arXiv subjects

Yu. L. Parfenova

Publications and source records attributed to Yu. L. Parfenova.

17 recordsLinked to original sources

arXiv2026

Role of the pre-equilibrium particle emission in the $^{249-251}$No production in the $^{204}$Pb($^{48}$Ca, xn)$^{252-x}$No reaction

Experimental data on the production of $^{250}$No in its ground and isomeric states in the $^{204}$Pb($^{48}$Ca,2n)$^{250}$No reaction at $^{48}$Ca beam energies from 200 to 240 MeV are analyzed within a unified approach combining the Hauser--Feshbach statistical model and the Griffin exciton model, assuming the emission of one pre-equilibrium particle. The influence of pre-equilibrium processes on the production cross sections of the $^{249-251}$No isotopes is investigated. The inclusion of pre-equilibrium light-particle emission significantly improves the description of the measured production cross sections, particularly in the high-energy region, where differences of several orders of magnitude are obtained, and for the population of the ground and isomeric states of $^{250}$No. The proposed approach also reproduces the observed incident-energy dependence of the residual-nucleus production cross sections.

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arXiv2024

Population of tetraneutron continuum in reactions of $^{8}$He on deuterium

Search for the population of the low-energy continuum of a tetraneutron system was performed for reactions of the $^{8}$He beam on a deuterium target. These studies are based on the data [I.A. Muzalevskii \textit{et al.}, Phys.\ Rev.\ C \textbf{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 $^4$n 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 events 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)$^4$n 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+$^4$n 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 state in the $^{3}$He+$^{3}$H continuum with $E^*=18$ MeV. Theoretical calculations of $^{8}$He in a five-body $α$+$4n$ 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.

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arXiv2024

Model for the Glauber-type calculations of beam fragmentation at low energies

In the present paper momentum distributions of nuclei produced in the heavy ion beam fragmentation at the relatively low energies (below 100 $A\cdot$MeV) are studied. For this study, a new theoretical approach is developed on the basis of the Glauber model modified for taking into account the energy and momentum conservation laws. In this approach, the longitudinal momentum of the most neutron rich nuclei, $^{10}$Be, $^9$Li, $^8$He, produced in a few neutron removal reactions in the $^{11}$B fragmentation in the Be target at a beam energy of 35 $A\cdot$MeV are calculated. The region of applicability of the new approach is discussed. This approach gives the asymmetric longitudinal momentum distributions at low energies, and the asymmetry is defined by the kinematical locus and geometry of the reaction (central of peripheral reactions). We analyze the changes of the phase volume and the longitudinal momentum distributions with the beam energy and number of the removed nucleons. The results of the calculations are compared to the parametrizations widely used for estimates of nuclear production in fragmentation for planning of nuclear experiments.

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arXiv2023

Study of Proton and Deuteron Pickup Reactions 2H(10Be,3He)9Li an 2H(10Be,4He)8Li with 44 A MeV 10Be Radioactive Beam at ACCULINNA-2 Fragment Separator

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.

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arXiv2022

The $^{6}$H states studied in the $^2\text{He}(^8\text{He},^4\text{He})$ reaction and evidence of extremely correlated character of the $^{5}$H ground state

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 $dσ/dΩ_{\text{c.m.}} \simeq 190^{+40}_{-80}$ $μ$b/sr in the angular range $5^{\circ}<θ_{\text{c.m.}}<16^{\circ}$. The obtained missing mass spectrum is practically free of the $^{6}$H events below 3.5 MeV ($dσ/dΩ_{\text{c.m.}} \lesssim 5$ $μ$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.

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arXiv2021

Resonant states in $^{7}$H. I. Experimental studies of the $^2$H($^8$He,$^3$He) reaction

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.

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arXiv2020

Asymptotic normalization coefficient method for two-proton radiative capture

The method of asymptotic normalization coefficients is a standard approach for studies of two-body non-resonant radiative capture processes in nuclear astrophysics. This method suggests a fully analytical description of the radiative capture cross section in the low-energy region of the astrophysical interest. We demonstrate how this method can be generalized to the case of three-body $2p$ radiative captures. It was found that an essential feature of this process is the highly correlated nature of the capture. This reflects the complexity of three-body Coulomb continuum problem. Radiative capture $^{15}$O+$p$+$p \rightarrow ^{\,17}$Ne+$γ$ is considered as an illustration.

