The one-neutron transfer
2
H(
9
Li,
p
)
10
Li reaction has been investigated at 29
A
MeV incident energy at the ACCULINNA-2 facility (Flerov Laboratory of Nuclear Reactions, Joint Institute for ...Nuclear Research). The setup has been used in order to detect the recoil protons at backward angles in coincidences with the outgoing
9
Li and neutrons from the
10
Li decay at forward angles. This setup allows to study the
10
Li emitted in the crucial region at forward angles in the center of mass. The preliminary results in the part of the analysis of double proton–
9
Li coincidence are reported.
Investigation of the
7
H-system in the experiment conducted at the fragment separator ACCULINNA-2 in the
8
He(
2
H,
3
He)
7
H reaction requires to detect the recoil
3
He ions with energy down to 6 ...MeV. For this purpose two
particle telescopes are used, with each telescope having in front a thin (20-μm) Si strip detector (
). The maps of thickness heterogeneity of the thin detectors were determined by measuring the energy losses of the
226
Ra α-particles. The adopted thickness normalization method provides a good identification of the
3
He nuclei being recorded in the presence of a high
4
He background. Two approaches were used for calculating the energy losses of the identified
3
He and
4
He reaction ejectiles and reconstructing their energy values available at the exit from the deuterium target. The developed techniques were applied for the
7
H missing-mass reconstruction.
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.
The ^{7}H system was populated in the ^{2}H(^{8}He,^{3}He)^{7}H reaction with a 26 AMeV ^{8}He beam. The ^{7}H missing mass energy spectrum, the ^{3}H energy and angular distributions in the ^{7}H ...decay frame were reconstructed. The ^{7}H missing mass spectrum shows a peak, which can be interpreted either as unresolved 5/2^{+} and 3/2^{+} doublet or one of these states at 6.5(5) MeV. The data also provide indications of the 1/2^{+} ground state of ^{7}H located at 1.8(5) MeV with quite a low population cross section of ∼25 μb/sr within angular range θ_{c.m.}≃(17°-27°).
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 proton and deuteron pickup reactions 2H(10Be,3He)9Li and 2H(10Be,4He)8Li radioactive beam produced by the new fragment separator ACCULINNA-2 at FLNR, JINR\@. These measurements were initially ...motivated as test reactions intended for the elucidation of results obtained in the study of the extremely neutron-rich 7H and 6H systems created in the 2H(10Be,3He)9Li and 2H(10Be,4He)8Li reactions using the same setup. In the 2H(10Be,3He)9Li reaction the 9Li ground-state (\(3/2^-\)) and its first excited state (2.69MeV, \(1/2^-\)) were identified in the low-energy region of its excitation spectrum. The differential cross sections for the 9Li g.~s.) population were extracted at forward center-of-mass angles (\(3^\circ-13^\circ\)) and compared with the FRESCO calculations. Spectroscopic factor of \(\sim 1.7\), derived by a model for the 10Be\( = p +\)9Li(g.s.) clustering was found in accord with the experimental data. The energy spectrum of 8Li populated in the 2H(10Be,4He)8Li reaction shows the strong peak which corresponds to excitation of the second excited state of 8Li (2.25 MeV, \(3^+\)). The fact that the ground and the first excited states of 8Li were not observed is fully consistent with Shell-Model calculations carried out for the 10Be g.\,s. and 8Li level structure applying momentum selection rules.
Mass measurements of the \(^{69}\)As, \(^{70,71}\)Se and \(^{71}\)Br isotopes, produced via fragmentation of a \(^{124}\)Xe primary beam at the FRS at GSI, have been performed with the ...multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) of the FRS Ion Catcher with an unprecedented mass resolving power of almost 1,000,000. For the \(^{69}\)As isotope, this is the first direct mass measurement. A mass uncertainty of 22 keV was achieved with only 10 events. For the \(^{70}\)Se isotope, a mass uncertainty of 2.6 keV was obtained, corresponding to a relative accuracy of \(\delta\)m/m = 4.0\(\times 10^{-8}\), with less than 500 events. The masses of the \(^{71}\)Se and \(^{71}\)Br isotopes were measured with an uncertainty of 23 and 16 keV, respectively. Our results for the \(^{70,71}\)Se and \(^{71}\)Br isotopes agree with the 2016 Atomic Mass Evaluation, and our result for the \(^{69}\)As isotope resolves the discrepancy between previous indirect measurements. We measured also the mass of \(^{14}\)N\(^{15}\)N\(^{40}\)Ar (A=69) with a relative accuracy of \(\delta\)m/m = 1.7\(\times 10^{-8}\), the highest yet achieved with a MR-TOF-MS. Our results show that the measured restrengthening of the proton-neutron interaction (\(\delta\)V\(_{pn}\)) for odd-odd nuclei at the N=Z line above Z=29 (recently extended to Z=37) is hardly evident at N-Z=2, and not evident at N-Z=4. Nevertheless, detailed structure of \(\delta\)V\(_{pn}\) along the N-Z=2 and N-Z=4 lines, confirmed by our mass measurements, may provide a hint regarding the ongoing \(\approx\)500 keV discrepancy in the mass value of the \(^{70}\)Br isotope, which prevents including it in the world average of \({Ft}\)-value for superallowed 0\(^+\rightarrow\) 0\(^+\) \(\beta\) decays. The reported work sets the stage for mass measurements with the FRS Ion Catcher of nuclei at and beyond the N=Z line in the same region of the nuclear chart, including the \(^{70}\)Br isotope.
