Precise measurement of magnetic moment of short-lived β-emitting nuclei12B ( I π=1+, T 1/2=20.18 ms)

The spin polarized β-emitting nuclei¹²B (I ^π=1⁺,T _1/2=20.18 ms) were produced by the nuclear reaction¹¹B(d, p)¹²B and by the selection technique of the incident deuteron energy and the¹²B recoil angle following the nuclear reaction. The nuclear magnetic moment of the short-lived nuclei¹²B was measured by β-NMR with the β-NMR and β-NQR setup established for the first time in China. The nuclear magnetic moment of¹²B was determined to be μ=0.99993±0.00048 nm org=0.99993±0.00048 after the precise correction of the Knight shift.     

Hyperfine quantum beat of short-lived beta-emitter8Li polarized by the tilted foil technique

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(I =2⁺,T _1/2=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.     

Quadrupole moment of41Sc by use of new nuclear quadrupole resonance detection

Quadrupole effects in -NMR spectra of⁴¹Sc(I =7/2^–,T _1/2=0.596 s) implanted in a TiO₂ single crystal were detected by use of a modified -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.     

Nuclear spin dependence of polarization enhancement by multi-tilted foils studied by short-lived beta-emitters8B and12B

In order to study the basic mechanism of polarization enhancement realized by the multitilted foil technique, nuclear polarization of short-lived beta-emitter⁸B(T_1/2=769 ms,I =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(I =1⁺,T _1/2=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.     

Beta decay and hyperfine interactions

Experimental searches for the second-class currents and the soft pion effects in the nuclear weak axial currents are discussed. Also discussed are the hyperfine interactions of light interstitial impurities in ferromagnetic Fe and Ni, as well as in fcc and bcc non-magnetic metals. For these spin-ray correlation experiments, it is emphasized that the technical developments and improvements of the nuclear spin control by NMR and the production of polarization in the short-lived nuclear states are vital necessities.     

Hyperfine interactions of polarized β-emitting12B and12N in Si,Ge, and GaP

Using a nuclear reaction, the polarized short-lived -emitters¹²B and¹²N were implanted into Si, Ge, and GaP crystals. Hyperfine fields were studied via both NMR techniques and an external magnetic holding field H_ext on-off techniques in an H_ext 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 T100 K and H_ext>4 kG, whereas for¹²B in Si at T>800 K almost full polarization was found at the Larmor frequency.     

Temperature dependence of the lattice locations of boron implanted in germanium

The β-NMR of the probe atom ¹²B implanted in In-doped germanium was measured as a function of temperature. As a result, three resonances were observed: sharp and broad resonances around the Larmor frequency and a resonance split by the electric quadrupole interaction. It was found that the appearance of the resonances is similar to the case of Si host (Izumikawa et al. Hyperfine Interact. 136/137:559–605, 2001). The quadrupole coupling constant for the split resonance was deduced as ∣eqQ/h∣ = 252(3) kHz under the assumption that it has <111> axial symmetry. And furthermore, assuming that the defect atom jumps thermally between the identical defect sites, the activation energy of the jump was deduced as 0.4 ± 0.1 eV.     

Electronic structure of substitutional nitrogen impurity in TiO 2 studied by the β-NMR method

In order to study the local electronic structure of nitrogen impurity in rutile TiO₂, we have measured double-quantum NMR spectra of short lived β-emitter ¹²N(I = 1, T _1/2 = 11 ms) implanted into a rutile single crystal by means of the β-NMR technique. The resonance line obtained at room temperature is well accounted for by the second order shift due to the quadrupole interaction at the oxygen substitutional site. The spectrum at 25 K has shown the other lines than the central diamagnetic line shifted by 10?15 kHz to both sides, which has been already shown in the previous data obtained with a different crystal orientation and an external field. The present results supports the existence of a paramagnetic state formed by the substitutional nitrogen impurities.