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1. ⁴⁰ Ar proposed as probe of neutron-induced reactions in a high-density stellar-like plasma at the National Ignition Facility

   https://doi.org/10.1051/epjconf/202327913004  

   Paul, M.; Sahoo, R. N.; Tessler, M.; Jeet, J.; Velsko, C.; Zylstra, A.; Avila, M.; Dickerson, C.; Fougères, C.; Jayatissa, H.; et al (January 2023, EPJ Web of Conferences)

   Freeman, S.; Lederer-Woods, C.; Manna, A.; Mengoni, A. (Ed.)

   The thermodynamical conditions and the neutron density produced in a laser-induced implosion of a deuterium-tritium (DT) filled capsule at the National Ignition Facility (NIF) are the closest laboratory analog of stellar conditions. We plan to investigate neutron-induced reactions on 40 Ar, namely the 40 Ar( n , 2 n ) 39 Ar( t 1/2 =268 y), the 40 Ar( n , γ) 41 Ar(110 min) and the potential rapid two-neutron capture reaction 40 Ar(2 n , γ) 42 Ar(33 y) in an Ar-loaded DT capsule. The chemical inertness of noble gas Ar enables reliable collection of the reaction products. 

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2. First application of a liquid argon time projection chamber for the search for intranuclear neutron-antineutron transitions and annihilation in ⁴⁰ Ar using the MicroBooNE detector

   https://doi.org/10.1088/1748-0221/19/07/P07032  

   Abratenko, P; Alterkait, O; Andrade_Aldana, D; Arellano, L; Asaadi, J; Ashkenazi, A; Balasubramanian, S; Baller, B; Barr, G; Barrow, D; et al (July 2024, Journal of Instrumentation)

   Abstract We present a novel methodology to search for intranuclear neutron-antineutron transition (n⟶n̅) followed byn̅-nucleon annihilation within an⁴⁰Ar nucleus, using the MicroBooNE liquid argon time projection chamber (LArTPC) detector. A discovery of n⟶n̅transition or a new best limit on the lifetime of this process would either constitute physics beyond the Standard Model or greatly constrain theories of baryogenesis, respectively. The approach presented in this paper makes use of deep learning methods to select n⟶n̅events based on their unique features and differentiate them from cosmogenic backgrounds. The achieved signal and background efficiencies are (70.22 ± 6.04)% and (0.0020 ± 0.0003)%, respectively. A demonstration of a search is performed with a data set corresponding to an exposure of 3.32 ×10²⁶neutron-years, and where the background rate is constrained through direct measurement, assuming the presence of a negligible signal. With this approach, no excess of events over the background prediction is observed, setting a demonstrative lower bound on the n⟶n̅lifetime in⁴⁰Ar of τ_m≳ 1.1×10²⁶years, and on the free n⟶n̅transition time of τ_n⟶n̅≳ 2.6×10⁵s, each at the 90% confidence level. This analysis represents a first-ever proof-of-principle demonstration of the ability to search for this rare process in LArTPCs with high efficiency and low background. 

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3. Fine-structure Transitions of Ne ⁺ , Ar ⁺ , Ne ²⁺ , and Ar ²⁺ Induced by Collisions with Atomic Hydrogen

   https://doi.org/10.3847/1538-4357/ad0e77  

   Yan, Pei-Gen; Babb, James F (January 2024, The Astrophysical Journal)

   Abstract We calculate cross sections for fine-structure transitions of Ne⁺, Ar⁺, Ne²⁺, and Ar²⁺in collisions with atomic hydrogen by using quantum-mechanical methods. Relaxation rate coefficients are calculated for temperatures up to 10,000 K. The temperature-dependent critical densities for the relaxation of Ne⁺, Ar⁺, Ne²⁺, and Ar²⁺in collisions with H have been determined and compared to the critical densities for collisions with electrons. The present calculations will be useful for studies utilizing the infrared lines [Neii] 12.8, [Neiii] 15.6, [Neiii] 36.0, [Arii] 6.99, [Ariii] 8.99, and [Ariii] 21.8μm as diagnostics of, for example, planetary nebulae and star formation. 