Setup fitting the requirements for the detailed study of the five-body decay
of the 7H nucleus obtained as a result of the proton transfer from the 8He
projectiles to the deuterium target nuclei is ...being built at the radioactive
beam line of ACCULINNA-2 separator in the G.N. Flerov Laboratory of Nuclear
Reactions. Described here is the assembly of 100 BC-404 plastic scintillators,
intended for neutron detection, the annular Si detector telescope for the 3He
recoils, and the detector array providing the $\Delta E$-$E$-TOF registration
of 3H nuclei emitted at the 7H decay. Results obtained by the Monte Carlo
simulations made for the energy values and flight passes of all these particles
are given together with the luminosity expected for the discussed experiments.
The extremely neutron-rich system $^{6}$H was studied in the direct
$^2\text{H}(^8\text{He},{^4\text{He}})^{6}$H transfer reaction with a $26 A$
MeV secondary $^{8}$He beam. The measured missing mass ...spectrum shows a broad
bump at $\sim 4-8$ MeV above the $^3$H+$3n$ decay threshold. This bump can be
interpreted as a broad resonant state in $^{6}$H at $6.8(5)$ MeV. The
population cross section of such a presumably $p$-wave state (or may be few
overlapping states) in the energy range from 4 to 8 MeV is
$d\sigma/d\Omega_{\text{c.m.}} \simeq 190^{+40}_{-80}$ $\mu$b/sr in the angular
range $5^{\circ}<\theta_{\text{c.m.}}<16^{\circ}$. The obtained missing mass
spectrum is practically free of the $^{6}$H events below 3.5 MeV
($d\sigma/d\Omega_{\text{c.m.}} \lesssim 5$ $\mu$b/sr in the same angular
range). The steep rise of the $^{6}$H missing mass spectrum at $\sim 3$ MeV
allows to derive the lower limit for the possible resonant-state energy in
$^{6}$H to be $4.5(3)$ MeV. According to the paring energy estimates, such a
$4.5(3)$ MeV resonance is a realistic candidate for the $^{6}$H ground state
(g.s.). The obtained results confirm that the decay mechanism of the $^{7}$H
g.s.\ (located at 2.2 MeV above the $^{3}$H+$4n$ threshold) is the "true" (or
simultaneous) $4n$ emission. The resonance energy profiles and the momentum
distributions of fragments of the sequential $^{6}$H$ \,\rightarrow \,
^5$H(g.s.)+$n\, \rightarrow \, ^3$H+$3n$ decay were analyzed by the
theoretically-updated direct four-body-decay and sequential-emission
mechanisms. The measured momentum distributions of the $^{3}$H fragments in the
$^{6}$H rest frame indicate very strong "dineutron-type" correlations in the
$^{5}$H ground state decay.
Phys. Rev. C 103, 044313 (2021) The extremely neutron-rich system $^{7}$H was studied in the direct
$^2$H($^8$He,$^3$He)$^7$H transfer reaction with a 26 AMeV secondary $^{8}$He
beam Bezbakh et al., ...Phys. Rev. Lett. 124 (2020) 022502. The missing mass
spectrum and center-of-mass (c.m.) angular distributions of $^{7}$H, as well as
the momentum distribution of the $^{3}$H fragment in the $^{7}$H frame, were
constructed. In addition to the investigation reported in Ref. Bezbakh et al.,
Phys. Rev. Lett. 124 (2020) 022502, we carried out another experiment with the
same beam but a modified setup, which was cross-checked by the study of the
$^2$H($^{10}$Be,$^3$He$)^{9}$Li reaction. A solid experimental evidence is
provided that two resonant states of $^{7}$H are located in its spectrum at
2.2(5) and 5.5(3) MeV relative to the $^3$H+4$n$ decay threshold. Also, there
are indications that the resonant states at 7.5(3) and 11.0(3) MeV are present
in the measured $^{7}$H spectrum. Based on the energy and angular
distributions, obtained for the studied $^2$H($^8$He,$^3$He)$^7$H reaction, the
weakly populated 2.2(5) MeV peak is ascribed to the $^7$H ground state. It is
highly plausible that the firmly ascertained 5.5(3) MeV state is the $5/2^+$
member of the $^7$H excitation $5/2^+$-$3/2^+$ doublet, built on the $2^+$
configuration of valence neutrons. The supposed 7.5 MeV state can be another
member of this doublet, which could not be resolved in Ref. Bezbakh et al.,
Phys. Rev. Lett. 124 (2020) 022502. Consequently, the two doublet members
appeared in the spectrum of $^{7}$H in Bezbakh et al., Phys. Rev. Lett. 124
(2020) 022502 as a single broad 6.5 MeV peak.
PDF