Population Of Magnetic Substates Research Articles

Use of hexapole magnet and spin flipper combined with time-of-flight analysis to characterize state-selected paramagnetic atomic/molecular beams.

In the past, the Stern-Gerlach experiment has been used as a standard method for analyzing the population of magnetic substates contained in spin-polarized and/or state-selected atomic/molecular beams. However, this experiment is quite demanding due to its low signal intensity and difficulty in beam alignment. The present study shows that the use of a hexapole magnet and a spin flipper, together with the time-of-flight analysis, allows us to conduct an almost equivalent analysis while greatly improving the signal intensity. Applications to the analysis of spin-polarized triplet excited helium and state-selected O2( 3 Σg -) beams are presented.

Analyzing the orientation characteristics of 12С(2+; 4.44 MeV) nuclei in the inelastic scattering of α particles on carbon at E α = 16–25 MeV

All even components of the spin-tensors of a density matrix reconstructed by means of angular correlation for 12С nuclei in the 2+ state (4.44 MeV), produced during the inelastic scattering of α particles with energies of 16 to 25 MeV in scattering angle range θα(lab) = 20°–90°, are presented. The energy dependences of its orientation characteristics (i.e., the population of magnetic substates and the orientation tensors of multipole moments) are determined. Experimental results are compared to calculations using the coupledchannel method and the compound nucleus model.

Comparison of the polarisation of line and continuum emission in a laser produced plasma

Anisotropic emission from a laser-produced aluminium plasma emission has been studied using time and polarisation resolved spectroscopy. The time-resolved degree of polarisation of emission from a bound – bound transition in Al+ (466.3 nm) was compared to the time-resolved degree of polarisation from nearby continuum emission. The results are interpreted in the framework of radiative recombination and statistical imbalances in the populations of magnetic sub-states. It is found that the continuum emission is more strongly polarised than the line emission. Thus, this technique is a valid alternative to gated LIBS.

Polarization of Li(nd → 2p, n = 3–5) emission resulting from He2+–Li collisions

The excitation of a ground state Li atom to its 1s2nd (n = 3–5) excited states in a collision with He2+ is investigated using the two-center atomic orbital close-coupling method. The Li(nd → 2p) emission cross-sections are calculated in the collision energy range of 1–150 keV u−1 and compared with the available experimental cross-sections and other theoretical results in the overlapping energy range, showing good overall agreement. The linear polarization degrees of the radiation from the nd 2D3/2–2p 2P1/2, nd 2D3/2–2p 2P3/2 and nd 2D5/2–2p 2P3/2 (n = 3–5) transitions in Li are also calculated from the ndm magnetic substate populations. It is found that polarization degrees for nd → 2p (n = 3–5) transitions exhibit sharp minima at ∼3 keV u−1 which originate from the peaks in the Li(nd → 2p) (n = 3–5) emission cross-sections at about the same energy.

Measurement of angular dependence of M X-ray production cross-sections in Re, Bi and U at 5.96 keV

The M X-ray production differential cross sections in Re, Bi and U elements have been measured at the 5.96 keV incident photon energy in an angular range 135°–155°. The measurements were performed using a 55Fe source and a Si(Li) detector. The present results contradict the predictions of Cooper and Zare [Atomic Collision Processes, Gordon and Breach, New York (1969)] and experimental results of Kumar et al. [J. Phys. B: At. Mol. Opt. 34, 613 (2001)]. that, after photoionization of inner shells, the vacancy state has equal population of magnetic substates and the subsequent X-ray emission is isotropic, but confirm the predictions of the calculations of Flugge et al. [Phys. Rev. Lett. 29, 7 (1972)] and experimental results of Sharma and Allawadhi [J. Phys. B: At. Mol. Opt. 32, 2343 (1999)] and Ertugrul [Nucl. Instrum. Meth. B 119, 345 (1996)]. Total M X-ray production cross sections from the decay at the 5.96 keV photon energies are found to be in good agreement with the calculated theoretical results using the theoretical values of M shell photoionization cross section.

Measurement of differential M-shell X-ray emission cross-sections for bismuth

Measurement of differential M-shell X-ray emission cross-sections for bismuth at different angles has been reported. The present results confirm the prediction of the calculations of Flugge et al. [S. Flugge, W. Mehlhron, V. Schmidt, Phys. Rev. Lett. 29 (1972) 7] that the atomic inner-shell vacancies produced after photoionization are aligned and the X-ray emission from the filling of these vacancy states with j > 1/2 are anisotropic. These results contradict the predictions of Cooper and Zare [J. Cooper, R.N. Zare, Atomic Collision Processes, vol. xic, Gordon & Breach, New York, 1969, p. 317] that, after photoionization of inner shells, the vacancy states have equal population of magnetic substates and the subsequent X-ray emission is isotropic.