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4. The Ocean's Global ³⁹ Ar Distribution Estimated With an Ocean Circulation Inverse Model

   https://doi.org/10.1029/2019GL082663  

   Holzer, Mark; DeVries, Timothy; Smethie, Jr., William (July 2019, Geophysical Research Letters)

   Abstract ³⁹Ar with its 269‐year half‐life has great potential for constraining ocean ventilation and transport. Here we estimate the distribution of³⁹Ar using a steady ocean circulation inverse model. Our estimates match available³⁹Ar measurements to within an absolute error of ∼9% modern argon without major biases. We find that³⁹Ar traces out the world ocean's ventilation pathways and that the³⁹Ar age Γ^Arand the ideal mean age have broadly similar large‐scale patterns. At the surface,³⁹Ar is close to saturated except at high latitudes. Undersaturation imparts a finite³⁹Ar age to surface waters relative to the atmosphere, with peak values exceeding 100 years in Antarctic waters. This reservoir age is propagated into the interior with Antarctic Bottom Water, elevating Γ^Arby ∼50 years in the deep Pacific and Indian oceans. Our estimates identify the large‐scale gradients and uncertainty patterns of³⁹Ar, thus providing guidance for future measurements. 

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5. Improved thermonuclear rate of ⁴² Ti( p , γ ) ⁴³ V and its astrophysical implication in the rp process

   https://doi.org/10.1051/0004-6361/202347054  

   Hou, S Q; Iliadis, C; Pignatari, M; Liu, J B; Trueman, T_C L; Li, J G; Xu, X X (September 2023, Astronomy & Astrophysics)

   Context.Accurate⁴²Ti(p,γ)⁴³V reaction rates are crucial for understanding the nucleosynthesis path of the rapid capture process (rpprocess) that occurs in X-ray bursts. Aims.We aim to improve the thermonuclear rates of⁴²Ti(p,γ)⁴³V based on more complete resonance information and a more accurate direct component, together with the recently released nuclear masses data. We also explore the impact of the newly obtained rates on therpprocess. Methods.We reevaluated the reaction rate of⁴²Ti(p,γ)⁴³V by the sum of the isolated resonance contribution instead of the Hauser-Feshbach statistical model. We used a Monte Carlo method to derive the associated uncertainties of new rates. The nucleosynthesis simulations were performed via the NuGrid post-processing code ppn. Results.The new rates differ from previous estimations due to the use of a series of updated resonance parameters and a direct S factor. Compared with the previous results from the Hauser-Feshbach statistical model, which assumes compound nucleus⁴³V with a sufficiently high-level density in the energy region of astrophysical interest, large differences exist over the entire temperature region ofrp-process interest, up to two orders of magnitude. We consistently calculated the photodisintegration rate using our new nuclear masses via the detailed balance principle, and found the discrepancies among the different reverse rates are much larger than those for the forward rate, up to ten orders of magnitude at the temperature of 10⁸K. Using a trajectory with a peak temperature of 1.95×10⁹K, we performed therp-process nucleosynthesis simulations to investigate the impact of the new rates. Our calculations show that the adoption of the new forward and reverse rates result in abundance variations for Sc and Ca of 128% and 49%, respectively, compared to the variations for the statistical model rates. On the other hand, the overall abundance pattern is not significantly affected. The results of using new rates also confirm that therp-process path does not bypass the isotope⁴³V. Conclusions.Our study found that the Hauser-Feshbach statistical model is inappropriate to the reaction rate evaluation for⁴²Ti(p,γ)⁴³V. The adoption of the new rates confirms that the reaction path of⁴²Ti(p,γ)⁴³V(p,γ)⁴⁴Cr(β⁺)⁴⁴V is a key branch of therpprocess in X-ray bursts. 

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