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In order to disclose the polarization mechanism of the tilted-foil technique, systematic experimental studies were performed through direct observations of the nuclear polarization of short-lived beta-emitters. The present studies concentrated on the mechanisms of the following processes: (1) production of atomic polarization in the beam–tilted-foil interaction, (2) polarization transfer between an atom and a nucleus, and (3) enhancement of nuclear polarization by the beam multi-tilted-foil interaction. The present results have confirmed the plausibility of a previous model in which the atomic-polarization process in the tilted-foil technique is attributed to the right–left asymmetry of the electron-capture process at the final surface of a tilted foil. The enhancement effect of nuclear polarization by the multi-tilted-foil technique could be consistently explained by a model proposed by Goldring and Niv. Further information on atomic processes is required to make a definite statement on hyperfine interactions and atomic configurations, which contribute to polarization transfer.

Hyperfine interactions of 8Li impurity nucleus imbedded in ferromagnetic Ni metal were studied using the β-NMR technique. Two kinds of hyperfine fields B82 were found, corresponding to two different final sites of Li atoms in the Ni lattice. The nuclear spin-lattice relaxation times T1 of 8Li in Ni were also determined for each field. Temperature dependencies of B82 and T1 were observed to deduce these values at T=0 K that can be compared with those calculated recently by Akai et al.

The magnetic moments of the proton drip-line nuclei13O(Iπ = 3/2−,T1/2 = 8.6 ms) and 9C(Iπ = 3/2−,T1/2 = 126 ms) have been determined for the first time through the combined techniques of polarized radioactive nuclear beams andβ-NMR detection. The observed magnetic moments are ¦μ(13O)¦ = 1.3891 ±0.0003μN and ¦μ(9C)¦ = 1.3914 ±0.0005μN. Spin expectation values 〈σ〉 are deduced to be 0.76 and 1.44 for13O and9C, respectively. While the 〈σ〉 of13O is consistent with the systematics from isospinT= 1/2 mirror pairs, the 〈σ〉 of9C is unusually large, even far larger than the single particle value, 〈σ〉 = 1.

The spin relaxation timeT 1 for short-lived beta emitters13O and23Mg implanted in Pt have been measured for the first time;T 1T13O) = 2.90 ±0.65 Ks andT 1 T(23Mg) = 1665 ±140 Ks. The Knight shift for13O in Pt was measured at 300 K to beK(13O) = +(4.23 ±0.14) × 10−3. In the case of13O, the Knight shift is unusually large and the relaxation time is unusually fast compared with other interstitial impurities in Pt. A KKR band-structure calculation reproduces the present large Knight shift fairly well.

The quadrupole coupling constants of8Li and12B in hcp Mg and Zn are determined by use of a newly developed nuclear quadrupole resonance technique (NNQR) as ¦eqQ(8Li in Mg)/h¦=3.0±0.3 kHz, ¦eqQ(8Li in Zn)/h¦=33.5±2 kHz, and ¦eqQ(12B in Mg)/h¦=47.0±0.1 kHz. Correspondingly, the electric field gradients at room temperature are deduced: ¦q(8Li in Mg)¦=(3.81±0.39)×1018, ¦q(8Li in Zn)¦=(4.25±0.27)×1019, and ¦q(12B in Mg)¦=(1.47±0.03)×1020, all in V/m2. The experiments are compared with the results of first-principles super-cell band structure calculations which can treat local lattice relaxations around the impurity nuclei. The calculations show that the most favorable location of these light interstitials in hcp Mg is not the octahedral-like sites which have the biggest interstitial volume, but the basal trigonal sites with a local lattice expansion of as big as 30%. Calculated electric field gradients at the impurity nuclei reproduce the experimental values fairly well.

In order to study the basic mechanism of polarization enhancement realized by the multitilted foil technique, nuclear polarization of short-lived beta-emitter8B(T1/2=769 ms,Iπ=2+) was induced. Utilizing up to ten tilted foils, the polarization enhancement was measured as a function of the foil numbers. The observed enhancement for8B was combined with the previous results for12B(Iπ=1+,T1/2=20 ms) which has the same atomic configurations but different nuclear spin. Analyzing these results in the framework of the classical vector model, the essential features of the enhancement depending on the nuclear spin was disclosed.

To disclose the basic mechanisms of nuclear polarization creation realized by the tilted foil technique, hyperfine quantum beats of the nuclear polarization of the short-lived beta-emitter8Li(Iπ=2+,T1/2=840 ms) were measured as a function of the distance between two tilted foils. From the observed beats of the8Li nuclear polarization, it was found that the Fermi-contact interaction of the8Li nucleus with the ground 1s-electron in LiIII plays a main role in the final stage of polarization transfer from polarized orbital electrons to the8Li nucleus.

