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We report measurements of the diffusion rate of isolated ion-implanted $^{8}{\mathrm{Li}}^{+}$ within $\ensuremath{\sim}120\text{ }\text{ }\mathrm{nm}$ of the surface of oriented single-crystal rutile ${\mathrm{TiO}}_{2}$ using a radiotracer technique. The $\ensuremath{\alpha}$ particles from the $^{8}\mathrm{Li}$ decay provide a sensitive monitor of the distance from the surface and how the depth profile of $^{8}\mathrm{Li}$ evolves with time. The main findings are that the implanted ${\mathrm{Li}}^{+}$ diffuses and traps at the (001) surface. The $T$ dependence of the diffusivity is described by a bi-Arrhenius expression with activation energies of 0.3341(21) eV above 200 K, whereas at lower temperatures it has a much smaller barrier of 0.0313(15) eV. We consider possible origins for the surface trapping, as well the nature of the low-$T$ barrier.

We report measurements of the diffusion rate of isolated ion-implanted ^{8}Li^{+} within ∼120 nm of the surface of oriented single-crystal rutile TiO_{2} using a radiotracer technique. The α particles from the ^{8}Li decay provide a sensitive monitor of the distance from the surface and how the depth profile of ^{8}Li evolves with time. The main findings are that the implanted Li^{+} diffuses and traps at the (001) surface. The T dependence of the diffusivity is described by a bi-Arrhenius expression with activation energies of 0.3341(21) eV above 200 K, whereas at lower temperatures it has a much smaller barrier of 0.0313(15) eV. We consider possible origins for the surface trapping, as well the nature of the low-T barrier.

Bunched-beam collinear laser spectroscopy is performed on neutron deficient $^{52,53}\mathrm{Fe}$ prepared through in-flight separation followed by a gas stopping. This novel scheme is a major step to reach nuclides far from the stability line in laser spectroscopy. Differential mean-square charge radii $\ensuremath{\delta}⟨{r}^{2}⟩$ of $^{52,53}\mathrm{Fe}$ are determined relative to stable $^{56}\mathrm{Fe}$ as $\ensuremath{\delta}⟨{r}^{2}{⟩}^{56,52}=\ensuremath{-}0.034(13)\text{ }\text{ }{\mathrm{fm}}^{2}$ and $\ensuremath{\delta}⟨{r}^{2}{⟩}^{56,53}=\ensuremath{-}0.218(13)\text{ }\text{ }{\mathrm{fm}}^{2}$, respectively, from the isotope shift of atomic hyperfine structures. The multiconfiguration Dirac-Fock method is used to calculate atomic factors to deduce $\ensuremath{\delta}⟨{r}^{2}⟩$. The values of $\ensuremath{\delta}⟨{r}^{2}⟩$ exhibit a minimum at the $N=28$ neutron shell closure. The nuclear density functional theory with Fayans and Skyrme energy density functionals is used to interpret the data. The trend of $\ensuremath{\delta}⟨{r}^{2}⟩$ along the Fe isotopic chain results from an interplay between single-particle shell structure, pairing, and polarization effects and provides important data for understanding the intricate trend in the $\ensuremath{\delta}⟨{r}^{2}⟩$ of closed-shell Ca isotopes.

Bunched-beam collinear laser spectroscopy is performed on neutron deficient ^{52,53}Fe prepared through in-flight separation followed by a gas stopping. This novel scheme is a major step to reach nuclides far from the stability line in laser spectroscopy. Differential mean-square charge radii δ⟨r^{2}⟩ of ^{52,53}Fe are determined relative to stable ^{56}Fe as δ⟨r^{2}⟩^{56,52}=-0.034(13) fm^{2} and δ⟨r^{2}⟩^{56,53}=-0.218(13) fm^{2}, respectively, from the isotope shift of atomic hyperfine structures. The multiconfiguration Dirac-Fock method is used to calculate atomic factors to deduce δ⟨r^{2}⟩. The values of δ⟨r^{2}⟩ exhibit a minimum at the N=28 neutron shell closure. The nuclear density functional theory with Fayans and Skyrme energy density functionals is used to interpret the data. The trend of δ⟨r^{2}⟩ along the Fe isotopic chain results from an interplay between single-particle shell structure, pairing, and polarization effects and provides important data for understanding the intricate trend in the δ⟨r^{2}⟩ of closed-shell Ca isotopes.