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arXiv2019

Observation of the $^7$H excited state

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 $\sim 10$ $μ$b/sr within angular range $θ_{\text{cm}} \simeq 6^{\circ} - 30^{\circ}$.

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arXiv2018

From Coulomb excitation cross sections to non-resonant astrophysical rates in three-body systems: $^{17}$Ne case

Coulomb and nuclear dissociation of $^{17}$Ne on light and heavy targets are studied theoretically. The dipole E1 strength function is determined in a broad energy range including energies of astrophysical interest. Dependence of the strength function on different parameters of the $^{17}$Ne ground state structure and continuum dynamics is analyzed in a three-body model. The discovered dependence plays an important role for studies of the strength functions for the three-body E1 dissociation and radiative capture. The constraints on the $[s^2]/[d^2]$ configuration mixing in $^{17}$Ne and on $p$-wave interaction in the $^{15}$O+$p$ channel are imposed based on experimental data for $^{17}$Ne Coulomb dissociation on heavy target.

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arXiv2018

Three-body correlations in direct reactions: Example of $^{6}$Be populated in $(p,n)$ reaction

The $^{6}$Be continuum states were populated in the charge-exchange reaction $^1$H($^{6}$Li,$^{6}$Be)$n$ collecting very high statistics data ($\sim 5 \times 10^6$ events) on the three-body $α$+$p$+$p$ correlations. The $^{6}$Be excitation energy region below $\sim 3$ MeV is considered, where the data are dominated by contributions from the $0^+$ and $2^+$ states. It is demonstrated how the high-statistics few-body correlation data can be used to extract detailed information on the reaction mechanism. Such a derivation is based on the fact that highly spin-aligned states are typically populated in the direct reactions.

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arXiv2017

Search for $2p$ decay of the first excited state of $^{17}$Ne

Two-proton decay of the $^{17}$Ne low-lying states populated in the $^1$H($^{18}$Ne,$d$)$^{17}$Ne transfer reaction was studied. The two-proton width $Γ_{2p}$ of the $^{17}$Ne first excited $3/2^-$ state at $E^*=1.288$ MeV is of importance for the two-proton radioactivity theory and nuclear-astrophysics applications. A dedicated search for the two-proton emission of this state was performed leading to the new upper limit obtained for the width ratio $Γ_{2p}/Γ_γ < 1.6(3) \times 10^{-4}$. A novel, "combined mass" method is suggested and tested capable to improve the resolution of the experiment which is a prime significance for the study of nuclear states with extremely small particle-to-gamma width ratios $Γ_{\mathrm{part}}/Γ_γ$. The condition $Γ_{\mathrm{part}} \ll Γ_γ$ is quite common for the states of astrophysical interest which makes the proposed approach promising in this field.

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arXiv2016

Problems to be clarified by means of redioactive ion beams provided by the ACCULINNA-2 separator

Fragment separator ACCULINNA-2 has been built in the Flerov Laboratory of Nuclear reactions (JINR, Dubna). It is timely now to choose meaningful and challenging objectives for experiments dedicated to the study of light drip-line nuclei. Considerable interest makes the search for the minor $2p$-decay branch of the first excited state of $^{17}$Ne. The knowledge on the $Γ_{2p}/Γ_γ$ width ratio for this excited state is of considerable interest because the reverse process of simultaneous two-proton radiative capture could be a bypass for the $^{15}$O "waiting point" occurring in the rp-process of nucleosynthesis. Accumulation of high-statistics data for the $^{10}$He excitation spectrum populated in the $^2$H($^8$He,$p$)$^9$He and $^3$H($^8$He,$p$)$^{10}$He reactions, as well as the study of cross-check reactions made with the $^{11}$Li and $^{14}$Be beams, will make an effective way to clarify the succession of $^{10}$He excited states. A hot topic beyond the neutron drip line makes the observation of results capable to elucidate the low-energy resonance states anticipated for the $4n$ decay of $^{7}$H. The RIB beams provided by ACCULINNA-2 will allow one to perform experiments where luminosity coming to a level of more than $2 \times 10^{26}$ cm$^{-2}$ s$^{-1}$ will be achievable in experiments aimed study of the $^2$H($^8$He,$^3$He)$^7$H and $^2$H($^{11}$Li,$^6$Li)$^7$H reactions.

