Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    ISSN: 1434-601X
    Keywords: 14.60.Cd ; 25.70.Cd ; 25.70.Ef
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present the results obtained from systematic studies of positron creation for a series of heavy-collision systems, with united chargeZ u =Z 1 +Z 2 ranging fromZ u =164 (Pb + Pb) toZ u =184 (U+U) at bombarding energies close to the Coulomb barrier, using the Orangeβ-spectrometer at GSI. For each collision system studied, the dominating continuous distributions due to quasiatomic and nuclear positron emission are determined accurately. This is essential in obtaining the characteristics of the still unexplained monoenergetic positron lines which appear in the energy range between 200 keV and 400 keV. Our results are compared with coupled-channels calculations for quasi-atomic positron creation. The latter describe quite well the global features of the measured spectra, but overestimate systematically their absolute values. From the comparison, a common normalization factor of about 0.75 can be established for the calculated spectra. In particular, the dependence onZ u of the measured emission probabilities was found to follow a power law (∝Z u 195±1), in fair agreement with the theoretical prediction.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 328 (1987), S. 129-145 
    ISSN: 1434-601X
    Keywords: 14.60.Cd ; 25.70.Cd ; 25.70.Ef
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Positron lines were observed in heavy ion-atom collisions at bombarding energies close to the Coulomb barrier in subcritical systems with the sum of the atomic numbers of the colliding nucleiZ u =Z 1+Z 2 being smaller thanZ u =172. Each collision system, studied,208Pb +208Pb(Zu=164),238U+181Ta(Zu=165), and238Au(Zu=171), exhibits the emission of two positron lines withZ u -independent c.m. energies of ∼ 258 keV and ∼ 340 keV, and with widths of about 30 keV, superimposed on continuous positron spectra from nuclear pair decay and pair emission induced by the time changing Coulomb field of the collision. The production cross section of thee +-lines rises with a high power ofZ u (ocZ u 22), which is comparable to theZ u 20-dependence for the collision induced positrons.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    ISSN: 1434-601X
    Keywords: 14.60.Cd ; 25.70.Cd ; 25.70.Ef
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present the results obtained from a series of ρ+ρ−-coincidence measurements in heavy-ion collisions using the double-Orangeβ-spectrometer at GSI. The collision systems U+U, U+Pb, and U+Ta were investigated at bombarding energies close to and slightly above (U+Ta) the Coulomb barrier. For all systems studied, very narrow (FWHM−20 keV) ρ+ρ− lines were observed in the sum-energy spectra, with kinetic energies ranging from ∼555 keV to ∼810 keV, superimposed on a continuous distribution mainly due to uncorrelated ρ+ρ− emission. Particularly in the U+Ta system, a pronounced sum-energy line appears at ∼634 keV, predominantly in deep-inelastic collisions. In some cases (e.g. U+Pb) the line characteristics is consistent with a two-body decay mode of an emitter which moves with the c.m. velocity of the colliding ions. However, other lines, and in particular the 634 keV line (U+Ta), exhibit a rather isotropical opening-angle distribution whereas their energy is unequally shared between positrons and electrons, thus being in clear disagreement with this scenario. In general, the data preclude an emission from the separated (moving) nuclei, and, in the latter cases, provide evidence that the e+e−-pair decay occurs in the vicinity of the Coulomb field of a third heavy (positively charged) partner having only a small transverse velocity (|v|⊥〈0.02c)
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...