The proton drip-line nucleus 17Ne is investigated experimentally in order to determine its two-proton halo character. A fully exclusive measurement of the 17Ne(p,2p)16F→15⁎O+p quasi-free one-proton ...knockout reaction has been performed at GSI at around 500 MeV/nucleon beam energy. All particles resulting from the scattering process have been detected. The relevant reconstructed quantities are the angles of the two protons scattered in quasi-elastic kinematics, the decay of 16F into 15O (including γ decays from excited states) and a proton, as well as the 15O+p relative-energy spectrum and the 16F momentum distributions. The latter two quantities allow an independent and consistent determination of the fractions of l=0 and l=2 motion of the valence protons in 17Ne. With a resulting relatively small l=0 component of only around 35(3)%, it is concluded that 17Ne exhibits a rather modest halo character only. The quantitative agreement of the two values deduced from the energy spectrum and the momentum distributions supports the theoretical treatment of the calculation of momentum distributions after quasi-free knockout reactions at high energies by taking into account distortions based on the Glauber theory. Moreover, the experimental data allow the separation of valence-proton knockout and knockout from the 15O core. The latter process contributes with 11.8(3.1) mb around 40% to the total proton-knockout cross section of 30.3(2.3) mb, which explains previously reported contradicting conclusions derived from inclusive cross sections.
New experimental data for dissociation of relativistic 17Ne projectiles incident on targets of lead, carbon, and polyethylene targets at GSI are presented. Special attention is paid to the excitation ...and decay of narrow resonant states in 17Ne. Distributions of internal energy in the O15+p+p three-body system have been determined together with angular and partial-energy correlations between the decay products in different energy regions. The analysis was done using existing experimental data on 17Ne and its mirror nucleus 17N. The isobaric multiplet mass equation is used for assignment of observed resonances and their spins and parities. A combination of data from the heavy and light targets yielded cross sections and transition probabilities for the Coulomb excitations of the narrow resonant states. The resulting transition probabilities provide information relevant for a better understanding of the 17Ne structure.
Two-proton decay of the unbound nucleus Ne-16 , produced in one-neutron knockout from a 500 MeV/u Ne-17 beam, has been studied at GSI. The ground state, at a resonance energy 1.388(15) MeV, ( MeV) ...above the O-14 +p+p threshold, and two narrow resonances at MeV and 7.57(6) MeV have been investigated. A comparison of the energy difference between the first excited 2(+) state and the 0(+) ground state in Ne-16 with its mirror nucleus C-16 reveals a small Thomas-Ehrman shift (TES) of keV. A trend of the TES for the T = 2 quintet is obtained by completing the known data with a prediction for F-16 obtained from an IMME analysis. The decay mechanisms of the observed three resonances were revealed from an analysis of the energy and angular correlations of the O-14 +p+p decay products. The ground state decay can be considered as a genuine three-body (democratic) mode and the excited states decay sequentially via states in the intermediate nucleus F-15 , the 3.22 MeV state predominantly via the F-15 ground-state resonance, while the 7.57 MeV state decays via the 5/2(+) resonance in F-15 at 2.8 MeV above the O-14 +p+p threshold. Further, from an analysis of angular correlations, the spin-parity of the 7.57 MeV state has been determined as and assigned as the third 2(+) state in Ne-16 based on a comparison with C-16.
We report on a new experimental setup for the investigation of proton induced reactions on exotic nuclei in inverse kinematics. It was installed and successfully used in the scattering study of ...intermediate-energy protons (
∼
700
MeV
/
u
) on neutron-rich nuclei
6,8He produced with the FRagment Separator (FRS) at the GSI facility, Darmstadt. A new pure liquid-hydrogen target was successfully adapted allowing to obtain low-background data as compared to commonly used (CH
2)
n
targets.
Absolute differential cross-sections for elastic (p,
6,8He) scattering were obtained at angles corresponding to
0.05
⩽
|
t
|
⩽
0.125
(GeV/
c)
2 of the four-momentum transfer squared (−
t) leading to the first diffraction minimum and spanning more than two orders of magnitude. They complement an earlier measurement at smaller angles
0.0025
⩽
|
t
|
⩽
0.05
(GeV/
c)
2 performed at the same energy with an active target. Both data sets agree well in the overlap region
t
≈
0.05
(GeV/
c)
2 and enable a refined and comparative study of the radial distribution of the nuclear matter density.
The time-reversed reaction 15O(2p, γ)17Ne has been studied by the Coulomb dissociation technique. Secondary 17Ne ion beams at 500 AMeV have been produced by fragmentation reactions of 20Ne in a ...beryllium production target and dissociated on a secondary Pb target. The incoming beam and the reaction products have been identified with the kinematically complete LAND-R3B experimental setup at GSI. The excitation energy prior to decay has been reconstructed by using the invariant-mass method. The preliminary differential and integral Coulomb Dissociation cross sections (σCoul) have been calculated, which provide a photoabsorption (σphoto) and a radiative capture cross section (σcap). Additionally, important information about the nuclear structure of the 17Ne nucleus will be obtained. The analysis is in progress.
In the present work, the differential cross sections for small-angle proton elastic scattering on the
12,14Be nuclei were measured in inverse kinematics, using secondary radioactive beams with ...energies near 700 MeV/u produced with the fragment separator FRS at GSI. The main part of the experimental setup was the active target IKAR, which was used simultaneously as a target and a detector for the recoil protons. Auxiliary detectors for projectile tracking and isotope identification completed the setup. The measured differential cross sections were analyzed using the Glauber multiple-scattering theory. For the evaluation of the data several phenomenological nuclear-matter density parametrizations and a sum of Gaussian parametrization were used. The nuclear-matter radii and radial density distributions of the isotopes
12,14Be were deduced. Extended nuclear-matter density distributions were observed in both isotopes, and the halo structure of
14Be was confirmed. The results were also compared with microscopic few-body and fermionic molecular dynamics model calculations concerning the structure of these neutron-rich nuclei.
β-Decay studies with an implantation technique Büscher, J.; Ponsaers, J.; Raabe, R. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
October 2008, 2008-10-00, 20081001, Letnik:
266, Številka:
19-20
Journal Article
Recenzirano
Odprti dostop
A method is presented for the detection of charged particles emitted in the β-decay of exotic nuclei. Direct implantation of radioactive nuclei in a very thin double-sided silicon strip detector is ...now feasible thanks to the advances in the production and post-acceleration of ISOL beams. The high degree of pixelazation, and consequently the small active volume of the detector, and the precise energy of the radioactive ion beam are the key features of the method. Among the advantages of the method are a good precision of the overall normalization and a reduction of the background due to β-radiation. Several developments are described in the present paper. The detection threshold at low energies is determined using pulsed signals. An alternative energy calibration for the decay events, free from any dead-layer effects can be performed by implanting radioactive ions decaying to known narrow resonances, e.g. 20Na. Time and position correlations in a small detection volume can be used to identify possible different decay channels. An overview of precision measurements using this technique is given to prove the strength of the method.
The investigation of light-ion induced direct reactions in inverse kinematics, using stored and cooled radioactive beams, interacting with internal H, He, etc. gas-jet targets, bears a large ...potential for nuclear structure and astrophysics studies on exotic nuclei. An extended research project EXL has been accepted for the future facility FAIR in Darmstadt, Germany. In order to explore the experimental conditions for measurements planned at FAIR, a first test experiment for proving the feasibility of the EXL concept was performed.
PDF
