UNT Libraries Government Documents Department - Browse

ABOUT BROWSE FEED

Excitation Function of the Reaction C12(p,pn)C11 at High Energies

Description: Chupp and McMillan have recently measured the excitation curve for the reaction C{sup 12}(pnpn)C{sup 11} at high energies. Using the model of the nucleus described by Serber, the excitation curve of the above reaction has been calculated for energies up to 100 Mev. The excitation of the nucleus is determined on the basis that the incident proton makes individual collisions with the nucleons, the transferred energy exciting the nucleus. n-p collisions are taken to be three times more probable than n-n or p-p collisions. Charge exchange is assumed. The calculations were made for both 50% and 100% charge exchange. The decay of the excited nucleus is treated by the usual evaporation mode.
Date: November 1, 1947
Creator: Heckrotte, W. & Wolff, Peter

The Half-Lives of Aluminum25 and Aluminum26

Description: The availability of separated isotopes of Mg makes it easy to determine the half life of Al{sup 26}, a member of the Wigner series which has long been suspected to have a half life of approximately 7 seconds, but which has not been confirmed because of the masking 7 second activity of Al{sup 26}. Mg{sup 24}, Mg{sup 25} and Mg{sup 26} (in the form of MgO) have been bombarded with protons from the Berkeley Linear Accelerator, with the following results: (1) Mg{sup 24} yields an activity of approximately 23 seconds half life, presumably due to Na{sup 21} from the reaction Mg{sup 24}(p,a)Na{sup 21}; (2) the Mg{sup 25} yields an activity of approximately 8 seconds half life, which they assign to the reaction Mg{sup 25}(p,n)Al{sup 25}; and (3) The Mg{sup 26} yields an activity of approximately 6 seconds half life, assigned to Al{sup 26} according to a similar reaction. It seems probable therefore that the 7 seconds half life normally given for Al{sup 26} is a mixture of these two activities.
Date: April 24, 1948
Creator: Bradner, Hugh & Gow, J.D.

Half-Scale Model Tests on the Three Quarter Wave R.F. System for the 184-inch Frequency Modulated Cyclotron

Description: Performance curves and test results on a half scale model of the radio frequency system designed to accelerate protons in the Berkeley 184-inch cyclotron are presented. This report is a sequel to K. R. Mackenzie's report on the three quarter wave radio frequency system for frequency modulated cyclotrons.
Date: December 30, 1947
Creator: Anderson, Robert L.

THE RELATION OF BACKSCATTERING TO SELF-ABSORPTION

Description: The effects of backscattering upon self-absorption correction curves are demonstrated. Data are given for the backscattering powers of several substances for the beta radiations from C{sup 14}, and for se1f-absorption of samples of barium carbonate and wax, containing C{sup 14}, mounted on aluminum.
Date: January 1, 1948
Creator: Yankwich, Peter E. & Weigl, John.

Research Progress Meeting for March 11,1948

Description: The linear accelerator is again in operation after a shutdown fore repairs and minor changes. Radiofrequency checks of the instrument were made while the Van de Graaff was open. The vacuum of the system is now very good, the base pressure being 1.7 x 10{sup -6} mm Hg with a rate of rise of 800 s/{micro}s. Some preliminary results have been obtained on the activation of carbon with protons. The experiments were done using 10 mil, 50 mg/cm{sup 2} polystyrene discs. The activation curve obtained is shown. The break shown in the curve was found on two separate runs and it yet unexplained. In another experiment a proton induced activity in nickel was found. This had a 3.3 second half-life. Positive mesons have been detected on plates exposed in the 184-inch cyclotron with an arrangement shown schematically. The beam ws allowed to strike a 1/16 inch carbon target, and the mesons, which are bent around by the magnetic field, were detected with photographic plaes placed beneath the circulating beam. A series of experiments were done in which the plates were placed at distances varying from 1-1/2 to 3/4 inch from the beam between 1/4 inch plates of copper. The plates obtained at 1 inch and 3/4 inch were so blackened as to be unusable. From the plates secuired at 1-1/4 inch Lattes has found a total of 30 positive meson tracks, of which 20 end in the emulsion. Eight of these were found to give rise to seconaries, none of which stopped in the emulsion. This work was done with 50 micron plates and will be extended using 100 micron plates. The data will be further analyzed to see if all of the positive mesons and in secondaries. The number of positive mesons produced seems to be comparable to the ...
Date: March 11, 1948
Creator: Wakerling, R.K.

