arXiv subjects

G. V. Rogachev

Publications and source records attributed to G. V. Rogachev.

At least 19 recordsLinked to original sources

arXiv2026

Differential cross sections for ${{^{12}\mathrm{C}(n,\alpha_{0})}}$, ${{^{16}\mathrm{O}(n,\alpha_{0})}}$ and ${{^{16}\mathrm{O}(n,\alpha_{1,2,3})}}$ between ${{E_n}}$ = 7.2 and 10 MeV with an active-target Time Projection Chamber

Data for the ${{^{12}\mathrm{C}(n,\alpha_{0})}}$, ${{^{16}\mathrm{O}(n,\alpha_{0})}}$ and ${{^{16}\mathrm{O}(n,\alpha_{1,2,3})}}$ differential cross sections are important for several different areas of nuclear physics such as understanding neutron transmutation in nuclear reactors. The TexAT Time Projection Chamber was used to measure the differential and angle-integrated cross sections in active-target mode. The chamber was filled with CO$_2$ gas and used a quasi-monoenergetic neutron beam from the $d(d,n)$ reaction at Edwards Accelerator Lab at Ohio University. A comparison between our current and previous results at overlapping energies and angles which showed good agreement in angular dependence and absolute cross section. A broader angular coverage than previous results demonstrated that the integrated cross section for the \po16 reaction deviates from ENDFVIII.0 evaluations. This first instance of neutron-induced measurements with an active-target Time Projection Chamber demonstrates the use of this method for high-quality differential cross section data across a broad angular range, generating good statistics with a relatively low-intensity beam.

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arXiv2025

Quantifying alpha clustering in the ground states of 16-O and 20-Ne

Understanding the role of multi-nucleon correlations in the structure of light nuclei is at the forefront of modern nuclear science. In this letter, we present a quantitative benchmark study of alpha-cluster correlations in the ground states of 16-O and 20-Ne. Experimental data provide direct evidence that the wave functions of the ground states of 16-O and 20-Ne are dominated by alpha-cluster correlations, in agreement with the predictions of sophisticated nuclear structure models. We also provide a new model-independent constraint for the alpha asymptotic normalization coefficient of the 16-O ground state and discuss the implications of these findings on the 12-C(alpha,gamma)16-O reaction, which is of critical importance for nuclear astrophysics.

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arXiv2025

Potential absence of observed $\pi^2$ linear-chain structures in $^{14}$O via $^{10}$C($\alpha,\alpha$) resonant scattering

Background: The preference for light nuclear systems to coagulate into $\alpha$-particle clusters has been well-studied. The possibility of a linear chain configuration of $\alpha$-particles would allow for a new way to study this phenomenon. Purpose: A rotational band of states in $^{14}$C has been claimed showing a $\pi^2$ linear chain structure. The mirror system, $^{14}$O, has been studied here to examine how this linear chain structure is affected by replacing the valence neutrons with protons. Method: A beam of $^{10}$C was incident into a chamber filled with He:CO$_2$ gas with the tracks recorded inside the TexAT Time Projection Chamber and the recoil $\alpha$-particles detected by a silicon detector array to measure the $^{10}\mathrm{C}(\alpha,\alpha)$ cross section. Results: The experimental cross section was compared with previous studies and fit using R-Matrix theory with the previously-observed $^{14}$O states being transformed to the $^{14}$C using mirror symmetry. The measured cross section does not replicate the claimed states, with the predicted cross section exceeding that observed at several energies and angles. Conclusion: A series of possibilities are highlighted with the most likely being that the originally-seen $^{14}$C states did not constitute a $\pi^2$ rotational band with a potentially incorrect spin assignment due to the limitations of the angular correlation method with non-zero spin particles. The work highlights the difficulties in measuring broad resonances corresponding to a linear chain state in a high level density.

