Search

The inverse perovskite Sr3SnO is a 3D cubic Dirac semimetal with a very small energy gap[1]. Its unusual electronic structure confers a variety of novel properties, such as chiral topological surface states, and very strong itinerant electron orbital magnetism. Remarkably, when doped it also becomes superconducting[2]. In the lowest carrier density samples, the Fermi level lies close to the Dirac points, and orbital magnetism is maximal. Here we report the results of ion-implanted 8Li+ βNMR in Au-capped epitaxial thin films of Sr3SnO as a function of carrier content. In addition, we stop the 8Li in the Au overlayer to seek proximal evidence of the chiral surface state. In high magnetic field (6.55 T), we find remarkably little contrast in spin-lattice relaxation (SLR) between low carrier density Sr3SnO and the Au overlayer. In the inverse perovskite layer, 1/T 1 ∼ 0.14 s-1, slightly faster than Au at 300 K, while in the overlayer, there is a small but systematic enhancement in 1/T 1 compared to a control film of Au. The resonance in the Sr3SnO layer is broad with a long tail towards negative shift without resolved quadrupolar splitting.

We report the β-detected NMR of implanted 8Li+ in the rhombohedrally distorted perovskite LaAlO3. As observed in other insulating perovskites, the resonance has large quadrupolar splitting. However, it exhibits additional splitting due to the rhombohedral distortion. In addition, the magnitude of the electric field gradient at the 8Li site is larger than in cubic perovskites, such as SrTiO3, with vQ ≈ 191.3 kHz.

To improve the thermal modelling of high power isotope separation on-line (ISOL) targets at TRIUMF, an optical technique is being developed that allows for direct off-line and on-line temperature measurements of targets for radioactive isotope production. In this setup the light coming from a hot target through the ionizer opening is collected via a set of optics and coupled into a spectrometer. Thus, from the emission spectrum and Planck’s law, the target temperature can be deduced. Tantalum targets were heated to high temperatures and preliminary temperature measurements confirm the correlation between the spectrum of the radiation emitted from the target and the currents used to resistively heat the targets. The final goal is to apply this technique to on-line targets and correlate the isotope releases with the target temperatures for a better understanding of the diffusion and effusion processes happening in the target and for optimizing the delivery of short-lived species.

Structure of the neutron-rich nucleus $^{30}\mathrm{Mg}$, which is located close to the region of the $N=20$ ``island of inversion,'' has been investigated by $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ spectroscopy of spin-polarized $^{30}\mathrm{Na}$. From the detailed $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence relations, nine new states have been established in $^{30}\mathrm{Mg}$. The spin-polarization of $^{30}\mathrm{Na}$ enabled firm spin-parity assignments for seven states in $^{30}\mathrm{Mg}$ by means of the spatial asymmetry of $\ensuremath{\beta}$-ray counts in coincidence with the $^{30}\mathrm{Mg}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$ rays. Based on the experimental information, it is shown that various characteristic structures coexist in $^{30}\mathrm{Mg}$: (i) the ground-state vibrational-like band, (ii) the deformed band built on the ${0}_{2}^{+}$ state at 1.788 MeV, (iii) the $\ensuremath{\gamma}$-vibrational band built on the ${2}_{3}^{+}$ state at 3.543 MeV, and (iv) four states around 5 MeV associated with large $\ensuremath{\beta}$-transition probabilities: ${1}^{+}$ and ${2}^{+}$ states with spherical nature, ${1}^{+}$ and ${2}^{+}$ states with collective nature. The experimental results are compared with three theoretical calculations of the CHFB $+$ LQRPA, the AMD $+$ GCM, and the large-scale shell model with the EEdf1 interaction. All these theories reasonably reproduce the three bands.

The structure of excited states in the neutron-rich nucleus 31 Mg, which is in the region of the “island of inversion” associated with the neutron magic number N = 20 , is studied by β – γ spectroscopy of spin-polarized 31 Na. Among the 31 Mg levels below the one neutron separation energy of 2.3 MeV, the spin values of all five positive-parity levels are unambiguously determined by observing the anisotropic β decay. Two rotational bands with K π = 1 / 2 + and 1 / 2 − are proposed based on the spins and energies of the levels. Comparison on a level-by-level basis is performed between the experimental results and theoretical calculations by the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM). It is found that various nuclear structures coexist in the low excitation energy region in 31 Mg.

