The characteristics of detectors made of silicon carbide (SiC) irradiated with various integral fluxes of both Xe ions with an energy of 165 MeV and fast neutrons were studied. With the help of
...-particles, it was found that the energy resolution of SiC detectors irradiated with the maximum fluxes of heavy ions (
ion/cm
) and neutrons (
n/cm
) deteriorates by an order of magnitude. It was shown that the efficiency of detector charge collection decreases to 70 and 5
, respectively, upon irradiation with Xe ions and neutrons.
The formation of the unbound heavy helium isotopes
He was studied in the reactions of stopped pion absorption by light nuclei. Measurements were carried out using two-arm multilayer semiconductor ...spectrometer. The data on the level structures obtained in different reaction channels are consistent with each other. Our results on the energies and widths of the low-lying states of the
He are consistent with the world data. Record values of resonance energies were obtained for highly excited states of
He (24.5 MeV) and
He (10.5 MeV).
Size Isomers at Threshold States Demyanova, A. S.; Danilov, A. N.; Starastsin, V. I. ...
Physics of atomic nuclei,
08/2023, Letnik:
86, Številka:
4
Journal Article
Recenzirano
Odprti dostop
An overview is provided for a new class of states, which we have named as the size isomers. Such states are weakly bound and have an exotic structure (cluster states, halo/‘‘skin’’). The development ...of methods for measuring the radii of nuclei in their short-lived excited states led to the discovery of new classes of states. The size of a nucleus defined by the radius of its nucleon (proton and neutron) density distribution and the proton charge distribution is one of the most fundamental and important nuclear characteristics. Nuclear radius determines the basic properties of nuclei and is a consequence of the fundamental features of the strong interaction. Up to now two groups of the size isomers were identified: the excited states with halos (
Be,
Be,
C,
N) and some specific alpha-cluster states (
B,
C,
C). All the observed states are dilute, however, some indication to possible existence of more compact than the ground states was obtained as well (in
C). The phenomenon of size isomerism occurred to be not a rare one especially if we take into account rotational bands based on some of such states. The structure of size isomers is related with some new features, e.g., rotating halos, halos in continuum, different types of quasimolecular configurations. Some rudimentary signs of alpha-particle condensation (a ‘‘ghost’’ of condensate) were observed in the Hoyle state of
C, however, we cannot speak about confirmation of this ambitious theory. Analogs to the Hoyle state, expected in
B,
C,
O,
Ne near the
-emission thresholds, are considered.
Proton spectra are measured upon the absorption of π
−
mesons at rest on a “live” (analog of
28
Si) target. The resulting data allow identification of the process without secondary interactions and ...acquisition of the spectrum of primary protons produced by the absorption of pions on intranuclear
pp
pairs.
A survey of experimental results on the level structure in the heavy helium isotope
He that were obtained in reactions induced by stopped pion absorption in
Be,
B, and
C light nuclei is presented. ...The respective measurements were performed on the low-energy pion channel of the accelerator at the Los Alamos National Laboratory (LANL) by means of a two-arm semiconductor spectrometer. A high statistical significance of the results was attained over a broad excitation-energy range extending up to 40 MeV. Several highly excited states, including
cluster resonances, were revealed for the first time.
A theoretical analysis of available experimental data on elastic and inelastic
C scattering in the energy region extending up to 90 MeV is performed. The parameters of a semimicroscopic potential are ...found on the basis of the dispersive optical model. The potentials found in this way are used in analyzing, by the distorted-wave Born approximation, data that the authors recently measured for inelastic scattering at energies of 65 and 90 MeV. Experimental data for the states at 3.68 and 7.55 MeV are presented for the first time. These states are considered under the assumption that, within the standard rotational model, they are members of the ground-state rotational band. A satisfactory description of angular distributions is obtained, and deformation lengths are determined. A model phenomenological form factor is used for the remaining excitations in the energy range extending up to 11 MeV. The present analysis confirms the presence of a neutron halo in the 3.09-MeV state. A similarity of form of the inelastic form factors obtained for the 8.86-, 10.996-, and 11.08 MeV states and the proximity of their radii gives grounds to assume that the
C nucleus in these three states has an enhanced size and similar structures. A comparison of the radial dependences of the form factors for the 9.90- and 8.86-MeV states shows that the wave function for the 9.90-MeV state has a substantially smaller spatial extension. These results agree with the values obtained for the radii of the states under discussion on the basis of the modified diffraction model.
The review is concerned with studies of one-nucleon and two-nucleon halos in isobar analog states of light nuclei with
. The study allow us to investigate manifestations of isotopic invariance in new ...objects and to relate properties of the neutrino and proton halos. The existence of a halo in isobar analog states has been little studied experimentally so far. It is proposed to solve the problem of experimentally determining the radii of some possible halo states in nuclei from
6
Li to
14
O that make up isobar analog doublets and triplets. New possible halo candidates are found in the
13
C and
13
N mirror nuclei, in the
= 12 and
= 14 isobar analog multiplets. Note that the isobar analog states with
in the
triplet are experimentally investigated for the first time in the transfer and charge-exchange reactions. It is established that the root-mean-square radii of the
states in the
multiplet coincide within errors. The results are obtained by two independent methods, ANC and MDM.
A description of a procedure for selecting events during the absorption of stopped pions in thin targets is presented. This approach is based on the use of two monitor Si-detectors and a “live” ...target, which is also an Si-detector, as the last layers of the moderator. Setting the thresholds on monitor detectors and analyzing signals from a “live” target allow one to select pions with a residual range corresponding to the target thickness and reliably exclude the background from stops in the monitor system. It is shown that this method provides an efficiency of identifying stopped π
–
-mesons of 90%.
The characteristics of detectors based on silicon carbide (SiC) before and after irradiation with integral neutron fluxes of 5.11 × 10
13
and 5.39 × 10
14
n/cm
2
are presented. On the samples ...irradiated with the maximum fluence, using alpha particles, a deterioration in the energy resolution by an order of magnitude and a decrease in the efficiency of charge collection by ∼25% are shown.
The properties of detectors based on epitaxial layers of silicon carbide (SiC) are presented. It is shown that the developed detectors have good spectrometric characteristics when detecting a ...particles with energies of up to 8 MeV. The pulse height defect was measured in SiC detectors under irradiation by accelerated xenon ions with different energies. It is shown that this parameter in the spectroscopic analysis of Xe ions is ∼45% of the true energy of the particles in question.
