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|Autori: ||Bondì, Mariangela|
|Titolo: ||Heavy-ion double charge exchange reactions as tools for 0bb decays. The 40Ca(18O,18Ne)40Ar reaction at 270 MeV by using MAGNEX|
|Abstract: ||This study is inserted in a research line that aims to access the Nuclear
Matrix Element (NME) involved in the half-life of the 0 bb decay, by measuring
the cross sections of heavy-ion induced Double Charge Exchange
(DCE) reactions with high accuracy. The basic point is that the initial
and nal state of both 0 bb decay and DCE processes are the same. In
addition, both processes pass through the same intermediate state and the
transition operators have a similar mathematical structure.
This work shows for the rst time experimental data on heavy-ion DCE
reaction in a wide range of transferred momenta, with an acceptable statistical
signi cance and good angular and energy resolution. In particular
(18O,18Ne) reaction at 270 MeV incident energy on 40Ca target was investigated.
In order to estimate the contribution of the concurrent channels the
40Ca(18O,18F)40K single charge exchange intermediate channel and the competing
processes 40Ca(18O,20Ne)38Ar two-proton transfer and 40Ca(18O,16O)42Ca
two-neutron transfer were also studied.
The experiment was performed at Laboratori Nazionali del Sud (LNSINFN)
in Catania using a 270 MeV energy 18O Cyclotron beam impinging
on a 279 g/cm2 thick 40Ca target. The ejectiles were momentum analysed
by the MAGNEX large acceptance magnetic spectrometer and detected by
its focal plane detector.
The energy spectra and angular distributions have been extracted. The
data analysis of experimental results have established that the transition to
40Args: is dominated by the direct processes.
Finally, an innovative technique to infer on the nuclear matrix elements by
measuring the cross section of a double charge exchange nuclear reaction
was proposed. The main assumption are that the DCE reaction is a twostep
charge exchange and a surface localized process. The model adopted to describe the cross section of the DCE reaction consists in a generalization
of the well-established factorization of the single charge-exchange cross section,
valid under certain hypothesis, discussed in the thesis. Therefore, the
cross section could be factorized in a nuclear structure term, containing the
matrix elements, and a nuclear reaction one (unit cross section). Despite the
used approximations, the extracted strength and nuclear matrix elements
are reasonable within +-50%, signalling that the main physics content has
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|BNDMNG87A69I754V-thesis_bondi.pdf||thesis_bondi||100,74 MB||Adobe PDF||Visualizza/apri
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