Rf Transitions Research Articles

Precision measurement of theg J factors of metastable atomic states of88Sr and138Ba using the atomic beam magnetic resonance method

Theg J factors of the metastable states3 P 2 of88Sr and3 D 1,3 D 2,3 D 3, and1 D 2 of138Ba have been measured using the atomic-beam magnetic resonance method. The metastable states were populated by an electric discharge within the atomic-beam source. From the measurements of rf transitions between the Zeeman levels (m J =+1)↔(m J =−1) we obtained:88Sr:g J (3 P 2) =1.501124(10)138Ba:g J (3 D 3)=1.3340823 (10)g J (3 D′2)=1.1637406(11)g J (3 D 1)=0.4985751(13)g J (1 D′2)=1.003 1449(10). The relativistic and diamagnetic corrections for theg J factor of the3 P 2 state of Sr have been calculated. With these and the Schwinger correction included we getg J (3 P 2)=1.501119(12).

Fine-Structure Measurement in the First Excited State of Positronium

The $2^{3}S_{1}\ensuremath{-}2^{3}P_{2}$ energy splitting of positronium has been observed by inducing rf transitions in a weak magnetic field (\ensuremath{\simeq} 50 G) in the absence of a buffer gas and observing a resonant increase in the Lyman-$\ensuremath{\alpha}$ emission. We obtain 8628.4\ifmmode\pm\else\textpm\fi{}2.8 MHz, which is within 2 standard deviations of the theoretical value computed to order $\ensuremath{\alpha}^{3}R$ by Fulton and Martin.

Spin and magnetic moment of25Na by ?-radiation detected optical pumping

25Na (T1/2 = 60 sec) has been produced in a22Ne target by the (α,p) reaction and polarized by means of spin-exchange scattering with optically pumped87Rb. The asymmetry in the β decay of polarized nuclei served to detect rf transitions between hfs Zeeman levels of the atomic ground state, yielding spinI = 5/2 and hyperfine splitting ΔW= 2648.5(3.0) MHz, from which the magnetic moment μI = 3.683(4)nm (corrected for diamagnetism) was deduced.

Spin exchange polarization and measurement of the hyperfine splitting of short-lived8Li

Free8Li (T1/2=0.84 sec) atoms were polarized by spin exchange with optically pumped rubidium vapour. The8Li nuclei were produced by the reaction7Li(d, p)8Li in a thin LiF target. They recoiled into helium which was used as a buffer gas for optical pumping as well. Nuclear polarization up to 2% was detected by β-decay asymmetry. Rf transitions between hfs levels of the atomic ground state yielded the hfs separation ΔW=382.543(7) MHz. The nuclear spin assignmentI=2 was confirmed.

Ground state hyperfine structure and nuclear magnetic dipole moments of177Hf and179Hf

Using the atomic beam magnetic resonance method the experimental hyperfine structure data of the 5d26s23F2 ground state of177Hf and179Hf described in a previous paper [1] have been completed. After applying corrections due to perturbations by other fine structure levels of the configuration 5d26s2 we got the following multipole interaction constants: $$\begin{gathered} ^{177} Hf:A = 113.43314 (7) MHz B = 624.3293 (13) MHz \hfill \\ C = 0.27 (18) KHz D = 0.045 (40) KHz \hfill \\ ^{179} Hf: A = - 71.42891 (9) MHz B = 705.5181 (24) MHz \hfill \\ C = - 0.43 (20) MHz D = 0.07 (6) KHz. \hfill \\ \end{gathered} $$ By measuring rf transitions at magnetic fields between 1100 and 1550 Gauss the nuclear ground state magnetic dipole moments were determined. The results are: $$\mu _I (^{177} Hf) = 0.7836 (6) \mu _N , \mu _I (^{179} Hf) = - 0.6329 (13) \mu _N $$ (uncorrected for diamagnetic shielding).

Direct measurement of the nuclear magnetic dipole moment of Ho165 with the atomic beam magnetic resonance method

With an atomic beam magnetic resonance apparatus four rf transitions between different Zeeman levels of the4I15/2 ground state of Ho165 have been measured in an external magnetic field of about 3000 Gauss. The interaction between the nuclear magnetic dipole moment and the external field could be deduced from these measurements. Because the magnetic field was measured by calibration transitions in K39, Rb85 and Rb87, the following value could be determined for the nuclear magnetic dipole moment: μI(Ho165)=4.094(44) μn (uncorrected for diamagnetic shielding). Thegj-factor of the ground state of Ho165 was measured to begj(4I15/2, Ho165)=1.1951445(40).

