ; and (3) Physics Section III.
Metallurgical Laboratory, Physics Section, Report for the Month Ending January 31, 1945: Technical report with short reports from the (1) Physics Section I; (2) Physics Section II ; and (3) Physics Section III.
Estimates of the Maximum Surface Temperature for a Slug Displaced from the Center of the Tube: When a slug has been displaced from its normal position the thickness of the water film is decreased over part of the surface, and higher temperatures may be expected where the film is thin. The experimental data necessary for an exact calculation is incomplete, but some approximate estimates ae made here with special assumption concerning the heat transfer coefficient h as a function of the angle p from the point where the water film is thinnest. Variation in water bulk temperature around the annulus due to poor mixing is not considered here.
Neutron Distribution Around a black Sphere with a Gap: Abstract. Successive approximations ae obtained from transport theory for the neutron distribution around a black sphere surrounded by a spherical gap and a non-absorbing medium extending to infinity. Six cases are calculated numerically to show the difference between this treatment and simple diffusion theory. The extrapolation distance and a quantity that is essentially the thermal utilization are calculated in different approximations. It is found that the neutron density in the gap, instead of being a constant as predicted by the simple theory, may vary by a factor of one-third in cases of practical interest.
Fission Product Poisoning in a Pile: Abstract. The effect of the neutron flux on the relative importance of different fission product poisons is discussed. The general expression for the poising of a fission product is given with the various equations for special cases of interest. The formulae are applied to the problem of finding the poisoning due to fission products at the end of one day in a pile operating with a flux of 4 x 10(14) neutrons/cm(2)/soc. These results are summarized in the table on page 12. Appendix I contains a revised list of cross sections x yields for all stable isotopes. Such a list was first given by Wheeler in CP-889. Appendix II contains a list of radioactive fission products with half lives greater than one day with data about yields, parents, gaseous ancestors, and numbers of neutrons.
Temperatures on the Surface of a Slug Jacket: Prior to operating a chain reacting, graphite moderated, water cooled uranium pile at Hanford, the corrosive action of water on uranium was studied. It was necessary to enclose the uranium cylinders in Al jackets. Preliminary data were available which indicated Al jacket corrosion might be influenced by the water temperature. Therefore, in order to specify safe operating conditions, it was desirable to know the temperature at any position on the Al jacket of a slug in the tube. Because of the experimental difficulties encountered in the measurement of the correct surface temperature, the problem has been attacked primarily from a mathematical standpoint. Mathematical formulae have been developed for most of the proposed Hanford designs. The purpose of this report was to evaluate and summarize the theoretical and experimental information for calculation of Al jackets surface temperatures for the design now installed at Hanford. Also, the summarized results were to be put into a form suitable for use in routine calculations. As a result of this survey, the Al surface temperature for the Hanford tube and slug design may be calculated with 15 degrees C by employing routine methods and certain simple factors and equations contained in this report. The factors have been assembled from mathematical analyses but agree closely with the existing experimental data available. The equations are of the usual type used in hear transfer calculations. Until adequate experimental data are available, it is recommended that the factors and formulae presented be employed in the calculation of the the jacket surface temperatures. Experimental work is need to substantiate the formulae and factors obtained. Also, additional work is needed to determine the surface temperatures necessary to cause early failure of the slug jacket by corrosion, erosion, or cavitation.
The Thermal Conductivity of Some Project Materials: Abstract. An apparatus for measuring the thermal conductivities materials which are moderately good conductors of heat is described. Results obtained with a sample of pure Th are given on p. 10, 12, and 13.
H-Metal Lined Sphere: The problem of lining a hollow aluminum sphere, 10 inches i.d., with lunes of heavy metal foil, was assigned to this group by Dr. E. Creutz. The work was carried out under the direct supervision of Dr. D.H. Gurinsky. the problem was divided naturally into tow parts: first, forming fitting the lunes, and second, cementing hem to the inside of the sphere.
Slug Jacket Temperatures: Abstract. A method for calculating jacket temperatures in a region of varying heat transfer coefficients is given Some applications are made for temperatures above a supporting rib.
The Thermal Conductivity of Uranium: Abstract. The thermal conductivity of uranium as a function of temperature is measured by comparing its conductivity with that of a sample of brass. An absolute measurement is then made of the conductivity of the brass sample. The thermal conductivities as a function of temperature of two samples of extruded uranium rod are given.
