"The evolution of the Z=28 shell gap towards 78Ni: Neutron-rich Cu isotopes"
Eda Sahin, INFN-LNL
(id #160)
Seminar: YesPoster: No
Invited talk: No
Neutron-rich Cu isotopes, having one proton outside the Z=28 shell, are also
good probes of the single particle structure in the region of 78Ni. The characterization
of their excited states allows searching for possible shell modifications due
to the tensor mechanism which is predicted to cause modifications into the known
shell gaps with their possible weakening or disappearance [1, 2, 3]. Shell model
calculations including the effect of the tensor force predict a lowering of the πf5/2
state causing an inversion of the πf5/2-πp3/2 effective single particle states around
75Cu which has been recently confirmed by nuclear spin and magnetic moment
measurements performed at the ISOLDE facility [4].
From the comparison with the S.M. predictions, three different configurations
can give rise to the I 7/2− states appeared in the tentative experimental level
scheme picture:
• either a coupling of the single-particle configuration of πp3/2 to the 2+ core
excitation leading to the 7/2− [πp3/2
2+] levels,
• or similarly, a coupling of the single-particle configuration of πf5/2 to the 2+
core excitation leading to the 7/2− and 9/2− [πf5/2
2+] levels,
• or finally, the excitation of one proton hole into the πf7/2 orbit, which results
with the 7/2− [πf7/2
−] levels.
The aim of the present work is, therefore, to determine the collective or singleparticle
character of those states, which would result in different lifetimes. The
characterization of such states and in particular the identification of the πf7/2
−
particle-hole excitations across the Z=28 shell will provide essential information
on the shell gap size and therefore on the evolution of the Z=28 energy gap afore
mentioned. The knowledge of the electromagnetic transition matrix elements deexciting
such states, obtained through lifetime measurements, combined with the
information coming from the Coulomb excitation measurement [5], will provide this
characterization. The experiment has been performed at the Laboratory Nazionali
di Legnaro (LNL, Italy), using the AGATA Demonstrator coupled to the PRISMA
magnetic spectrometer. The neutron-rich Cu nuclei have been populated as products
of multi-nucleon transfer reactions following the collision of a 76Ge beam with
an energy of 540 MeV onto a 1.5 mg/cm2 thick 238U target.
The lifetime of excited states in 71,73Cu the has been studied recoil-distance
Doppler shift (RDDS) technique [6] in which a 4 mg/cm2 thick 24Mg degrader was
placed to degrade the ions produced in the reaction. The projectile-like reaction
products will be detected and identified in the magnetic spectrometer PRISMA
positioned at 55◦ with respect to the beam axis, close to the grazing angle for the
proposed reaction. The γ rays emitted from the reaction products were detected
with the AGATA Demonstrator, which was placed at sensitive backward angles with
a total absorption efficiency of ǫ=5%.
In the present work, the preliminary results on the first
good probes of the single particle structure in the region of 78Ni. The characterization
of their excited states allows searching for possible shell modifications due
to the tensor mechanism which is predicted to cause modifications into the known
shell gaps with their possible weakening or disappearance [1, 2, 3]. Shell model
calculations including the effect of the tensor force predict a lowering of the πf5/2
state causing an inversion of the πf5/2-πp3/2 effective single particle states around
75Cu which has been recently confirmed by nuclear spin and magnetic moment
measurements performed at the ISOLDE facility [4].
From the comparison with the S.M. predictions, three different configurations
can give rise to the I 7/2− states appeared in the tentative experimental level
scheme picture:
• either a coupling of the single-particle configuration of πp3/2 to the 2+ core
excitation leading to the 7/2− [πp3/2
2+] levels,
• or similarly, a coupling of the single-particle configuration of πf5/2 to the 2+
core excitation leading to the 7/2− and 9/2− [πf5/2
2+] levels,
• or finally, the excitation of one proton hole into the πf7/2 orbit, which results
with the 7/2− [πf7/2
−] levels.
The aim of the present work is, therefore, to determine the collective or singleparticle
character of those states, which would result in different lifetimes. The
characterization of such states and in particular the identification of the πf7/2
−
particle-hole excitations across the Z=28 shell will provide essential information
on the shell gap size and therefore on the evolution of the Z=28 energy gap afore
mentioned. The knowledge of the electromagnetic transition matrix elements deexciting
such states, obtained through lifetime measurements, combined with the
information coming from the Coulomb excitation measurement [5], will provide this
characterization. The experiment has been performed at the Laboratory Nazionali
di Legnaro (LNL, Italy), using the AGATA Demonstrator coupled to the PRISMA
magnetic spectrometer. The neutron-rich Cu nuclei have been populated as products
of multi-nucleon transfer reactions following the collision of a 76Ge beam with
an energy of 540 MeV onto a 1.5 mg/cm2 thick 238U target.
The lifetime of excited states in 71,73Cu the has been studied recoil-distance
Doppler shift (RDDS) technique [6] in which a 4 mg/cm2 thick 24Mg degrader was
placed to degrade the ions produced in the reaction. The projectile-like reaction
products will be detected and identified in the magnetic spectrometer PRISMA
positioned at 55◦ with respect to the beam axis, close to the grazing angle for the
proposed reaction. The γ rays emitted from the reaction products were detected
with the AGATA Demonstrator, which was placed at sensitive backward angles with
a total absorption efficiency of ǫ=5%.
In the present work, the preliminary results on the first
