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Fission Spectrum

Description: Measurements of the spectrum of the fission neutrons of 25 are described, in which the energy of the neutrons is determined from the ionization produced by individual hydrogen recoils. The slow neutrons producing fission are obtained by slowing down the fast neutrons from the Be-D reaction of the Stanford cyclotron. In order to distinguish between fission neutrons and the remaining fast cyclotron neutrons both the cyclotron current and the pusle amplifier are modulated. A hollow neutron container, in which slow neutrons have a lifetime of about 2 milliseconds, avoids the use of large distances. This method results in much higher intensities than the usual modulation arrangement. The results show a continuous distribution of neutrons with a rather wide maximum at about 0.8 MV falling off to half of its maximum value at 2.0 MV. The total number of netrons is determined by comparison with the number of fission fragments. The result seems to indicate that only about 30% of the neutrons have energies below .8 MV. Various tests are described which were performed in order to rule out modification of the spectrum by inelastic scattering.
Date: August 18, 1943
Creator: Bloch, F. & Staub, H.
Partner: UNT Libraries Government Documents Department

The Fission Neutron Spectrum of 25

Description: Abstract: "Photographic plates have been used to measure the energy of neutrons from the fission of 25. The spectrum as inferred from the ranges of 850 protons recoiling in the forward direction shows a very wide maximum at ~1.5 Mev with an exponentially decreasing high energy tail which extends beyond 7 Mev. The minimum energy neutrons recorded were ~700 kv. If the spectrum is extrapolated to zero, one finds that this average neutron energy is about 1.85 Mev. The stopping power of the plates was calibrated by the use of monochromatic neutrons from the Li-7(pn) Be-7 reaction and the d-d reaction."
Date: February 11, 1944
Creator: Richards, Hugh T. & Perlman, Isadore
Partner: UNT Libraries Government Documents Department

Ultraviolet Absorption Spectra of Aromatic Amines in Isooctane and in Water

Description: Report discusses the results of a study of the ultraviolet absorption spectra in the 3200 A to 2500 A region of 27 aromatic amines in iscoctane and and in water solutions. Factors that affect the absorption spectra of aromatic amines were investigated, and the spectra in the two different solvents were compared. The main variables affecting the absorption are the nature of the solvent, the purity of the aromatic amines, and photochemical decomposition of the aromatic amines.
Date: November 1945
Creator: Tischler, Adelbert O. & Howard, J. Nelson
Partner: UNT Libraries Government Documents Department

Observed Differences in the Arc Spectra of U²³⁵ and U²³⁸

Description: Abstract: "It has been found that the two principal uranium isotopes exhibit slightly different arc spectra. Certain U-235 lines have been found to be displaced from corresponding U-238 lines by about one reciprocal centimeter. The intensity ratio, IU235/IU238, has been shown to be a steadily increasing function of the U-235 concentration. These data indicate the possibility of developing a method for the determination of isotopic concentration by means of emission spectra."
Date: January 15, 1947
Creator: Long, D. R. & Smith, D. D.
Partner: UNT Libraries Government Documents Department

The Spectrographic Determination of Iron in Uranium and Its Compounds

Description: Abstract: A spectrophotometric determination of iron employing the ferrous-1, 10-phenanthroline complex has been developed. The colored complex is measured at a wave-length where interference of the yellow uranyl ion is a minimum. Recommended procedures and analytical results using these procedures are given. Data are presented which indicate that the iron in the acid-insoluble residue is negligible. A method for the determination of iron in ammonium oxalate is included.
Date: July 1947
Creator: Fassel, Velmer A.; Tuthill, S. M. & Buckheim, O. J.
Partner: UNT Libraries Government Documents Department