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arXiv2024

Study of the $in ^{34}$Ar($\alpha,p$)$^{37}$K reaction rate via proton scattering on $^{37}$K, and its impact on properties of modeled X-Ray bursts

Background: Type I X-Ray bursts (XRBs) are energetic stellar explosions that occur on the surface of a neutron star in an accreting binary system with a low-mass H/He-rich companion. The rate of the $^{34}$Ar($\alpha,p$)$^{37}$K reaction may influence features of the light curve that results from the underlying thermonuclear runaway, as shown in recent XRB stellar modelling studies. Purpose: In order to reduce the uncertainty of the rate of this reaction, properties of resonances in the compound nucleus $^{38}$Ca, such as resonance energies, spins, and particle widths, must be well constrained. Method: This work discusses a study of resonances in the $^{38}$Ca compound nucleus produced in the $^{34}$Ar($\alpha,p$) reaction. The experiment was performed at the National Superconducting Cyclotron Laboratory, with the ReA3 facility by measuring proton scattering using an unstable $^{37}$K beam. The kinematics were designed specifically to identify and characterize resonances in the Gamow energy window for the temperature regime relevant to XRBs. Results: The spins and proton widths of newly identified and previously known states in $^{38}$Ca in the energy region of interest for the $^{34}$Ar($\alpha,p$)$^{37}$K reaction have been constrained through an R-Matrix analysis of the scattering data. Conclusions: Using these constraints, a newly estimated rate is applied to an XRB model built using Modules for Experiments in Stellar Astrophysics (MESA), to examine its impact on observables, including the light curve. It is found that the newly determined reaction rate does not substantially affect the features of the light curve.

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arXiv2024

Cluster structure of 3$α$+p states in $^{13}$N

Background: Cluster states in $^{13}$N are extremely difficult to measure due to the unavailability of $^{9}$B+$α$ elastic scattering data. Purpose: Using $β$-delayed charged-particle spectroscopy of $^{13}$O, clustered states in $^{13}$N can be populated and measured in the 3$α$+p decay channel. Method: One-at-a-time implantation/decay of $^{13}$O was performed with the Texas Active Target Time Projection Chamber (TexAT TPC). 149 $β3αp$ decay events were observed and the excitation function in $^{13}$N reconstructed. Results: Four previously unknown $α$-decaying excited states were observed in $^{13}$N at an excitation energy of 11.3 MeV, 12.4 MeV, 13.1 MeV and 13.7 MeV decaying via the 3$α$+p channel. Conclusion: These states are seen to have a [$^{9}\mathrm{B}(\mathrm{g.s}) \bigotimes α$/ $p+^{12}\mathrm{C}(0_{2}^{+})$], [$^{9}\mathrm{B}(\frac{1}{2}^{+}) \bigotimes α$], [$^{9}\mathrm{B}(\frac{5}{2}^{+}) \bigotimes α$] and [$^{9}\mathrm{B}(\frac{5}{2}^{+}) \bigotimes α$] structure respectively. A previously-seen state at 11.8 MeV was also determined to have a [$p+^{12}\mathrm{C}(\mathrm{g.s.})$/ $p+^{12}\mathrm{C}(0_{2}^{+})$] structure. The overall magnitude of the clustering is not able to be extracted however due to the lack of a total width measurement. Clustered states in $^{13}$N (with unknown magnitude) seem to persist from the addition of a proton to the highly $α$-clustered $^{12}$C. Evidence of the $\frac{1}{2}^{+}$ state in $^{9}$B was also seen to be populated by decays from $^{13}$N$^{\star}$.