Slug Temperatures in an Off-Center Annulus: Abstract. Temperatures are measured at two points in an internally heated jacketed slug which is cooled by water flowing in an off-center annulus around the slug. The variations of these temperatures with water velocity, water temperature, power, and the amount the annulus is off center are measured. The temperature near the slug surface which approaches and comes in contact with the water jacket does not increase as much as anticipated. The temperature near the slug surface on the side which is moved away from the water jacket increases nearly as much as on the side approaching the slug. An explanation for this unexpected increase of temperature as on side moving away from the jacket is given.
Thermal Transfer to an Annular Water Stream in the Neighborhood of a Rib: Abstract. Steady-state temperatures were measured in an electrically heated brass cylinder which was water cooled in a four-ribbed Al tube. Thermal transfer coefficients h were calculated from the measured temperatures. Curves of h values are presented for the regions of high and low ribs. the h curve is found to show a much sharper break in the region of high rib than in a low rib region. There is some evidence that h decreases linearly with annular thickness in the range considered. The low rib is found to exert a much greater effect than the high rib in decreasing the h value at points distant from the rib.
The Temperature Coefficient of the Diffusion Length for Thermal Neutrons in Water: Abstract. The diffusion length of thermal neutrons in water as a function of the water temperature has been measured. The results are expressed as a linear relation: L = 2.644 + 0.0061T where L is the diffusion length in centimeters and T is the temperature in degrees centigrade.
The Slow Neutron Transmission of Be Metal as Measured by a Neutron Beam Spectrometer in the Energy Region 0.004 eV to 50 eV: Abstract. Slow neutron transmission measurements as a function of the time of flight of the incident neutron have been made for three different thicknesses of Beryllium. The energy region from 0.004 eV to 50 eV was investigated using the Columbia neutron beam spectrometer system. Particular emphasis was placed on the very low energy region (from 0.004 eV tp 0/2 eV or from 0.6 to 5 [length]) where pronounced crystal interference effects were observed. The effective slow neutron cross section (in the unity of X 10(-24)ce(2)atom) for several different energy values were: 6.1 at 0.2 [length], 3.5 at 1.5 [length], 2.3 at 2.5 [length] and 0.6 at 4.6 [length]. The positions of the discontinuities in the cross section agree fairly well with the values obtained from the X-ray measurements.
Maximum Force of a Warped Rod Against a Rigid Constraint: Abstract. Given the maximum intrinsic curvature of a rod, the maximum force required to confine it between parallel rigid walls is computed.
Passage of a Rod Around a Corner: Maximum curvatures and forces set up in taking a rod in a tube are considered.
A Method for Neutron Energy Measurement: This technical report discusses a method proposed to measure neutron energies by accurately determining the momenta of recoil protons in a magnetic spectrometer specially designed for this purpose. The main consideration in the design of the spectrometer is the shielding of the detector from the high radiation background associated with intense neutron beams.
A Sensitive Particle Ionization Chamber for Neutron Detection: Abstract. A particle ionization chamber of sensitivity sufficient to detect a source of one neutron per second has been used to measure the neutron yield from a thick target of sulfur upon bombardment with polonium alpha particles. The high-geometry boron trifluoride chamber used had an efficiency of 1.9 percent for fission neutrons. The neutron yield from a thick target of sulfur was measured by this instrument and found to be .0035 +- .0013 neutrons per million incident polonium alpha particles.
A Final Report on the Experiment : the Penetration of Graphite of Different Purities by Lead Bismuth Eutectic: Bi-Pb eutectic and pure Bi penetration of graphites of various densities under 300 degrees C and pressures up to 20 psi was found be of the order of magnitude of 1.0 g/cm(2) and was uniform throughout the graphite. Bi was absorbed less than the eutectic but the oxidation rate of Bi would be prohibitive. There was heavy nitriding in N atmospheres with the Bi and the eutectic.
Flexibility of a Tube in Which Slugs Slide: An approximate calculation is made of the variations of the flexibility of a long cartridge with the length of the slug used, assuming that the jacket slides without friction.
Engineering Group Instrument Specification Report : Tests on Aquadag Treated Polyethylene Cable: Effect of aquadag coating on noise reduction in polyethylene coaxial cable was tested. A satisfactory combination of coaxial cables and connectors interconnecting sources of small ion currents or ionizing impulses with the measuring device is described.