Proton Angular Distribution for 90 Mev Neutron-proton Scattering

Description: The angular distribution of the recoil protons in neutron-proton scattering at 90 Mev has been measured for angles between 5{sup o} and 65{sup o} from the direction of the neutron beam. The neutrons were produced by stripping 190 Mev deuterons in a 1/2 inch Be target in the 184-inch F.M. cyclotron. R. Serber has calculated the neutron energy distribution; it has a peak at 90 Mev and a half width of 27 Mev. This distributiQn has been checked experimentally for the neutrons by Wilson Powell and by W.Chupp, E.Gardner, and T.B.Taylor for the protons also produced by stripping. The neutrons were collimated by a two-inch hole through 8 feet of concrete. Thin paraffin scatters of known hydrogen and carbon content were used; the number of protons arising from neutron-carbon and neutron-air reactions was determined by using pure carbon scatters and by making blank runs. The scatters were placed in the beam outside of the concrete shielding at a point approximately 52 feet from the cyclotron target. The scattered protons were detected by a telescope of four proportional counters used in coincidence, and set at a constant distance from the scatterer but at a varying angle from the neutron beam. A copper absorber was placed between the scatterer and the counters. The thickness of the absorber was adjusted for each angle so that only protons scattered by incident neutrons of energy greater than 66 Mev could be counted. It was found that the results did not depend on whether the absorber was placed in front of all four counters, or between the first two. The beam was monitored by placing a second one inch piece of paraffin in the neutron beam and measuring the protons scattered from it by means of two additional proportional counters. Fig. 1 is a plot of ...
Date: November 3, 1947
Creator: Hadley, James; Leith, Cecil E. & York, Herbert F.
Partner: UNT Libraries Government Documents Department

Neutron Deficient Isotopes of Tellurium and Antimony

Description: While investigating the relative yields for the many reactions resulting from the irradiation of antimony with 200-Mev deuterons in the Berkeley 184-inch cyclotron several previously unreported isotopes of tellurium and antimony were encountered. The tellurium fraction when followed on a thin mica window counter could be resolved into half-life periods of 2.5 hrs, 6.0 days and a small amount of a long-lived component. The 2.5 hour period has not been further characterized with respect to mass number or mode of decay other than to note that the radiation is predominantly electrons. The 6.0-day period is accompanied by positrons which were shown to be due to a 3.5 minute antimony daughter which is undoubtedly the same activity assigned to Sb{sup 118} by Risser, Lark-Horowitz and Smith. The positron energy was found to be 3.1 {+-} 0.2 Mev by absorption in berylllum and from the end point of the energy distribution curve taken with a low-resolution beta-ray spectrometer. Gamma activity is also present with this period. The 6.0-day tellurium showed a high abundance of x-rays, little or no conversion electrons and some gamma-ray activity which could be due to the 3.5 minute antimony daughter. The tellurium fraction contained another component of 4.5-day half-life which could not be observed in the decay curve because of its low abundance but which was detected by means of its 39-hour antimony daughter. The 39-hour antimony showed x-rays of tin (critical absorption with cadmiium, silver and palladium), no detectable hard radiation or electrons and is apparently identical with an activity recently assigned to Sb{sup 119} by Coleman and Pool.
Date: January 1, 1948
Creator: Lindner, M. & Perlman, I.
Partner: UNT Libraries Government Documents Department

Research Progress Meeting of February 19, 1948

Description: Much of the cloud chamber work has been directed toward obtaining the angular distribution of protons bombarded by deuterons from the 184-inch cyclotron. The observations have been restricted to those protons arising from neutrons of energy greater than 65 Mev. The cloud chamber used for this work is of 16-inch diruneter and employs a magnetic field of 14000 gauss. The chamber is filled with hydrogen at a pressure of 1/2 atmosphere; the vapor used is water and alchohol. Nearly 800 proton tracks were measured and calculated before analysis of the data indicated that the measuring procedure should be revised. They gave the angular and energy distributions shown in Figures 1 and 2. The discrepencies between the theoretical and experimental energy distribution of the neutrons shows that serious errors were being made. As a first check of possible sources of error, random parts of the data were remeasured. They indicated that errors in the measurements of the angles were being made that gave a mean deviation of about {+-} 2{sup o} in the beam angle and {+-} 4{sup o} in the dip angle. These errors were largest at large scatter angles. In addition, a more serious error occured in the measurements of the curvature. The mean deviation was as large as 15 percent, with many tracks having errors of 50 to 100 percent in the measured curvature. These errors were dUd to the fact that an adequate measuring technique had not been developed, that the original measuring apparatus and projector were difficult to operate, and that the cloud chamber technique had not been perfected. A systematic analysis of the errors and difficulties involved in the experiment made it evident that revisions in the technique were necessary. In view of the inaccuracy of the original measurements it is not possible to make ...
Date: February 19, 1948
Creator: Wakerling, R.K.
Partner: UNT Libraries Government Documents Department

