"Safe" Coulomb excitation of 30Mg.

We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient $\gamma$ -spectrometer MINIBALL. Using $^{30}$Mg ions accelerated to an energy of 2.25MeV/u together with a thin $^{nat}$Ni target, Coulomb excitation of the first excited 2+ states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative de-excitation $\gamma$ -ray yields the B(E2; 0$^{+}_{gs} \rightarrow 2^{+}_{1}$) value of $^{30}$Mg was determined to be 241(31)$e^{2}$fm$^{4}$. Our result is lower than values obtained at projectile fragmenttion facilities using the intermediate-ene…

The neutron-rich Mg isotopes: first results from MINIBALL at REX-ISOLDE

After the successful commissioning of the Radioactive beam EXperiment (REX) at ISOLDE (CERN) in 2002, first physics experiments were performed in 2003 which focussed on the neutron-rich Mg isotopes in the vicinity of the “island of inversion”. After introducing the REX facility and the modern γ spectrometer MINIBALL first preliminary results will be presented showing the high potential and physics opportunities offered by this new radioactive beam facility.

Evolution of quadrupole collectivity in N=80 isotones toward the Z=64 subshell gap: The B(E2;2+1→0+1) value of 142Sm

It was shown that the evolution of the B(E2; 2+ 1 → 0+ 1 ) values in N = 80 isotones from Te to Nd is affected by the underlying subshell structure. This manifests itself in the observation of the local suppression of the B(E2) value at Z = 58 with respect to the neighboring nuclei 136Ba and 140Nd. To investigate this shell sensitivity toward the Z = 64 subshell gap, the B(E2; 2+ 1 → 0+ 1 ) value of the unstable nucleus 142Sm was measured utilizing the projectile Coulomb excitation technique. The radioactive ion beam (RIB) experiment was performed at the REX-ISOLDE facility at CERN. The B(E2) value of 32 (4) W.u. reflects the impact of the π(1g7/2 2d5/2) subshell closure at Z = 64 with resp…

Shape coexistence in the neutron-deficient even-even Hg182-188 isotopes studied via Coulomb excitation

Coulomb-excitation experiments to study electromagnetic properties of radioactive even-even Hg isotopes were performed with 2.85  MeV/nucleon mercury beams from REX-ISOLDE. Magnitudes and relative signs of the reduced E2 matrix elements that couple the ground state and low-lying excited states in Hg182-188 were extracted. Information on the deformation of the ground and the first excited 0+ states was deduced using the quadrupole sum rules approach. Results show that the ground state is slightly deformed and of oblate nature, while a larger deformation for the excited 0+ state was noted in Hg182,184. The results are compared to beyond mean field and interacting-boson based models and interp…

Deformation and mixing of coexisting shapes in neutron-deficient polonium isotopes

Coulomb-excitation experiments are performed with postaccelerated beams of neutron-deficient Po196,198,200,202 isotopes at the REX-ISOLDE facility. A set of matrix elements, coupling the low-lying states in these isotopes, is extracted. In the two heaviest isotopes, Po200,202, the transitional and diagonal matrix elements of the 2+1 state are determined. In Po196,198 multistep Coulomb excitation is observed, populating the 4+1,0+2, and 2+2 states. The experimental results are compared to the results from the measurement of mean-square charge radii in polonium isotopes, confirming the onset of deformation from Po196 onwards. Three model descriptions are used to compare to the data. Calculati…

Structure of low-lying states in 140Sm studied by Coulomb excitation

The electromagnetic structure of 140Sm was studied in a low-energy Coulomb excitation experiment with a radioactive ion beam from the REX-ISOLDE facility at CERN. The 2+ and 4+ states of the ground-state band and a second 2+ state were populated by multistep excitation. The analysis of the differential Coulomb excitation cross sections yielded reduced transition probabilities between all observed states and the spectroscopic quadrupole moment for the 2+ 1 state. The experimental results are compared to large-scale shell model calculations and beyond-mean-field calculations based on the Gogny D1S interaction with a five-dimensional collective Hamiltonian formalism. Simpler geometric and alge…

Microscopic structure of coexisting $0^+$ states in $^{68}$Ni probed via two-neutron transfer

© 2019 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. The structure of low-spin states originating from shape-coexisting configurations in Ni284068 was directly probed via the two-neutron transfer reaction Ni66(t,p)Ni68 in inverse kinematics using a radioactive ion beam on a radioactive target. The direct feeding to the first excited 0+ state was measured for center-of-mass angles 4-16 and amounts to an integral of 4.2(16)% rela…

Shape Coexistence in the Neutron-Deficient Even-EvenHg182−188Isotopes Studied via Coulomb Excitation

Coulomb-excitation experiments to study electromagnetic properties of radioactive even-even Hg isotopes were performed with 2.85 MeV/nucleon mercury beams from REX-ISOLDE. Magnitudes and relative signs of the reduced E2 matrix elements that couple the ground state and low-lying excited states in Hg182-188 were extracted. Information on the deformation of the ground and the first excited 0(+) states was deduced using the quadrupole sum rules approach. Results show that the ground state is slightly deformed and of oblate nature, while a larger deformation for the excited 0(+) state was noted in Hg-182; 184. The results are compared to beyond mean field and interacting-boson based models and i…

