First energy and angle differential measurements of
-pairs emitted by internal pair conversion of excited heavy nuclei
U. Leinberger1 - E. Berdermann1 - F. Heine2 - S. Heinz2 - O. Joeres2 - P. Kienle2 - I. Koenig1 - W. Koenig1 - C. Kozhuharov1 - A. Schröter1 - H. Tsertos3,a - (ORANGE Collaboration at GSI) - C. Hofmann4 - G. Soff4
1 Gesellschaft für Schwerionenforschung (GSI), D-64291
Darmstadt, Germany
2 Technical University of Munich, D-85748 Garching, Germany
3 University of Cyprus, CY-1678 Nicosia, Cyprus
4 Institut für Theoretische Physik, Technical University Dresden, D-01062
Dresden, Germany
Received: 22 April 1997 / Revised version: 16 December 1997 Communicated by P. Armbruster
Abstract
We present the first energy and angle resolved measurements of
-pairs emitted from heavy nuclei (
) at rest by internal pair
conversion (IPC) of
transitions with energies of less than 2MeV as well as recent theoretical
results using the DWBA method, which takes full account of relativistic
effects, magnetic substates and finite size of the nucleus. The 1.76MeV E0
transition in
(
source) and the 1.77MeV M1 transition in
(
source) have been investigated experimentally using the essentially
improved setup at the double-ORANGE
-spectrometer of GSI. The
measurements prove the capability of the setup to cleanly identify the IPC
pairs in the presence of five orders of magnitude higher
and
background from the same source and to
yield essentially
background-free sum spectra despite the large background.
Using the ability
of the ORANGE setup to directly determine the opening angle
of the
-pairs (
), the angular
correlation of the emitted pairs was measured
within the range covered experimentally
(
).
In the
case the
correlation could be deduced for a wide range of energy differences
of
the pairs (-530 keV
keV).
The
results are in good agreement with recent theory. The
angular correlation deduced for the M1 transition in
is in strong
disagreement with theoretical predictions derived within the Born
approximation and shows almost isotropic character. This is again in
agreement with the new theoretical results.
PACS
14.60.Cd Electrons (including positrons) -
23.20.En Angular distributions and correlation measurements -
23.20.Ra Internal pair production -
29.25.Rm Sources of radioactive nuclei -
29.30.Aj Charged-particle spectrometers: electric and magnetic
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