By measuring the prototypical antiferromagnet α-Fe_{2}O_{3}, we show that it is possible to determine the static spin orientation and dynamic spin correlations within nanometers from an antiferromagnetic surface using the nuclear spin polarization of implanted ^{8}Li^{+} ions detected with β-NMR. Remarkably, the first-order Morin spin reorientation in single crystal α-Fe_{2}O_{3} occurs at the same temperature at all depths between 1 and 100 nm from the (110) surface; however, the implanted nuclear spin experiences an increased 1/T_{1} relaxation rate at shallow depths revealing soft-surface magnons. The surface-localized dynamics decay towards the bulk with a characteristic length of ε=11±1 nm, closely matching the finite-size thresholds of hematite nanostructures.

We have measured the hyperfine splitting of the 7P_{1/2} state at the 100 ppm level in Fr isotopes (^{206g,206m,207,209,213,221}Fr) near the closed neutron shell (N=126 in ^{213}Fr). The measurements in five isotopes and a nuclear isomeric state of francium, combined with previous determinations of the 7S_{1/2} splittings, reveal the spatial distribution of the nuclear magnetization, i.e., the Bohr-Weisskopf effect. We compare our results with a simple shell model consisting of unpaired single valence nucleons orbiting a spherical nucleus, and find good agreement over a range of neutron-deficient isotopes (^{207-213}Fr). Also, we find near-constant proton anomalies for several even-N isotopes. This identifies a set of Fr isotopes whose nuclear structure can be understood well enough for the extraction of weak interaction parameters from parity nonconservation studies.

We have performed precision measurements in a magneto-optical trap of the 7P1/2 hyperfine structure of the isotopes 209-210Fr. The ratio of these hyperfine constants to the previously measured 7S1/2 ground state values reveals a significant hyperfine anomaly. This anomaly results from the different radial dependence of the electron density in the two atomic levels. The measurements are sensitive to changes in the radial distribution of the neutron magnetism.

We report the observation of weak magnetism in superlattices of LaAlO3/SrTiO3 using beta-detected nuclear magnetic resonance. The spin lattice relaxation rate of Li-8 in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO3 exhibits a strong peak near similar to 35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO3/SrTiO3 interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of similar to 4-6 unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments (similar to 0.002 mu(B)) in the two samples with a larger LaAlO3 spacer thickness. DOI: 10.1103/PhysRevLett.109.257207

We report a precise determination of the $^{19}\mathrm{Ne}$ half-life to be ${T}_{1/2}=17.262\ifmmode\pm\else\textpm\fi{}0.007\text{ }\text{ }\mathrm{s}$. This result disagrees with the most recent precision measurements and is important for placing bounds on predicted right-handed interactions that are absent in the current standard model. We are able to identify and disentangle two competing systematic effects that influence the accuracy of such measurements. Our findings prompt a reassessment of results from previous high-precision lifetime measurements that used similar equipment and methods.

We report the observation of weak magnetism in superlattices of LaAlO(3)/SrTiO(3) using β-detected nuclear magnetic resonance. The spin lattice relaxation rate of ^{8}Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO(3) exhibits a strong peak near ~35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO(3)/SrTiO(3) interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of ~4-6 unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments (~0.002μ(B)) in the two samples with a larger LaAlO(3) spacer thickness.