Shape dynamics in neutron-rich Kr isotopes: Coulomb excitation of 92Kr, 94Kr and 96Kr

We report on the study of excited states in 92,94,96Kr populated via projectile Coulomb excitation at safe energies. The radioactive ion beams at energies of 2.85 MeV/u were delivered by the REX-ISOLDE facility at CERN and impinged on self-supporting 194,196Pt targets. The emitted γ -rays were detected by the Miniball detector-array. A detailed description of the experimental techniques used for extracting diagonal and transitional matrix elements and of the theoretical framework is given. The present experiment reveals the moderate evolution of the collective structure in the considered neutron-rich Kr isotopic chain, which is supported by the interacting boson model combined with the self…

“Safe” Coulomb Excitation ofMg30

We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient γ spectrometer MINIBALL. Using Mg-30 ions accelerated to an energy of 2.25 MeV/u together with a thin Ni-nat target, Coulomb excitation of the first excited 2(+) states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation γ-ray yields the B(E2;0(gs)(+)R 2(1)(+)) value of Mg-30 was determined to be 241(31)e(2) fm(4). Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the …

Evidence for a Smooth Onset of Deformation in the Neutron-Rich Kr Isotopes

The neutron-rich nuclei Kr94,96 were studied via projectile Coulomb excitation at the REX-ISOLDE facility at CERN. Level energies of the first excited 2 + states and their absolute E2 transition strengths to the ground state are determined and discussed in the context of the E(21+) and B(E2;21+→01+) systematics of the krypton chain. Contrary to previously published results no sudden onset of deformation is observed. This experimental result is supported by a new proton-neutron interacting boson model calculation based on the constrained Hartree-Fock-Bogoliubov approach using the microscopic Gogny-D1M energy density functional. © 2012 American Physical Society.

Testing refined shell-model interactions in thesdshell: Coulomb excitation ofNa26

Background: Shell-model calculations crucially depend on the residual interaction used to approximate the nucleon-nucleon interaction. Recent improvements to the empirical universal $sd$ interaction (USD) describing nuclei within the $sd$ shell yielded two new interactions---USDA and USDB---causing changes in the theoretical description of these nuclei.Purpose: Transition matrix elements between excited states provide an excellent probe to examine the underlying shell structure. These observables provide a stringent test for the newly derived interactions. The nucleus $^{26}\mathrm{Na}$ with 7 valence neutrons and 3 valence protons outside the doubly-magic ${}^{16}\mathrm{O}$ core is used a…

Erratum: Evidence for a Smooth Onset of Deformation in the Neutron-Rich Kr Isotopes [Phys. Rev. Lett.108, 062701 (2012)]

Coulomb Excitation of Neutron-Rich Zn Isotopes: First Observation of the21+State inZn80

Neutron-rich, radioactive Zn isotopes were investigated at the Radioactive Ion Beam facility REX-ISOLDE (CERN) using low-energy Coulomb excitation. The energy of the 2(1)+ state in 78Zn could be firmly established and for the first time the 2+ --> 0(1)+ transition in 80Zn was observed at 1492(1) keV. B(E2,2(1)+ --> 0(1)+) values were extracted for (74,76,78,80)Zn and compared to large scale shell model calculations. With only two protons outside the Z=28 proton core, 80Zn is the lightest N=50 isotone for which spectroscopic information has been obtained to date. Two sets of advanced shell model calculations reproduce the observed B(E2) systematics. The results for N=50 isotones indicate a g…

Corrigendum to: “Shape dynamics in neutron-rich Kr isotopes: Coulomb excitation of 92Kr, 94Kr and 96Kr” [Nucl. Phys. A 899 (2013) 1–28]

Determination of the B(E3, 0+ → 3−)-excitation strength in octupole-correlated nuclei near A ≈224 by the means of Coulomb excitation at REX-ISOLDE

The IS475 collaboration conducted Coulomb-excitation experiments with postaccelerated radioactive 220Rn and 224Ra beams at the REX-ISOLDE facility. The beam particles (Ebeam ≈ 2.83 MeV/u) were Coulomb excited using 60Ni, 114Cd, and 120Sn scattering targets. De-excitation γ-rays were detected employing the Miniball array and scattered particles were detected in a silicon detector. Exploiting the Coulomb-excitation code GOSIA for each nucleus several matrix elements could be obtained from the measured γ-ray yields. The extracted 3−||Ê3||0+ matrix element allows for the conclusion that, while 220Rn represents an octupole vibrational system, 224Ra has already substantial octupole correlations i…

The structure of low-lying states in ${}^{140}$Sm studied by Coulomb excitation

The electromagnetic structure of $^{140}$Sm was studied in a low-energy Coulomb excitation experiment with a radioactive ion beam from the REX-ISOLDE facility at CERN. The $2^+$ and $4^+$ states of the ground-state band and a second $2^+$ state were populated by multi-step excitation. The analysis of the differential Coulomb excitation cross sections yielded reduced transition probabilities between all observed states and the spectroscopic quadrupole moment for the $2_1^+$ state. The experimental results are compared to large-scale shell model calculations and beyond-mean-field calculations based on the Gogny D1S interaction with a five-dimensional collective Hamiltonian formalism. Simpler …

