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The occurrence of plutonium in nature

Description: Plutonium has been chemically separated from seven different ores and the ratios of plutonium to uranium determined. This ratio was found to be fairly constant in pitchblende and monazite ores, in which the uranium content varied from 50% t o 0.24%, and substantially less in carnotite and fergusonite.
Date: November 29, 1950
Creator: Levine, Charles A. & Seaborg, Glenn T.
Partner: UNT Libraries Government Documents Department

Spontaneous Fission

Description: The first attempt to discover spontaneous fission in uranium was made by Libby, who, however, failed to detect it on account of the smallness of effect. In 1940, Petrzhak and Flerov, using more sensitive methods, discovered spontaneous fission in uranium and gave some rough estimates of the spontaneous fission decay constant of this substance. Subsequently, extensive experimental work on the subject has been performed by several investigators and will be quoted in the various sections. Bohr and Wheeler have given a theory of the effect based on the usual ideas of penetration of potential barriers. On this project spontaneous fission has been studied for the past several years in an effort to obtain a complete picture of the phenomenon. For this purpose the spontaneous fission decay constants {lambda} have been measured for separated isotopes of the heavy elements wherever possible. Moreover, the number {nu} of neutrons emitted per fission has been measured wherever feasible, and other characteristics of the spontaneous fission process have been studied. This report summarizes the spontaneous fission work done at Los Alamos up to January 1, 1945. A chronological record of the work is contained in the Los Alamos monthly reports.
Date: November 22, 1950
Creator: Segre, Emilio
Partner: UNT Libraries Government Documents Department

A MEASUREMENT OF THE POSITIVE pi- Mu DECAY LIFETIME

Description: The lifetime for the decay of a {pi} meson into {mu} meson and neutral particle was first measured by Richardson and later by Martinelli and Panofsky. The method was the same in both cases: The fraction of {pi} mesons surviving various times of flight is measured by placing photographic detectors at various path lengths from the target. In the experiment reported here we observe the time lag between the two bursts of fluorescence due to mesons decaying in a scintillation crystal. The first burst is due to the stopping of the entering {pi} meson, the second to the {mu}-meson. As is shown in Fig. 1, a particle penetrating the first and into the second crystal starts the sweep (10{sup -8} sec/mm) of an oscilloscope. The pulses in the second crystal are delayed 0.5 x 10{sup -6} sec to allow the sweep to start and brighten and are then photographed. If the responsible particle is a {pi}{sup +} meson which stops in the crystal, it undergoes {pi}-{mu} decay and two pulses appear on the trace. The {mu}{sup +} meson has a range of only 2 mm in the crystal. If its decay electron is detected some time (.5-2.5 x 10{sup -6} sec) later; a neon light flashes and is photographed together with the scope trace. Only such marked traces are measured. Of these marked traces, 650 or roughly one-half, show the two pulses of the {pi}-{mu} event. Five percent are calculated to be due to random delayed coincidences, and another 3 percent due to {pi} mesons which have decayed in flight and come to rest in the second crystal as {mu} mesons. The remaining traces are due to {pi}{mu} decays which are too fast to be resolved. The sweep speed of the oscilloscope is calibrated periodically with an oscillator of known ...
Date: May 10, 1950
Creator: Chamberlain, O.; Mozely, R.F.; Steinberger, J. & Wiegand, C.
Partner: UNT Libraries Government Documents Department

THE NEW ELEMENT BERKELIUM (ATOMIC NUMBER 97)

Description: An isotope of the element with atomic number 97 has been discovered as a product of the helium-ion bombardment of americium. This isotope decays with the emission of alpha-particles of maximum energy 6.72 Mev (30 percent) and it emits lower energy alpha-particles of energies 6.55 Mev (53 percent) and 6.20 Mev (17 percent). The half-life of this isotope is 4.6 hours and it decays primarily by electron capture with about 0.1 percent branching decay by alpha-particle emission. The mass number is probably 243 as indicated by chemical separation of the alpha-particle and electron-capture daughters. The name berkelium, symbol Bk, is proposed for element 97. The chemical separation of element 97 from the target material and other reaction products was made by combinations of precipitation and ion exchange adsorption methods making use of its anticipated (III) and (IV) oxidation states and its position as a member of the actinide transition series. The distinctive chemical properties made use of in its separation and the equally distinctive decay properties of the particular isotope constitute the principal evidence for the new element.
Date: April 26, 1950
Creator: Thompson, S.G.; Ghiorso, A. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

