MeV Positrons Research Articles

Annihilation in flight of 800 MeV positrons

The total cross-section for positron-electron annihilation in flight was measured at incident positron energy of 789 MeV. The measured value is (1.118 ±0.024) mb; which is in agreement with the Dirac cross-section. If the radiative corrections are taken into account this value is two standard deviations too low. The positron beam was obtained by conversion of the γ-ray beam of the Frascati Synchrotron.

Annihilation in flight of 200 and 800 MeV positrons

The total cross-sections for annihilation in flight of 200 and 800 MeV positrons have been measured. The ratio of the two cross-sections has been determined to an accuracy of 2.5% and is in accord with theory, while their absolute values are about (5±2.5)% low. From the measured ratio, there is no evidence for a deviation from theory which depends on the momentum transfer. The possible discrepancy in absolute value may arise from systematic corrections to the experiment.

The KS-3 MeV Van de Graaf injector of the Frascattielectron synchrotron

Abstract The modifications apported to a standard 3 MeV Van de Graaff, used as injector for the 1100 MeV Frascati synchrotron, are reported. They concern the voltage stabilizer, a compensation circuit that takes care of the fast variations of the voltage at the belt frequency, and the Pierce type electron source. A few data concerning the synchrotron operation in the period Jan. 1–Aug. 31, 1960, are added. Finally it is shortly described the project of a storage ring for 250 MeV electrons and positrons which being built in Frascati.

New Nuclide, Krypton-74

A new nuclide of krypton, ${\mathrm{Kr}}^{74}$, has been produced by high-energy proton interaction with strontium. It was found to have a half-life of (20\ifmmode\pm\else\textpm\fi{}1) minutes and to decay by (3.1\ifmmode\pm\else\textpm\fi{}0.1)-Mev positrons. No gamma rays in the energy range 0.04 to 4.0 Mev were observed. Evidence for the production of ${\mathrm{Kr}}^{75}$ was also observed. Calculations indicate an upper limit for the half-life of (0.8\ifmmode\pm\else\textpm\fi{}0.4) minutes.

The Scattering of Fast Charged Particles VI: The Multiple Scattering of 10 MeV Electrons and Positrons in Nuclear Emulsions

Nuclear emulsions were used to study the multiple scattering of iast particles. The resulting mean energies from the electron and positron distributions are compared to calculated energies obtained from the Moliere theory. Good agreement was obtained when the experimental and calculated values were plotted. (B.O.G.)

The Scattering of Fast Charged Particles IV: On the Measurement of the Detour Factor for 10 MeV Electrons and Positrons

The path length-foil thickness ratio of absorbers is called the detour factor. A method of measuring the detour factor in G5 nuclear emulsions for 10- Mev electrons and positrons is described, and the results are compared with theory. (L.T.W.)

The Scattering of Fast Charged Particles: II - On the Single Scattering of 9.8 MeV Positrons in Xenon

The Scattering of Fast Charged Particles: II - On the Single Scattering of 9.8 MeV Positrons in Xenon

A comparison of electron and positron single scattering in argon

Abstract A combination of lens spectrometer and diffusion cloud chamber was used to study the difference in the scattering of 0·3 mev positrons and electrons by argon. 611 electron and 506 positron scatters were observed with projected angles ø > 30°. The ratio of the number of electron scatters per unit track length to that of positrons was 1·21 with a standard error of 6%; the theoretical value is 1.18. The measured absolute value of the cross section agreed with the theoretical value within the experimental error of about 10%.

Decay of Neutron-Deficient Isotopes of Pd and Rh

Pd isotopes of masses 98, 99, and 101 were prepared by $\ensuremath{\alpha}$-particle bombardment of ruthenium. The radiations of these isotopes and of their Rh daughters were investigated with a scintillation coincidence spectrometer. ${\mathrm{Rh}}^{98}$ decays with a half-life of 8.7\ifmmode\pm\else\textpm\fi{}0.1 minutes by emission of 2.5\ifmmode\pm\else\textpm\fi{}0.2 Mev positrons in coincidence with 650\ifmmode\pm\else\textpm\fi{}10 kev $\ensuremath{\gamma}$ rays. Its ${\mathrm{Pd}}^{98}$ parent was shown by successive daughter extractions to decay with a half-life of 17.5\ifmmode\pm\else\textpm\fi{}0.5 minutes. ${\mathrm{Rh}}^{99}$ (4.7\ifmmode\pm\else\textpm\fi{}0.1 hours) showed 0.74-Mev positrons (10%) in coincidence with 335\ifmmode\pm\else\textpm\fi{}10 kev $\ensuremath{\gamma}$ rays (70%). Other $\ensuremath{\gamma}$ rays were observed at 615\ifmmode\pm\else\textpm\fi{}15 kev (20%), 890\ifmmode\pm\else\textpm\fi{}20 kev (weak line coincident with 335-kev $\ensuremath{\gamma}$), 1.26\ifmmode\pm\else\textpm\fi{}0.03 Mev, and 1.41\ifmmode\pm\else\textpm\fi{}0.04 Mev (weak). ${\mathrm{Pd}}^{99}$ (21.6\ifmmode\pm\else\textpm\fi{}0.6 minutes) was identified by successive Rh daughter extractions. Its maximum positron energy is 2.0\ifmmode\pm\else\textpm\fi{}0.1 Mev and the following $\ensuremath{\gamma}$ rays were observed: 140, 275, 420, and 670 kev. The 140-kev $\ensuremath{\gamma}$ ray is the most intense and the 420-kev peak represents two $\ensuremath{\gamma}$ rays of about the same energy in cascade. ${\mathrm{Rh}}^{101}$ (4.7\ifmmode\pm\else\textpm\fi{}0.2 days) decays by electron capture followed by emission of 312\ifmmode\pm\else\textpm\fi{}10 kev $\ensuremath{\gamma}$ rays. ${\mathrm{Pd}}^{101}$ (8.5\ifmmode\pm\else\textpm\fi{}0.3 hours) emits 0.58\ifmmode\pm\else\textpm\fi{}0.04 Mev positrons (4%) by decay to the ground state of ${\mathrm{Rh}}^{101}$. The $\ensuremath{\gamma}$ rays observed were at 288 kev (15%), 590 kev (15%), 720, 1190, and 1280 kev (last three less intense). The photopeak at 288 kev represents two coincident $\ensuremath{\gamma}$ rays of about the same energy. Tentative spin and parity assignments were made for the ground states of the nuclides investigated. Mass assignments were confirmed by a study of the relative yields of the various radioactive isotopes as the bombarding $\ensuremath{\alpha}$-particle energy and isotopic composition of the Ru target were varied.

The Scattering of Fast Charged Particles I: On the Single Scattering of 13.5 MeV Electrons in Xenon

The scattering of 9.8 MeV positrons in xenon in the angular interval 5-40° has been investigated using the cloud chamber method. The results agree reasonably well in this angular interval with the calculations of McKinley and Feshbach, in which Z is replaced by -Z. The ratio e-/e+ using the previous electron scattering results (Part I), normalized to 9.8 MeV, also agree well with McKinley and Feshbach in the 5-30° interval.

The Scattering of Fast Positrons by Nuclei

It is shown that the effects of finite nuclear size and radiative correction cause considerable modifications to the Mott formula for the cross sections. An exact calculation of the phase shifts is carried through for a simple nuclear model and 20 MeV positrons scattered by gold nuclei. Two approximate phase shift calculations are made and the singularity occurring in the radial wave equation is investigated. The radiative correction for scattering from light nuclei is found to be the same as for electron scattering.