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Rogachev, G. V.

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

18 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Potential absence of observed π2 linear-chain structures in 14O via 10C(α,α) resonances scattering

Background: The preference for light nuclear systems to coagulate into -particle clusters has been well-studied. The possibility of a linear chain configuration of -particles would allow for a new way to study this phenomenon. Purpose: A rotational band of states in C has been claimed showing a linear chain structure. The mirror system, 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 C was incident into a chamber filled with He:CO gas with the tracks recorded inside the TexAT Time Projection Chamber and the recoil -particles detected by a silicon detector array to measure the cross section. Results: The experimental cross section was compared with previous studies and fit using R-Matrix theory with the previously-observed O states being transformed to the 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 C states did not constitute a 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.

Bishop, J.↗
DOE OSTI2024

Signatures of clustering accessible with a Time Projection Chamber: TexAT

Many experimental observables in clustering require high-sensitivity, almost background-free measurements. The use of Time Projection Chambers (TPCs) over the past 15 years have demonstrated their capability as a step change in the accessibility of many of these observables, as well as the possibility to study clustering via new techniques. A summary of the difficulties and pitfalls of determining the type of clustering from observables is briefly discussed, with a focus on α-condensation and the possibility of an additional (Efimov) 0 + state in 12 C, below the Hoyle state. The expansion of the technique used to tackle this challenge to study 3α + p clustering in 13 N is also discussed, highlighting the exciting opportunities TPCs provide to study clustering inaccessible by conventional means. Finally, an overview of the recent and upcoming advances in TPC technology is given as well as listing additional future challenges that are needed to be overcome, in the context of discussing the next-generation upgrade to the existing TexAT TPC, known as TeBAT (TExas Birmingham Active Target).

Bishop, Jack↗
DOE OSTI2024

Cluster structure of 3⁢𝛼+𝑝 states in 13 N

Cluster states in 13 N are extremely difficult to measure due to the unavailability of 9 B +𝛼 elastic-scattering data. 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. One-at-a-time implantation and decay of 13 O was performed with the Texas Active Target Time Projection Chamber. 149⁢𝛽⁢3⁢𝛼⁢𝑝 decay events were observed and the excitation function in 13 N reconstructed. Four previously unknown 𝛼-decaying excited states were observed in 13 N at an excitation energy of 11.3, 12.4, 13.1, and 13.7 MeV decaying via the 3⁢𝛼+𝑝 channel. These states are seen to have a [ 9 B ⁡(g.s) ⁢⨂𝛼/𝑝 + 12 C ⁡(0$^+_2$)], [ 9 B ⁡($\frac{1}{2}$ + )⁢ ⨂𝛼], [ 9 B ⁡($\frac{5}{2}$ + )⁢ ⨂𝛼], and [ 9 B⁡ ($\frac{5}{2}$) ⁢⨂𝛼] structure, respectively. A previously seen state at 11.8 MeV was also determined to have a [𝑝+ 12 C ⁡(g.s.)/𝑝+ 12 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 ★ .

Physics↗
DOE OSTI2024

𝑅-matrix analysis of 22 Ne states populated in 18 O ⁡(𝛼,𝛼) resonant elastic scattering

The properties of resonances in the 18 O + 𝛼 interaction are important for analyses of astrophysical processes and for understanding of the development of the 𝛼-cluster structure with addition of neutrons to 4N nuclei. Previous high-energy resolution measurements have not been treated using the contemporary 𝑅-matrix approach. We have performed an 𝑅-matrix analysis of the resonant data [D. Powers, J. K. Bair, J. L. C. Ford, Jr., and H. B. Willard, Phys. Rev. 134, B1237 (1964)] and obtained new data on 15 levels in the excitation region of 11.7–12.5 MeV 22 Ne. It appears that the model calculations did not predict the observed tendency in the 20–22 Ne 𝛼 clustering. This paper is the first step of our program of investigation of the 22 Ne spectrum in resonant reactions.

6 ≤ A ≤ 19↗
DOE OSTI2024

Radiative decay branching ratio of the Hoyle state

The triple-alpha process is a vital reaction in nuclear astrophysics, characterized by two consecutive reactions [2α ⇌ 8 Be (α, γ) 12 C] that drive carbon formation. The second reaction occurs through the Hoyle state, a 7.65 MeV excited state in 12 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. Here, this work aims to utilize charged-particle spectroscopy with magnetic selection as a means to accurately measure the total radiative branching ratio (Γ rad /Γ) of the Hoyle state in 12 C.