Angular correlation, spin alignment, and resonance behavior in12C+12Cinelastic scattering

We have studied $\ensuremath{\alpha}{\ensuremath{-}}^{12}\mathrm{C}$ angular correlations for peaks observed in the ${}^{12}\mathrm{C}{[}^{12}\mathrm{C}{,}^{12}\mathrm{C}{(3}_{1}^{\ensuremath{-}}){]}^{12}\mathrm{C}{(0}_{1}^{+})$ inelastic-scattering excitation function in the energy range between ${E}_{\mathrm{c}.\mathrm{m}.}=25$ to 35 MeV. The excitation-function data for $\ensuremath{\alpha}$-particle angles that correspond to the population of specific magnetic substates in the excited, decaying ${}^{12}\mathrm{C}$ nucleus suggest that these peaks are associated with a preferentially aligned configuration. The angular-correlation data are consistent with spin assignments of ${J}^{\ensuremath{\pi}}{=16}^{+}$ and ${18}^{+}$ for the resonancelike structures observed at ${E}_{\mathrm{c}.\mathrm{m}.}=27.5 \mathrm{MeV}$ and 33.1 MeV, respectively. The observed alignment, and the deduced spin values are consistent with a dinuclear configuration for these peaks.

Measurement of angular dependence of photon-induced differential cross-sections of M X-rays from Pt, Au and Hg at 5.96 keV

The differential cross-section for the emission of M shell fluorescence X-rays from Pt, Au and Hg by 5.96 keV photons at seven angles ranging from 50° to 110° have been measured. The differential cross-section is found to decrease with increase in the emission angle, showing an anisotropic spatial distribution of M shell fluorescence X-rays. The present results contradict the predictions of Cooper and Zare (Cooper, J., Zare, R.N., 1969. Atomic Collisions Processes, vol. XIC. Gordon and Breach, New York. p.317) that after photoionization of inner shells, the vacancy state has equal population of magnetic substates and that the subsequent X-ray emission is isotropic, but confirm the predictions of the calculations of Flugge, Mehlhorn and Schmidt that the atomic inner-shell vacancies produced after photoionization are aligned and X-ray emission from the filling of vacancies in states with J>1/2 is anisotropic. The vacancies were created by the 5.96 keV γ-rays from an 55Fe source and the M X-rays were measured using a Si(Li) detector.

Study of electron-impact excitation of metastable Ne (2p53s 3P2) substates using laser-induced fluorescence

Electron-impact excitation of metastable 2p53s 3P2 substates has been studied by means of laser-induced fluorescence. The polarization of the fluorescence induced by polarized laser light has been used to determine the relative population of magnetic substates. Comparison with two recent calculations (R-matrix and RDW) is made. The apparent population of the magnetic substates at energies far above the excitation thresholds of higher-lying states is strongly influenced by cascading. Below 20 eV the experimental values show the correct tendency towards the threshold laws for LS coupling. Apart from depolarization problems associated with the experimental method, there remain significant discrepancies between the R-matrix and the RDW predictions.

Installation of an on-line Lamb shift spin-filter polarimeter in the Triangle Universities Nuclear Laboratory atomic beam polarized ion sourcea)

An atomic beam polarized ion source, used heavily since 1989 for producing polarized H± and D± beams for experiments between 25 keV and 20 MeV, has been modified to accept a Lamb shift, spin-filter polarimeter. In this source, polarized ground-state H or D atoms enter an electron cyclotron resonance ionizer where they are stripped to produce an outgoing positive polarized ion beam. When negative ions are desired, cesium vapor is introduced into a downstream charge-exchange canal. The polarimeter, based on an atomic physics concept first developed to produce nuclear-spin-polarized beams at Los Alamos, is designed to monitor the polarization of 2S1/2 metastable H or D atoms emerging from the cesium canal. Metastable 2S1/2 atoms created by electron pickup in a collision with cesium are ‘‘filtered’’ by the polarimeter according to magnetic substate, as the magnetic field imposed on the polarimeter cavity is tuned between 53 and 61 mT. Photons produced by subsequent quenching of these filtered atoms to their ground state are monitored downstream by a phototube to reveal the magnetic substate population of the incident positive beam. To install the polarimeter cavity and phototube assembly, the existing polarized ion source was lengthened by 30 cm. Installation is complete, and comparisons with calibrated nuclear polarimeters have shown agreement to better than 0.023. Principles of operation, a description of the hardware, measurements for cross calibration, and impressions gained from its use are all presented.