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arXiv2024

Radiative decay branching ratio of the Hoyle state

Background: The triple-alpha process is a vital reaction in nuclear astrophysics, characterized by two consecutive reactions [$2α\leftrightarrows{^{8}\rm{Be}}(α,γ){^{12}\rm{C}}$] that drive carbon formation. The second reaction occurs through the Hoyle state, a 7.65 MeV excited state in ${^{12}\rm{C}}$ with $J^π=0^{+}$. The rate of the process depends on the radiative width, which can be determined by measuring the branching ratio for electromagnetic decay. Recent measurements by Kibédi et al. conflicted with the adopted value and resulted in a significant increase of nearly 50\% in this branching ratio, directly affecting the triple-alpha reaction. Purpose: This work aims to utilize charged-particle spectroscopy with magnetic selection as a means to accurately measure the total radiative branching ratio ($Γ_{\rm{rad}}/Γ$) of the Hoyle state in $^{12}{\rm C}$. Methods: The Hoyle state in $^{12}{\rm C}$ was populated via $^{12}\rm{C}(α, α')^{12}\rm{C^{*}}$ inelastic scattering. The scattered $α$ particles were detected using a $Δ$E-E telescope, while the recoiled $^{12}{\rm C}$ ions were identified in a magnetic spectrometer. Results: A radiative branching ratio value of $Γ_{\rm{rad}}/Γ\times10^{4}=4.0\pm0.3({\rm stat.})\pm0.16({\rm syst.})$ was obtained. Conclusions: The radiative branching ratio for the Hoyle state obtained in this work is in agreement with the original adopted value. Our result suggests that the proton-$γ$-$γ$ spectroscopy result reported by Kibédi et al. may be excluded.

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arXiv2023

First observation of the $β$3$α$p decay of $^{13}\mathrm{O}$ via $β$-delayed charged-particle spectroscopy

Background: The $β$-delayed proton-decay of $^{13}\mathrm{O}$ has previously been studied, but the direct observation of $β$-delayed $α$+$α$+$α$+p decay has not been reported. Purpose: Observing rare 3$α$+p events from the decay of excited states in $^{13}\mathrm{N}^{\star}$ allows for a sensitive probe of exotic highly-clustered configurations in $^{13}$N. Method: To measure the low-energy products following $β$-delayed 3$α$p-decay, the TexAT Time Projection Chamber was employed using the one-at-a-time $β$-delayed charged-particle spectroscopy technique at the Cyclotron Institute, Texas A&M University. Results: A total of $1.9 \times 10^{5}$ $^{13}\mathrm{O}$ implantations were made inside the TexAT Time Projection Chamber. 149 3$α$+p events were observed yielding a $β$-delayed 3$α+p$ branching ratio of 0.078(6)%. Conclusion: Four previously unknown $α$-decaying states were observed, one with a strong $^{9}\mathrm{B(g.s)}+α$ characteristic at 11.3 MeV, one with a $^{9}\mathrm{B}(\frac{1}{2}^{+})+α$ nature at 12.4 MeV, and another two that are dominated by $^{9}\mathrm{B}({\frac{5}{2}}^{+})+α$ at 13.1 and 13.7 MeV. Population of the $\frac{1}{2}^{+}$ state in $^{9}\mathrm{B}$ has been unambiguously seen, cementing the predicted existence of the mirror-state based on the states observed in $^{9}\mathrm{Be}$.

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arXiv2023

Restoring Original Signal From Pile-up Signal using Deep Learning

Pile-up signals are frequently produced in experimental physics. They create inaccurate physics data with high uncertainty and cause various problems. Therefore, the correction to pile-up signals is crucially required. In this study, we implemented a deep learning method to restore the original signals from the pile-up signals. We showed that a deep learning model could accurately reconstruct the original signal waveforms from the pile-up waveforms. By substituting the pile-up signals with the original signals predicted by the model, the energy and timing resolutions of the data are notably enhanced. The model implementation significantly improved the quality of the particle identification plot and particle tracks. This method is applicable to similar problems, such as separating multiple signals or correcting pile-up signals with other types of noises and backgrounds.

