Measurement of sub threshold resonance contributions to fusion reactions: the case of the 13C(α, n)16O astrophysical neutron source

The 13C(α, n)16O reaction is the neutron source for the main component of the s-process. It is is active inside the helium-burning shell of asymptotic giant branch stars, at temperatures ≲ 108 K. In this temperature region, corresponding to an energy interval of 140 − 230 keV, the 13C(α, n)16O cross section is dominated by the −3 keV sub-threshold resonance due to the 6.356 MeV level in 17O. Direct measurements could not establish its contribution owing to the Coulomb barrier between interacting nuclei, strongly reducing the cross section at astrophysical energies. Similarly, indirect measurements and extrapolations yielded inconsistent results, calling for further investigations. The Trojan Horse Method was applied to the 13C(6Li, n16O)d quasi-free reaction to access the low as well as the negative energy region of the 13C(α, n)16O reaction. By using the generalized R-matrix approach, the asymptotic normalization coefficient (C̃17O(1/2+)α13C)2 of the 6.356 MeV level was deduced. For the first time, the Trojan Horse Method and the asymptotic normalization coefficient were used in synergy. Our indirect approach lead to (C̃17O(1/2+)α13C)2 = 7.7−1.5+1.6 fm−1, slightly larger than the values in the literature, determining a 13C(α, n)16O reaction rate slightly larger than the one in the literature at temperatures lower than 108 K, with enhanced accuracy

Radiative capture and electromagnetic dissociation involving loosely bound nuclei: the 8^8B example

Electromagnetic processes in loosely bound nuclei are investigated using an analytical model. In particular, electromagnetic dissociation of $^8$B is studied and the results of our analytical model are compared to numerical calculations based on a three-body picture of the $^8$B bound state. The calculation of energy spectra is shown to be strongly model dependent. This is demonstrated by investigating the sensitivity to the rms intercluster distance, the few-body behavior, and the effects of final state interaction. In contrast, the fraction of the energy spectrum which can be attributed to E1 transitions is found to be almost model independent at small relative energies. This finding is of great importance for astrophysical applications as it provides us with a new tool to extract the E1 component from measured energy spectra. An additional, and independent, method is also proposed as it is demonstrated how two sets of experimental data, obtained with different beam energy and/or minimum impact parameter, can be used to extract the E1 component.Comment: Submitted to Phys. Rev. C. 10 pages, 7 figure

Measurement of the 13C(α, n)16O reaction at astrophysical energies using the Trojan Horse Method. Focus on the -3 keV sub-threshold resonance

Most of the nuclei in the mass range 90 ≲ A ≲ 208 are produced through the so-called s-process, namely through a series of neutron capture reactions on seed nuclei followed by β-decays. The 13C(α, n)16O reaction is the neutron source for the main component of the s-process. It is active inside the helium-burning shell of asymptotic giant branch stars, at temperatures ≲ 108 K, corresponding to an energy interval of 140 − 230 keV. In this region, the astrophysical S(E)-factor is dominated by the −3 keV sub-threshold resonance due to the 6.356 MeV level in 17O. Direct measurements could not soundly establish its contribution owing to the cross section suppression at astrophysical energies determined by the Coulomb barrier between interacting nuclei. Indirect measurements and extrapolations yielded inconsistent results, calling for further investigations. The Trojan Horse Method turns out to be very suited for the study of the 13C(α, n)16O reaction as it allows us to access the low as well as the negative energy re- gion, in particular in the case of resonance reactions. We have applied the Trojan HorseMethod to the 13C(6Li, n16O)d quasi-free reaction. By using the modified R-matrix approach, the asymptotic normalization coefficient (C˜α13 C17O(1/2+))2${\left( {\tilde C_{{\alpha ^{13}}{\rm{C}}}^{17{\rm{O(1/}}{{\rm{2}}^{\rm{ + }}}{\rm{)}}}} \right)^2}$ of the 6.356 MeV level has been deduced as well as the n-partial width, allowing to attain an unprecedented accuracy for the 13C(α, n)16O astrophysical factor. A preliminary analysis of a partial data set has lead to (C˜α13C17O(1/2+))2 = 6.7−0.6+0.9 fm−1,${\left( {\tilde C_{{\alpha ^{13}}{\rm{C}}}^{17{\rm{O(1/}}{{\rm{2}}^{\rm{ + }}}{\rm{)}}}} \right)^2}\, = \,6.7_{ - 0.6}^{ + 0.9}\,{\rm{f}}{{\rm{m}}^{ - 1}},$ slightly larger than the values in the literature, determining a 13C(α, n)16O reaction rate in agreement with the most results in the literature at ∼ 108 K, with enhanced accuracy thanks to this innovative approach