ELEMENT 98

Description: Definite identification has been made of an isotope of the element with atomic number 98 through the irradiation of Cm{sup 242} with 35 Mev helium ions in the Berkeley Orocker Laboratory 60-inch cyclotron. The isotope which has been identified has an observed half-life of about 45 minutes and probably has the mass number 244. The observed mode of decay of the 98{sup 244} is through the emission of alpha-particles, with energy about 7.1 Mev, which agrees with predictions, and other considerations involving the systematics of radioactivity in this region indicate that it should also be unstable toward decay by electron-capture. The chemical separation and identification of the new element was accomplished through the use of ion exchange adsorption methods employing the resin Dowex-50. The element 98 isotope appears in the eka-dysprosium position on elution curves containing 4.6-hour Bk{sup 243} (formed by a d,n reaction in the same bombardment) and the bombarded Cm{sup 242} as reference points; that is, it preceded berkelium and curium off the column just as dysprosium precedes terbium and gadolinium. The experiments so far have revealed only the tripositive oxidation state of eka-dysprosium character but practically no attempts at oxidation to possible IV and V states have been made as yet.
Date: February 27, 1950
Creator: Thompson, S.G.; Street, K.,Jr.; Ghiorso, A. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

THE NEW ELEMENT CALIFORNIUM (ATOMIC NUMBER 98)

Description: Definite identification has been made of an isotope of the element with atomic number 98 through the irradiation of Cm{sup 242} with about 35-Mev helium ions in the Berkeley Crocker Laboratory 60-inch cyclotron. The isotope which has been identified has an observed half-life of about 45 minutes and is thought to have the mass number 244. The observed mode of decay of 98{sup 244} is through the emission of alpha-particles, with energy of about 7.1 Mev, which agrees with predictions. Other considerations involving the systematics of radioactivity in this region indicate that it should also be unstable toward decay by electron capture. The chemical separation and identification of the new element was accomplished through the use of ion exchange adsorption methods employing the resin Dowex-50. The element 98 isotope appears in the eka-dysprosium position on elution curves containing berkelium and curium as reference points--that is, it precedes berkelium and curium off the column in like manner that dysprosium precedes terbium and gadolinium. The experiments so far have revealed only the tripositive oxidation state of eka-dysprosium character and suggest either that higher oxidation states are not stable in aqueous solutions or that the rates of oxidation are slow. The successful identification of so small an amount of an isotope of element 98 was possible only through having made accurate predictions of the chemical and radioactive properties.
Date: June 19, 1950
Creator: Thompson, S.G.; Street, K.,Jr.; Ghiorso, A. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

Proton-Proton Scattering at 340 MeV

Description: Measurements of the proton-proton differential scattering cross section using 340 Mev protons show a cross section approximately constant between 41{sup o} and 90{sup o} in the center of mass system. Two methods of counting the scattered protons have been used. The first method uses a counter telescope to count the scattered protons. The second method utilizes coincidences between counters which record the two protons involved in a single scattering process. The first method gives slightly higher cross sections; the average value of the differential cross section is (5.5 {+-} 1.0) x 10{sup -27} cm{sup 2} steradian{sup -1} in the center of mass system. Although the scattering appears isotropic it is larger than can be accounted for with pure S-scattering. There is a strong suggestion, but no positive proof, that n-p and p-p forces are different.
Date: January 1, 1950
Creator: Chamberlain, Owen & Wiegand, Clyde
Partner: UNT Libraries Government Documents Department

STOPPING POWER AND ENERGY FOR ION PAIR PRODUCTION FOR 340 MEVPROTONS

Description: The relative stopping powers for 300 Mev protons of H, Li, Be, C, Al, Fe, Cu, Ag, Sn, W, Pb, and U have been measured. The results are shown in Table I. The energy spent per ion-pair production in the gases H{sub 2}, He, N{sub 2}, O{sub 2}, and A at 340 Mev proton energy has also been measured. The results are shown in Table II.
Date: August 3, 1950
Creator: Bakker, C.J. & Segre, E.
Partner: UNT Libraries Government Documents Department

