Open AccessFeature PaperArticle
Combining Multiconfiguration and Perturbation Methods: Perturbative Estimates of Core–Core Electron Correlation Contributions to Excitation Energies in Mg-Like Iron
Atoms 2017, 5(1), 3; doi:10.3390/atoms5010003 -
Abstract
Large configuration interaction (CI) calculations can be performed if part of the interaction is treated perturbatively. To evaluate the combined CI and perturbative method, we compute excitation energies for the 3l3l, 3l4l and 3
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Large configuration interaction (CI) calculations can be performed if part of the interaction is treated perturbatively. To evaluate the combined CI and perturbative method, we compute excitation energies for the 3l3l, 3l4l and 3s5l states in Mg-like iron. Starting from a CI calculation including valence and core–valence correlation effects, it is found that the perturbative inclusion of core–core electron correlation halves the mean relative differences between calculated and observed excitation energies. The effect of the core–core electron correlation is largest for the more excited states. The final relative differences between calculated and observed excitation energies is 0.023%, which is small enough for the calculated energies to be of direct use in line identifications in astrophysical and laboratory spectra. Full article
Open AccessArticle
An Investigation on the He(1s2s22S) Resonance in Debye Plasmas
Atoms 2017, 5(1), 2; doi:10.3390/atoms5010002 -
Abstract
The effect of Debye plasma on the 1s2s22S resonance states in the scattering of electron from helium atom has been investigated within the framework of the stabilization method. The interactions among the charged particles in Debye plasma
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The effect of Debye plasma on the 1s2s22S resonance states in the scattering of electron from helium atom has been investigated within the framework of the stabilization method. The interactions among the charged particles in Debye plasma have been modelled by Debye–Huckel potential. The 1s2s excited state of the helium atom has been treated as consisting of a He+ ionic core plus an electron moving around. The interaction between the core and the electron has then been modelled by a model potential. It has been found that the background plasma environment significantly affects the resonance states. To the best of our knowledge, such an investigation of 1s2s22S resonance states of the electron–helium system embedded in Debye plasma environment is the first reported in the literature. Full article
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Open AccessEditorial
Acknowledgement to Reviewers of Atoms in 2016
Atoms 2017, 5(1), 1; doi:10.3390/atoms5010001 -
Abstract The editors of Atoms would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2016.[...] Full article
Open AccessFeature PaperArticle
Spectrum and Energy Levels of Four-Times Ionized Yttrium (Y V)
Atoms 2016, 4(4), 31; doi:10.3390/atoms4040031 -
Abstract
The analysis of the spectrum of four-times-ionized yttrium, Y V, was extended to provide a large number of new spectrum lines and energy levels. The new analysis is based on spectrograms made with sliding-spark discharges on 10.7 m normal- and grazing-incidence spectrographs. The
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The analysis of the spectrum of four-times-ionized yttrium, Y V, was extended to provide a large number of new spectrum lines and energy levels. The new analysis is based on spectrograms made with sliding-spark discharges on 10.7 m normal- and grazing-incidence spectrographs. The measurements cover the region 184–2549 Å. The results revise levels for this spectrum by Zahid-Ali et al. (1975) and by Ateqad et al. (1984). Five hundred and seventy lines were classified as transitions between 23 odd-parity and 90 even-parity levels. The 4s24p5, 4s4p6, 4s24p44d, 5s, 5p, 5d, 6s configurations are now complete. Results for the 4s24p46d and 7s configurations are tentative. Ritz-type wavelengths were determined from the optimized energy levels, with uncertainties as low as ±0.0004 Å. The observed configurations were interpreted with Hartree-Fock calculations and least-squares fits of the energy parameters to the observed levels. Oscillator strengths for all classified lines were calculated with the fitted parameters. The results are compared with values for the level energies, percentage compositions, and transition probabilities from recent ab initio theoretical calculations. The ionization energy was revised to 607,760 ± 300 cm−1 (75.353 ± 0.037 eV). Full article
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Open AccessFeature PaperArticle
Cross Sections and Rate Coefficients for Vibrational Excitation of HeH+ Molecule by Electron Impact
Atoms 2016, 4(4), 30; doi:10.3390/atoms4040030 -
Abstract
Cross sections and thermally-averaged rate coefficients for vibration (de-)excitation of HeH+ by an electron impact are computed using a theoretical approach that combines the multi-channel quantum defect theory and the UK R-matrix code. Fitting formulas with a few numerical parameters are derived
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Cross sections and thermally-averaged rate coefficients for vibration (de-)excitation of HeH+ by an electron impact are computed using a theoretical approach that combines the multi-channel quantum defect theory and the UK R-matrix code. Fitting formulas with a few numerical parameters are derived for the obtained rate coefficients. The interval of applicability of the formulas is from 40 to 10,000 K. Full article
