An official website of the United States government
Radiative double electron capture (RDEC), occurring when two electrons are captured to a projectile ion with the simultaneous emission of a single photon, has been investigated. RDEC can be considered as the time inverse process of double photoionization. Strong evidence for RDEC is found in F9++ N2collisions and additionally for one‐electron F8+for which the probability for the process is expected to be considerably smaller. Preliminary values for the cross sections for RDEC have been determined. A significant advantage of the gas target is that multiple‐collision effects seen for a solid target are avoided due to the single‐collision conditions that prevail for gas targets.
more »
« less
Single and double electron capture associated with target K‐shell ionization for F 7 + ,8 + ,9+ +Ar
Ratios for target Ar K‐shell ionization associated with single and double electron capture, as well as the ratios corresponding to total capture and the projectile K x rays, were determined for 1.8‐ to 2.2‐MeV/u F7 + ,8 + ,9+projectiles. This work was performed at Western Michigan University with the tandem Van de Graaff accelerator. Coincidences between emitted K‐shell X‐rays (both target and projectile) and the corresponding charge‐changed particles were observed. The F9+Ar K X‐ray coincidence ratios for double to single capture are found to well exceed unity over the limited energy range of the measurements. Possible explanations for this anomalous behavior are discussed.
more »
« less
- Award ID(s):
- 1707467
- PAR ID:
- 10453926
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- X-Ray Spectrometry
- Volume:
- 49
- Issue:
- 1
- ISSN:
- 0049-8246
- Format(s):
- Medium: X Size: p. 60-64
- Size(s):
- p. 60-64
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)We have measured differential yields for double capture and double capture accompanied by ionization in 75 keV p + Ar collisions. Data were taken for two different transverse projectile coherence lengths. A small effect of the projectile coherence properties on the yields were found for double capture, but not for double capture plus ionization. The results suggest that multiple projectile–target interactions can lead to a significant weakening of projectile coherence effects.more » « less
-
Context.An accurate28P(p,γ)29S reaction rate is crucial to defining the nucleosynthesis products of explosive hydrogen burning in ONe novae. Using the recently released nuclear mass of29S, together with a shell model and a direct capture calculation, we reanalyzed the28P(p,γ)29S thermonuclear reaction rate and its astrophysical implication. Aims.We focus on improving the astrophysical rate for28P(p,γ)29S based on the newest nuclear mass data. Our goal is to explore the impact of the new rate and associated uncertainties on the nova nucleosynthesis. Methods.We evaluated this reaction rate via the sum of the isolated resonance contribution instead of the previously used Hauser-Feshbach statistical model. The corresponding rate uncertainty at different energies was derived using a Monte Carlo method. Nova nucleosynthesis is computed with the 1D hydrodynamic code SHIVA. Results.The contribution from the capture on the first excited state at 105.64 keV in28P is taken into account for the first time. We find that the capture rate on the first excited state in28P is up to more than 12 times larger than the ground-state capture rate in the temperature region of 2.5 × 107K to 4 × 108K, resulting in the total28P(p,γ)29S reaction rate being enhanced by a factor of up to 1.4 at ~1 × 109K. In addition, the rate uncertainty has been quantified for the first time. It is found that the new rate is smaller than the previous statistical model rates, but it still agrees with them within uncertainties for nova temperatures. The statistical model appears to be roughly valid for the rate estimation of this reaction in the nova nucleosynthesis scenario. Using the 1D hydrodynamic code SHIVA, we performed the nucleosynthesis calculations in a nova explosion to investigate the impact of the new rates of28P(p,γ)29S. Our calculations show that the nova abundance pattern is only marginally affected if we use our new rates with respect to the same simulations but statistical model rates. Finally, the isotopes whose abundance is most influenced by the present28P(p,γ)29S uncertainty are28Si,33,34S,35,37Cl, and36Ar, with relative abundance changes at the level of only 3% to 4%.more » « less
-
Mattoon, C.M.; Vogt, R.; Escher, J.; Thompson, I. (Ed.)The cross-section of the thermal neutron capture41Ar(n,γ)42Ar(t1/2=32.9 y) reaction was measured by irradiating a40Ar sample at the high-flux reactor of Institut Laue-Langevin (ILL) Grenoble, France. The signature of the two-neutron capture has been observed by measuring the growth curve and identifying the 1524.6 keV γ-lines of the shorter-lived42K(12.4 h) β−daughter of42Ar. Our preliminary value of the41Ar(n,γ)42Ar thermal cross section is 240(80) mb at 25.3 meV. For the first time, direct counting of42Ar was performed using the ultra-high sensitivity technique of noble gas accelerator mass spectrometry (NOGAMS) at Argonne National Laboratory, USA.more » « less
-
Abstract The millimeter-wave spectrum of the SiP radical (X2Πi) has been measured in the laboratory for the first time using direct-absorption methods. SiP was created by the reaction of phosphorus vapor and SiH4in argon in an AC discharge. Fifteen rotational transitions (J+ 1 ←J) were measured for SiP in the Ω = 3/2 ladder in the frequency range 151–533 GHz, and rotational, lambda doubling, and phosphorus hyperfine constants determined. Based on the laboratory measurements, SiP was detected in the circumstellar shell of IRC+10216, using the Submillimeter Telescope and the 12 m antenna of the Arizona Radio Observatory at 1 mm and 2 mm, respectively. Eight transitions of SiP were searched: four were completely obscured by stronger features, two were uncontaminated (J= 13.5 → 12.5 and 16.5 → 15.5), and two were partially blended with other lines (J= 8.5 → 7.5 and 17.5 → 16.5). The SiP line profiles were broader than expected for IRC+10216, consistent with the hyperfine splitting. From non-LTE radiative transfer modeling, SiP was found to have a shell distribution with a radius ∼300R*, and an abundance, relative to H2, off∼ 2 × 10−9. From additional modeling, abundances of 7 × 10−9and 9 × 10−10were determined for CP and PN, respectively, both located in shells at 550–650R*. SiP may be formed from grain destruction, which liberates both phosphorus and silicon into the gas phase, and then is channeled into other P-bearing molecules such as PN and CP.more » « less