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 used the 8$\pi$ $\gamma$-ray spectrometer at the TRIUMF-ISAC radiocative ion beam facility to obtain high-precision branching ratios for $^{19}$Ne $\beta^+$ decay to excited states in $^{19}$F. Together with other previous work, our measurements determine the superallowed $1/2^+ \to 1/2^+$ beta branch to the ground state in $^{19}$F to be 99.9878(7)\%, which is three times more precise than known previously. The implications of these measurements for testing a variety of weak interaction symmetries are discussed briefly.

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.

The level structure of $^{31}\mathrm{Mg}$, which is located close to the region of the $N$ = 20 ``island of inversion'' in the nuclear chart, has been studied by $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ spectroscopy with spin-polarized $^{31}\mathrm{Na}$. In $^{31}\mathrm{Mg}$, shape coexistence is expected as a result of subtle competition between the spherical mean field and the nuclear correlation which favors deformed configurations. In the present work, our unique method utilizing the anisotropic $\ensuremath{\beta}$ decay of spin-polarized $^{31}\mathrm{Na}$ enables us to firmly assign the spins of all positive-parity excited levels in $^{31}\mathrm{Mg}$ below the neutron separation energy at 2.3 MeV. Furthermore, by constructing a very detailed decay scheme, including two newly found levels, the spins of negative-parity levels are restricted. The examination of the spectroscopic information shows that the deformed rotational bands with ${K}^{\ensuremath{\pi}}=1/{2}^{+}$ and $1/{2}^{\ensuremath{-}}$, which have very similar structures to those observed in a higher excitation energy region of $^{25}\mathrm{Mg}$, appear as the ground-state and low-lying bands, respectively, in $^{31}\mathrm{Mg}$. The experimental levels of $^{31}\mathrm{Mg}$ are compared, on the level-by-level basis, with two types of theoretical calculations. These are, first, the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM) and, second, the shell model with the EEdf1 interaction, which is microscopically derived from chiral effective field theory. It is understood that 8 levels among the experimental 11 levels are the members of four types of largely deformed rotational bands and 2 levels are of spherical nature. The $1/{2}^{+}$ 2.244-MeV level is successfully reproduced by the shell-model calculation with a dominant 4p4h configuration. The present work clearly demonstrates that various structures coexist in a low excitation energy region of $^{31}\mathrm{Mg}$.

A new radiofrequency quadrupole (RFQ) based ion beam cooler and buncher is under development for the CANadian Rare-isotope facility with Electron Beam ion source (CANREB) project at TRIUMF. The CANREB project requires an RFQ buncher that will efficiently accept continuous beams of rare isotopes from either the Advanced Rare IsotopE Laboratory (ARIEL) or Isotope Separator and ACcelerator (ISAC) target by way of a high resolution magnetic spectrometer, with energies up to 60 keV and deliver bunched beams to an electron beam ion source (EBIS) for charge breeding. The energy of the bunched beam delivered to the EBIS will be adjustable to match the requirements of the existing post acceleration infrastructure. The CANREB RFQ incorporates design considerations to facilitate ease of use over a wide range of ion masses, and is intended to accommodate incident beam rates as high as 10 8 pps, delivering beam bunches at 100 Hz. An overview of the CANREB RFQ design concept will be presented, informed by results from both ion optical simulations as well as commissioning efforts with other beam cooler and buncher devices. Simulation results indicate that the design is well suited to deliver high quality bunched beams with high efficiency with as many as 10 6 ions per bunch.

Laser spectroscopy experiments at radioactive ion beam facilities around the world investigate properties of exotic nuclei for scientific endeavours such as, but not limited to, the investigation of nuclear structure. Advancements in experimental sensitivity and performance are continuously needed in order to extend the reach of nuclei that can be measured. The collinear fast beam laser spectroscopy ( Cfbs ) setup at Triumf , coupled to an out-of-plane radio-frequency quadrupole Paul trap, enables measurements of some of the most fundamental nuclear properties for long-lived ground and isomeric states. The first comprehensive overview of the Cfbs experiment is provided along with descriptions of key developments that extend the reach of laser spectroscopy experiments. A novel data acquisition technique structured around three-dimensional spectra is presented, where the integration of a custom multi-channel-scalar provides photon counts correlated with arrival time and acceleration voltage for post-experiment analysis. In addition, new rapid light manipulation techniques are discussed that suppress undesirable hyperfine pumping effects and regain losses in experimental efficiency.