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arXiv2014

The observation of long-range three-body Coloumb effects in the decay of 16Ne

The interaction of an $E/A$=57.6-MeV $^{17}$Ne beam with a Be target was used to populate levels in $^{16}$Ne following neutron knockout reactions. The decay of $^{16}$Ne states into the three-body $^{14}$O+$p$+$p$ continuum was observed in the High Resolution Array (HiRA). For the first time for a 2p emitter, correlations between the momenta of the three decay products were measured with sufficient resolution and statistics to allow for an unambiguous demonstration of their dependence on the long-range nature of the Coulomb interaction. Contrary to previous experiments, the intrinsic decay width of the $^{16}$Ne ground state was found to be narrow ($Γ<60$~keV), consistent with theoretical estimates.

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arXiv2012

10He low-lying states structure uncovered by correlations

The 0+ ground state of the 10He nucleus produced in the 3H(8He,p)10He reaction was found at about $2.1\pm0.2$ MeV (Γ~ 2 MeV) above the three-body 8He+n+n breakup threshold. Angular correlations observed for 10He decay products show prominent interference patterns allowing to draw conclusions about the structure of low-energy excited states. We interpret the observed correlations as a coherent superposition of the broad 1- state having a maximum at energy 4-6 MeV and the 2+ state above 6 MeV, setting both on top of the 0+ state "tail". This anomalous level ordering indicates that the breakdown of the N=8 shell known in 12Be thus extends also to the 10He system.

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arXiv2011

Isovector soft dipole mode in 6Be

By using the 1H(6Li,6Be)n charge-exchange reaction, continuum states in 6Be were populated up to E_t=16 MeV, E_t being the 6Be energy above its three-body decay threshold. In kinematically complete measurements performed by detecting alpha+p+p coincidences, an E_t spectrum of high statistics was obtained, containing approximately ~5x10^6 events. The spectrum provides detailed correlation information about the well-known 0^+ ground state of 6Be at E_t=1.37 MeV and its 2^+ state at E_t=3.05 MeV. Moreover, a broad structure extending from 4 to 16 MeV was observed. It contains negative parity states populated by Delta L=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.

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arXiv2010

Lifetime of 26S and a limit for its 2p decay energy

Unknown isotope 26S, expected to decay by two-proton (2p) emission, was studied theoretically and was searched experimentally. The structure of this nucleus was examined within the relativistic mean field (RMF) approach. A method for taking into account the many-body structure in the three-body decay calculations was developed. The results of the RMF calculations were used as an input for the three-cluster decay model worked out to study a possible 2p decay branch of this nucleus. The experimental search for 26S was performed in fragmentation reactions of a 50.3 A MeV 32S beam. No events of 26S or 25P (a presumably proton-unstable subsystem of 26S) were observed. Based on the obtained production systematics an upper half-life limit of T_{1/2}<79 ns was established from the time-of-flight through the fragment separator. Together with the theoretical lifetime estimates for two-proton decay this gives a decay energy limit of Q_{2p}>640 keV for 26S. Analogous limits for 25P are found as T_{1/2}<38 ns and Q_{p}>110 keV. In the case that the one-proton emission is the main branch of the 26S decay a limit Q_{2p}>230 keV would follow for this nucleus. It is likely that 26S resides in the picosecond lifetime range and the further search for this isotope is prospective for the decay-in-flight technique.

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arXiv2005

Possibility to study a two-proton halo in $^{17}$Ne

The nuclide $^{17}$Ne is studied theoretically in a three-body $^{15}$O+$p$+$p$ model. We demonstrate that the experimental condition for existence of a proton halo in $^{17}$Ne can be reasonably quantified in terms of $s/d$ configuration mixing. We discuss experimental evidences for a proton halo in $^{17}$Ne. We define which kind of experimental data could elucidate this issue.

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