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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 Mechanism of Proton Polarization in High-EnergyCollisions

Description: Recently experimental evidence has accumulated showing that high-energy collisions of protons with various nuclei induce a considerable polarization in proton beams, and a mechanism has been proposed to account for this effect.
Date: June 9, 1954
Creator: Chamberlain, Owen; Segre, Emilio; Tripp, Robert; Wiegand, Clyde & Ypsilantis, Thomas
Partner: UNT Libraries Government Documents Department

Example of an Antiproton-Nucleon Annihilation

Description: The existence of antiprotons has recently been demonstrated at the Berkeley Bevatron by a counter experiment. The antiprotons were found among the momentum-analyzed (1190 Mev/c) negative particles emitted by a copper target bombarded by 6.2-Bev protons. Concurrently with the counter experiment, stacks of nuclear emulsions were exposed in the beam adjusted to 1090 Mev/c negative particles in an experiment designed to observe the properties of antiprotons when coming to rest. This required a 132 g/cm2 copper absorber to slow down the antiprotons sufficiently to stop them in the emulsion stack. Only one antiproton was found in stacks in which seven were expected, assuming a geometric interaction cross section for antiprotons in copper. It has now been found that the cross section in copper is about twice geometric, which explains this low yield.
Date: February 27, 1956
Creator: Chamberlain, O.; Chupp, W.W.; Ekspong, A.G.; Goldhaber, G.; Goldhaber, S.; Lofgren, E.J. et al.
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

Elastic Scattering of 190 MEV Deuterons by Protons

Description: The elastic differential scattering cross section of 190 MeV deuterons by protons has been measured from 15 degrees to 170 degrees in the center of mass system. The cross sections were obtained by subtracting the carbon counts from those received with a polyethylene target. Part I presents a description of the experiments. Results are shown in Table IV and Fig. 3. Part II compares these results with those expected from theory by making use of a method developed by Chew. A summary of this comparison is given in Table VII.
Date: June 3, 1953
Creator: Chamberlain, Owen & Stern, Martin O.
Partner: UNT Libraries Government Documents Department

The Electron Spin Resonance Spectrum of Dibenzene ChromiumCation

Description: The electron spin paramagnetic resonance of dibenzene chromium cation h a s been observed. I t s c e n t e r is a t a valhe of g = 1.98. I t shows eleven hyperfine components s e p a r a t e d by 3.5 gauss. These a r e i n t e r p r e t e d to b e eleven of the thirteen components expected to r e s u l t f r o m the interaction of the twelve equivalent protons with the unpaired electron.
Date: December 20, 1956
Creator: Feltham, Robert D.; Sogo, Power & Calvin, Melvin
Partner: UNT Libraries Government Documents Department

Observation of Antiprotons

Description: One of the striking features of Dirac's theory of the electron was the appearance of solutions to his equations which required the existence of an antiparticle, later identified as the positron.
Date: October 19, 1955
Creator: Chamberlain, Owen; Segre, Emilio; Wiegand, Clyde & Ypsilantis,Thomas
Partner: UNT Libraries Government Documents Department

Nuclear Thermodynamics of the Heaviest Elements. II

Description: The masses of the isotopes of the heaviest elements have been calculated from known decay data in the region, extended by means of decay energies calculated from closed decay-energy cycles and estimated from the systematics of alpha and beta decay energies. The absolute values of the masses are based on the mass-spectrometrically determined mass of Pb{sup 208} and a few measured neutron binding energies. The half-life systematics of alpha decay and spontaneous fission are also presented, and some predictions of the properties of as yet undiscovered nuclides are made.
Date: October 1, 1957
Creator: Foreman Jr., Bruce M. & Seaborg, Glenn T.
Partner: UNT Libraries Government Documents Department