Installation of an on-line Lamb–shift spin–filter polarimeter in the Triangle Universities Nuclear Laboratory atomic beam polarized ion source (abstract)a)

An atomic beam polarized ion source, used heavily since 1989 for producing polarized H± and D± beams for experiments between 25 keV and 20 MeV, have been modified to accept a Lamb–shift, spin–filter polarimeter. In this source, polarized ground-state H or D atoms enter an electron cyclotron resonance ionizer where they are stripped to produce an outgoing positive polarized ion beam. When negative ions are desired, cesium vapor is introduced into a downstream charge-exchange canal. The polarimeter, based on an atomic physics concept first developed to produce nuclear–spin-polarized beams at Los Alamos, is designed to monitor the polarization of 2S1/2 metastable H or D atoms emerging from this cesium canal. Metastable 2S1/2 atoms created by electron pickup in a collision with cesium are ‘‘filtered’’ by the polarimeter according to a magnetic substate, as the magnetic field imposed on the polarimeter cavity is tuned between 53 and 61 mT. Photons produced by subsequent quenching of these filtered atoms to their ground state are monitored downstream by a phototube to reveal the magnetic substate population of the incident positive beam. To install the polarimeter cavity and phototube assembly, the existing polarized ion source was lengthened by 30 cm. Installation is complete, its calibration has been checked, and initial impressions gained from its use are presented.

New approach to spin assignments of intermediate structures in 12C(16O,12C

Magnetic substate populations for the ${2}^{+}$ state at 4.44 MeV in $^{12}\mathrm{C}$ were measured in resonant $^{12}\mathrm{C}$${+}^{16}$O inelastic scattering by the \ensuremath{\gamma}-ray recoil method. The m-substate population has been determined in the coordinate frame where a quantization axis is taken along the center of mass scattering angle of a reaction product. This coordinate frame gives an advantage that a resonance spin J can be obtained directly from m-substate angular distributions compared with the beam-axis frame. In addition a decay L value is sensitive to the relative intensity between each m-substate cross section. Our data suggest a spin assignment of ${\mathit{J}}^{\mathrm{\ensuremath{\pi}}}$=${16}^{+}$ or ${17}^{\mathrm{\ensuremath{-}}}$ for the structures at ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.}$=29.8 MeV and 31.8 MeV. Both structures are determined to decay dominantly through the aligned configuration of L=J-2.

Partial cross sections for single- and double-electron capture by multiply charged ions colliding with He

Partial cross sections for single- and double-electron capture by multiply charged ions ([ital q]=4 and 5) in low- and intermediate-energy collisions with He were calculated within the two-electron two-center atomic-orbital coupled-channel method. Special care was exerted to account for electron-correlation effects in the reaction process. Absolute single-capture cross sections compare reasonably well with available experiments. The relative behavior of partial cross sections for double-electron capture as well as the relative population of magnetic substates are in good agreement with experiments for B[sup 4+](1[ital s]) and C[sup 5+](1[ital s]) impact.

Non-statistical population of magnetic substates of the erbium L3 subshell in photoionization

Angular distributions of the Ll, L alpha 1,2 and L beta 2,15 transitions of erbium were measured following photoionization by 8.904 keV photons. A Johansson-type monochromator was used to select the CuK beta 1 line for ionization. The angular distributions were well described by the function W( theta )=W0(1+ beta P2(cos theta )), with anisotropy parameters beta (Ll)=0.052+or-0.016, beta (L alpha 1,2)=0.016+or-0.022 and beta (L beta 2,15)=0.012+or-0.015. These values are slightly higher than the theoretical values of Berezhko and co-workers (1978). The effect of partially polarized photons on the angular distribution is discussed.

Alignment of M-subshell vacancy states after photoionization

Alignment of M-subshell vacancy states after photoionization in Pb by 5.959 keV photons has been reported. The present results contradict the predictions of Cooper and Zare (1969) that, after photoionization of inner shells, the vacancy state has equal population of magnetic substates and the subsequent X-ray emission is isotropic, but confirm the predictions of the calculations of Flugge et al. (1972) that the atomic inner-shell vacancies produced after photoionization are aligned and the X-ray emission from the filling of vacancies in states with J>1/2 is anisotropic.