Neutron-upscattering enhancement of the triple-alpha process

The neutron inelastic scattering of carbon-12, populating the Hoyle state, is a reaction of interest for the triple-alpha process. The inverse process (neutron upscattering) can enhance the Hoyle state’s decay rate to the bound states of 12C, effectively increasing the overall triple-alpha reaction rate. The cross section of this reaction is impossible to measure experimentally but has been determined here at astrophysically-relevant energies using detailed balance. Using a highly-collimated monoenergetic beam, here we measure neutrons incident on the Texas Active Target Time Projection Chamber (TexAT TPC) filled with CO2 gas, we measure the 3α-particles (arising from the decay of the Hoyle state following inelastic scattering) and a cross section is extracted. Here we show the neutron-upscattering enhancement is observed to be much smaller than previously expected. The importance of the neutron-upscattering enhancement may therefore not be significant aside from in very particular astrophysical sites (e.g. neutron star mergers)

Restoring original signals from pile-up using deep learning

Pile-up signals are frequently produced in experimental physics. They create inaccurate physics data with high uncertainties and cause multiple problems. Therefore, the correction of pile-up signals is crucially required. In this study, we implemented a deep learning method to restore the original signals from signals piled up with unwanted 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 resolution 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. © 2023 Elsevier B.V.11Nsciescopu

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. 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. © 2023 Elsevier B.V.11Nsciescopu

Study of the A+13C interaction at heavy ION acceleration DC-60

In astrophysics, nuclear reactions play a great role in understanding the formation of our universe.The reaction 13C(α,n)16O is considered to be the main source of neutrons for the s process at low temperatures in low mass stars in the asymptotic giant branch. Many problems exist in analyzing this reaction using conventional experimental methods; therefore, we aimed to obtain and analyze data from the a +13C resonance elastic scattering reaction at small angles and low energies using Thick Target Inverse Kinematic method (TTIK) at heavy ion accelerator DC-60

Study of the A+13C interaction at heavy ION acceleration DC-60

In astrophysics, nuclear reactions play a great role in understanding the formation of our universe.The reaction 13C(α,n)16O is considered to be the main source of neutrons for the s process at low temperatures in low mass stars in the asymptotic giant branch. Many problems exist in analyzing this reaction using conventional experimental methods; therefore, we aimed to obtain and analyze data from the a +13C resonance elastic scattering reaction at small angles and low energies using Thick Target Inverse Kinematic method (TTIK) at heavy ion accelerator DC-60

Structure of 9^9C through proton resonance scattering with Texas Active Target detector

International audienceBackground: Level structure of the most neutron-deficient nucleon-bound carbon isotope, C9, is not well known. Definitive spin-parity assignments are only available for two excited states. No positive-parity states have been conclusively identified so far and the location of the sd shell in the A=9, T=3/2 isospin quadruplet is not known. Purpose: We have studied the level structure of exotic nucleus C9 at excitation energies below 6.4 MeV. Methods: Excited states in C9 were populated in B8+p resonance elastic scattering and excitation functions were measured using the active target approach. Results: Two excited states in C9 were conclusively observed, and R-matrix analysis of the excitation functions was performed to make the spin-parity assignments. The first positive-parity state in the A=9, T=3/2 nuclear system, the 5/2+ resonance at 4.3 MeV, has been identified. Conclusions: The new 5/2+ state at 4.3 MeV in C9 is a single-particle ℓ=0 broad resonance and it determines the energy of the 2s shell. The 2s shell in this exotic nucleus appears well within the region dominated by the p-shell states