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Register a new userDoppler-tuned Bragg Spectroscopy of Excited Levels in He-Like Uranium: a discussion of the uncertainty contributions
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Martino Trassinelli
Publication date
2009
fields
Physics
and research's language is
English
Authors
Martino Trassinelli
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We present the uncertainty discussion of a recent experiment performed at the GSI storage ring ESR for the accurate energy measurement of the He-like uranium 1s2p3P2- 1s2s3S1 intra-shell transition. For this propose we used a Johann-type Bragg spectrometer that enables to obtain a relative energy measurement between the He-like uranium transition, about 4.51 keV, and a calibration x-ray source. As reference, we used the Ka fluorescence lines of zinc and the Li-like uranium 1s22p2P3/2 - 1 s22s 2S1/2 intra-shell transition from fast ions stored in the ESR. A comparison of the two different references, i.e., stationary and moving x-ray source, and a discussion of the experimental uncertainties is presented.
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We present the first observation of the 1s2p 3P2 ? 1s2s 3S1 transition in He-like uranium. The experiment was performed at the internal gas-jet target of the ESR storage ring at GSI exploiting a Bragg crystal spectrometer and a germanium solid state detector. Using the 1s2 2p 2P3/2 ? 1s2 2s 2S1/2 transition in Li-like uranium as reference and the deceleration capabilities of the ESR storage rings, we obtained the first evaluation of the He-like heavy ion intra-shell transition energy.
The average pixel distance as well as the relative orientation of an array of 6 CCD detectors have been measured with accuracies of about 0.5 nm and 50 $mu$rad, respectively. Such a precision satisfies the needs of modern crystal spectroscopy experiments in the field of exotic atoms and highly charged ions. Two different measurements have been performed by illuminating masks in front of the detector array by remote sources of radiation. In one case, an aluminum mask was irradiated with X-rays and in a second attempt, a nanometric quartz wafer was illuminated by a light bulb. Both methods gave consistent results with a smaller error for the optical method. In addition, the thermal expansion of the CCD detectors was characterized between -105 C and -40 C.
Accurate photodissociation cross sections have been computed for transitions from the X $^1Sigma^+$ ground electronic state of CS to six low-lying excited electronic states. New ab initio potential curves and transition dipole moment functions have been obtained for these computations using the multi-reference configuration interaction approach with the Davidson correction (MRCI+Q) and aug-cc-pV6Z basis sets. State-resolved cross sections have been computed for transitions from nearly the full range of rovibrational levels of the X $^1Sigma^+$ state and for photon wavelengths ranging from 500 $text{AA}$ to threshold. Destruction of CS via predissociation in highly excited electronic states originating from the rovibrational ground state is found to be unimportant. Photodissociation cross sections are presented for temperatures in the range between 1000 and 10,000 K, where a Boltzmann distribution of initial rovibrational levels is assumed. Applications of the current computations to various astrophysical environments are briefly discussed focusing on photodissociation rates due to the standard interstellar and blackbody radiation fields.
Binding energies of high-L Rydberg states (L^3 7) of Th2+ with n=27-29 were studied using the Resonant Excitation Stark Ionization Spectroscopy (RESIS) method. The core of the Th2+ Rydberg ion is the Fr-like ion Th3+ whose ground state is a 5 2F5/2 level. The large core angular momentum results in a complex Rydberg fine structure pattern consisting of six levels for each value of L that is only partially resolved in the RESIS excitation spectrum. The pattern is further complicated, especially for the relatively low L levels, by strong non-adiabatic effects due to the low-lying 6d levels. Analysis of the observed RESIS spectra leads to determination of five properties of the Th3+ ion: its electric quadrupole moment, Q = 0.54(4), its adiabatic scalar and tensor dipole polarizabilities, ad,0 = 15.42(17) and ad,2 = -3.6(1.3), and the dipole matrix elements connecting the ground 52F5/2 level to the low lying 62D3/2 and 62D5/2 levels, |<52F5/2||D||62D3/2>| = 1.435(10) and |<52F5/2||D||62D5/2>| = 0.414(24). All are in atomic units. These are compared with theoretical calculations.
A general formalism is used to express the long-range potential energies in inverse powers of the separation distance between two like atomic or molecular systems with $P$ symmetries. The long-range molecular interaction coefficients are calculated for the molecular symmetries $Delta$, $Pi$, and $Sigma$, arising from the following interactions: He($2 ^1P$)--He($2 ^1P$), He($2 ^1P$)--He($2 ^3P$), and He($2 ^3P$)--He($2 ^3P$). The electric quadrupole-quadrupole term, $C_{5}$, the van der Waals (dispersion) term $C_{6}$, and higher-order terms, $C_{8}$, and $C_{10}$, are calculated textit{ab initio} using accurate variational wave functions in Hylleraas coordinates with finite nuclear mass effects. A comparison is made with previously published results where available.
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