1,163 research outputs found
Phonon coupling effects in magnetic moments of magic and semi-magic nuclei
Phonon coupling (PC) corrections to magnetic moments of odd neighbors of
magic and semi-magic nuclei are analyzed within the self-consistent Theory of
Finite Fermi Systems (TFFS) based on the Energy Density Functional by Fayans et
al. The perturbation theory in g_L^2 is used where g_L is the phonon-particle
coupling vertex. A model is developed with separating non-regular PC
contributions, the rest is supposed to be regular and included into the
standard TFFS parameters. An ansatz is proposed to take into account the
so-called tadpole term which ensures the total angular momentum conservation
with g_L^2 accuracy. An approximate method is suggested to take into account
higher order terms in g_L^2. Calculations are carried out for four odd-proton
chains, the odd Tl, Bi, In and Sb ones. Different PC corrections strongly
cancel each other. In the result, the total PC correction to the magnetic
moment in magic nuclei is, as a rule, negligible. In non-magic nuclei
considered it is noticeable and, with only one exception, negative. On average
it is of the order of -(0.1 - 0.5) \mu_N and improves the agreement of the
theory with the data. Simultaneously we calculated the gyromagnetic ratio
g_L^{ph} of all low-lying phonons in 208Pb. For the 3^-_1 state it is rather
close to the Bohr-Mottelson model prediction whereas for other L-phonons, two
5^- and six positive parity states, the difference from the Bohr-Mottelson
values is significant.Comment: 21 pages, 24 figure
Microscopic description of the pygmy and giant electric dipole resonances in stable Ca isotopes
The properties of the pygmy (PDR) and giant dipole resonance (GDR)in the
stable , and isotopes have been calculated within
the \emph{Extended Theory of Finite Fermi Systems}(ETFFS). This approach is
based on the random phase approximation (RPA) and includes the single particle
continuum as well as the coupling to low-lying collectives states which are
considered in a consistent microscopic way. For we also include
pairing correlations. We obtain good agreement with the experimental data for
the gross properties of both resonances. It is demonstrated that the recently
measured A-dependence of the strength of the PDR below 10 MeV is well
understood in our model:due to the phonon coupling some of the strength in
is simply shifted beyond 10 MeV. The predicted fragmentation of the
PDR can be investigated in and experiments.
Whereas the isovector dipole strength of the PDR is small in all Ca isotopes,
we find in this region surprisingly strong isoscalar dipole states, in
agreement with an experiment. We conclude that for the
detailed understanding of the structure of excited nuclei e.g. the PDR and GDR
an approach like the present one is absolutely necessary.Comment: 6 figure
The natural resources of Bolinas Lagoon: their status and future
This publication is an integral part of the Department's high-priority inventory and assessment of coastal marshland and tideflat resources. It is intended as a guide for citizens, planners, administrators, and all others interested in the use and development of coastal lands and waters.
Although the resources and problems of Bolinas Lagoon have probably been the subject of more biological and physical investigations than any small estuarine area of the California coast, many of the pertinent reports and information are not readily available to the public.
Consequently, it is one purpose of this report to summarize the lagoon's history, ecological attractions, educational values and the problems facing its continued existence. At the same time, it should provide concerned citizens with a knowledge of the sources of additional and more specific information.
Publication of this report is consistent with the obligation of the Department of Fish and Game to do everything in its power to protect and maintain the State's fish and wildlife resources. Therefore, its purpose transcends local issues on pollution and development, and the Department is, in fact, submitting a report to the people on the status and future of part of its inheritance and the dowry of coming generations.
The report is the third of a scheduled series. It follows similar releases on Upper Newport Bay (Orange County) and Goleta Slough (Santa Barbara county) in March and June of 1970. Documentation of the resources of other critical areas is in progress. There will be future reports of this nature on Elkhorn Slough, Morro Bay, Tomales Bay, Humboldt Bay, and highly threatened marshlands in southern California. (137 pp.
A microscopic investigation of the transition form factor in the region of collective multipole excitations of stable and unstable nuclei
We have used a self-consistent Skyrme-Hartree-Fock plus Continuum-RPA model
to study the low-multipole response of stable and neutron/proton-rich Ni and Sn
isotopes. We focus on the momentum-transfer dependence of the strength
distribution, as it provides information on the structure of excited nuclear
states and in particular on the variations of the transition form factor (TFF)
with the energy. Our results show, among other things, that the TFF may show
significant energy dependence in the region of the isoscalar giant monopole
resonance and that the TFF corresponding to the threshold strength in the case
of neutron-rich nuclei is different compared to the one corresponding to the
respective giant resonance. Perspectives are given for more detailed future
investigations.Comment: 13 pages, incl. 9 figures; to appear in J.Phys.G,
http://www.iop.org/EJ/jphys
A nonlinear classical model for the decay widths of Isoscalar Giant Monopole Resonances
The decay of the Isoscalar Giant Monopole Resonance (ISGMR) in nuclei is
studied by means of a nonlinear classical model consisting of several
noninteracting nucleons (particles) moving in a potential well with an
oscillating nuclear surface (wall). The motion of the nuclear surface is
described by means of a collective variable which appears explicitly in the
Hamiltonian as an additional degree of freedom. The total energy of the system
is therefore conserved. Although the particles do not directly interact with
each other, their motions are indirectly coupled by means of their interaction
with the moving nuclear surface. We consider as free parameters in this model
the degree of collectivity and the fraction of nucleons that participate to the
decay of the collective excitation. Specifically, we have calculated the decay
width of the ISGMR in the spherical nuclei , ,
and . Despite its simplicity and its purely
classical nature, the model reproduces the trend of the experimental data which
show that with increasing mass number the decay width decreases. Moreover the
experimental results (with the exception of ) can be well fitted
using appropriate values for the free parameters mentioned above. It is also
found that these values allow for a good description of the experimentally
measured and decay widths. In addition, we give
a prediction for the decay width of the exotic isotope for which
there is experimental interest. The agreement of our results with the
corresponding experimental data for medium-heavy nuclei is dictated by the
underlying classical mechanics i.e. the behaviour of the maximum Lyapunov
exponent as a function of the system size
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