Testing refined shell-model interactions in the sd shell: Coulomb excitation of 26Na

Background: Shell-model calculations crucially depend on the residual interaction used to approximate the nucleon-nucleon interaction. Recent improvements to the empirical universal sd interaction (USD) describing nuclei within the sd shell yielded two new interactions—USDA and USDB—causing changes in the theoretical description of these nuclei. Purpose: Transitionmatrix elements between excited states provide an excellent probe to examine the underlying shell structure. These observables provide a stringent test for the newly derived interactions. The nucleus 26Na with 7 valence neutrons and 3 valence protons outside the doubly-magic 16O core is used as a test case. Method: A radioactive b…

The Miniball spectrometer

The Miniball germanium detector array has been operational at the REX (Radioactive ion beam EXperiment) post accelerator at the Isotope Separator On-Line facility ISOLDE at CERN since 2001. During the last decade, a series of successful Coulomb excitation and transfer reaction studies have been performed with this array, utilizing the unique and high-quality radioactive ion beams which are available at ISOLDE. In this article, an overview is given of the technical details of the full Miniball setup, including a description of the γ-ray and particle detectors, beam monitoring devices and methods to deal with beam contamination. The specific timing properties of the REX-ISOLDE facility are hi…

Spectroscopy of $^{46}$Ar by the (t,p) two-neutron transfer reaction

States in the $N=28$ nucleus $^{46}$Ar have been studied by a two-neutron transfer reaction at REX-ISOLDE (CERN). A beam of radioactive $^{44}$ at an energy of 2.16~AMeV and a tritium loaded titanium target were used to populate $^{46}$ by the t($^{44}$,p) two-neutron transfer reaction. Protons emitted from the target were identified in the T-REX silicon detector array. The excitation energies of states in $^{46}$ have been reconstructed from the measured angles and energies of recoil protons. Angular distributions for three final states were measured and based on the shape of the differential cross section an excited state at 3695~keV has been identified as $J^\pi = 0^+$. The angular diffe…

Spectroscopy of Low-lying States in $^{140}$Sm

International audience; Electromagnetic transition strengths and spectroscopic quadrupole moments for Sm-140 were measured by means of multi-step Coulomb excitation with radioactive beam at the ISOLDE facility at CERN. A complementary experiment was performed at the Heavy Ion Laboratory in Warsaw to assign spins for non-yrast states using the angular correlation technique. Based on the new experimental data previous spin assignments need to be revised.

Studies of pear-shaped nuclei using accelerated radioactive beams

There is strong circumstantial evidence that certain heavy, unstable atomic nuclei are ‘octupole deformed’, that is, distorted into a pear shape. This contrasts with the more prevalent rugby-ball shape of nuclei with reflection-symmetric, quadrupole deformations. The elusive octupole deformed nuclei are of importance for nuclear structure theory, and also in searches for physics beyond the standard model; any measurable electric-dipole moment (a signature of the latter) is expected to be amplified in such nuclei. Here we determine electric octupole transition strengths (a direct measure of octupole correlations) for short-lived isotopes of radon and radium. Coulomb excitation experiments we…

Accelerated radioactive beams from REX-ISOLDE

In 2001 the linear accelerator of the Radioactive beam EXperiment (REX-ISOLDE) delivered for the first time accelerated radioactive ion beams, at a beam energy of 2 MeV/u. REX-ISOLDE uses the method of charge-state breeding, in order to enhance the charge state of the ions before injection into the LINAC. Radioactive singly-charged ions from the on-line mass separator ISOLDE are first accumulated in a Penning trap, then charge bred to an A/q < 4.5 in an electron beam ion source (EBIS) and finally accelerated in a LINAC from 5 keV/u to energies between 0.8 and 2.2 MeV/u. Dedicated measurements with REXTRAP, the transfer line and the EBIS have been carried out in conjunction with the first co…

Electromagnetic properties of low-lying states in neutron-deficient Hg isotopes: Coulomb excitation of Hg-182, Hg-184, Hg-186 and Hg-188

The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass 182-188 Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of $ 0^{+}_{1,2}$01,2+, $ 2^{+}_{1,2}$21,2+and $ 4^{+}_{1}$41+states was observed in all nuclei under study. Reduced E2 matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate…

Do nuclei go pear-shaped? Coulomb excitation of 220Rn and 224Ra at REX-ISOLDE (CERN)

Artículo escrito por muchos autores, sólo se referencian el primero, los autores que firman como Universidad Autónoma de Madrid y el grupo de colaboración en el caso de que aparezca en el artículo

Coulomb excitation of Na-29,Na-30: Mapping the borders of the island of inversion

Seidlitz, M., et all ; 10 pags. ; 9 figs. ; 1 tab. ; PACS number(s): 21.60.Cs, 23.20.Js, 25.70.De, 29.38.Gj