6 ≤ A ≤ 19↗
DOE OSTI2023

Spectroscopy of 13 Be through isobaric analog states in 13 B

Spectroscopy of the exotic, neutron-unbound beryllium isotope, 13 Be, is still a puzzle despite significant experimental efforts. To observe T = 5/2 states in 13 B, establish spin parities and spectroscopic factors, and use isospin symmetry to inform spectroscopy of 13 Be, excitation functions for resonance elastic scattering of 12 Be on protons were measured in the c.m. energy range from 1 MeV to 5 MeV. Two T = 5/2 states in 13 B at excitation energies 18.25 MeV and 19.95 MeV were observed. Unambiguous 1/2 + and 5/2 + spin-parity assignments were made, and spectroscopic factors were established using R-matrix analysis of the measured 12 Be + p excitation functions. Here, we provide the first direct and unambiguous spin-parity assignments and spectroscopic factor measurements for the resonances in the A = 13, T = 5/2 isobaric multiplet. This puts us on a solid footing to identify the 2.3 MeV state in 13 Be as 5/2 + and infer the existence of an s-wave (1/2 + ) resonance at around 0.6 MeV with a relatively small spectroscopic factor.

6 ≤ A ≤ 19↗
DOE OSTI2023

Search for an s -wave resonance in Li 7 just above the proton-decay threshold

Near-threshold resonances play an important role in nucleosynthesis and applied nuclear science. The study of nuclei removed from stability has greatly extended the list of resonances close to decay thresholds. The no core shell model with continuum (NCSMC) recently predicted an s-wave resonance just above the proton-decay threshold of 7 Li at an excitation energy of 10.2 MeV. This potential case of a near-threshold resonance is dependent on the quantum mechanics of the p + 6 He fragments extended into the continuum. Further, the 6 He(d,n) 7 Li* reaction was employed in an attempt to populate this resonance and search for its proton decay via the invariant-mass method. No evidence of this resonance was found. However, the data collected in this search led to better constraints on the energy and width of the isobaric analog state (IAS) with (J π ,T) = (3/2 - , 3/2) and revealed a new weak resonance just above the IAS in energy, predicted by the NCSMC as a (J π , T ) = (3/2 – , 1/2) state and potentially a part of the antianalog structure.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

First Observation of the β3αp Decay of 13 O via β-Delayed Charged-Particle Spectroscopy

The β-delayed proton decay of 13 O has previously been studied, but the direct observation of β-delayed 3⁢α⁢p decay has not been reported. Rare 3⁢α⁢p events from the decay of excited states in 13 N* provide a sensitive probe of cluster configurations in 13 N*. To measure the low-energy products following β-delayed 3⁢αp decay, the Texas Active Target (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. A total of 1.9 × 10 5 13 O implantations were made inside the TexAT time projection chamber. Furthermore, a total of 149 3⁢αp events were observed, yielding a β-delayed 3⁢αp branching ratio of 0.078(6)%. Four previously unknown α-decaying excited states were observed in 13 N at 11.3, 12.4, 13.1, and 13.7 MeV decaying via the 3⁢α + p channel.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

TexAT detector upgrade for 14 O($α$, $p$) 17 F cross section measurement

A direct cross-section measurement of the 14 O($α$, $p$) 17 F reaction is important to understand the light curves of x-ray bursts. The measurement will be performed using the Texas Active Target TPC version 2 (TexAT_v2). The TexAT_v2 aims at measuring lower energy protons from the reaction than the original TexAT. Newly developed silicon and CsI(Tl) detector arrays are added at the left, right and bottom of a modified field cage to increase its detection efficiency. Furthermore, this paper describes the overall specifications and two commissioning experiments performed at Texas A&M University.

14O(α, p)17F↗
DOE OSTI2023

Noise signal identification in time projection chamber data using deep learning model

Deep learning has been employed in various scientific fields and has provided promising results. Here, in this study, a deep learning classifier was implemented to improve the quality of data obtained from a time projection chamber. Digital waveforms of the detected signals were classified into the following three categories: particles, noises, and particles piled up with noises. A simple 1-dimensional convolutional neural network was developed for the classification. The model demonstrated an excellent performance on the test dataset. Its practical performance was also examined using track images and particle identification plots by comparing the original and clean data without the noise signals. The comparison clearly showed that the deep learning model improved the quality of data. The current study presents an effective application of the deep learning model for the time projection chamber data.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2022

α-cluster structure of 18 Ne

In this work, we investigate α-clustering in 18 Ne and compare it with what is known about clustering in the mirror nucleus 18 O. The excitation function for resonant elastic scattering of 14 O + α was measured in inverse kinematics using the TexAT active-target detector system, covering excitation energies from 8 to 17 MeV. The data were analyzed using a multi-channel R-matrix approach. Detailed spectroscopic information—including excitation energies, spin and parity assignments, and partial α and total widths—was extracted from the R-matrix analysis and compared with theoretical models and previously available data. Correspondence between levels in 18 O and 18 Ne is established. An extensive shell-model analysis of the 18 O– 18 Ne mirror pair shows very good agreement between theory and experiment, especially in the distribution of clustering strength. The comparison reveals that certain states, particularly at higher excitation energies, exhibit significantly stronger α-cluster character than predicted. This suggests that these states have a collective structure aligned with the corresponding α-reaction channel.