Experimental investigation of alignment of the L3 subshell vacancy state produced after photoionisation in lead by 59.57 keV photons

Experimental investigation of the alignment of the L3 subshell vacancy state produced after photoionisation in lead by 59.57 keV photons has been reported. The results confirm the prediction of the calculations of Flugge et al (1972) that the atomic inner-shell vacancies produced after photoionisation are aligned and the X-ray emission from the filling of vacancies in states with J>or=3/2 is anisotropic, but contradict the predictions of Cooper et al. (1969) that after photoionisation of the inner shell, the vacancy state has an equal population of magnetic substates and the subsequent X-ray emission is isotropic.

Experimental investigation of angular dependence of photon induced L-shell X-ray emission intensity

The angular dependence of emission intensity of L shell X-rays induced by 59.57 keV photons in Pb and U is investigated by measuring the normalized intensities of the resolved L X-ray peaks at different angles varying from 40° to 120°. It is observed that while L l and Lα X-ray peaks (originating fromJ = 3/2 state) show some anisotropic angular distribution, the emission of Lβ and Lγ X-ray peaks is isotropic. The present results contradict the calculations of Co-oper and Zare (1969) that after photoionization of inner shell, the vacancy state has equal population of magnetic substates and the subsequent X-ray emission is isotropic but confirm the predictions of Fluggeet al (1972) that the atomic inner shell vacancies produced after photoionization are aligned and the x-ray emission from the filling of vacancies in state withJ ⩾ 3/2 is anisotropic.

Information on magnetic substate population obtained by particle-particle angular correlations

A simple closed-form expression of the in-plane b-c angular correlation for a sequential process of the type A(a, b)B(c)C is given. In particular, it is outlined how the amplitudes for a reaction A(a, b)B can be obtained. As an example, the application to the in-plane α′-t angular correlation for the sequential process7Li(α, α′)7Li(t)4He at 27.2 MeV is quoted.

Nuclear spin polarized alkali beams (Li and Na): Production and acceleration

Recent improvements of the Heidelberg source for polarized heavy ions (PSI) are described. By means of optical pumping in combination with the existing multipole separation magnet the beam figure of merit (polarization 2 × intensity) was doubled. 7Li and 23Na atomic beams can now be produced in pure hyperfine magnetic substrates. Fast switching of the polarization is achieved by an adiabatic medium field transition. The hyperfine magnetic substate population is determined by laser-induced fluorescence spectroscopy. In routine operation atomic beams with nuclear polarization p α ≧ 0.85 ( α = z, zz) are obtained. The acceleration of polarized 23na − ions by a 12 MV tandem accelerator introduces a new problem: the energy at the terminal stripper foil is not sufficient to produce a usable yield of naked ions. For partially stripped ions hyperfine interaction of the remaining electrons with the nuclear spin reduces the polarization. Using in addition the Heidelberg postaccelerator 23Na 9+ beams of energies between 49 and 184 MeV were obtained with an alignment on target of P zz ≊ 0.45 . 7Li beams have also been accelerated up to 45 MeV with an alignment of P zz = 0.69.

Nonequilibrium population of magnetic substates and excitation-energy division in the decay of an orbiting complex.

$\ensuremath{\gamma}$-ray angular correlations have been measured for the strongly damped reaction $^{12}\mathrm{C}$($^{28}\mathrm{Si}$, $^{12}\mathrm{C}$)$^{28}\mathrm{Si}$ at ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}=180\ifmmode^\circ\else\textdegree\fi{}$ for ${E}_{\mathrm{c}.\mathrm{m}.}=42.7 \mathrm{and} 33.7$ MeV. The $^{12}\mathrm{C}$ 4.44-MeV, ${J}^{\ensuremath{\pi}}={2}^{+}$ state is found to be produced almost exclusively in the $m=0$ magnetic substate with respect to the beam axis. Comparison of singles and coincidence yields shows that the $^{12}\mathrm{C}$ comes out in its ground state most of the time (\ensuremath{\cong} 70%) resulting in the entire excitation energy \ensuremath{\cong} 15-20 MeV appearing in $^{28}\mathrm{Si}$. These results can be reproduced by a constrained phase-space calculation.