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Open AccessFeature PaperArticle
Rovibrationally Resolved Time-Dependent Collisional-Radiative Model of Molecular Hydrogen and Its Application to a Fusion Detached Plasma
Atoms 2016, 4(4), 29; doi:10.3390/atoms4040029 -
Abstract
A novel rovibrationally resolved collisional-radiative model of molecular hydrogen that includes 4,133 rovibrational levels for electronic states whose united atom principal quantum number is below six is developed. The rovibrational X1Σg+ population distribution in a SlimCS fusion demo detached
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A novel rovibrationally resolved collisional-radiative model of molecular hydrogen that includes 4,133 rovibrational levels for electronic states whose united atom principal quantum number is below six is developed. The rovibrational X1Σg+ population distribution in a SlimCS fusion demo detached divertor plasma is investigated by solving the model time dependently with an initial 300 K Boltzmann distribution. The effective reaction rate coefficients of molecular assisted recombination and of other processes in which atomic hydrogen is produced are calculated using the obtained time-dependent population distribution. Full article
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Open AccessArticle
Decoherence in Excited Atoms by Low-Energy Scattering
Atoms 2016, 4(4), 28; doi:10.3390/atoms4040028 -
Abstract
We describe a new mechanism of decoherence in excited atoms as a result of thermal particles scattering by the atomic nucleus. It is based on the idea that a single scattering will produce a sudden displacement of the nucleus, which will be perceived
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We describe a new mechanism of decoherence in excited atoms as a result of thermal particles scattering by the atomic nucleus. It is based on the idea that a single scattering will produce a sudden displacement of the nucleus, which will be perceived by the electron in the atom as an instant shift in the electrostatic potential. This will leave the atom’s wave-function partially projected into lower-energy states, which will lead to decoherence of the atomic state. The decoherence is calculated to increase with the excitation of the atom, making observation of the effect easier in Rydberg atoms. We estimate the order of the decoherence for photons and massive particles scattering, analyzing several commonly presented scenarios. Our scheme can be applied to the detection of weakly-interacting particles, like those which may be the constituents of Dark Matter, the interaction of which was calculated to have a more prominent effect that the background radiation. Full article
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Open AccessArticle
Positron-Hydrogen Scattering, Annihilation, and Positronium Formation
Atoms 2016, 4(4), 27; doi:10.3390/atoms4040027 -
Abstract
In previous papers (Bhatia A.K. 2007, 2012) a hybrid theory for the scattering of electrons from a hydrogenic system was developed and applied to calculate scattering phase shifts, Feshbach resonances, and photoabsorption processes. This approach is now being applied to the scattering of
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In previous papers (Bhatia A.K. 2007, 2012) a hybrid theory for the scattering of electrons from a hydrogenic system was developed and applied to calculate scattering phase shifts, Feshbach resonances, and photoabsorption processes. This approach is now being applied to the scattering of positrons from hydrogen atoms. Very accurate phase shifts, using the Feshbach projection operator formalism, were calculated previously (Bhatia A.K. et al. 1971 and Bhatia et al. 1974a). The present results, obtained using shorter expansions in the correlation function, along with long-range correlations in the Schrödinger equation, agree very well with the results obtained earlier. The scattering length is also calculated and the present results are compared with the previous results. Annihilation cross-sections, and positronium formation cross-sections, calculated in the distorted-wave approximation, are also presented. Full article
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Open AccessArticle
Evaluation of State-Resolved Reaction Probabilities and Their Application in Population Models for He, H, and H2
Atoms 2016, 4(4), 26; doi:10.3390/atoms4040026 -
Abstract
Population models are a prerequisite for performing qualitative analysis of population densities measured in plasmas or predicting the dependence of plasma emission on parameter variations. Models for atomic helium and hydrogen as well as molecular hydrogen in low-pressure plasmas are introduced. The cross-sections
