Total charge-changing cross sections at relativistic energies on a carbon target have been measured for the light stable and neutron-rich radioactive nuclei
14
Be,
10−19
B,
12−20
C,
14−23
N,
16−24
O, ...and
18−27
F. A combined analysis of interaction and total charge-changing cross sections allows to draw definite conclusions concerning the thickness of the neutron skins or the size of the neutron halos for very neutron-rich isotopes. The obtained cross sections are also important in astrophysical applications to describe the propagation of galactic cosmic rays through the interstellar medium. A simple parameterization can reproduce the total charge-changing cross section within an accuracy of 5% for light nuclei from the valley of
β -stability up to the drip line. These systematics improve the predictive capability of the formulae used to describe the unknown cross sections.
Dissociation of 227 MeV/u He-8 in a carbon target has been studied in kinematically complete experiments. The data include the relative energy spectrum, angular distributions in the neutron knock-out ...channel (He-6 + n) as well as diffractive dissociation and inelastic scattering into the (He-6 + 2n) channel. The data are compared with corresponding results from the well-known halo nucleus He-6. In both cases it is found that neutron knock-out is the: dominating reaction channel. The relative energy spectrum (He-6 + n) shows a structure, which is interpreted as being due to the I-pi = 3/2(-) resonance in the He-7 ground state with about equal contribution from its I-pi = 1/2(-) spin-orbit partner. The He-7 resonance shows a spin alignment similar to that observed in He-5, but with a smaller anisotropy indicating that the structure of the He-8 ground state is more complicated than that of He-6. The data in the (He-6 + 2n) channel were used to identify resonances in the excitation energy spectrum of He-8. If the spectrum is interpreted as two overlapping resonances, the spin-parity assignment for these is found to be 2(+) and 1(-), respectively.
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->15O+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 gamma 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 ratio 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.
The evolution of the traditional nuclear magic numbers away from the valley of stability is an active field of research. Experimental efforts focus on providing key spectroscopic information that ...will shed light into the structure of exotic nuclei and understanding the driving mechanism behind the shell evolution. In this work, we investigate the Z = 6 spin-orbit shell gap towards the neutron dripline. To do so, we employed \(^{A}\)N(p,2p)\(^{A-1}\)C quasi-free scattering reactions to measure the proton component of the 2\(^+_1\) state of \(^{16,18,20}\)C. The experimental findings support the notion of a moderate reduction of the proton 1p\(_{1/2}\)-1p\(_{3/2}\) spin-orbit splitting, at variance to recent claims for a prevalent Z = 6 magic number towards the neutron dripline.
New experimental data for dissociation of relativistic Ne-17 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 Ne-17. Distributions of internal energy in the 150 + 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 Ne-17 and its mirror nucleus N-17. 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 Ne-17 structure.
.
Two-proton decay of the unbound
nucleus
16
Ne , produced in one-neutron knockout from a 500 MeV/u
17
Ne beam, has been studied at GSI. The ground state, at a resonance energy 1.388(15) MeV, (
MeV) ...above the
14
O +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
16
Ne with its mirror nucleus
16
C 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
16
F 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
14
O +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
15
F , the 3.22 MeV state predominantly via the
15
F ground-state resonance, while the 7.57 MeV state decays via the 5/2
+
resonance in
15
F at 2.8 MeV above the
14
O +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
16
Ne based on a comparison with
16
C.
Matter radii of Na and Mg isotopes Suzuki, T.; Geissel, H.; Bochkarev, O. ...
Nuclear physics. A,
04/1997, Letnik:
616, Številka:
1
Journal Article
Recenzirano
The interaction cross sections (
σ
I
) of
A
Na (A = 20–23, 25–32) and
A
Mg (A = 20, 22–25, 27, 29–33) on carbon target have been measured at a beam energy of around 950
A MeV. The effective ...root-mean-square matter radii of these isotopes were deduced from
σ
I
by a Glauber-type calculation. Combining the isotope-shift data with the present Na data the radii of neutrons have been compared with those of protons for the first time along a chain of stable and unstable isotopes. A monotonic increase in the neutron skin thickness has been observed as the neutron number increases in Na isotopes. The Mg data are also consistent with the claim that the formation of a neutron/proton skin is a universal feature in β-unstable nuclei.
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