We observe the electric-dipole forbidden $7s\rightarrow8s$ transition in the francium isotopes $^{208-211}$Fr and $^{213}$Fr using a two-photon excitation scheme. We collect the atoms online from an accelerator and confine them in a magneto optical trap for the measurements. In combination with previous measurements of the $7s\rightarrow7p_{1/2}$ transition we perform a King Plot analysis. We compare the thus determined ratio of the field shift constants (1.230 $\pm$ 0.019) to results obtained from new ab initio calculations (1.234 $\pm$ 0.010) and find excellent agreement.

CANREB (CANadian Rare isotope facility with Electron Beam ion source) at TRIUMF will deliver pure, highly charged, radioactive ion beams suitable for acceleration in order to perform experiments to investigate nuclear reactions. Radioactive isotopes at TRIUMF are produced by bombarding solid targets with high energy particle beams. Singly charged ions are extracted from an ion source immediately coupled to the target. CANREB will complement the presently used ECRIS based charge state breeder system by providing higher purity beams and extending the available mass range. Ions are first sent through a high resolution mass separator, where most of the isobaric contaminants can be removed. After this, the ions are injected into an RFQ cooler buncher and finally bunches are injected into an EBIS for charge state breeding. The bunch repetition time is set to 10 ms. This will also allow operation with short lived isotopes. To guarantee the short breeding time for the entire mass range up to uranium and to have a high injection efficiency, the EBIS is designed to operate at an electron beam density of up to 20 000 A/cm2. With the EBIS being operated at ultra-high vacuum, and no plasma wall interactions, additional contaminants induced by the charge state breeding process are expected to be significantly reduced compared with the ECRIS. Total beam intensity is limited mainly by space charge in the buncher to about 107 ions per bunch.

We report a comparison of the $1/T_1$ spin lattice relaxation rates (SLR) for $^9Li$ and $^8Li$ in Pt and SrTiO$_{3}$, in order to differentiate between magnetic and electric quadrupolar relaxation mechanisms. In Pt, the ratio of the $1/T_{1}$ spin relaxation rates $R_{Pt}$ was found to be 6.82(29), which is close to but less than the theoretical limit of $\sim7.68$ for pure magnetic relaxation. In SrTiO$_{3}$ this ratio was found to be 2.7(3), which is close but larger than the theoretical limit of $\sim2.14$ expected for pure electric quadrupolar relaxation. These results bring new insight into the nature of the fluctuations in the local environment of implanted $^8Li$ observed by $\beta$-NMR.

The MTV (Mott Polarimetry for T-Violation) experiment is running at TRIUMF-ISAC (Isotope Separator and ACcelerator), searching for a large T violation in polarized Li-8 beta decay via measurements of the triple vector correlation, R, in the beta decay rate function. The left/right backward scattering asymmetry of Mott scattering from a thin metal foil is measured using an electron tracking detector including a cylindrical drift chamber (CDC). To achieve 10-ppm precision in the Mott scattering asymmetry, we performed multiple studies on the expected systematic effects. The sources of the systematics have been identified and calibration systems have been developed to evaluate the fake effects. The first physics data was collected in 2016 and significantly improved on the result of our previous measurement, which achieved 100-ppm precision in 2010 using the first generation detector (planer drift chamber) at TRIUMF. The data measurement status, together with the results of the systematics studies, is described here. In addition to the T violation, we are preparing to test the Lorentz invariance in the weak sector via our Mott analyzer system. Unexplored Lorentz violating correlations can be tested using the MTV experimental setup. The testing principle and preparation status are also described here.

The span of most chemical shifts recorded in conventional 25Mg-NMR spectroscopy is ~ 100 ppm. Accordingly, linewidths of ~ 10 ppm or better are desirable to achieve adequate resolution for applications in chemistry. Here we present first high-field 31Mg- β-NMR measurements of 31Mg+ ions implanted into a MgO single crystal carried out at the ISAC facility at TRIUMF. The resonances recorded at 2.5 T and 3.5 T show strong linewidth dependency on the applied RF power, ranging from ~ 419 ppm for the highest RF power down to ~ 48 ppm for the lowest one.