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Population models are a prerequisite for performing qualitative analysis of population densities measured in plasmas or predicting the dependence of plasma emission on parameter variations. Models for atomic helium and hydrogen as well as molecular hydrogen in low-pressure plasmas are introduced. The cross-sections and transition probabilities used as input in the atomic models are known very accurately, and thus a benchmark of these models against experiments is very successful. For H2, in contrast, significant deviations exist between reaction probabilities taken from different literature sources. The reason for this is the more complex internal structure of molecules compared to atoms. Vibrationally resolved models are applied to demonstrate how these deviations affect the model results. Steps towards a consistent input data set are presented: vibrationally resolved Franck–Condon factors, transition probabilities, and ionization cross-sections have been calculated and are available now. Additionally, ro-vibrational models for selected transitions are applied successfully to low-density, low-temperature plasmas. For further improving the accuracy of population models for H2, however, it is necessary to establish a comprehensive data set for ro-vibrationally resolved excitation cross-sections based on the most recent calculation techniques. Full article
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Open AccessArticle
Decoherence Spectroscopy for Atom Interferometry
Atoms 2016, 4(3), 25; doi:10.3390/atoms4030025 -
Abstract
Decoherence due to photon scattering in an atom interferometer was studied as a function of laser frequency near an atomic resonance. The resulting decoherence (contrast-loss) spectra will be used to calibrate measurements of tune-out wavelengths that are made with the same apparatus. To
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Decoherence due to photon scattering in an atom interferometer was studied as a function of laser frequency near an atomic resonance. The resulting decoherence (contrast-loss) spectra will be used to calibrate measurements of tune-out wavelengths that are made with the same apparatus. To support this goal, a theoretical model of decoherence spectroscopy is presented here along with experimental tests of this model. Full article
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Open AccessArticle
Scalar Aharonov–Bohm Phase in Ramsey Atom Interferometry under Time-Varying Potential
Atoms 2016, 4(3), 23; doi:10.3390/atoms4030023 -
Abstract
In a Ramsey atom interferometer excited by two electromagnetic fields, if atoms are under a time-varying scalar potential during the interrogation time, the phase of the Ramsey fringes shifts owing to the scalar Aharonov–Bohm effect. The phase shift was precisely examined using a
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In a Ramsey atom interferometer excited by two electromagnetic fields, if atoms are under a time-varying scalar potential during the interrogation time, the phase of the Ramsey fringes shifts owing to the scalar Aharonov–Bohm effect. The phase shift was precisely examined using a Ramsey atom interferometer with a two-photon Raman transition under the second-order Zeeman potential, and a formula for the phase shift was derived. Using the derived formula, the frequency shift due to the scalar Aharonov–Bohm effect in the frequency standards utilizing the Ramsey atom interferometer was discussed. Full article
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Open AccessArticle
Electron Impact Excitation of F-Like W LXVI
Atoms 2016, 4(3), 24; doi:10.3390/atoms4030024 -
Abstract
Electron impact excitation collision strengths are calculated for all transitions among 113 levels of the 2s22p5, 2s2p6, 2s22p43, 2s2p53, and 2p63 configurations of F-like
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Electron impact excitation collision strengths are calculated for all transitions among 113 levels of the 2s22p5, 2s2p6, 2s22p43, 2s2p53, and 2p63 configurations of F-like W LXVI. For this purpose, Dirac Atomic R-matrix Code (DARC) has been adopted and results are listed over a wide energy range of 1000 to 6000 Ryd. For comparison purposes, analogous calculations have also been performed with the Flexible Atomic Code (FAC), and the results obtained are comparable with those from DARC. Full article
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Open AccessArticle
Atomic Structure Calculations and Study of Plasma Parameters of Al-Like Ions
Atoms 2016, 4(3), 22; doi:10.3390/atoms4030022 -
Abstract
In the present paper, the spectroscopic properties and plasma characteristics of Al-like ions are investigated in an extensive and detailed manner by adopting the GRASP2K package based on fully relativistic Multi-Configuration Dirac–Hartree–Fock (MCDHF) wave-functions in the active space approximation. We have presented energy
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In the present paper, the spectroscopic properties and plasma characteristics of Al-like ions are investigated in an extensive and detailed manner by adopting the GRASP2K package based on fully relativistic Multi-Configuration Dirac–Hartree–Fock (MCDHF) wave-functions in the active space approximation. We have presented energy levels for Al-like ions for Valence-Valence (VV) and Core-Valence (CV) correlations under the scheme of active space. We have also provided radiative data for E1 transitions for Al-like ions and studied the variation of the transition wavelength and transition probability for electric dipole (E1) Extreme Ultraviolet (EUV) transitions with nuclear charge. Our calculated energy levels and transition wavelengths match well with available theoretical and experimental results. The discrepancies of the GRASP2K code results with CIV3 and RMPBT (Relativistic Many Body Perturbation Theory) results are also discussed. The variations of the line intensity ratio, electron density, plasma frequency and plasma skin depth with plasma temperature and nuclear charge are discussed graphically in detail for optically thin plasma in Local Thermodynamic Equilibrium (LTE). We believe that our obtained results may be beneficial for comparisons and in fusion and astrophysical plasma research. Full article
