Abstract The transition between the spherical and deformed shapes of the nuclei (shape phase transition) is an interesting property of nuclei that enriches our understanding of the nuclear structure. ...One method for studying it is through measurement of a wide range of atomic masses and derivation of the two-neutron separation energies (S 2n ). Using a multiple-reflection time-of-flight mass spectrometer at the FRS Ion Catcher, GSI, atomic masses in the region of A ∼ 150 were measured. This allowed an wide study of phase shape transitions in this region of the nuclear chart. In addition, comparison with the Skyrme Hartree–Fock plus BCS approach are done; showing a remarkable good agreement between theory and experiment.
The computer simulations of the angular distributions of low-Z relativistic isotopes channeled in a half-wavelength-crystal (HWC) revealed that at equal beam energy, crystal thickness and its ...alignment, the HWC channeling is sensitive to a mass number A of the low-Z isotope. That means, besides well-known applications of relativistic channeling for beam deflection and splitting, probably the new one is possible – light isotopes mass filter.
A study of cooled ¹⁹⁷Au projectile-fragmentation products has been performed with a storage ring. This has enabled metastable nuclear excitations with energies up to 3 MeV, and half-lives extending ...to minutes or longer, to be identified in the neutron-rich nuclides ¹⁸³(,)¹⁸⁴(,)¹⁸⁶Hf and ¹⁸⁶(,)¹⁸⁷Ta. The results support the prediction of a strongly favored isomer region near neutron number 116.
The neutron-rich 213Pb isotope was produced in the fragmentation of a primary 1 GeV A238U beam, separated in FRS in mass and atomic number, and then implanted for isomer decay γ-ray spectroscopy with ...the RISING setup at GSI. A newly observed isomer and its measured decay properties indicate that states in 213Pb are characterized by the seniority quantum number that counts the nucleons not in pairs coupled to angular momentum J=0. The conservation of seniority is a consequence of a geometric phase associated with particle-hole conjugation, which becomes observable in semi-magic nuclei where nucleons half-fill the valence shell. The γ-ray spectroscopic observables in 213Pb are thus found to be driven by two mechanisms, particle-hole conjugation and seniority conservation, which are intertwined through a Berry phase.
The nucleus 212Po has been produced through the fragmentation of a 238U primary beam at 1 GeV/nucleon at GSI, separated with the FRagment Separator, FRS, and studied via isomer γ-decay spectroscopy ...with the RISING setup. Two delayed previously unknown γ rays have been observed. One has been attributed to the E3 decay of a 21− isomeric state feeding the α-emitting 45-s (18+) high-spin isomer. The other γ-ray line has been assigned to the decay of a higher-lying 23+ metastable state. These are the first observations of high-spin states above the 212Po (18+) isomer, by virtue of the selectivity obtained via ion-by-ion identification of 238U fragmentation products. Comparison with shell-model calculations points to shortfalls in the nuclear interactions involving high-j proton and neutron orbitals, to which the region around Z∼100 is sensitive.
Abstract
The matter radius of the doubly magic
$$^{56}$$
56
Ni was extracted from a measurement of the differential cross section by employing, for the first time, elastic proton scattering in ...inverse kinematics with a radioactive beam at
$$E_{kin}=390.2$$
E
kin
=
390.2
MeV/nucleon circulating in a storage ring and passing an internal hydrogen gas-jet target with a revolution frequency of around 2 MHz. The novel experimental scheme is based on UHV-compatible Si detectors operated as active vacuum windows, which were implemented in the ESR storage ring at GSI. A matter radius
$$<r_{m}^{2}>^{1/2}=3.74^{+0.03}_{-0.06}$$
<
r
m
2
>
1
/
2
=
3
.
74
-
0.06
+
0.03
fm was extracted for the doubly-magic self-conjugate nucleus
$$^{56}$$
56
Ni.