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.

Electronic Circuits Lectures

Description: The two-electrode vacuum tube, or diode, consists of an electron-emitting cathode surrounded by a positive anode (plate). A plot of plate current (i{sub b}) vs plate voltage (e{sub b}) is shown. At low anode voltages, the anode current is limited by the repelling effect that the negative electrons already in the space have on the electrons just being emitted (space-charge effect). When a full space charge is present, the plate current depends upon the plate voltage according to Childs law: i{sub b} {approx} e{sub b}{sup 3/2}. Increasing the plate voltage eventually results in an electron flow equal to total cathode emission, after which further increases in anode voltage will produce practically no additional current (voltage saturation). However, for high field stresses, additional electrons are pulled out of the cathode (field emission), increasing the current even further.
Date: December 1, 1947
Creator: Mozley, Robert

Chemical Properties of Uranium Hexafluoride, UF6

Description: Uranium hexafluoride has the distinction of being the only stable gaseous compound of uranium known up to the present moment. Because of this property it is the only compound that can be used for processes of isotope separation, such as diffusion, thermal diffusion, centrifuge separation, distillation, and other of a similar nature. Here is a short description of the properties of UF{sub 6} and is intended for a reader interested only casually in this compound. UF{sub 6} is a very reactive compound and a very strong fluorinating agent. It is immediately hydrolized by water. In fluorinating reactions it is reduced to the green highly stable UF{sub 4}. It reacts instantaneously with hydrogen at room temperature. It fluorinates many metals; sodium and mercury are attacked in the cold, lead, zinc, tin and iron on heating; platinum and gold react only above 400 C. With organic compounds like alcohol, ether, benzene or toluene, immediate fluorination takes place with formation of HF and carbon or carbonaceous material. The compound forms colorless, very volatile, beautiful transparent crystals of high refractive index. Melting point = 69.5{sup o}; boiling point at 760 mm = 56.2{sup o}; D20{sup o} = 4.68. The crystals melt water pressure to a transparent colorless liquid of high density, but great mobility.
Date: June 25, 1941
Creator: Grosse, Aristid V.

The Fission of Thorium with Alpha Particles

Description: The fission distribution of fission of thorium with alpha particle of average energy 37.5 Mev has been measured by the chemical method. The distribution found shows that the characteristic dip in the fission yield mass spectrum has been raised to within a factor of two of the peaks compared to a factor of 600 in slow neutron fission of U{sup 235}. The raise in the deip has caused a corresponding lowering in fission yield of these elements at the peaks. The cross section for fission of thorium with 37.5 Mev alphas was found to be about 0.6 barn, and the threshold for fission was found to be 23 to 24 Mev.
Date: April 15, 1948
Creator: Newton, Amos S.

The Fission of thorium with Alpha Particles

Description: Soon after the discovery of fission, Meitner, Bretscher and Cook found differences in the decay of various chemical fractions separated from uranium irradiated with slow neutrons and thorium irradiated with fast neutrons respectively and suggested that a difference existed in the distribution of fission products in the two cases. In 1940, Turner suggested that the distribution in various modes of fission should be investigated. The fact that elements such as tin, cadmium, palladium, and silver were found in fast neutron and deuteron fission of uranium and thorium before they were found in slow neutron fission of uranium suggested that the middle region of the distribution was raised as the energy of the incident particle was increased. Since the compound nucleus formed in the fission of thorium with alpha particles is U{sup 236}, the same compound nucleus formed in the fission of U{sup 235} with neutrons, it is of interest to study the fission of thorium with alphas and compare the resulting distribution of fission products with that found with uranium with slow and thorium with fast neutrons. Any difference between the various results where the same compound nucleus is formed must be due to differences in energy content and possible differences in distribution of the nucleons in the compound nucleus at the time of fission.
Date: October 15, 1948
Creator: Newton, Amos S.

