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Giant Dipole Resonance in Photonuclear Experiments
of Various Types: Discrepancies, Reasons,
Methods of Overcoming, Consequenses
Varlamov V. V., Ishkhanov B. S.
The photonuclear reaction investigation plays very
important role in both basic and applied nuclear physics research. Parameters
of Giant Dipole Resonance (GDR) observed in cross sections of various
reactions induced by g quanta are of great
interest for study of structure and dynamics of atomic nuclei, nuclear
reaction mechanisms, involved into the research in the field of relativistic
heavy ions. Absolute majority of photonuclear reaction cross section
data has been obtained in experiments using electron bremsstrahlung
and quasimonoenergetic photons produced by annihilation in flight of
relativistic positrons. There are many clear systematical disagreements
between data obtained in these types of experiments: they are clearly
larger than statistical data uncertainties and depend directly on the
method used to obtain data. All of them embarrass the data practical
using. The development of complete advanced databases gave the possibility
to overview jointly all photonuclear reaction data obtained, to carry
out new analysis of data accuracy and reliability, and to produce recommendation
how to take into account systematical discrepancies of various experiments
caused by differences of experimental methods, procedures of measured
data processing to obtain the information on reaction cross section.
With the aim of studying possible reasons of systematical disagreements
between the results of various experiments, developing methods of taking
them into account and bringing the results of various experiments to
consistency, the joint investigation of many photonuclear reaction cross
section data obtained in various experiments was carried out. Special
treatment was devoted to the yields and cross sections of total (g, xn) and partial
(g, n) and (g, 2n) photoneutron reactions
that put the main contributions to the GDR forming. The main attention
was paid to the specifics of experiments with quasimonoenergetic annihilation
photons carried out primarily at Livermore (USA) and Saclay (France).
Significant systematical discrepancies arising due to the difference
between these experiments effective photon spectra as well as in procedures
of neutron multiplicity sorting for reactions (g, n) and (g, 2n) are analyzed.
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