Collinear-laser spectroscopy with the bunched-beams technique was used for the study of neutron deficient Rb isotopes, out to $^{74}\mathrm{Rb}$ ($N=Z=37$) at TRIUMF. The measured hyperfine coupling constants of $^{76,78m}\mathrm{Rb}$ were in agreement with literature values. The nuclear spin of $^{75}\mathrm{Rb}$ was confirmed to be $I=3/2$, and its hyperfine coupling constants were measured for the first time. The mean-square charge radius of $^{74}\mathrm{Rb}$ was determined for the first time. This result has improved the isospin symmetry breaking correction term used to calculate the $\mathcal{F}t$ value, with implications for tests of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix.

Collinear-laser spectroscopy with the bunched-beams technique was used for the study of neutron deficient Rb isotopes, out to (74)Rb (N = Z = 37) at TRIUMF. The measured hyperfine coupling constants of (76,78m)Rb were in agreement with literature values. The nuclear spin of (75)Rb was confirmed to be I = 3/2, and its hyperfine coupling constants were measured for the first time. The mean-square charge radius of (74)Rb was determined for the first time. This result has improved the isospin symmetry breaking correction term used to calculate the Ft value, with implications for tests of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix.

The branching ratio for the superallowed ${\ensuremath{\beta}}^{+}$ decay of $^{38}\mathrm{K}^{m}$ was measured at TRIUMF's ISAC radioactive ion beam facility. The $M3$ internal transition between the isomer and the ground state of $^{38}\mathrm{K}^{m}$ was observed with a branching ratio of 330(43) ppm. A search for the nonanalogue $\ensuremath{\beta}$-decay branch to the first excited ${0}^{+}$ state in $^{38}\mathrm{Ar}$ was also performed and yielded an upper limit of $\ensuremath{\le}12\text{ }\text{ }\mathrm{ppm}$ at 90% C.L. These measurements lead to a revised superallowed branching ratio for $^{38}\mathrm{K}^{m}$ of 99.967(4)%, and increase the $^{38}\mathrm{K}^{m}$ $ft$ value by its entire quoted uncertainty to $ft=3052.1(10)\text{ }\text{ }\mathrm{s}$. Implications for tests of the nuclear-structure dependent corrections in superallowed $\ensuremath{\beta}$ decays and the extraction of the Cabibbo-Kobayashi-Maskawa matrix element ${V}_{\mathrm{ud}}$ are discussed.

The branching ratio for the superallowed beta(+) decay of (38)K(m) was measured at TRIUMF's ISAC radioactive ion beam facility. The M3 internal transition between the isomer and the ground state of (38)K(m) was observed with a branching ratio of 330(43) ppm. A search for the nonanalogue beta-decay branch to the first excited 0(+) state in (38)Ar was also performed and yielded an upper limit ofor =12 ppm at 90% C.L. These measurements lead to a revised superallowed branching ratio for (38)K(m) of 99.967(4)%, and increase the (38)K(m) ft value by its entire quoted uncertainty to ft=3052.1(10) s. Implications for tests of the nuclear-structure dependent corrections in superallowed beta decays and the extraction of the Cabibbo-Kobayashi-Maskawa matrix element V(ud) are discussed.

The temperature dependence of the frequency shift and spin-lattice relaxation rate of isolated, nonmagnetic Li-8 impurities implanted in a nearly ferromagnetic host (Pd) are measured by means of beta-detected nuclear magnetic resonance (b-NMR). The shift is negative, very large and increases monotonically with decreasing T in proportion to the bulk susceptibility of Pd for T > T*~ 100 K. Below T*, an additional shift occurs which we attribute to the response of Pd to the defect. The relaxation rate is much slower than expected for the large shift and is linear with T below T*, showing no sign of additional relaxation mechanisms associated with the defect., 4 pages, 3 figures

A high-precision branching ratio measurement for the superallowed {beta}{sup +} decay of {sup 62}Ga was performed at the Isotope Separator and Accelerator radioactive ion beam facility. Nineteen {gamma} rays emitted following {beta}{sup +} decay of {sup 62}Ga were identified, establishing the dominant superallowed branching ratio to be (99.861{+-}0.011)%. Combined with recent half-life and Q-value measurements, this branching ratio yields a superallowed ft value of 3075.6{+-}1.4 s for {sup 62}Ga decay. These results demonstrate the feasibility of high-precision superallowed branching ratio measurements in the A{>=}62 mass region and provide the first stringent tests of the large isospin-symmetry-breaking effects predicted for these decays.