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Open AccessArticle
Analysis of Polarizability Measurements Made with Atom Interferometry
Atoms 2016, 4(3), 21; doi:10.3390/atoms4030021 -
Abstract
We present revised measurements of the static electric dipole polarizabilities of K, Rb, and Cs based on atom interferometer experiments presented in [Phys. Rev. A 2015, 92, 052513] but now re-analyzed with new calibrations for the magnitude and geometry of the applied electric
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We present revised measurements of the static electric dipole polarizabilities of K, Rb, and Cs based on atom interferometer experiments presented in [Phys. Rev. A 2015, 92, 052513] but now re-analyzed with new calibrations for the magnitude and geometry of the applied electric field gradient. The resulting polarizability values did not change, but the uncertainties were significantly reduced. Then, we interpret several measurements of alkali metal atomic polarizabilities in terms of atomic oscillator strengths fik, Einstein coefficients Aik, state lifetimes τk, transition dipole matrix elements Dik, line strengths Sik, and van der Waals C6 coefficients. Finally, we combine atom interferometer measurements of polarizabilities with independent measurements of lifetimes and C6 values in order to quantify the residual contribution to polarizability due to all atomic transitions other than the principal ns-npJ transitions for alkali metal atoms. Full article
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Open AccessArticle
Neutrons and Gamma-Ray Dose Calculations in Subcritical Reactor Facility Using MCNP
Atoms 2016, 4(3), 20; doi:10.3390/atoms4030020 -
Abstract
In nuclear experimental, training and teaching laboratories such as a subcritical reactor facility, huge measures of external radiation doses could be caused by neutron and gamma radiation. It becomes imperative to place the health and safety of staff and students in the reactor
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In nuclear experimental, training and teaching laboratories such as a subcritical reactor facility, huge measures of external radiation doses could be caused by neutron and gamma radiation. It becomes imperative to place the health and safety of staff and students in the reactor facility under proper scrutiny. The protection of these individuals against ionization radiation is facilitated by expected dose mapping and shielding calculations. A three-dimensional (3D) Monte Carlo model was developed to calculate the dose rate from neutrons and gamma, using the ANSI/ANS-6.1.1 and the ICRP-74 flux-to-dose conversion factors. Estimation for the dose was conducted across 39 areas located throughout the reactor hall of the facility and its training platform. It was found that the range of the dose rate magnitude is between 7.50 E−01 μSv/h and 1.96 E−04 μSv/h in normal operation mode. During reactor start-up/shut-down mode, it was observed that a large area of the facility can experience exposure to a significant radiation field. This field ranges from 2.99 E+03 μSv/h to 3.12 E+01 μSv/h. There exists no noticeable disparity between results using the ICRP-74 or ANSI/ANS-6.1.1 flux-to-dose rate conversion factors. It was found that the dose rate due to gamma rays is higher than that of neutrons. Full article
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Open AccessArticle
Prospects for Precise Measurements with Echo Atom Interferometry
Atoms 2016, 4(3), 19; doi:10.3390/atoms4030019 -
Abstract
Echo atom interferometers have emerged as interesting alternatives to Raman interferometers for the realization of precise measurements of the gravitational acceleration g and the determination of the atomic fine structure through measurements of the atomic recoil frequency ωq. Here we review
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Echo atom interferometers have emerged as interesting alternatives to Raman interferometers for the realization of precise measurements of the gravitational acceleration g and the determination of the atomic fine structure through measurements of the atomic recoil frequency ωq. Here we review the development of different configurations of echo interferometers that are best suited to achieve these goals. We describe experiments that utilize near-resonant excitation of laser-cooled rubidium atoms by a sequence of standing wave pulses to measure ωq with a statistical uncertainty of 37 parts per billion (ppb) on a time scale of ∼50 ms and g with a statistical precision of 75 ppb. Related coherent transient techniques that have achieved the most statistically precise measurements of atomic g-factor ratios are also outlined. We discuss the reduction of prominent systematic effects in these experiments using off-resonant excitation by low-cost, high-power lasers. Full article
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Open AccessArticle
A Wigner Function Approach to Coherence in a Talbot-Lau Interferometer
Atoms 2016, 4(2), 18; doi:10.3390/atoms4020018 -