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arXiv2022

alpha-cluster structure of 18Ne

In this work we study alpha-clustering in 18Ne and compare it with what is known about clustering in the mirror nucleus 18O. The excitation function of 18Ne was measured in inverse kinematics from the resonant elastic scattering reaction of 14O on 4He in the excitation energy range from 8 to 17 MeV, using the active target TexAT. The analysis was performed using a multi-channel R-matrix approach. Detailed spectroscopic information is obtained from the R-matrix analysis: excitation energy of the states, spin and parity as well as partial alpha and total widths. This information is compared with theoretical models and previous data. Clustering structures appear to be robust and mostly isospin symmetric. A good correspondence was found between the levels in 18O and 18Ne. We carried out an extensive shell model analysis of the experimental data. This comparison suggests that strongly clustered states remain organized in relation to the corresponding reaction channel identified by the number of nodes in the relative alpha plus core wave function. The agreement between theory and experiment is very good and especially useful when it comes to understanding the clustering strength distribution. The comparison of the experimental data with theory shows that certain states, especially at high excitation energies, are significantly more clustered than predicted. This indicates that the structure of these states is collective and is aligned towards the corresponding alpha reaction channel.

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arXiv2021

Study of ($^6$Li, $d$) and ($^6$Li, $t$) reactions on $^{22}$Ne and implications for $s$-process nucleosynthesis

We studied $α$ cluster states in $^{26}$Mg via the $^{22}$Ne($^{6}$Li,$dγ$)$^{26}$Mg reaction in inverse kinematics at an energy of $7$ MeV/nucleon. States between $E_x$ = 4 - 12 MeV in $^{26}$Mg were populated and relative $α$ spectroscopic factors were determined. Some of these states correspond to resonances in the Gamow window of the $^{22}$Ne($α$,n)$^{25}$Mg reaction, which is one of the main neutron sources in the astrophysical $s$-process. We show that $α$-cluster strength of the states analyzed in this work have critical impact on s-process abundances. Using our new $^{22}$Ne($α$,n)$^{25}$Mg and $^{22}$Ne($α$,$γ$)$^{26}$Mg reaction rates, we performed new s-process calculations for massive stars and Asymptotic Giant Branch stars and compared the resulting yields with the yields obtained using other $^{22}$Ne+$α$ rates from the literature. We observe an impact on the s-process abundances up to a factor of three for intermediate-mass AGB stars and up to a factor of ten for massive stars. Additionally, states in $^{25}$Mg at $E_x$ $<$ 5 MeV are identified via the $^{22}$Ne($^{6}$Li,$t$)$^{25}$Mg reaction for the first time. We present the ($^6$Li, $t$) spectroscopic factors of these states and note similarities to the $(d,p$) reaction in terms of reaction selectivity.

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arXiv2021

A Position and Pulse Shape Discriminant p-Terphenyl Detector Module

We present the development of a neutron detector array module made with $\textit{para}$-terphenyl, a bright, fast, n/$γ$ discriminating crystalline organic scintillator. The module is comprised of 2 cm $\times$ 2 cm $\times$ 2 cm $\textit{p}$-terphenyl crystals that have been optically coupled together to create a $\textit{pseudo-bar}$ module. While only relying on two photo detectors, the module is capable of distinguishing interactions between up to eight crystals. Furthermore, the module retains the $\textit{p}$-terphenyl's pulse shape discrimination (PSD) capability. Together this makes the pseudo-bar module a promising position-sensitive neutron detector. Here we present characteristics of the pseudo-bar module - its timing resolution as well as its pulse shape and position discrimination capabilities, and briefly discuss future plans for utilizing an array of pseudo-bar modules in a useful neutron detector system.