The Distribution of Radioactivity in the Mouse Following Administration of Dibenzanthracene Labeled in the 9 and 10 Positions with Carbon Fourteen

Description: Dibenzanthracene, labeled in the 9 and 10 positions with carbon fourteen has been administered to mice intravenously and by stomach tube as an aqueous colloid, and intraperitoneally, subcutaneously, and by stomach tube in tricaprylin solution. The distribution of radioactivity in the mice at various time intervals after administration of the carcinogen has been determined. The radioactivity is rapidly eliminated, largely through the feces, and ordinarily very little is absorbed. The distribution and rate of elimination depends upon the mode of administration. There is an appreciable quantity of radioactivity in tumors produced several months after a single subcutaneous injection of dibenzanthracene. There appear to be no detectable effects from the radiation of the labeled carcinogen.
Date: January 30, 1948
Creator: Heidelberger, Charles & Jones, Hardin, B.

Progress Report for October 1947, Physics Section

Description: This summary discusses the following topics: (1) 184-inch cyclotron program; (2) a 60-inch cyclotron program; (3) synchrotron program; (4) Linear accelerator program; (5) Experimental physics, experiments with the 184-inch cyclotron, fast neutron scattering, and neutron-proton scattering; (6) Theoretical physics; and (7) isotope research program.
Date: October 1, 1947
Creator: Brobeck, W.M.; Hamilton, J.G.; Martin, M.; Alvarez, L.W.; Thornton, R.L.; Serber, R. et al.

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.

Production of Mesons by the 184-inch Berkeley Cyclotron

Description: The authors have observed tracks which they believe to be due to mesons in photographic plates placed near a target bombarded by 380 Mev alpha particles. For a 10-minute exposure in the cyclotron, about 50 meson tracks are found along the 3-inch edge of a photographic plate. The mass has been determined by measuring the bending in the magnetic field and the range in emulsion. From the first 50 meson tracks measured they find a mass of 313 {+-} 16 electron masses. It is highly probable that these mesons are the heavy mesons described by Lattes, Occhialini, and Powell.
Date: January 1, 1948
Creator: Gardner, Eugene & Lattes, C.M.G.

Production of Mesons by the 184-inch Berkeley Cyclotron Part I. Experimental Arrangement

Description: The authors have observed traks which they believe to be due to mesons in photographic plates placed near a ta5rget bombarded by 380 Mev alpha particles. The plates used were Ilford Nuclear Research Plates, type C.2. the identification of the particles responsible for the tracks was first made on the basis of the appearance of the tracks; they show the same type of scattering and variation of grain density with residual range found in cosmic ray meson tracks and about two-thirds of them produce observable stars at the end of their range. For a 10-minute exposure in the cyclotron, about 50 meson tracks are found along the 3-inch edge of a photographic plate. Carbon, beryllium, copper, and uranium have been used so far as target materials, and all are found to give mesons. When a carbon target was bombarded with 300 Mev alpha particles, mesons were found but with reduced yield.
Date: April 1, 1948
Creator: Gardner, Eugene & Lattes, C.M.G.

The Production of Thin Be Foils

Description: A procedure for making Be foils between 10{sup -5} cm. and 10{sup -3} cm. thick, and with diameters up to an inch and a half is described, and methods of mounting these foils are indicated.The problem of making thin Be foils was presented in connection with focusing the proton beam in the Berkeley Linear Accelerator, and although the foils are not now used in the accelerator, they have proved to be quite useful as thin targets, target supports, thin windows, etc. The Be was evaporated in vacuum and deposited on a metal collector plate. The problems encountered were: (1) obtaining reproducible quantities of evaporated Be; (2) stripping of Be from the collector plates; (3) preventing curl of the foils when they were stripped; and (4) mounting the foils.
Date: March 18, 1948
Creator: Bradner, Hugh

Products of High-Energy Deuteron and Helium Ion Bombardments of Copper

Description: The identity and relative yields of about twenty of the radioisotopes produced by the bombardment of natural copper with 190 Mev deuterons and 380 Mev helium ions have been determined. Two previously unreported isotopes were detected: Zn{sup 62}, decaying by orbital electron capture with a 9.5-hour half-life, and Fe{sup 52}, decaying by positron emission with a 7.8-hour half-life.
Date: March 1, 1948
Creator: Miller, D.R.; Thompson, R.C. & Cunningham, B.B.