EXPERIMENTS ON N-P SCATTERING WITH 260 MEV NEUTRONS

Description: Neutrons produced by 350 Mev protons impinging on beryllium are scattered by hydrogen. We measure the differential scattering cross section as a function of the scattering angle. Results are summarized in Fig. 3 of the paper.
Date: March 6, 1950
Creator: Kelly, E.; Leith, C.; Segre, E. & Wiegand, C.
Partner: UNT Libraries Government Documents Department

Extension of Alpha- and Beta-Decay Systematics of ProtactiniumIsotopes

Description: As part of the program for obtaining data to extend the scope of the systematics of alpha-radioactivity and to obtain more data pertaining to the energy surface in the heavy region of elements, they have made some pertinent new measurements on protactinium isotopes. The heaviest isotope of protactinium hitherto reported is that of mass 234 and hence it would be of interest to know the beta-emission properties of heavier isotopes in order to tie them in with the known radioactive data in this general region. Since low-energy deuteron bombardment of U{sup 238} might be expected to lead to Pa{sup 235} and Pa{sup 236} by (d,{alpha}n) and (d,{alpha}) reactions and proton bombardment to Pa{sup 235} by the (p,{alpha}) reaction, these irradiations were made in the 60-inch cyclotron at energies of 19 and 9.5 Mev, respectively. The protactinium was chemically separated following the bombardment of natural uranium by a procedure which involved a number of manganese dioxide cycles coupled with extractions of protactinium from aqueous into organic solvents. The manganese dioxide cycles consisted of precipitating this compound from the solution of uranium in nitric acid, followed by centrifugation, dissolution of the solid with hydroxylamine solution, dilution, and reprecipitation. The dissolved precipitate from the last cycle was acidified, salted with ammonium nitrate, and the protactinium extracted with diisopropyl ketone, several washings with salted solutions being made to insure good separation from fission products. The protactinium was then washed back into a low acidity aqueous solution and after acidification was extracted into a benzene solution of thenoyltrifluoroacetone which forms a complex ion with the protactinium. This solution was then evaporated to dryness on a platinum counting plate leaving a weightless deposit of protactinium.
Date: January 30, 1950
Creator: Meinke, W. Wayne & Seaborg, Glenn T.
Partner: UNT Libraries Government Documents Department

'FISSION' OF MEDIUM WEIGHT ELEMENTS

Description: The fission reaction has been observed with high energy accelerator projectiles for elements as light as tantalum but has not been reported for medium weight elements. The present note presents evidence for the occurrence of reactions which are probably most properly described by the term 'fission' and which seem to occur with very small yield throughout the region where this type of reaction is only slightly exoergic or even endoergic with respect to mass balance. In the course of detailed investigation of the spallation of copper and the variation of the product yields with energy of the bombarding particle the threshold for formation of radioactive Cl{sup 38} (38-minute half-life) from elemental studied. The energetically most economical way in which Cl{sup 38} might be spallation reactions is by emission from the bombarded copper nucleus of nucleons in groups such as alpha-particles instead of single nucleons 0 The energetic requirements for the reaction Cu{sup 63}(p,pn6a)Cl{sup 38}, in which the maximum number of alpha-particles are emitted, include (1) the mass difference between the reactants and the products and (2) the excitation energy which the alpha-particles must have in order to pass over the coulombic barrier, Since the reaction is endoergic with respect to atomic masses, about 50 Mev must be supplied by the impinging proton to make up the mass difference. If the alpha-particles are considered as coming out consecutively, a value of about 50 Mev can be obtained for the coulombic requirement and thus the threshold for this spallation reaction is roughly 100 Mev.
Date: May 29, 1950
Creator: Batzel., Roger T. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

THE ISOTOPES OF AMERICIUM

Description: Three new americium activities (Am{sup 238}?, Am{sup 243}, and Am{sup 244?}, the latter two formed by n,{gamma} reactions) are described and some additional information is given on previously reported americium isotopes.
Date: April 11, 1950
Creator: Street, K.; Ghiroso, A. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