Spectral Lines of Curium from 3100 A to 4200 A

Description: Fifty-four spectral lines of curium are listed together with estimated intensities. A brief description of the manner of taking the spectra and of measuring the lines is given. Three separate samples of curium, in all seven micrograms, were submitted for spectrochemical analysis. The samples in acidic solution (HCl) were evaporated on copper electrodes and analyzed as outlined for the copper spark method. An Applied Research Laboratories spark source was used. The spectra were taken on a Baird Associates spectrograph of the modified Eagle type which has a dispersion of 5.6 A/mm in the first order. Spectrum Analysis photographic plates were used and were processed according to the manufacturer's recommendations. The plates were placed in the projection comparator (also an Applied Research Laboratories Unit) and the lines measured using the scale associated with the projection screen. The copper lines of the spectra were used as a wavelength standard. In all 54 lines which we feel can be attributed to curium were found. These, together with an estimated intensity based on an arbitrary 1 to 10 scale, are listed in Table 1. Due to the high alpha-activity of curium special care had to be exercised in handling the samples. In this case a pyrex bulb with quartz windows attached was made and all the sparking of curium was done in this container. An outlet from this bulb was connected through a glass wool filter system to a water aspirator. Upon completion of the work the bulb was flushed with nitric acid and then discarded. The acid wash and the glass wool were then returned for recovery of the curium.
Date: April 7, 1948
Creator: Conway, John G. & Moore, Milton F.
Partner: UNT Libraries Government Documents Department

Electronic Structure of the Heaviest Elements

Description: All of the available evidence leads to the view that the 5f electron shell is being filled in the heaviest elements giving rise to a transition series which begins with actinium in the same sense that the rare earth or 'lanthanide' series begins with lanthanum. Such an 'actinide' series is suggested on the basis of evidence in the following lines: (1) chemical properties, (2) absorption spectra in aqueous solution and crystals, (3) crystallographic structure data, (4) magnetic susceptibility data and (5) spectroscopic data. The salient point is that the characteristic oxidation state (i.e., the oxidation state exhibited by the member containing seven 5f and presumably also by the member containing fourteen 5f electrons, curium and element 103) is the III state, and the group is placed in the periodic table on this basis. The data also make it possible to give a suggested table of electronic configurations of the ground state of the gaseous atom for each of the elements from actinium to curium inclusive.
Date: July 14, 1948
Creator: Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

Methods of Opacity Calculations

Description: "Methods for calculating the opacity of materials at high temperatures are discussed in this report. Minor improvements are outlined for the treatment of continuous absorption processes, and a small error usually made in treating the scattering process is corrected. In contrast to all previous calculations of opacity, the effect of line absorption is carefully examined, for it may well be the dominant process under certain conditions of temperature and density. Detailed methods for calculating the line absorption contribution are, therefore, developed. To illustrate the principles involved, the opacity of pure iron at a temperature of 1000 volts and normal density is worked out in detail" (p. ii).
Date: 1949
Creator: Mayer, Harris
Partner: UNT Libraries Government Documents Department

Limitations and past applications of the cloud chamber

Description: The cloud chamber is a means of observing the path of ionizing radiation. It does not reveal the radiation directly, but gives a visible trail of the path along which the radiation has traveled. The trail is formed by vapor condensing upon pairs of ions remaining after an ionizing particle has passed through the medium. The mutual interaction among rays, atoms, nuclei, and particles, can be studied and measured with the aid of vapor trails. Measurements of changes in direction and range as recorded on the photographs may be interpreted in terms of changes in momentum and energy of the particles in these reactions. To obtain a precision measurement is difficult with a cloud chamber. The dependence of the apparatus upon a sudden gas expansion is certain to create distortions resulting from turbulence. Furthermore, since any radiation is subject to variations, precision measurements can be obtained only be the collection of numerous observations for statistical analysis. This document details the design, operation, and limitations of cloud chambers.
Date: March 23, 1949
Creator: Chaplin, R.L. Jr.
Partner: UNT Libraries Government Documents Department