Measurement of 19F(p, γ)20Ne reaction suggests CNO breakout in first stars.

Proposed mechanisms for the production of calcium in the first stars (population III stars)-primordial stars that formed out of the matter of the Big Bang-are at odds with observations1. Advanced nuclear burning and supernovae were thought to be the dominant source of the calcium production seen in all stars2. Here we suggest a qualitatively different path to calcium production through breakout from the 'warm' carbon-nitrogen-oxygen (CNO) cycle through a direct experimental measurement of the 19F(p, γ)20Ne breakout reaction down to a very low energy point of 186 kiloelectronvolts, reporting a key resonance at 225 kiloelectronvolts. In the domain of astrophysical interest2, at around 0.1 gigakelvin, this thermonuclear 19F(p, γ)20Ne rate is up to a factor of 7.4 larger than the previous recommended rate3. Our stellar models show a stronger breakout during stellar hydrogen burning than previously thought1,4,5, and may reveal the nature of calcium production in population III stars imprinted on the oldest known ultra-iron-poor star, SMSS0313-67086. Our experimental result was obtained in the China JinPing Underground Laboratory7, which offers an environment with an extremely low cosmic-ray-induced background8. Our rate showcases the effect that faint population III star supernovae can have on the nucleosynthesis observed in the oldest known stars and first galaxies, which are key mission targets of the James Webb Space Telescope9.

Fast atom-trap analysis of 39Ar with isotope pre-enrichment.

We demonstrate fast analysis of 39Ar/Ar at the 10-16 level using a mass spectrometer for isotope pre-enrichment and an atom trap for counting. An argon gas sample first passes through a dipole mass separator that reduces the dominant isotope 40Ar by two orders of magnitude while preserving both the rare tracer isotope 39Ar and a minor stable isotope 38Ar for control purposes. Measurements of both natural and enriched samples with atom trap trace analysis demonstrate that the 39Ar/38Ar ratios change less than 10%, while the overall count rates of 39Ar are increased by one order of magnitude. By overcoming the analysis-speed bottleneck, this advance will benefit large-scale applications of 39Ar dating in the earth sciences, particularly for mapping ocean circulation.

First result from the Jinping Underground Nuclear Astrophysics experiment JUNA: precise measurement of the 92 keV 25Mg(p, γ)26Al resonance.

The 25Mg(p, γ)26Al reaction plays an important role in the study of cosmic 1.809 MeV γ-ray as a signature of ongoing nucleosynthesis in the Galaxy. At astrophysical temperature around 0.1 GK, the 25Mg(p, γ)26Al reaction rates are dominated by the 92 keV resonance capture process. We report a precise measurement of the 92 keV 25Mg(p, γ)26Al resonance in the day-one experiment at Jinping Underground Nuclear Astrophysics experiment (JUNA) facility in the China Jinping Underground Laboratory (CJPL). The resonance strength and ground state feeding factor are determined to be 3.8±0.3 ×10-10 eV and 0.66±0.04, respectively. The results are in agreement with those reported in the previous direct underground measurement within uncertainty, but with significantly reduced uncertainties. Consequently, we recommend new 25Mg(p, γ)26Al reaction rates which are by a factor of 2.4 larger than those adopted in REACLIB database at the temperature around 0.1 GK. The new results indicate higher production rates of 26gAl and the cosmic 1.809 MeV γ-ray. The implication of the new rates for the understanding of other astrophysical situations is also discussed.

Key elements of space charge compensation on a low energy high intensity beam injector.

Space charge effect (SCE) along the beam line will decrease beam quality. Space charge compensation (SCC) with extra gas injection is a high-efficiency method to reduce SCE. In this paper, we will report the experimental results on the beam profile, potential distribution, beam emittance, and beam transmission efficiency of a 35 keV∕90 mA H(+) beam and a 40 keV∕10 mA He(+) beam compensated by Ar∕Kr. The influence of gas type, gas flow, and injection location will be discussed. Emphasis is laid on the consideration of SCC when designing and commissioning a high intensity ion beam injector. Based on measured data, a new definition of space charge compensation degree is proposed.

The study of helicon plasma source.

Helicon plasma source is known as efficient generator of uniform and high density plasma. A helicon plasma source was developed for investigation of plasma neutralization and plasma lens in the Institute of Modern Physics in China. In this paper, the characteristics of helicon plasma have been studied by using Langmuir four-probe and a high argon plasma density up to 3.9x10(13) cm(-3) have been achieved with the Nagoya type III antenna at the conditions of the magnetic intensity of 200 G, working gas pressure of 2.8x10(-3) Pa, and rf power of 1200 W with a frequency of 27.12 MHz. In the experiment, the important phenomena have been found: for a given magnetic induction intensity, the plasma density became greater with the increase in rf power and tended to saturation, and the helicon mode appeared at the rf power between 200 and 400 W.