The MTV experiment (Mott Polarimetry for T-Violation Experiment) is running from 2009 at TRIUMF, which aims to search a large non-standard T-Violation in polarized nuclear beta decay. Existence of transverse polarization of electrons emitted from polarized 8Li nuclei, which are produced at TRIUMF-ISAC and stopped inside an aluminum stopper, is investigated. We utilize a Mott polarimeter consists of a planer drift chamber, measuring backward scattering left-right asymmetry from a thin lead analyzer foil. In this paper, preliminary results from the first physics run performed in 2010 are described.

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.

The observation of a permanent electric dipole moment (EDM) at current experimentally accessible levels would provide clear evidence of physics beyond the Standard Model. EDMs violate CP symmetry, making them a possible route to explaining the size of the observed baryon asymmetry in the universe. The Radon EDM Experiment aims to search for an EDM in radon isotopes whose sensitivity to CP-odd interactions is enhanced by octupole-deformed nuclei. A prototype apparatus currently installed in the ISAC hall at TRIUMF includes a gas handling system to move radon from a collection foil to a measurement cell and auxiliary equipment for polarization diagnostics and validation. The features and capabilities of the apparatus are described and an overview of the experimental design for a gamma-ray-anisotropy based EDM measurement is provided.

The MTV (Mott Polarimetry for T-Violation Experiment) experiment at TRIUMF-ISAC (Isotope Separator and ACcelerator), which aims to achieve the highest precision test of time reversal symmetry in polarized nuclear beta decay by measuring a triple correlation (R-correlation), is motivated by the search for a new physics beyond the Standard Model. In this experiment, the existence of non-zero transverse electron polarization is examined utilizing the analyzing power of Mott scattering from a thin metal foil. Backward scattering electron tracks are measured using a multi-wire drift chamber for the first time. The MTV experiment was commissioned at ISAC in 2009 using an 80%polarized 8Li beam at 107 pps, resulting in 0.1%statistical precision on the R-parameter in the first physics run performed in 2010. Next generation cylindrical drift chamber (CDC) is now being installed for the future run.

Spin-polarized radioactive nuclear beams at TRIUMF enable a new spectroscopic method which efficiently assigns spins and parities of the daughter levels by taking advantage of the asymmetric β-decay of the polarized parent nucleus. This method was successfully applied to structure studies of 29Mg and 30Mg in connection with the physics of the “island of inversion”. In 29Mg, two low-lying levels with intruder configuration were assigned. In 30Mg, coexistence of spherical shape, prolate shape and γ-collectivity was strongly suggested.

An overview of the laser polarizer facility at ISAC is provided. The chargeexchange cell is described in some detail.

A novel technique to measure electron-capture branching ratios is being introduced, where the TITAN ion traps and the ISAC radioactive beam facility at TRIUMF are the central components. The technique will be applied to the intermediate odd-odd nuclei in double-beta decay. The decay properties of these nuclei will constrain theoretical models dealing with the evaluation of the nuclear matrix elements for both the 2v and the 0v mode. The present setup and its potential for measuring extremely low branching ratios at low instrumental backgrounds is described.

TRIUMF’s neutral atom trap for β decay (TRINAT) has been used to measure the most accurate β-ν correlation. Plans include improving that measurement, and also carrying out a full program of spin-polarized β decay correlation measurements complementary to the decay of the neutron

The ISAC facility at TRIUMF in Vancouver, Canada, produces intense beams of radioactive ions that are used in a broad research program encompassing fundamental properties of nuclei, nuclear astrophysics, medical physics, condensed matter physics, and physical chemistry. The focus of this article is on the latter subject and in particular recent developments in the use of β-detected NMR to probe electronic, magnetic, and structural properties of thin films and interfaces. Over the last 10 years considerable progress has been made developing the technique and applying it to current problems.

We present a method for measuring the nuclear anapole in a string of francium isotopes. The anapole is a parity non-conserving electromagnetic moment that enables parity-forbidden transitions between ground state hyperfine levels of an atom. The experiment is run by the FrPNC collaboration and relies on a beam of artificially-produced francium from the ISAC facility at TRIUMF.