Recent improvements in isotope separators can be utilized along with the availability of a wide range of nuclear species from the heavy-ion fragmentation process to study hyperfine interactions. We have measured the magnetic moments of mirror nuclei using this method at the Lawrence Berkeley Laboratory's Bevalac heavy-ion accelerator. We present the merits, applicability and limitations of the technique.

Spin polarization of43Ti produced through the projectile fragmentation process in46Ti on C collisions at 116 MeV/nucleon has been observed as a function of fragment momentum by means of beta-decay asymmetry. From the momentum dependence of the fragment polarization, it was concluded that negative angle deflection of the43Ti fragment due to the nuclear attractive potential is the main reaction path in the case of light targets.

The nuclear quadrupole moment of8B(I π=2+,T 1/2=769 ms) has been determined by use of a modified β-NMR detection as |Q(8B)|=68.3±2.1 mb, which is twice the prediction of the Cohen-Kurath shell model calculation. The anomalous quadrupole moment which is carried mainly by the protons in the nucleus, has been accounted for by the proton halo effect.

To complete the systematic study on hyperfine interactions of light impurities in ferromagnetic Ni, the short-lived beta-emitter8Li was implanted in a thin polycrystal Ni foil. One of the final sites of8Li in Ni was found by means of the beta-NMR technique andits hyperfine field was determined to be -3.65(3) kOe. Simultaneously, the spin lattice relaxation time of8Li at the site in Ni was found to be 1.6(4) s. Based on the comparison between these values and theoretical predictions recently made by a first principle calculation, the probable site of8Li in Ni is implied to be an octahedral interstitial site.

NMR on the beta emitter43Ti has been observed by use of the β-NMR technique. From the observed NMR spectrum, the magnetic moment of43Ti was determined to be |μ| =0.85±0.02 µN. The value is significantly quenched from the single particle value −1.91 µN, which shows a strong effect resulting from meson-exchange currents andconfiguration mixing.

The magnetic moment of the23Mg (Iπ=3/2+, T1/2=11.3 s), has been determined as |μ(23Mg)|=0.5364±0.003 µN by use of β-NMR detection with the recoil polarization obtained through a low energy nuclear reaction.

The nuclear quadrupole moment of8B(Iπ=2+,T1/2=769 ms) has been determined by use of a modified β-NMR detection as |Q(8B)|=68.3±2.1 mb. A field gradient was obtained in a single crystal Mg at room temperature.

Quadrupole effects in NMR spectra of8Li(I π=2+;T 1/2=0.84 s) in LiIO3 andLiNbO3 single crystals have been detected by use of a modified β-NMR. The coupling constants for both crystals are in agreement with known ones. Field gradients in the crystals were measured by detecting pulsed-Fourier transformed NMR of7Li. The quadrupole moments deduced from both samples agree, and|Q(8Li; 2+)|=32.7±0.6 mb has been determined.

Hyperfine interactions of β-emitting17F implanted in single crystals of NaF and CaF2 were studied. The nuclear magnetic moment of theIπ=5/2+ state was determined with improved precision to be |μ(17F;Iπ=5/2+,T1/2=64.5s)|=4.72130±0.00025 µN.

Beta-ray angular distributions from aligned12B and12N have been observed in order to study the meson-exchange effect in a nucleus. Alignment-correlation coefficients α∓ for12B and12N were determined to be α−=−(0.0174±0.0059)%/MeV and α+=−(0.2774±0.0086)%/MeV, respectively. These values are fairly consistent with the previous values, while the reliability was greatly improved. From these coefficients, the nuclear parametery, i.e. the ratio of the time component of the axial vector currents of the Gamow-Teller matrix element, was determined to bey=4.13±0.15. The value is enhanced by 33% from that calculated by use of the impulse approximation, which clearly shows a considerable effect due to meson-exchange currents.

Quadrupole effects in β-NMR spectra of41Sc(Iπ=7/2−,T1/2=0.596 s) implanted in a TiO2 single crystal were detected by use of a modified β-NMR technique. Using the field gradient in the crystal determined by the pulsed-Fourier-transformed NMR of45Sc in TiO2, the quadrupole moment of41Sc has been determined as |Q(41Sc; 7/2−)|=166±8 mb.