Polarization ofTm169andF19in CaF2:Tm2+by Optical Pumping

Nuclear polarization of $^{169}\mathrm{Tm}(I=\frac{1}{2})$ is achieved in a crystal of Ca${\mathrm{F}}_{2}$ containing a small fraction of paramagnetic ${\mathrm{Tm}}^{2+}$ ions ($S=\frac{1}{2}$) by optically pumping with circularly polarized light in the region 5400-6000 \AA{}, where there is a large magnetic circular dichroism. By optical pumping alone at $T=1.65$ \ifmmode^\circ\else\textdegree\fi{} K and in a field $H=750$ G a nuclear polarization of 9% is observed. If the ${I}_{+}{S}_{\ensuremath{-}}$ rf transition is simultaneously saturated, the polarization increases to 18%. The polarization is reversed by changing from left- to right-circularly polarized light. These results are understood in terms of a model in which a large degree (\ensuremath{\sim}90%) of nuclear-spin memory exists in the optical-pumping cycle. The experiment proves the feasibility of significant nuclear polarizations in solids by optical pumping. A small polarization of the abundant $^{19}\mathrm{F}$ nuclei is produced by a three-spin cross-relaxation process with two optically pumped $^{169}\mathrm{Tm}^{2+}$ ions.

Spin exchange polarization and hfs anomaly measurement of β-active37K

Rf-spectroscopic measurements in the atomic ground state of the 1.2 sec-isotope37K yielded independent values of magnetic moment μI(37K)=0.20320 (6) nm (diamagnetically corrected), hfs separation ΔW(37K)=240.2672 (7) MHz and the resulting hfs anomaly37Δ39=(0.249±0.035) · 10−2. The37K was polarized by spin exchange scattering with optically pumped87Rb; as a detector for rf transitions the asymmetry of the β-decay of the polarized37K nuclei was used. A detailed analysis of the spin exchange mechanism under the conditions of experiments of this type was performed. This led to an explanation for the observed strong enhancement of the resonance signal heights by the spin bath. Furthermore the dependence of the nuclear polarization and relaxation time constants on the strength of the hfs coupling could be demonstrated.

Alkali-Rare-Gas van der Waals Molecules and Ground-State Relaxation Processes in Optical Pumping

Relaxation experiments performed on alkali atoms polarized in their ground state by optical pumping in the presence of a rare gas have been previously reported and interpreted. It was shown that the relaxation governed by the spin-orbit interaction is strongly affected by the formation of chemically unstable Rb-Kr molecules bound by van der Waals forces. The previous theoretical analysis, restricted to the longitudinal relaxation, is extended here to relaxation processes involving the transverse components of the electronic polarization and hyperfine "coherences" (elements of the density matrix between different hyperfine states). The effects resulting from the action of a rf field are also examined. The main results of this work, among others, are (a) the prediction of a Zeeman transition-line pressure shift, in some circumstances larger by several orders of magnitude than the one calculated by Herman, and having a very peculiar variation with the rare-gas pressure; (b) a quantitative explanation of the anomalous pressure dependence of the hyperfine transition linewidth discovered by Bender and Cohen; (c) a proposal of a method of detection of rf transitions between states of the alkali---rare-gas molecules by their effect on the relaxation process.

Source of polarized negative hydrogen ions for a tandem accelerator

A source of polarized negative hydrogen ions is described. It consists of an atomic beam apparatus with strong-field ionizer producing polarized proton or deuteron beams of 1.1 μA. Negative ions are formed without depolarization by charge exchange in sodium vapour. Different spin polarizations and orientations for deuterons can be induced by the use of rf transitions and a crossed field analyzer. The source yields after acceleration to 60 keV a polarized negative ion intensity of 10 to 20 nA. After acceleration in the tandem generator a pure vector polarization of typically P 3 = 0.5 and a tensor component P 33 = 0.75 was measured. The beam intensity focussed on a spot of 0.3 cm diameter in a scattering chamber is typically 1.5 nA.

