By using the 1H(6Li, 6Be)n charge-exchange reaction, population of continuum states in 6Be was observed up to ET=16 MeV, ET being the 6Be energy above its three-body decay threshold. In kinematically ...complete measurements performed by detecting α+p+p coincidences, an ET spectrum of high statistics was obtained, containing approximately ∼5×106 events. The spectrum provides detailed correlation information about the well-known 0+ ground state of 6Be at ET=1.37 MeV and its 2+ state at ET=3.05 MeV. Moreover, a broad structure extending from 4 to 16 MeV was observed. It contains negative parity states populated by ΔL=1 angular momentum transfer without other significant contributions. This structure can be interpreted as a novel phenomenon, i.e. the isovector soft dipole mode associated with the 6Li ground state. The population of this mode in the charge-exchange reaction is a dominant phenomenon for this reaction, being responsible for about 60% of the cross-section obtained in the measured energy range.
Attempt to observe a 7H resonance produced in the reaction 2H(8He,3He)7H resulted only in setting a limit dsigma/dOmega < or = 20 mub/sr for the reaction exit channel which could populate a resonance ...lying between 0 and 3 MeV above the 7H decay threshold. The quasi-free scattering of the alpha core bound in 6He was explored keeping in mind the possible study of the cluster structure of this halo nucleus. For the first time coincident particles emitted in the 4He(6He, 2alpha)nn reaction were detected in wide angular ranges giving a wide kinematical range of the measured angular and momentum distributions. The contribution of processes, competing with QFS in the alpha + alpha + n + n output channel, was considerably suppressed by the selection of events with Ealpha1(2)-nn > 10 MeV. A number of experimental distributions, relevant to the reaction mechanism and to the 6He structure, were compared with the results of MC simulations based on the PWIA formalism. The PWIA predictions showed consistency with the experimental data.
New experimental measurements of the total reaction cross sections for the {sup 6}He + {sup nat}Si and {sup 9}Li + {sup nat}Si processes in the energy range of 5 to 40 A MeV are presented. A modified ...transmission method based on high-efficiency detection of prompt n–γ radiation has been used in the experiment. A bump is observed for the first time in the energy dependence σ{sub R}(E) at E ∼ 10–30 A MeV for the {sup 9}Li + {sup nat}Si reaction, and existence of the bump in σ{sub R}(E) at E ∼ 10–20 A MeV first observed in the standard transmission experiments is experimentally confirmed for the {sup 6}He + {sup nat}Si reaction. Theoretical analysis of the measured {sup 6}He + {sup nat}Si and {sup 9}Li + {sup nat}Si reaction cross sections is performed within the microscopic double folding model. Disagreement is observed between the experimental and theoretical cross sections in the region of the bump at the energies of 10 to 20 A MeV, which requires further study.
Characteristics of a new separator of radioactive ion beams (RIBs) are described. It was recently commissioned at the Flerov Laboratory of Nuclear Reactions (FLNR JINR) and is in operation at the ...primary beam line of the U-400M heavy ion cyclotron providing RIBs in energy range of 10–50 MeV/nucleon. Preliminary results obtained in the first experiments performed with this separator in 2018 are presented. A medium-term program of scientific research is discussed.
Search for the population of the low-energy continuum of tetraneutron system was performed for reactions of the \(^{8}\)He beam on deuterium target. These studies are performed for the data I.A. ...Muzalevskii et al., Phys. Rev. C 103, 044313 (2021), previously used for the studies of \(^{7}\)H and \(^{6}\)H in the \(^2\text{H}(^8\text{He},{^3\text{He}})^{7}\)H and \(^2\text{H}(^8\text{He},{^4\text{He}})^{6}\)H reactions. Evidence for a hump in the \(^4n\) continuum at \(3.5 \pm 0.7\) and \(3.2 \pm 0.8\) MeV, was observed in the \(^2\)H(\(^8\)He,\(^6\)Li)\(^4\)n and \(^2\)H(\(^8\)He,\(^3\)He)\(^7\)H\(\rightarrow ^3\)H+\(^4\)n reactions, respectively. The observed statistics is quite low (6 and up to 40 events) corresponding to very low cross sections of few microbarns or tens of microbarns. The background conditions for the \(^2\)H(\(^8\)He,\(^6\)Li)\(^4n\) reaction are shown to be good, favoring the physical nature of the observed events. The \(^2\)H(\(^8\)He,\(^3\)He)\(^7\)H\(\rightarrow ^3\)H+\(^4n\) process transforms to the \(^2\)H(\(^8\)He,\(^6\)Li\(^{\ast})^4n\) reaction in the limit of the highest \(^7\)H decay energies. The population of the low-energy region in the \(^{4}\)n spectrum is found to be perfectly correlated with the population of the lowest \(^{6}\)Li states in the \(^{3}\)He+\(^{3}\)H continuum. Theoretical calculations of \(^{8}\)He in a five-body \(\alpha\)+\(4n\) and of \(^{4}\)n in a four-body hyperspherical models are presented. The \(^{8}\)He wave function is shown to contain strong specific correlations, which may give rise to very low-energy structures in tetraneutron continuum in extreme-peripheral reaction scenarios.
The differential cross sections of the charge exchange reaction
d
p
→
(
p
p
)
n
has been measured at 1.75 GeV/c per nucleon for small transferred momenta using the one arm magnetic spectrometer ...STRELA at the Nuclotron accelerator in JINR Dubna. The ratio of the differential cross section of the charge exchange reaction
d
p
→
(
p
p
)
n
to that of the
n
p
→
p
n
elementary process is discussed in order to estimate the spin-dependent part of the
n
p
→
p
n
charge exchange amplitude. The
n
p
→
p
n
amplitude turned out to be predominantly spin-dependent.
Unbound states studied by direct reactions Wolski, R; Golovkov, M S; Grigorenko, L V ...
Journal of physics. Conference series,
05/2008, Letnik:
111, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The t(6He,8He)p t(8He,10He)p reactions were studied in experiments with 25A MeV 6He beam and 27.4A MeV 8He beams and an unique tritium gas target. Results on the 8He and 10He excitation energy ...spectra are presented. The 8He spectrum exhibits 3 states, apart of the ground state and known (2+) state at 3.6 MeV, the third state is seen at 5.4 MeV. A tentative assignment 1+ is proposed for this structure. The 10He spectrum shows no event at the excitation energy below 3 MeV what is in contradiction with the earlier reports on this nucleus. A high statistics of α-n coincidence events collected for the 8He beam run has been subjected to analysis in order search for the bound tetraneutron. The search produced a negative result.
Three-body continuum
p-p-
α for the charge exchange reaction
1
H(
6
Li,
6
Be)
n
is studied in detail. The data are obtained with a high volume of statistics (approximately 4.7 million events), making ...it possible to analyze three-particle correlations. Detailed information about the structure of
6
Ве and the reaction is obtained as a result.
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