Further End Cap Temperature Calculations: Abstract. Recently (CP-1989) it has been shown that the neutron density, and thus the heat production, at the end of a slug with an A1 cap may be appreciably higher than that at the middle of the slag. A re-examination of earlier temperature calculations is made in light of this effect.
Warping Instability in Long Rods: Abstract. If a pile rod gets bowed within its cooling tube it becomes warmer on the side which approaches the tube wall, and thermal expansion tends to warp it in the same direction as the original displacement. This was discussed roughly in N-601, and it was there concluded that the mechanism was not important for an isolated short slug. In connection with current development of continuous jacket (cartridge) assemblies, it seems desirable to look at this question again. In this case it is possible that the effect may be of some concern.
Progress Report : Low Geometry Alpha Particle Ionization Chambers: ABSTRACT. When solutions of high specific alpha activity are to be assayed for product, it is often difficult to obtain reproducible results by diluting the solution sufficiently to remove a small volume from which a sample can be prepared and counted at 52% geometry. In order to assay such a solution, most reproducible results have been obtained with minimum effort in sample preparation by making use of low geometry chambers. Two types of low geometry chambers are described: 1) The air-screen type which reduces the geometry simply by placing screens of various transparencies above the sample; and 2) The vacuum low geometry chamber which accomplishes geometry reduction by increasing the distance between sample and collecting electrode thus decreasing the solid angle subtended by the sample and aperture through which the particles pass into the ionization chamber. This type chamber was developed concurrently by this group and the instrument group of Chemistry Section C-I at the Metallurgical Laboratory. Because the geometry of the air-screen type chamber is quite critical to sample spreading and be- cause 12 mm sample plates are required, it has found very little use. On the other hand, the vacuum chamber, because it is noncritical to sample spreading and especially noncritical to sample thickness, has found widespread use in product chemistry studies and high alpha activity experiments. Photographs and drawings are included.
The Distribution of Thermal Neutrons in a Slug with Thick End Caps: The distribution of thermal neutrons in a W slug having a one centimeter aluminum end cap has been calculated on the basis of simple diffusion theory. It is found that the average neutron density, and therefore the power output, at the end of the slug is about 34% higher than the density far from the end cap. This result agrees well with the recent Argonne pile experiments (CP-1729).
Temperature and Heat Flow in a Graphite Electrode: In making various experimental heat studies a power producing metal slug is simulated by a slug with a graphite rod electrode of 3/8" diameter inserted lengthwise through it. There is a helium filled annular space between the graphite and the inner surface of the slug cylinder. Radiant heat passes from the electrode to the metal; with proper adjustment of the electrode current the slug in the steady state will therefor "produce" the same amount of energy from its exterior surface as it would under operating conditions. The question arises, however, as to how uniform the electrode temperature is along its length. And also, in some cases one end of the electrode is embedded in the slug metal; it is then desirable to know how much heat flows by conduction from the electrode into the slug.
Sealing of Holes in Aluminum Sheet by Oxidation: Aluminum oxide occupies a larger volume than the aluminum it contains would fill as metal, consequently, the assumption has been made that holes in metallic aluminum would close by a sufficient amount of oxidation. Therefore, we were asked to investigate the rate of plug formation under conditions to be expected in the pile. For the latter we were requested to approach the pile conditions as nearly as we could by employing the Chicago cyclotron. It seems to us that the problem divides itself into two separate questions: (1) under what conditions may holes be expected to close? (2) if holes do close how much corrosion of uranium may be expected before the closure becomes impervious to water vapor? In this report only the first question is considered. The experiments and theory coupled with the data collected by other workers on the project definitely define the limits within which pores in the aluminum cans may be expected to close by an oxidation process. Under the most favorable conditions only small holes may be sealed in this manner. In the large majority of the cases the holes not only fail to close but become larger.