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arXiv2021

The Lowest Broad Alpha Cluster Resonances in $^{19}$F

There is a deep astrophysical interest in the structure of $^{19}$F states close to the alpha decay threshold. The nuclear structure of these states is important for understanding of the development of $α$ clustering in the $^{20}$Ne region. Emergence of clustered states and generally states that favor coupling to reaction channels near the corresponding decay thresholds is currently of special interest in theoretical physics. Excitation function for $^{15}$N($α$,$α$) elastic scattering was measured by the TTIK method. These new data together with old, high energy resolution data, were analyzed using the R matrix approach. $^{19}$F nuclear structure was calculated using configuration interaction methods with the recently developed effective interaction Hamiltonian. The parameters of broad low spin $\ell = 0$ and 1 relative partial wave resonances close to the $α$ decay threshold in $^{19}$F were identified. Detailed theoretical analysis was carried out identifying all states coupled to the $\ell = 0$ and 1 alpha cluster channels. Considering hierarchy of states with different harmonic oscillator shell excitations allows to evaluate coupling to the alpha channels with different number of nodes in the relative wave function and helps to explain the distribution of the clustering strength and emergence of broad clustering resonances. Comparison of clustering in $^{20}$Ne into $^{16}$O+$α$ and consideration of spin-orbit splitting of the $^{15}$N+$α$ channel provides additional evidence. Detailed analysis of new and old experimental data allows to identify a series of $α$ clustering resonances in $^{19}$F and to assess the distribution of the clustering strength which is of importance to questions of astrophysics and for theoretical understanding of many-body physics and emergence of clustering in loosely bound or unstable nuclei.

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arXiv2021

Evidence against the Efimov effect in $^{12}\mathrm{C}$ from spectroscopy and astrophysics

Background: The Efimov effect is a universal phenomenon in physics whereby three-body systems are stabilized via the interaction of an unbound two-body sub-systems. A hypothetical state in $^{12}\mathrm{C}$ at 7.458 MeV excitation energy, comprising of a loose structure of three $α$-particles in mutual two-body resonance, has been suggested in the literature to correspond to an Efimov state in nuclear physics. The existence of such a state has not been demonstrated experimentally. Method: Using the combined data sets from two recent experiments, one with the TexAT TPC to measure $α$-decay and the other with Gammasphere to measure $γ$-decay of states in $^{12}\mathrm{C}$ populated by $^{12}\mathrm{N}$ and $^{12}\mathrm{B}$ $β$-decay respectively, we achieve high sensitivity to states in close-proximity to the $α$-threshold in $^{12}\mathrm{C}$. Results: No evidence of a state at 7.458 MeV is seen in either data set. Using a likelihood method, the 95\% C.L. $γ$-decay branching ratio is determined as a function of the $β$-decay feeding strength relative to the Hoyle state. In parallel, calculations of the triple-alpha reaction rate show the inclusion of the Efimov corresponds to a large increase in the reaction rate around $5 \times 10^{7}$ K. Conclusion: From decay spectroscopy - at the 95\% C.L., the Efimov state cannot exist at 7.458 MeV with any $γ$-decay branching ratio unless the $β$-strength is less than 0.7\% of the Hoyle state. This limit is evaluated for a range of different excitation energies and the results are not favorable for existence of the hypothetical Efimov state in $^{12}\mathrm{C}$. Furthermore, the triple-alpha reaction rate with the inclusion of a state between 7.43 and 7.53 MeV exceeds the rate required for stars to undergo the red giant phase.

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arXiv2020

Almost medium-free measurement of the Hoyle state direct-decay component with a TPC

Background: The structure of the Hoyle state, a highly $α$-clustered state at 7.65 MeV in $^{12}\mathrm{C}$, has long been the subject of debate. Understanding if the system comprises of three weakly-interacting $α$-particles in the 0s orbital, known as an $α$-condensate state, is possible by studying the decay branches of the Hoyle state. Purpose: The direct decay of the Hoyle state into three $α$-particles, rather than through the $^{8}\mathrm{Be}$ ground state, can be identified by studying the energy partition of the 3 $α$-particles arising from the decay. This paper provides details on the break-up mechanism of the Hoyle stating using a new experimental technique. Method: By using beta-delayed charged-particle spectroscopy of $^{12}\mathrm{N}$ using the TexAT (Texas Active Target) TPC, a high-sensitivity measurement of the direct 3 $α$ decay ratio can be performed without contributions from pile-up events. Results: A Bayesian approach to understanding the contribution of the direct components via a likelihood function shows that the direct component is $<0.043\%$ at the 95\% confidence level (C.L.). This value is in agreement with several other studies and here we can demonstrate that a small non-sequential component with a decay fraction of about $10^{-4}$ is most likely. Conclusion: The measurement of the non-sequential component of the Hoyle state decay is performed in an almost medium-free reaction for the first time. The derived upper-limit is in agreement with previous studies and demonstrates sensitivity to the absolute branching ratio. Further experimental studies would need to be combined with robust microscopic theoretical understanding of the decay dynamics to provide additional insight into the idea of the Hoyle state as an $α$-condensate.