Abstract
Using a thermal gas, we model the signal of a trapped interferometer. This interferometer uses two short laser pulses, separated by time T, which act as a phase grating for the matter waves. Near time 2T, there is an echo
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Using a thermal gas, we model the signal of a trapped interferometer. This interferometer uses two short laser pulses, separated by time T, which act as a phase grating for the matter waves. Near time 2T, there is an echo in the cloud’s density due to the Talbot-Lau effect. Our model uses the Wigner function approach and includes a weak residual harmonic trap. The analysis shows that the residual potential limits the interferometer’s visibility, shifts the echo time of the interferometer, and alters its time dependence. Loss of visibility can be mitigated by optimizing the initial trap frequency just before the interferometer cycle begins. Full article
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Open AccessArticle
Series of Broad Resonances in Atomic Three-Body Systems
Atoms 2016, 4(2), 17; doi:10.3390/atoms4020017 -
Abstract
We re-examine the series of resonances found earlier in atomic three-body systems by solving the Faddeev-Merkuriev integral equations. These resonances are rather broad and line up at each threshold with gradually increasing gaps. This lining up takes place in the same way for
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We re-examine the series of resonances found earlier in atomic three-body systems by solving the Faddeev-Merkuriev integral equations. These resonances are rather broad and line up at each threshold with gradually increasing gaps. This lining up takes place in the same way for all thresholds and is irrespective of the spatial symmetry. We relate these resonances to the Gailitis mechanism, which is a consequence of the polarization potential. Full article
Open AccessArticle
Multi-Configuration Dirac–Hartree–Fock (MCDHF) Calculations for B-Like Ions
Atoms 2016, 4(2), 13; doi:10.3390/atoms4020013 -
Abstract
Relativistic configuration interaction results are presented for several B-like ions (Ge XXVIII, Rb XXXIII, Sr XXXIV, Ru XL, Sn XLVI, and Ba LII) using the multi-configuration Dirac–Hartree–Fock (MCDHF) method. The calculations are carried out in the active space approximation with the inclusion of
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Relativistic configuration interaction results are presented for several B-like ions (Ge XXVIII, Rb XXXIII, Sr XXXIV, Ru XL, Sn XLVI, and Ba LII) using the multi-configuration Dirac–Hartree–Fock (MCDHF) method. The calculations are carried out in the active space approximation with the inclusion of the Breit interaction, the finite nuclear size effect, and quantum electrodynamic corrections. Results for fine structure energy levels for 1s22s22p and 2s2p2 configurations relative to the ground state are reported. The transition wavelengths, transition probabilities, line strengths, and absorption oscillator strengths for 2s22p–2s2p2 electric dipole (E1) transitions are calculated. Both valence and core-valence correlation effects were accounted for through single-double multireference (SD-MR) expansions to increasing sets of active orbitals. Comparisons are made with the available data and good agreement is achieved. The values calculated using core–valence correlation are found to be very close to other theoretical and experimental values. The behavior of oscillator strengths as a function of nuclear charge is studied. We believe that our results can guide experimentalists in identifying the fine-structure levels in their future work. Full article
Open AccessCommunication
The Faddeev-Merkuriev Differential Equations (MFE) and Multichannel 3-Body Scattering Systems
Atoms 2016, 4(2), 16; doi:10.3390/atoms4020016 -
Abstract
Numerical implementation of the modified Faddeev Equation (MFE) is presented in some detail. The Faddeev channel wave function displays unique properties of each and every open channel, respectively. In particular, near resonant energies, the structures of the resonances are beautifully displayed, from which,
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Numerical implementation of the modified Faddeev Equation (MFE) is presented in some detail. The Faddeev channel wave function displays unique properties of each and every open channel, respectively. In particular, near resonant energies, the structures of the resonances are beautifully displayed, from which, the life-time of the resonances can be determined by simply using the uncertainty principle. The phase shift matrix, or the K-matrix, provides unique information for each and every resonance. This information enables the identification of the physical formation mechanism of the Gailitis resonances. A few of these resonances, previously known as the mysterious shape resonances, have occurred in a number of different collision systems. The Gailitis resonances are actually produced by a quantized Stark-effect within the various collision systems. Since the Stark-effect is a universal phenomenon, the Gailitis resonances are expected to occur in much broader classes of collision systems. We will present the results of a precision calculation using the MFE method in sufficient detail for interested students who wish to explore the mysteries of nature with a powerful theoretical tool. Full article