6 ≤ A ≤ 19↗
DOE OSTI2022

β -delayed charged-particle decay of Si 22 , 23

The β decay of 22,23 Si by emission of delayed charged particles was investigated in an experiment at the Cyclotron Institute of Texas A&M University by means of an optical-readout time-projection chamber. The previously-known decay of the two isotopes by β-delayed one- and two-proton emission was confirmed. Here for the first time, a new, rare, decay mode for 23 Si, β-delayed three-proton emission, was observed and β-delayed proton-α emission tentatively identified. Moreover, the β-decay pattern for the ground state of 23 Si was studied by means of multireference density-functional-rooted calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Lowest-energy broad 𝛼-cluster resonances in 19 F

There is strong astrophysical interest in the structure of 19 F states near the α-decay threshold, as their properties are important for understanding the development of α clustering in the 20 Ne region. The emergence of clustered states, and more generally of states that couple strongly to reaction channels near their decay thresholds, is also a topic of current interest in theoretical nuclear physics. In this work, we determine the parameters of broad low-spin states in 19 F near the α-decay threshold and present a theoretical study of these states. The analysis is restricted to ℓ = 0 and 1 resonances in the α + 15 N system close to the α threshold in 19 F. Excitation functions for 15 N(α,α) elastic scattering were measured using the Thick Target Inverse Kinematics (TTIK) method, and these new data, together with older high–energy-resolution measurements, were analyzed within the R-matrix framework. The nuclear structure of 19 F was calculated using configuration-interaction methods with a recently developed effective interaction Hamiltonian. As a result, we identify a sequence of α-cluster resonances in 19 F and map the distribution of clustering strength, which is relevant for astrophysical reaction modeling and for the theoretical understanding of many-body dynamics and the emergence of clustering in loosely bound or unstable nuclei. Furthermore, the work advances theoretical insight into the origins of clustering and highlights open questions for future theoretical and experimental studies.

19F↗
DOE OSTI2022

𝛼-cluster structure in 19 F and 19 Ne in resonant scattering

This work investigates the nuclear structure of 19 F and 19 Ne, which is important for understanding α clustering in the A = 20 mass region and for astrophysical applications. The only high-resolution, broad angular- and energy-range study of the 19 F resonance structure in α + 15 N scattering was published over 60 years ago, when a detailed analysis of complex excitation functions with overlapping resonances and multiple decay channels was not feasible. We have performed a modern R-matrix analysis of these data to assign spins and determine resonance parameters for levels in 19 F up to an excitation energy of 8.2 MeV. Our R-matrix parameters were successfully tested by fitting recent α + 15 N data obtained with the Thick Target Inverse Kinematics (TTIK) method at 180°. The new 19 F parameters were then used to fit TTIK data for α + 15 O, the mirror resonant reaction. In conclusion, comparison of these isobaric mirror reactions provides valuable insight into the underlying nuclear structure.

6 ≤ A ≤ 19↗
DOE OSTI2021

( 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 = 4–14 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. Using our new 22 Ne(α,n) 25 Mg and 22Ne(α,γ) 26 Mg reaction rates, we performed new s-process calculations for massive stars and asymptotic giant branch stars and compared the resulting abundances with the abundances 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 < 7.5 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.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

A position and pulse shape discriminant p -terphenyl detector module

We present the development of a neutron detector array module made with para-terphenyl, a bright, fast, n/γ discriminating crystalline organic scintillator. The module is comprised of 2 cm × 2 cm × 2 cm p-terphenyl crystals that have been optically coupled together to create a 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 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.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Evidence against the Efimov effect in 12 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 subsystems. A hypothetical state in 12 C at 7.458-MeV excitation energy, comprising 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. Purpose: Using a combination of γ spectroscopy, charged-particle spectroscopy, and astrophysical rate calculations allowing for strict limits on the existence of such a state to been established here. Method: Using the combined data sets from two recent experiments, one with the TexAT (Texas Active Target) TPC (Time Projection Chamber) to measure α decay and the other with Gammasphere to measure γ decay of states in 12 C populated by 12 N and 12 B β decay, respectively, we achieve high sensitivity to states in close proximity to the α threshold in 12 C. Results: No evidence of a state at 7.458 MeV is seen in either data set. Using a likelihood method, the 95% confidence limit 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 3α reaction rate show the inclusion of the Efimov corresponds to a large increase in the reaction rate around 5 × 10 7 K. Conclusion: From decay spectroscopy—at the 95% confidence limit, 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 C . Furthermore, the 3α 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.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