Hyperfine interactions of12B(Iπ=1+,T1/2=21 ms) implanted in the substitutional site of B in BN (hexagonal) was studied by detecting β-NMR. In order to measure the quadrupole coupling constant efficiently, we employed a newly developed quadrupole resonance technique (NNQR). The quadrupole moment of12B was determined to be |Q(12B)|=13.21±0.26 mb.

Hyperfine interactions of β-emitting17F implanted in single crystals of NaF and CaF2 were studied. The nuclear magnetic moment of theTπ=5/2+ state was determined with an improved precision to be |μ(17F;π=5/2+,T1/2=64.5s|=4.72130±0.00025. nm. Isoscalar magnetic moments of the doubly closed shell ±1 nucleon nuclei around mass number 16 were derived and the effective nucleon mass in the nucleus was discussed.

The nuclear magnetic moment of41Sc(Iπ=7/2−, Tl/2=0.59sec) was remeasured, and the precision of the value was improved about 10 times compared with the previously known one. The value was determined to be |μ(41Sc;Iπ=7/2)|=(5.4305±0.0018) nm. Comparing the value with the previously known NMR of the nuclei in Pt, the knight shift, K=−(0.4±5.3)·10−4 was determined.

The nuclear electric quadrupole moment of41Sc(Iπ=7/2−) was experimentally determined by use of the NMR detection in which the asymmetric β-ray distribution from spin polarized nuclei was monitored. The magnetic interaction of the state with high external magnetic field and the nuclear quadrupole interaction with the electric field gradient obtained in TiO2 crystal were studied. The field gradient seen to the implanted41Sc was measured independently by the high field NMR detection on the stable isotope45Sc located in the equivalent41Sc site with. |Q(41Sc;Iπ=7/2−)|=(0.120±0.006) b was determined.

Experimental developments recently made in the beta-NMR measurements are reviewed. For production of polarized beta-emitters, the tilted foil technique has been successfully combined with the NMR. The low- and intermediate-energy heavy-ion reactions were recently found to be another sources of polarized beta-emitters. To achieve wide applicability of the NMR technique to nuclei far from stability, the tilted foil technique and the projectile fragmentation process in high-energy heavy-ion collisions were recently combined with the beta-NMR technique in the fragment separator built at the LBL.

Electromagnetic moments of doubly closed shell ±1 nucleon nuclei were studied. Recent technical developments of the β-NMR was shown that was applicable for the polarized β emitters. Also, the implication of those new moments were discussed especially on the nuclear interactions and non nucleonic degrees of freedom.

The lifetime and magnetic moment of43Ti (Iπ-7/2−, T1/2=0.50 sec), one of the mirror beta-radioactive nuclei in the f7/2-shell, have been measured with a fragment separator built at the Bevalac of the LBL. By means of the beta-NMR method on43Ti, a preliminary value of the magnetic moment of43Ti was determined to be μ=(0.70±0.07) μπ.

A polymer foil of polyethylene-terephthalate was successfully used for the tilted foil to create nuclear polarization of beta-emitters. The foil was carefully prepared to produce atomic flatness on the surfaces. The resultant smoothness was confirmed with beta-NMR measurements on12B and found to be as good as those of carbon foils used previously in the measurements.

Chemical degradation of anodes in solid oxide fuel cells (SOFCs) induced by phosphorous impurities has been investigated by thermochemical calculations, electrochemical characterization, and microstructural analysis. Thermochemical calculations indicate that Ni phosphides (Ni m P n ) such as Ni 5 P 2 are readily formed under SOFC operational conditions even in the case where the concentration of phosphorous impurities is as low as ppb level. Phosphorous impurities in fuels resulted in the formation of the secondary phase Ni phosphides during operation especially at an operating temperature ~ 1000°C. The formation of Ni phosphides and change in anode microstructure were confirmed by using a field-emission-scanning electron microscope coupled with an energy dispersive X-ray analyzer, scanning transmission electron microscope, and X-ray diffraction, leading to the fatal cell performance degradation in the manner that anodic overpotential increased, current incorporation was obstructed, and internal fuel reforming reaction was deactivated.

Nuclear dipolar brondening in the NMR spectra of beta-emitting12B and12N implanted in single crystal Mg with h.c.p. structure was studied as function of orientation of the crystal axes relative to the external magnetic field. The implanted12N was located in interstitial trigonal site. The surrounding Mg atoms nearest to the12N were displaced from the regular lattice position, and lattice expansion δa/a=0.15 was determined.