We demonstrate that zero-field beta-detected nuclear quadrupole resonance and spin relaxation of low energy (8)Li can be used as a sensitive local probe of structural phase transitions near a surface. We find that the transition near the surface of a SrTiO(3) single crystal occurs at T(c) approximately 150K, i.e., approximately 45K higher than T(c)bulk, and that the tetragonal domains formed below T(c) are randomly oriented.

A high-precision branching ratio measurement for the superallowed beta+ decay of 62Ga was performed at the Isotope Separator and Accelerator radioactive ion beam facility. Nineteen gamma rays emitted following beta+ decay of 62Ga were identified, establishing the dominant superallowed branching ratio to be (99.861+/-0.011)%. Combined with recent half-life and Q-value measurements, this branching ratio yields a superallowed ft value of 3075.6+/-1.4 s for 62Ga decay. These results demonstrate the feasibility of high-precision superallowed branching ratio measurements in the Aor=62 mass region and provide the first stringent tests of the large isospin-symmetry-breaking effects predicted for these decays.

The nuclear charge radius of 11Li has been determined for the first time by high-precision laser spectroscopy. On-line measurements at TRIUMF-ISAC yielded a 7Li-11Li isotope shift (IS) of 25 101.23(13) MHz for the Doppler-free [FORMULA: SEE TEXT]transition. IS accuracy for all other bound Li isotopes was also improved. Differences from calculated mass-based IS yield values for change in charge radius along the isotope chain. The charge radius decreases monotonically from 6Li to 9Li, and then increases from 2.217(35) to 2.467(37) fm for 11Li. This is compared to various models, and it is found that a combination of halo neutron correlation and intrinsic core excitation best reproduces the experimental results.

We demonstrate that zero-field beta-detected nuclear quadrupole resonance and spin relaxation of low energy (8)Li can be used as a sensitive local probe of structural phase transitions near a surface. We find that the transition near the surface of a SrTiO(3) single crystal occurs at T(c) approximately 150K, i.e., approximately 45K higher than T(c)bulk, and that the tetragonal domains formed below T(c) are randomly oriented.

The nuclear charge radius of 11Li has been determined for the first time by high-precision laser spectroscopy. On-line measurements at TRIUMF-ISAC yielded a 7Li-11Li isotope shift (IS) of 25 101.23(13) MHz for the Doppler-free [FORMULA: SEE TEXT]transition. IS accuracy for all other bound Li isotopes was also improved. Differences from calculated mass-based IS yield values for change in charge radius along the isotope chain. The charge radius decreases monotonically from 6Li to 9Li, and then increases from 2.217(35) to 2.467(37) fm for 11Li. This is compared to various models, and it is found that a combination of halo neutron correlation and intrinsic core excitation best reproduces the experimental results.

We have set limits on contributions of scalar interactions to nuclear beta decay. A magneto-optical trap (MOT) provides a localized source of atoms suspended in space, so the low-energy recoiling nuclei can freely escape and be detected in coincidence with the beta. This allows reconstruction of the neutrino momentum, and the measurement of the beta-neutrino correlation, in a more direct fashion than previously possible. The beta-neutrino correlation parameter of the 0+ to 0+ pure Fermi decay of 38mK is $\tilde{a}$=0.9981+-0.0030+-0.0037, consistent with the standard model prediction a=1. Comment: 4 pages, 3 figures, accepted by Phys. Rev. Lett., centroid changed