Die experimentelle Bestimmung der Koeffizienten der Anlagerung der neutralen und elektrisch geladenen Radon-Folgeprodukte an Aerosole

The attachment of the neutral and charged²¹²Pb atoms to monodisperse polystyene latex aerosols with diameters 10^?5-2·10^?4 cm is measured and compared with the theoretical values. The method of measurement allowed to determine the difference between the attachment coefficients of the ions and neutral atoms. The obtained values are explained with the diffusion model by considering the electrostatic forces between the diffusing ions and the aerosol particles. The best agreement of the measured attachment coefficients with those of theory is obtained if the image forces of the²¹²Pb ions (good dried latex aerosols!) are neglected in the computations.     

Die Anlagerung von radioaktiven Atomen und Ionen an Aerosolteilchen

The attachment of radioactive atoms and ions to spherical aerosol particles has been studied theoretically. For uncharged atoms the deposition is considered to be solely governed by thermal diffusion. With calculations based on the “limiting-sphere”-method ofArendt-Kallman it is found, that the attached activity is proportional toΦ ² for aerosol particle diametersΦ smaller than 0.1 μm, and proportional toΦ forΦ greater than 1 μm. For charged ions the diffusion process is modified by the influence of electrostatic forces between the diffusing ions and the aerosol particles. In the frequently occurring case of a symmetrically bipolar charged aerosol this influence can be expressed by a functionG _p(Φ), which depends on the diameterΦ and the effective numberp of elementary charges on the aerosol particle. For an aerosol particle diameterΦ greater than 0.1 μm the attached activity is proportional toΦ ^1.1, and forΦ smaller than 0.01 μm it is proportional toΦ ^1.55. The effects of neglecting various terms in the calculation are considered. The distribution of natural radioactivity on atmospheric aerosols has been calculated for various particle size distributions according toJunge. The calculation shows that about 90% of the total natural activity should be attached to particles smaller thanΦ=0.5 μm, and about 35% to particles smaller thanΦ=0.1 μm. The time T_1/2, in which the concentration of the radioactive particles decreases to half the initial value, depends on the concentration of the aerosol particles and on their size distribution. For 10⁴ aerosol particles per cm³ and the size distributions mentioned,T _1/2 varies between 15 and 30 seconds for radioactive ions. For radioactive atomsT _1/2 is greater than it is for ions in the range of aerosol particle diameters belowΦ=0.25 μm, and smaller ifΦ greater than 0.25 μm.     

Die Streuung kurzwelliger Strahlung durch Atome nach der Diracschen Strahlungstheorie

Zeitschrift für Physik A Hadrons and nuclei - Die Streuung kurzwelliger Strahlung durch Atome oder Atomsysteme wird nach den Methoden der Diracschen Dispersionstheorie behandelt. Es ergibt...     

Die (γ,p)-Reaktion an einigen leichten und mittelschweren Kernen

Photoproton spectra have been obtained from gaseous¹⁸O,²⁰Ne,²²Ne,³⁶Ar,⁴⁰Ar,⁸⁴Kr, Kr and Xe and from foils of²³Na and K irradiated with bremsstrahlung from 24 to 32.5 MeV endpoint energy. The charged particles have been detected at 90° to theγ-beam by a Cs I(Tl)-spectrometer with pulse shape discrimination. Yields and lower limits for the integrated cross sections are given. For argon and the heavier nuclei, the results are compared with statistical-model calculations.     

Die Exoelektronen-Emission (Kramer-Effekt) von Zinkoxyd

This work was done, to get new informations about the processes leading to the emission of exoelectrons. The emission-glowcurves of single crystals and of pure and doped powders, after stimulation by X-rays, were measured by means of a G.-M.-counter. Maxima were found at 135° C, 192° C and 260° C. Conductivity-glow-curves of single crystals and films, which were also measured, showed no maximum between 20° C and 280° C. The experiments show that the emission of exo-electrons cannot be a consequence of an enrichement of electrons (?Maxwell-tail“) in the conduction band set free from metastable states in the forbidden gap of ZnO during the heating of the specimen. Theoretical considerations lead to the same conclusion. Further it could be shown, that the emission-phenomenon cannot be explained by recombination processes in the depletion layer, if our knowledge of the ZnO band model is correct. It is assumed that the emission-maxima are due to centers in the sorption layer.     

Die Korrektur des Bildes der Anger-Kamera (Teil II)

Ausgehend von der im ersten Teil begründeten Notwendigkeit, die mit der Szintillationskamera Impulsverteilung korrigieren zu müssen, wird in der vorliegenden Arbeit der Programmablanfplan für diese Korrekturrechnung mit Hilfe der elektronischen Datenverarbeitung (R 300) erläutert. Im gegenwärtigen Stadium der Entwicklung eines umfangreichen Konzepts zum Einsatz der EDV für die Szintigraphie – an der alle Nuklearmedizinischen Abteilungen der DDR beteiligt sind – erfolgt bei den Autoren die Ein- und ausgabe der Daten über Lochstreifen. Die Wirkung der Korrekturrechnung wird am homogenen Phantom selbst und an einer Pankreasunfersuchung demonstriert.     

i(h-) (a-at)是算符吗

指出将ｉｈδ／δｔ作为算符来讨论没有多大意义,且ｉｈδ／δｔ≠Ｈ,△ｔ△Ｅ≥ｈ／２不可能通过ｔ与ｉｈδ／δｔ或ｔ与Ｈ的对易关系得出。