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.
The H7 system was populated in the H2(He8,He3)H7 reaction with a 26 AMeV He8 beam. The H7 missing mass energy spectrum, the H3 energy and angular distributions in the H7 decay frame were ...reconstructed. The H7 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 H7 located at 1.8(5) MeV with quite a low population cross section of ∼25 μb/sr within angular range θc.m.≃(17°-27°).
The start of operation of a new separator ACCULINNA-2 makes an important upgrade for the Radioactive-Ion Beam (RIB) research done at the Flerov Laboratory of Nuclear Reactions (FLNR, JINR). Test ...results indicate that the separator meets the project specifications. Intensities obtained for the 6,8He, 9,11Li, 12Be RIBs are 15 times higher in comparison with the results achieved at the old separator ACCULINNA. An overview of the design, construction and commissioning studies of the ACCULINNA-2 separator is presented. The separator will be equipped with some key facilities: a cryogenic tritium target, zero degree spectrometer following the physical target bombarded by the RIBs, and with a neutron detector array, and the Time Projection Chamber (TPC). This opens a wide range of experimental possibilities. Overview is presented on the two first experiments devoted to the study of d + 6He elastic scattering and search for a 7H low-lying resonance state populated in the 2H(8He,3He)7H reaction.
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°).
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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 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.
Phys. Rev. Lett. 124, 022502 (2020) 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 on the $1/2^+$ ground state of $^7$H located
at 2.0(5) MeV with quite a low population cross section of $\sim 10$ $\mu$b/sr
within angular range $\theta_{\text{cm}} \simeq 6^{\circ} - 30^{\circ}$.
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