Optical pumping of short lived Β-radioactive isotopes and the magnetic moment of37K

21Na (T1/2=23 sec) and37K(T1/2=1.25 sec) have been produced in gas targets by (d, n) reactions and polarized by means of optical pumping or spin exchange scattering with optically pumped87Rb. An asymmetry up to 3% in theΒ-decay of the polarized nuclei was found, which served to detect rf transitions between hfs levels of the atomic ground states of21Na and37K.δF=0 andδF=1 resonances have been recorded, yielding spin, hfs separation and magnetic moment, especiallyI(37K)=3/2,δW(37K)=240.266 (3) Mc/sec andΜI(37K)=0.02033(6) nm (diamagnetically corrected). For21Na earlier rf-spectroscopic data have been confirmed.

The University of Minnesota polarized proton source

A new polarized proton source has been built and is in use on the University of Minnesota linear accelerator. This source utilizes an rf transition scheme and a strong field ionizer, together with an improved geometry, to almost double the polarization and produces a significant increase in beam intensity over the old University of Minnesota polarized proton source. Using the new source, the 40 MeV beam intensity (with a 1.2% accelerator duty cycle) is 4 × 10 7 proton/sec, and the polarization is 55%.

"Bolometric" Technique for the rf Spectroscopy of Stored Ions

A simple technique is proposed in which rf transitions between suitable energy levels of an atomic or molecular ion, a member of a stored, radiatively thermalized ion gas, may be detected by monitoring the translational temperature of the ion gas. An experimental study of the cyclotron resonance of an electron gas confined in a Penning trap demonstrates its usefulness, and possible applicability to spin resonance.

Rotational Hfs Spectra ofH2+Molecular Ions

Rf transitions characteristic of interaction between the electron spin and the molecular rotation have been observed in para-${\mathrm{H}}_{2}^{+}$. Values of the coupling coefficients ($\ensuremath{\rho}$- type doubling constant) are given for two vibrational states tentatively identified as $v=5$ and $v=6$. An approximate determination of the rotational magnetic moment in the rotational state $K=2$ has also been made.

Stark Broadening by Electron and Ion Impacts of NA Hydrogen Lines of Large Principal Quantum Number

Stark broadening of hydrogen lines of large principal quantum number for RF transitions by electron and ion impact approximation

Effect of Spin-Exchange Collisions on the Optical Orientation of Atomic Sodium

The effect of spin-exchange collisions on the state populations obtained in an optically pumped ${\mathrm{Na}}^{23}$ vapor is studied in the limit of low light intensity. These state populations and hence the intensity of the rf Zeeman transitions are found theoretically to depend strongly on the spin-exchange cross sections. The various Zeeman rf transitions are found experimentally to be very different in intensity and this is interpreted as being partially due to spin-exchange collisions. From the intensity of the rf transitions in a magnetic field large enough to separate the six Zeeman components and from the observed relaxation time a spin-exchange cross section for two sodium atoms of $\ensuremath{\pi}{{S}_{0}}^{2}=6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ ${\mathrm{cm}}^{2}$ is found.

Hyperfine Structure of the Metastable Hydrogen Atom

The hyperfine separation $\ensuremath{\Delta}\ensuremath{\nu}(2S)$ of the metastable $2^{2}S_{\frac{1}{2}}$ state has been measured by a new atomic-beam magnetic-resonance method. Rf transitions were detected by utilizing a property peculiar to metastable hydrogen atoms, namely, that atoms with ${m}_{J}=\ensuremath{-}\frac{1}{2}$ decay much more rapidly in passing through a magnetic field of about 575 gauss than do atoms with ${m}_{J}=+\frac{1}{2}$. We found that $\ensuremath{\Delta}\ensuremath{\nu}(2S)=177556.86\ifmmode\pm\else\textpm\fi{}0.05$ kc/sec. From this result and the very accurately known hyperfine separation $\ensuremath{\Delta}\ensuremath{\nu}(1S)$ of the ground state, we obtain $R\ensuremath{\equiv}\frac{\ensuremath{\Delta}\ensuremath{\nu}(2S)}{\ensuremath{\Delta}\ensuremath{\nu}(1S)}=\frac{1}{8}(1.0000346\ifmmode\pm\else\textpm\fi{}0.0000003)$. The deviation of $R$ from the presently available theoretical value suggests the existence of a higher-order quantum-electrodynamic term.A method of velocity selection by electron impact is described.