211Po ions in the ground and isomeric states were produced via 238U projectile fragmentation at 1000 MeV/u. The 211Po ions were spatially separated in flight from the primary beam and other reaction ...products by the fragment separator FRS. The ions were energy-bunched, slowed-down and thermalized in a gas-filled cryogenic stopping cell (CSC). They were then extracted from the CSC and injected into a high-resolution multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS). The excitation energy of the isomer and, for the first time, the isomeric-to-ground state ratio were determined from the measured mass spectrum. In the subsequent experimental step, the isomers were spatially separated from the ions in the ground state by an ion deflector and finally collected with a silicon detector for decay spectroscopy. This pioneering experimental result opens up unique perspectives for isomer-resolved studies. With this versatile experimental method new isomers with half-lives longer than a few milliseconds can be discovered and their decay properties can be measured with highest sensitivity and selectivity. These experiments can be extended to studies with isomeric beams in nuclear reactions.
•An overview of the FRS Ion Catcher experiment at GSI is given.•The FRS Ion Catcher consists of the FRS, a cryogenic stopping cell, an RF quadrupole-based beam transport and diagnostics unit and a ...multiple-reflection time-of-flight mass spectrometer.•Off-line tests of the stopping cell with 219Rn ions.•First on-line operation of a stopping cell for exotic nuclei at cryogenic temperatures.•First mass measurements of heavy projectile fragments using a multiple-reflection time-of-flight mass spectrometer.
At the FRS Ion Catcher at GSI, projectile and fission fragments are produced at relativistic energies, separated in-flight, range-focused, slowed down and thermalized in a cryogenic stopping cell. A multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) is used to perform direct mass measurements and to provide an isobarically clean beam for further experiments, such as mass-selected decay spectroscopy. A versatile RF quadrupole transport and diagnostics unit guides the ions from the stopping cell to the MR-TOF-MS, provides differential pumping, ion identification and includes reference ion sources. The FRS Ion Catcher serves as a test facility for the Low-Energy Branch of the Super-FRS at the Facility for Antiproton and Ion Research (FAIR), where the cryogenic stopping cell and the MR-TOF-MS will be key devices for the research with stopped projectile and fission fragments that will be performed with the experiments MATS and LaSpec. Off-line tests of the stopping cell yield a combined ion survival and extraction efficiency for 219Rn ions of about 30% and an extraction time of about 25ms. The stopping cell and the MR-TOF-MS were commissioned on-line as part of the FRS Ion Catcher. For the first time, a stopping cell for exotic nuclei was operated on-line at cryogenic temperatures. Using a gas density almost two times higher than ever reached before for a stopping cell with RF ion repelling structures, various 238U projectile fragments were thermalized and extracted with very high efficiency. Direct mass measurements of projectile fragments were performed with the MR-TOF-MS, among them the nuclide 213Rn with a half-life of 19.5ms only.
Low-energy investigations on rare ion beams are often limited by the available intensity and purity of the ion species in focus. Here, we present the first application of a technique that combines ...in-flight production at relativistic energies with subsequent secondary beam storage, accumulation and finally deceleration to the energy of interest. Using the FRS and ESR facilities at GSI, this scheme was pioneered to provide a secondary beam of 118Te52+ for the measurement of nuclear proton-capture at energies of 6 and 7 MeV/u. The technique provided stored beam intensities of about 106 ions at high purity and brilliance, representing a major step towards low-energy nuclear physics studies using rare ion beams.
The conceptual design of a next-generation cryogenic stopping cell (CSC) for the Low-Energy Branch (LEB) of the Super-FRS has been developed. It builds on advanced techniques implemented in the ...prototype version of the CSC, which has recently been commissioned as part of the FRS Ion Catcher with 238U projectile and fission fragments produced at 1000MeV/u. These techniques include cryogenic operation to ensure a high purity of the stopping gas and high-density operation enabled using an RF carpet with a small electrode structure size. The next generation CSC implements several novel concepts (e.g. perpendicular extraction) which lead to enhanced performance compared to the prototype CSC: (i) extremely short extraction times, (ii) higher rate capability, (iii) increased areal density without deteriorating extraction times, efficiencies or rate capability, (iv) minimized RF power, (v) precise range measurement of the ions and (vii) improved cleanliness of the CSC.
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