Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMeasurement of $^{34}$S($^{3}$He,p)$^{36}$Cl cross sections for early solar system nuclide enrichment
81
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Isotopic studies of meteorites have provided ample evidence for the presence of short-lived radionuclides (SLRs) with half-lives of less than 100 Myr at the time of the formation of the solar system. The origins of all known SLRs is heavily debated and remains uncertain, but the plausible scenarios can be broadly separated into either local production or outside injection of stellar nucleosynthesis products. The SLR production models are limited in part by reliance on nuclear theory for modeling reactions that lack experimental measurements. Reducing uncertainty on critical reaction cross sections can both enable more precise predictions and provide constraints on physical processes and environments in the early solar system. This goal led to the start of a campaign for measuring production cross sections for the SLR $^{36}$Cl, where Bowers et al. found higher cross sections for the ${}^{33}$S($alpha$,p)$^{36}$Cl reaction than were predicted by Hauser-Feshbach based nuclear reaction codes TALYS and NON-SMOKER. This prompted re-measurement of the reaction at five new energies within the energy range originally studied, resulting in data slightly above but in agreement with TALYS. Following this, efforts began to measure cross sections for the next most significant reaction for $^{36}$Cl production, $^{34}$S($^{3}$He,p)$^{36}$Cl. Activations were performed to produce 9 samples between 1.11 MeV/nucleon and 2.36 MeV/nucleon. These samples were subsequently measured with accelerator mass spectrometry at two labs. The resulting data suggest a sharper-than-expected rise in cross sections with energy, with peak cross sections up to 30% higher than predictions from TALYS.
rate research
Read More
Short-lived radionuclides (SLRs) with half-lives less than 100 Myr are known to have existed around the time of the formation of the solar system around 4.5 billion years ago. Understanding the production sources for SLRs is important for improving our understanding of processes taking place just after solar system formation as well as their timescales. Early solar system models rely heavily on calculations from nuclear theory due to a lack of experimental data for the nuclear reactions taking place. In 2013, Bowers et al. measured ${}^{36}$Cl production cross sections via the ${}^{33}$S($alpha$,p) reaction and reported cross sections that were systematically higher than predicted by Hauser-Feshbach codes. Soon after, a paper by Peter Mohr highlighted the challenges the new data would pose to current nuclear theory if verified. The ${}^{33}$S($alpha$,p)${}^{36}$Cl reaction was re-measured at 5 energies between 0.78 MeV/A and 1.52 MeV/A, in the same range as measured by Bowers et al., and found systematically lower cross sections than originally reported, with the new results in good agreement with the Hauser-Feshbach code TALYS. Loss of Cl carrier in chemical extraction and errors in determination of reaction energy ranges are both possible explanations for artificially inflated cross sections measured in the previous work.
Short-lived radionuclides (SLRs) with lifetimes tau < 100 Ma are known to have been extant when the Solar System formed over 4.5 billion years ago. Identifying the sources of SLRs is important for understanding the timescales of Solar System formation and processes that occurred early in its history. Extinct 36Cl (t_1/2 = 0.301 Ma) is thought to have been produced by interaction of solar energetic particles (SEPs), emitted by the young Sun, with gas and dust in the nascent Solar System. However, models that calculate SLR production in the early Solar System (ESS) lack experimental data for the 36Cl production reactions. We present here the first measurement of the cross section of one of the main 36Cl production reactions, 33S(alpha,p)36Cl, in the energy range 0.70 - 2.42 MeV/A. The cross section measurement was performed by bombarding a target and collecting the recoiled 36Cl atoms produced in the reaction, chemically processing the samples, and measuring the 36Cl/Cl ratio of the activated samples with accelerator mass spectrometry (AMS). The experimental results were found to be systematically higher than the cross sections used in previous local irradiation models and other Hauser-Feshbach calculated predictions. However, the effects of the experimentally measured cross sections on the modeled production of 36Cl in the early Solar System were found to be minimal. Reactions channels involving S targets dominate 36Cl production, but the astrophysical event parameters can dramatically change each reactions relative contribution.
The cross-sections and analyzing powers for $(p,n)$ reactions on ${}^{3}{rm He}$ and ${}^{4}{rm He}$ have been measured at a bombarding energy of $T_p$ = 346 MeV and reaction angles of $theta_{rm lab}$ = $9.4^{circ}$--$27^{circ}$. The energy transfer spectra for ${}^{3}{rm He}(p,n)$ at large $theta_{rm lab}$ ($ge$ $16^{circ}$) are dominated by quasielastic contributions, and can be reasonably reproduced by plane-wave impulse approximation (PWIA) calculations for quasielastic scattering. By contrast, the known $L$ = 1 resonances in ${}^{4}{rm Li}$ are clearly observed near the threshold in the ${}^{4}{rm He}(p,n)$ spectra. Because these contributions are remarkable at small angles, the energy spectra are significantly different from those expected for quasielastic scattering. The data are compared with the PWIA calculations, and it is found that the quasielastic contributions are dominant at large $theta_{rm lab}$ ($ge$ $22^{circ}$). The nuclear correlation effects on the quasielastic peak for ${}^{4}{rm He}(p,n)$ are also discussed.
Recent astronomical data have provided the primordial deuterium abundance with percent precision. As a result, Big Bang nucleosynthesis may provide a constraint on the universal baryon to photon ratio that is as precise as, but independent from, analyses of the cosmic microwave background. However, such a constraint requires that the nuclear reaction rates governing the production and destruction of primordial deuterium are sufficiently well known. Here, a new measurement of the $^2$H($p,gamma$)$^3$He cross section is reported. This nuclear reaction dominates the error on the predicted Big Bang deuterium abundance. A proton beam of 400-1650keV beam energy was incident on solid titanium deuteride targets, and the emitted $gamma$-rays were detected in two high-purity germanium detectors at angles of 55$^circ$ and 90$^circ$, respectively. The deuterium content of the targets has been obtained in situ by the $^2$H($^3$He,$p$)$^4$He reaction and offline using the Elastic Recoil Detection method. The astrophysical S-factor has been determined at center of mass energies between 265 and 1094 keV, addressing the uppermost part of the relevant energy range for Big Bang nucleosynthesis and complementary to ongoing work at lower energies. The new data support a higher S-factor at Big Bang temperatures than previously assumed, reducing the predicted deuterium abundance.
In this paper we report cross-section measurements for $Xi^-p$ elastic and inelastic scatterings at low energy using a scintillating fiber active target. Upper limit on the total cross-section for the elastic scattering was found to be 24 mb at 90% confidence level, and the total cross section for the $Xi^-ptoLambdaLambda$ reaction was found to be $4.3^{+6.3}_{-2.7}$ mb. We compare the results with currently competing theoretical estimates.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