Extrusion of Compound Tubes of Aluminum and B4C: Various experimenters have shown (H.H. Gersman U.S. Patent 2,335,590, Nov. 30, 1943; Aluminum Co. of America, various technical papers; also CT-482) that when a billet is extruded by proper technique into a rod (or tube by a floating mandril) that flow of material is streamline and and the extruded article is essentially a space replica of the billet, with linearly distorted coordinates. Advantage is taken of this fact in the manufacture of alclad tubing in which a billet containing an inner core of one alloy with the outer part of another alloy cast around it is extruded together into an integral tube, e.g., to combine high corrosion resistance with high strength. The following experiments were carried out because of the desirability of obtaining a control rod which can be water cooled (or immersed in P9) and which contains boron. For some pile structures it may be desirable to have the major portion of the energy released by the neutron absorption of the control rod be spend in the rod itself by the nuclear reactions [formula] rather than in the surrounding media as is the case when absorption of neutrons is by cadmium according to the reaction [formula]. In the later case most of the energy appears as gamma rays so the heating effect cannot be localized to an easily cooled region. One possible objection to the use of boron (as in boron-steel and other alloys) is the possibility of building up high pressures when an appreciable fraction of it is converted to helium n a confined space. the present method provides channels for the diffusion of this gas away from the region where it is produced so that there is no danger of its cracking the material in which it is formed.
The Effect of the Maxwell Distribution of Velocities on the Neutron Density and Diffusion Length in a Metal Sphere: The change in the simple [formula] distribution of neutrons in a spherical lump of uranium caused by the distribution in velocities of thermal neutrons is calculated. If the calculated curve is fitted as well as possible by a simple [formula] curve, it is shown that the value of [formula] obtained in this way is a function of [formula], the radius of the sphere. For small radii the [formula] obtained in this manner will be as much as 25% greater than the [formula] corresponding to average velocity neutrons. The change in the thermal utilization caused by the distribution in velocities is discussed. The flux of neutrons into a sphere is calculated taking into account the velocity distribution and this is compared with the usual theory.
Representation of Slowing Down Functions in Water by Synthetic Kernels: Fermi, Anderson, and Nagle's experimental distribution of Indium resonance neutrons around a point source of fission neutrons in water has been fitted by analytic expressions which are source functions in the two-group, three-group, Fermi and Christy-Wheeler pile theory. The Christy-Wheeler function (exponential followed by a Gaussian) is the best fit; the two-group function (exponential) is slightly better than the Fermi Gaussian.
Jacket Temperature Near End of Slug: Some situations which give rise to a hot ring around the slug near the end are considered; namely rounded slug ends in the long cartridge design, and the Wilkins effect in the current unbonded short slug design.
A Case of Rod Warping: Warping of a rod by a variation in heat transfer coefficient around the periphery is considered. Estimates for some simple cases are given, and a more precise numerical calculation is carried out in ne instance.
Experiments on the Evaporation of Boron in Vacuo : Progress Report No. 1 on a Phase of Problem No. 132 - ML - 56-3; File Serial 13: It was desired to determine a method of evaporating boron to form a rather pure uniform tenacious coat of specified thickness. These coats are needed as monitoring films for neutron intensities, particularly in steel ionization cylinders. The most satisfactory method of evaporating boron employed a graphite filament. A mixture of amorphous boron and Carbenoid A was painted onto the filament which was then heated by electrical resistance method to 2300 degree C at which temperature the boron evaporated. Opaque films with purities up to 98% boron or better could be deposited by this method. Much heat was liberated by the filament, and it was found necessary to cool the steel cylinders during evaporation to prevent alloying of boron with the steel. Cathodic deposition also proved satisfactory for producing high purity films; this method has the advantage that little or no heat is produced during the process, but requires much time. Other less efficacious methods of depositing lighter films of born were developed; these are included in the following discussion.
Metallurgical Laboratory, Nuclear Physics Division, Report for the Month Ending May 25, 1944: Technical report with short reports from the (1) Experimental Nuclear Physics Group; (2) Theoretical Physics Group ; (3) Lattice Design Group; (4) Pile Design Group; (5) Exponential Experimental Group; (6) Radiation Group; and (7) Shielding Group.
Thermal Stresses Arising from Defective Strip in Bond: Stresses set up by an insulating strip in the bond are estimated and found to be small compared to those normally present without the defect.
The Diffusion Length of Thermal Neutrons in Uranium: Measurements made in a uranium cylinder result in a mean value of 1.55 cm. for the diffusion length L for distances of 1 to 4 cm. from the base of the cylinder. Calculations give a value which agrees with the experimental result and show further that L increases from 1.40 to 1.63 cm. as the neutrons diffuse a distance of 5 cm. into the uranium.

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