HIGH ENERGY EXCITATION FUNCTIONS IN THE HEAVY REGION

Description: The electrostatically deflected beam of the 184-inch cyclotron has been used with the stacked foil and absorber technique to determine the excitation functions for the following reactions: Th{sup 232}(p,6n)Pa{sup 227}, Th{sup 232}(p,3n)Pa{sup 230}, Th{sup 232}(d,7n)Pa{sup 227}, Th{sup 232}({alpha},p8n)Pa{sup 227}, Th{sup 232}({alpha},p5n)Pa{sup 230}, and U{sup 238}(p,{alpha}8n)Pa{sup 227}. The data are presented graphically and discussed individually for each of the reactions. Some rough excitation function data have also been determined for the reactions Th{sup 232}(d,4n)Pa{sup 230}, U{sup 238}(p,{alpha}5n)Pa{sup 230}, Th{sup 232}({alpha},7n)U{sup 229}, and Th{sup 232}({alpha},6n)U{sup 230}. The results are discussed in terms of compound nucleus formation, transparency effects, and other factors in order to arrive at a qualitative picture for the mechanism of high energy nuclear reactions with heavy nuclei.
Date: September 26, 1950
Creator: Meinke, W.W.; Wick, G.C. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

THREE NEW DELAYED ALPHA EMITTERS OF LOW MASS

Description: Two new positron active isotopes, B{sup 8} and Na{sup 20}, have been found to decay to excited states of Be{sup 8} and Ne{sup 20}, which in turn decay 'instantaneously' by alpha emission. Their half-lives are 0.65 {+-} 0.1 sec. and 1/4 sec. respectively. N{sup 12} is also found to have a low energy positron group which leads to an {alpha}-unstable excited state in C{sup 12}. The masses of B{sup 8} and Na{sup 20} are 8.027 and 20.015 respectively. B{sup 8} decays by a 13.7 {+-} 0.3 Mev positron, through the same excited state of Be{sup 8} as does Li{sup 8}. Estimates of the energies of the excited state in C{sup 12} and Ne{sup 20} are made.
Date: May 31, 1950
Creator: Alvarez, Luis W.
Partner: UNT Libraries Government Documents Department

THE RELATION OF PHOTOSYNTHESIS TO RESPIRATION

Description: The gas exchange by barley leaves of oxygen, carbon dioxide, and added radiocarbon dioxide has been measured in a closed system, with the following results: 1. Carbon dioxide follows different but not necessarily independent paths in photosynthesis and light respiration. 2. The carbon of newly formed photosynthetic intermediates is not available for respiration while the light is on, but becomes immediately respirable in the dark, The enhancement of dark respiration after a light period is largely due to built-up ''photosynthates.'' 3. Photosynthesis proceeds at a measurable rate even at the lowest CO{sub 2} pressures observed (0.03 mm Hg). There is no evidence for a ''threshold'' concentration of carbon dioxide for the reaction; at the lowest concentrations reached, respiration exactly equals assimilation, 4. The mean rate of respiratory CO{sub 2} evolution in strong light was found to be less than that in the dark. Internal re-photosynthesis of respiratory carbon may have been sufficient to account for this effect. 5. The assimilation of C{sup 14}O{sub 2} is about 17% slower than that of C{sup 12}O{sub 2}.
Date: July 20, 1950
Creator: Weigl, J.W.; Warrington, P.M. & Calvin, M.
Partner: UNT Libraries Government Documents Department

The Path of Carbon in Photosynthesis IX. Photosynthesis,Photoreduction and the Hydrogen-Oxygen-Carbon Dioxide Dark Reaction

Description: A comparison of the rates of fixation of Carbon 14 dioxide in algae for the processes of photosynthesis, photoreduction and the hydrogen-oxygen-carbon dioxide dark reaction has been made. For the same series of experiments, rates of incorporation of tracer carbon into the separate soluble components using the radiogram method have been determined. The mechanism of carbon dioxide uptake has been shown to occur via two distinct paths. In all cases studied, essentially the same compounds appear radioactive. The distribution with time, however, differs markedly.
Date: February 1, 1950
Creator: Badin, Elmer J. & Calvin, Melvin
Partner: UNT Libraries Government Documents Department

The Path of Carbon in Photosynthesis VIII. The Role of MalicAcid

Description: Malonate has been found to inhibit the formation of malic acid during short periods of photosynthesis with radioactive carbon dioxide. This result, together with studies which show the photosynthetic cycle to be operating normally at the same time, indicates that malic acid is not an intermediate in photosynthesis but is probably closely related to some intermediate of the cycle. Absence of labeled succinic and fumaric acids in these experiments, in addition to the failure of malonate to inhibit photosynthesis, precludes the participation of these acids as intermediates in photosynthesis.
Date: January 25, 1950
Creator: Bassham, James A.; Benson, Andrew A. & Calvin, Melvin
Partner: UNT Libraries Government Documents Department