Nuclear Thermodynamics of the Heaviest Elements. II

Description: The masses of the isotopes of the heaviest elements have been calculated from known decay data in the region, extended by means of decay energies calculated from closed decay-energy cycles and estimated from the systematics of alpha and beta decay energies. The absolute values of the masses are based on the mass-spectrometrically determined mass of Pb{sup 208} and a few measured neutron binding energies. The half-life systematics of alpha decay and spontaneous fission are also presented, and some predictions of the properties of as yet undiscovered nuclides are made.
Date: January 1, 1958
Creator: Foreman Jr., Bruce M. & Seaborg, Glenn 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

Quadrupole Focusing Lenses for Charged Particles

Description: A set of four strong focusing magnetic quadrupole lenses has been constructed and operated. Each lens consists of four air cooled electromagnets with pole tips having a hyperbolic cross section. Each lens is 4 in. long and has an aperture 2 in. in diameter. Measurements of the magnetic field demonstrate that the hyperbolic cross section satisfies the requirements of a constant magnetic field gradient very well. The technique of deflecting a current carrying flexible wire has been used to measure the trajectory of charged particles through the system of lenses. It has been observed that the strong focusing requirements are satisfied. The system of lenses was then used to focus 0.5 Mev protons, 20 Mev deuterons, and 40 Mev alpha particles. The parallel beam of 0.5 Mev protons was detected by observing the incandescence of a quartz plate while the protons were bombarding it. The focused beam was less than 1 mm in diameter. The astigmatic 20 Mev deuteron beam from the 60 in. cyclotron was increased in current density by a factor greater than 30.
Date: April 15, 1953
Creator: Cork, Bruce & Zajec, Emery
Partner: UNT Libraries Government Documents Department

High Energy Proton Spallation -- Fission of Uranium

Description: The fission and spallation reactions caused in uranium by bombardment with high energy protons (340 t o 350 MeV) were investigated. The reaction products were separated from the target by chemical processes and identified by their radioactive properties. The relative yields of the observed fission products were measured, and the results plotted as a function of mass number. Several of the spallation products were identified and their yields estimated. An attempt was made to determine the most probable atomic number for a nuclide of given mass formed directly from fission. Studies were made of the relative yields along several isobaric chains as a function of atomic number. From these data predictions of the mass and charge of the fissioning nucleus are made.
Date: May 28, 1951
Creator: Folger, R.L.; Stevenson, P.C. & Seaborg, G.T.
Partner: UNT Libraries Government Documents Department

Spallation-Fission Competition in Heaviest Elements; TritonProduction

Description: Stacked f o i l s of Au{sup 197}, Th{sup 232}, and U{sup 238} were bombarded, i n a series of experiments, with 48-Mev helium ions, 24-Mev deuterons, and 32-Mev protons. Tritium from each f o i l was collected and then measured by a gas-counting technique. The qualitative r e s u l t s indicate t h a t high-energy t r i t o n s are emitted i n r e l a t i v e l y large abundance from a l l targets and with each of the bombarding p a r t i c l e s . Cross sections f o r t r i t o n production from fissionable U 238 and Th{sup 232} and from non-f i s s ionable Au{sup 197} are comparable. The integrated (ci,t) cross sections thus determined for and 9lk-1' are nearly the same a s the integrated cross sections f o r the '(,pZn)' reactions as determined by measuring the yield of t h e product heavy isotopes i n radiochemical experiments. A l l of the f a c t s axe consistent with a picture of emission of high-energy t r i t o n s (whether due t o a stripping, pick-up, or other mechanism) i n which fissionable intermediate nuclei are formed mainly a t l e v e l s of excitation be-low t h e i r f i s s i o n thresholds.
Date: March 1, 1957
Creator: Wade, William H.; Gonzalez-Vidal, Jose; Glass, Richard A. & Seaborg, Glenn T.
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

Some Comments on the Mechanism of Fission

Description: A correlation of spontaneous fission rates with Z and A is made to show that these rates depend on the nuclear type. Some suggestions as to the mechanisms are given and it is also shown how these relate to the mechanism of slow neutron and photo fission.
Date: July 25, 1951
Creator: Seaborg, Glenn T.
Partner: UNT Libraries Government Documents Department