Lattice expansions of Cu in the nearest octahedral surroundings of interstitial 12 N were determined to be Δr / r = 0.11 ± 0.02 and 0.13 ± 0.06 respectively using NMR detection. The results are informative to the study of the hyperfine interactions of the impurities in ferromagnetic Ni.

The location of12B in bcc V and Ta crystals following implantation is determined by use of NMR detection and asymmetric β-decay. The expansion in the immediate surrounding of V is Δa/a=(21∓4) %. Magnetic hyperfine interactions of12B in bcc Fe are also discussed, as the parameters regarding the location and expansion as inferred from the results on nonmagnetic bcc metals.

Nuclear dipolar broadening in the NMR spectra of β-emitting12N implanted in single crystal V was studied as a function of external magnetic field, orientation of the crystal axes relative to the field, and temperature of the sample. The implanted12N was located in an interstitial tetrahedral site. The surrounding V atoms nearest to the12N were displaced from the regular lattice position; the lattice expansion of large size Δa/a=0.5 was determined.

The physical principles of atomic and nuclear polarization by the tilted-foil interaction as applied to the production of polarizedβ emitters for NMR probes are discussed.

Induction of atomic and nuclear polarization by grazing-incidence collisions (scattering) and by the tilted-foil interaction (transmission) is discussed. By direct observation of asymmetric Β decay, the foil can become a practical nuclear polarizer.

A new on-line isotope separator was constructed and used successfully for the study on short-lived isotopes at the Bevalac at Lawrence Berkeley Laboratory. The isotopes were produced through projectile fragmentation processes of high energy heavy-ion reactions. Various isotopes were rigidity-separated by use of a beam line and, finally, the desired single isotope was range analyzed to stop in a catcher. A large number of β-emitting21F nuclei were successfully collected and the nuclear lifetime was determined by detecting β-rays.

NMR measurements on12B nuclei implanted in a thin sheet of highly oriented pyrolytic graphite (Grafoil) have been made to study the magnitude of the polarization of12B and its electric quadrupole coupling. The magnitude of the residual polarization of12B held in carbon material is of crucial importance to the experiment measuring the average polarization of12B produced in the muon capture by12C. It was found that the polarization of12B can be maintained at 101.0±2.2% in Grafoil under a magnetic field of 3 kG. The electric quadrupole coupling was determined to bee 2 qQ/h=+1207.3±8.2 kHz. From the magnitude and the sign of the electric field gradienteq, the location of12B was found to be a substitutional site in the carbon lattice. The anomalous B-C bond involving thesp 2 hybrid orbitals with partially filledp z electrons is also discussed.

Hyperfine magnetic fields in a single crystal Fe were measured by use of asymmetric β decay and NMR detection of spin polarized β-emitting12N.

Magnetic hyperfine fields and spin-lattice relaxation times of interstitial and substitutional12B nuclei in Fe are studied in a temperature range, 100 K

A new dynamic polarization technique by means of the Overhauser effect in ametal has been employed in the magnetic moment measurement of a short-lived β-emitter. The magnetic moment of 28 Al (I π = 3 + , T 1 2 = 136 s ) has been determined as |μ( 28 Al )| = 3.242 ± 0.005 nm .

Nuclear quadrupole effects in the NMR spectra of12N implanted in GaN crystal was studied. Broad quadrupole spectra were observed almost independent of the crystal orientation relative to the external magnetic field. Homogeneously oriented field gradients distributed in the range 0

Using a nuclear reaction, the polarized short-lived β-emitters12B and12N were implanted into Si, Ge, and GaP crystals. Hyperfine fields were studied via both NMR techniques and an external magnetic holding field Hext on-off techniques in an Hext range 0–8 kG and a temperature range 100–1000 K. No significant NMR signal was observed between 2 and 30 MHz for12N in Si and Ge despite maintenance of 60% polarization at T∼100 K and Hext>4 kG, whereas for12B in Si at T>800 K almost full polarization was found at the Larmor frequency.

Systematic study of polarization of projectile like fragment12B in14N induced reactions on light mass-number targets has been continued. A large positive polarization at small energy loss region was observed for an27Al target at various reaction angles. Polarization is studied as a function of kinetic energy and reaction angle of12B in terms of a classical frictional force.

Nuclear spin polarization created by use of the beam-tilted-foil interaction, was studied by use of asymmetric β decay and NMR detection.

β-ray angular distributions from nuclear spin aligned12B and12N were detected and the correlation coefficients were determined. From the comparison of these with the experimental weak magnetism term, it was concluded that the parity of the weak nucleon currents in the iso-spin space was strictly conserved.