The 12C(α, γ)16O reaction and stellar helium burning

The cross section for the reaction ¹²C(α, γ)¹⁶O has been measured for a range of c.m. energies extending from 1.41 MeV to 2.94 MeV, by using ¹²C targets of high isotopic purity, large NaI(T1) crystals, and the time-of-flight technique for the suppression of prompt neutron background and time-independent background. Gamma-ray angular distributions were measured at c.m. energies of 2.18, 2.42, 2.56 and 2.83 MeV. By means of theoretical fits, which include the coherent effects of the 1^? states of ¹⁶O at 7.12 MeV, 9.60 MeV, and those at higher energies, the electric-dipole portion of the cross section at astrophysically relevant energies has been determined. A three-level R-matrix parametrization of the data yields an S-factor at E_c.m. = 0.3 MeV, S(0.3 MeV) = 0.14^+0.14_?0.12 MeV · b. A “hybrid” R-matrix optical-m parameterization yields S(0.3 MeV) = 0.08^+0.05_?0.04 MeV · b. This S-factor is of crucial importance in determining the abundances of ¹²C and ¹⁶O at the end of helium burning in stars.     

Ice forming activity and the surface properties of nucleating materials

Zusammenfassung Die bereits früher beschriebenen Messungen [1] der Eiskeimbildungsaktivität von Silberjodid in unterkühlten Wolken aus verschieden konzentrierten wässerigen NaCl-Lösungen ergeben zusammen mit neueren Protonspinresonanz-Untersuchungen von an eiskeimbildenden Stoffen adsorbierten Wasserschichten [5] neue Aspekte des Eiskeimbildungsmechanismus: Aus Tabelle 1 lässt sich entnehmen, dass die Aktivität weitgehend von der Wasserdampfsättigung bezüglichEis abhängt, die für das Wachsen eines Eiskeimes verantwortlich ist; von der Wasserdampfsättigung bezüglichWasser hängt hingegen die Dicke der an der eiskeimaktiven Substanz adsorbierten Wasserschicht ab, die dann ihrerseits die Wahrscheinlichkeit der Bildung von Eiskeimen beeinflussen dürfte. Die Annahme, dass die Bildung der Eiskeime in der adsorbierten Wasserchicht stattfindet, wird durch das in Figur 1 gezeigte neue Resultat des Protonspinresonanz-Experimentes an CuO gestützt, das mit Hilfe empfindlicherer Apparaturen gewonnen wurde.

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Paper presented at the International Conference on Cloud Physics, Canberra and Sydney. Australia, September 11–20, 1961.     

Buchbesprechungen

Ohne Zusammenfassung

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Book revies

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Notices bibliographiques

     

QQG hybrid mesons in the MIT bag model

We suggest that hybrid (q$\text{q}$g) mesons could exist with rather light masses. The spectrum of the ground state nonets, J^PC = (0, 1, 2)^?+; 1^?? is calculated in the MIT bag model including O(α_s) energy shifts. We discuss hadronic transitions among these states, consider their possible production at LEAR and SPEAR and indicate some interesting decay signatures.     

Computer simulation of a nitrogen ICP discharge

A theoretical model for calculating radial and axial temperature profiles in a nitrogen ICP discharge was improved to include the normal distribution of magnetic flux density and a three-gas flow pattern commonly used in spectrochemical applications. Calculated radial temperature and particle velocity distributions for nitrogen ICP discharges compare well with experimentally obtained data.     

The EPR and LMR spectra of the DO2 radical: Determination of ground-state parameters

The detection of lines in both the gas phase EPR spectrum at 9 GHz and the far-infrared LMR spectrum of the DO₂ radical is reported. The measurements are fitted with an appropriate Hamiltonian and several parameters for the molecule in the $\text{X}\text{?}{}^2\text{A″}$ state are determined. The majority of the transitions in the EPR spectrum are K-type doubling transitions and involve the a-component of the electric dipole moment. However the observation of one b-type transition (5₀₅-4₁₄) permits the determination of the off-diagonal component of the spin-rotation tensor, ?_ab, and an estimate of the relative magnitudes of the a- and b-components of the dipole moment. A combination of the parameters for HO₂ with those for DO₂ leads to a better understanding of the properties of the molecule. In particular, the r₀ molecular geometry has been determined more reliably than previously to be $\text{r}{}_0\text{(OH) = 0.9774}\text{A}\text{?}$, $\text{r}{}_0\text{(OO) = 1.3339}\text{A}\text{?}$, ∠HOO = 104.15°.