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arXiv2020

Observation of T=3/2 Isobaric Analog States in 9Be using p+8Li resonance scattering

Background: Resonance scattering has been extensively used to study the structure of exotic, neutron-deficient nuclei. Extension of the resonance scattering technique to neutron-rich nuclei was suggested more than 20 years ago. This development is based on the isospin conservation law. In spite of broad field of the application, it has never gained a wide-spread acceptance. Purpose: To benchmark the experimental approach to study the structure of exotic neutron-rich nuclei through resonance scattering on a proton target. Method: The excitation function for p+8Li resonance scattering is measured using a thick target by recording coincidence between light and heavy recoils, populating T=3/2 isobaric analog states (IAS) in 9Be. Results: A good fit of the 8Li(p,p)8Li resonance elastic scattering excitation function was obtained using previously tentatively known 5/2- T=3/2 state at 18.65 MeV in 9Be and a new broad T=3/2 s-wave state - the 5/2+ at 18.5 MeV. These results fit the expected iso-mirror properties for the T=3/2 A=9 iso-quartet. Conclusions: Our analysis confirmed isospin as a good quantum number for the investigated highly excited T=3/2 states and demonstrated that studying the structure of neutron-rich exotic nuclei through IAS is a promising approach.

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arXiv2020

The TTIK approach for neutrons

We applied Thick Target Inverse Kinematics Method for a study of resonances decaying through neutron emission. As a test we used a well-studied, because of its role in s-process in stars, $^{13}$C($α$; n) reaction. The observed energy resolution for the $^{13}$C($α$; n) excitation function was $\sim$60 keV, the largest contributions coming from the time structure of the beam and the thickness of the neutron detector. These measurements demonstrated the high efficiency of the approach and revealed a disagreement with R-matrix calculations based on parameters of the most recent previous analysis.

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arXiv2020

Texas Active Target (TexAT) detector for experiments with rare isotope beams

The TexAT (Texas Active Target) detector is a new active-target time projection chamber (TPC) that was built at the Cyclotron Institute Texas A$\&$M University. The detector is designed to be of general use for nuclear structure and nuclear astrophysics experiments with rare isotope beams. TexAT combines a highly segmented Time Projection Chamber (TPC) with two layers of solid state detectors. It provides high efficiency and flexibility for experiments with low intensity exotic beams, allowing for the 3D track reconstruction of the incoming and outgoing particles involved in nuclear reactions and decays.

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arXiv2020

Constraining the $^{22}$Ne($α$,$γ$)$^{26}$Mg and $^{22}$Ne($α$,n)$^{25}$Mg reaction rates using sub-Coulomb $α$-transfer reactions

The $^{22}$Ne($α$,$γ$)$^{26}$Mg and $^{22}$Ne($α$,n)$^{25}$Mg reactions play an important role in astrophysics because they have significant influence on the neutron flux during the weak branch of the s-process. We constrain the astrophysical rates for these reactions by measuring partial $α$-widths of resonances in $^{26}$Mg located in the Gamow window for the $^{22}$Ne+$α$ capture. These resonances were populated using $^{22}$Ne($^6$Li,d)$^{26}$Mg and $^{22}$Ne($^7$Li,t)$^{26}$Mg reactions at energies near the Coulomb barrier. At these low energies $α$-transfer reactions favor population of low spin states and the extracted partial $α$-widths for the observed resonances exhibit only minor dependence on the model parameters. The astrophysical rates for both the $^{22}$Ne($α$,$γ$)$^{26}$Mg and the $^{22}$Ne($α$,n)$^{25}$Mg reactions are shown to be significantly different than the previously suggested values.

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