THE PATH OF CARBON IN PHOTOSYNTHESIS. X. CARBON DIOXIDEASSIMILATION IN PLANTS

Description: The conclusions which have been drawn from the results of C{sup 14}O{sub 2} fixation experiments with a variety of plants are developed in this paper. The evidence for thermochemical reduction of carbon dioxide fixation intermediates is presented and the results are interpreted from such a viewpoint.
Date: April 1, 1950
Creator: Calvin, M.; Bassham, J .A.; Benson, A.A.; Lynch, V.; Ouellet, C.; Schou, L. et al.
Partner: UNT Libraries Government Documents Department

THE PATH OF CARBON IN PHOTOSYNTHESIS, XI THE ROLE OF GLYCOLICACID

Description: The metabolism of C{sup 14} labeled glycolic acid by Scenedesmus has been studied using radiochromatographic techniques for the separation and identification of products. When the pH of the medium was 2.8, appreciable assimilation occurred. The products were identical to those observed in C{sup 14}O{sub 2} photosynthesis. A major reaction anaerobically in the dark resulted in incorporation of C{sup 14} in almost equal amounts in the glycine and serine reservoirs. When the algae were illuminated, a diminution in the amount of glycine was observed.
Date: September 11, 1950
Creator: Schou, L.; Benson, A.A.; Bassham, J.A. & Calvin, M.
Partner: UNT Libraries Government Documents Department

CALIFORNIUM ISOTOPES FROM BOMBARDMENT OF URANIUM WITH CARBONIONS

Description: The recent production and identification of isotopes of elements with atomic numbers up to six higher than the target element through bombardment with hexapositive 120-Mev carbon ions made it seem worthwhile to apply this technique to the transuranium region. Accordingly, small pieces of natural uranium metal (about 0.5 mil thick and 205 cm by 0.6 cm area) were irradiated in the internal carbon ion beam in the Berkeley 60-inch cyclotron. Following the irradiations, the uranium was dissolved in dilute hydrochloric acid containing hydrogen peroxide and a transplutonium fraction was isolated through the use of lanthanum fluoride, and lanthanum hydroxide precipitation steps followed by the ion exchange adsorption column procedure in which concentrated hydrochloric acid is used to separate the tripositive actinide elements from the rare earth elements. The transplutonium fractions in hydrochloric acid were evaporated as weightless films on platinum plates which were placed in the ionization chamber of the 48 channel pulse analyzer apparatus in order to measure the yield and energies of any alpha-particles which might be present. In the best experiment at about one hour after the end of the 90-minute bombardment, some 50 disintegrations per minute of the distinctive 7.1-Mev alpha-particles of Cf{sup 244} were observed to be present and to decay with the 45-minute half-life. The Cf{sup 244} was presumably formed by the reaction U{sup 238}(C{sup 12},6n). After the decay of the alpha-particles due to Cf{sup 244}, about five disintegrations per minute of alpha-particles with 6.8-Mev energy was observed and this alpha-radioactivity decayed with a half-life of about 35 hours. A consideration of the systematics of alpha-radioactivity leads us to the view that this activity is due to the new isotope Cf{sup 246} formed by the reaction U{sup 238}(C{sup 12},4n) . The measured half-life agrees with the expected alpha half-life for the observed energy for ...
Date: September 6, 1950
Creator: Ghiorso, A.; Thompson, S.G.; Street, K. Jr. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

Carbon Dioxide Fixation by Green Plants

Description: Since the end of the war when the long-lived isotope of carbon, C{sup 14} became available a new tool has been applied in the study of photosynthesis. Because of the interest evoked by the tracer method, research in all areas of photosynthesis has expanded. There have been reviews on various aspects of photosynthesis such as the primary photochemical reaction, quantum efficiency products, and comparative biochemistry, many discussions of which were included in the monograph of The American Society of Plant Physiologists, ''Photosynthesis in Plants''.
Date: January 3, 1950
Creator: Benson, A.A. & Calvin, M.
Partner: UNT Libraries Government Documents Department