A 28 keV beam of 31Mg+ ions was extracted from a uranium carbide, proton-beam-irradiated target coupled to a laser ion source. The ion beam was nuclear-spin polarized by collinear optical pumping on the $^{2}\textit {S}_{1/2}$ – $^{2}\textit {P}_{1/2}$ transition at 280 nm. The polarization was preserved by an extended 1 mT guide field as the beam was transported via electrostatic bends into a 2.5 T longitudinal magnetic field. There the beam was implanted into a single crystal MgO target and the beta decay asymmetry was measured. Both hyperfine ground states were optically pumped with a single frequency light source, using segmentation of the beam energy, which boosted the polarization by approximately 50 % compared to pumping a single ground state. The total decay asymmetry of 0.06 and beam intensity were sufficient to provide a useful spin-1/2 beam for future BNMR experiments. A variant of the method was used previously to optically pump the full Doppler-broadened absorption profile of a beam of 11Be+ with a single-frequency light source.

We report on the status of the FrPNC experiments and summarize our plans for measurements of parity non-conservation (PNC) in a sample of cold francium. The FrPNC collaboration has commissioned a laser cooling apparatus at the TRIUMF accelerator that collects and cools francium atoms for PNC experiments. We have recently demonstrated the robust, high efficiency transfer (50 %) of laser cooled francium atoms to a second laser cooling apparatus, located 0.7 m below the first, where the PNC experiments will be conducted.

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.

The MTV experiment (Mott Polarimetry for T-Violation Experiment) is running at TRIUMF, to search for a large T-violating transverse electron-polarization in polarized 8Li β-decay. We aim at reaching precision of 10−4 for the R-correlation, which is defined as a T-violating triple vector correlation in the β-decay rate function. A Mott polarimeter system using a CDC (Cylindrical Drift Chamber) is used to measure the left-right scattering asymmetry in the Mott scattering from a thin metal foil. In the present study, we aim to discuss systematic effects in Mott polarimetry using the CDC.

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 been studying the structure of Mg isotopes in the region of the N = 20 island of inversion, to clarify the structure change as a function of the neutron number. The experiments are being performed by our unique method of β-decay spectroscopy taking advantage of highly-spin-polarized radioactive nuclear beams at TRIUMF. The β-decay asymmetry in the Na-isotope decay enables unambiguous spin-parity assignments of the levels in the daughter Mg isotope, and it becomes possible to compare the experimental data and theoretical predictions on a level-by-level basis. The present paper reports on the results of the β decay of 30Na→30Mg. From the detailed decay scheme of Na, it is suggested that the Mg levels at 1.788 MeV [(0+2 )], 3.460 MeV [(2) ], 4.967 MeV [1], and 5.414 MeV [2] have deformed shapes with intruder configurations, whereas the level at 2.466 MeV [(2+2 )] has different nature both from the spherical ground state and the deformed four levels. It is proposed that the 2+2 level is the band-head of the predicted γ-band.

To test for the microscopic magnetic phase separation in the dilute magnetic semiconductor Ga1− x Mn x As sug-gested by low energy muon spin rotation measurements [1] , we present a detailed analysis of the amplitudes of the 8 Li β-detected nuclear magnetic resonance in an epitaxially grown thin film of x = 5.4% Mn doped GaAs on a semi-insulating GaAs substrate with magnetic transition temperature TC =72 K. The spectrum at 100 K corresponds to 73% of the full room temperature amplitude, and at 60 K to about 62%. The 11% loss of signal through the magnetic tran-sition is much smaller than that ∼ 50% found by low energy μ SR [1] , and may be entirely due to an amplitude change intrinsic to GaAs. This lack of evidence for phase separation is, however, consistent with the full volume fraction magnetism found by a second low energy μSR measurement on a different sample using weak transverse field [2] .

We report the behavior of 8 Li + implanted into Platinum foil as revealed by β -detected Nuclear Magnetic Resonance ( β -NMR). At an applied field of 4.1 T, a single resonance is observed, which is attributed to Li in an octahedral interstitial site. The temperature dependence of the Knight shift for this resonance is monitored at temperatures ranging from 4 to 300 K. Over this range the Knight shift is found to be linearily dependent on the temperature.

Collinear laser spectroscopy with reverse-extracted cooled bunched beams was performed at TRIUMF with radioactive ion beams. Surface-ionized 78,78mRb ions were injected into TITAN’s cooler-buncher, and reverse-extracted to the laser beam line. There they were neutralised and excited with a counter-propagating laser beam. The fluorescence signal from the D 2 line was recorded with a photomultiplier tube. The cooler provided typically 50 ion bunches per second, with each bunch containing approximately 105 ions, temporally distributed with a 1.6 μs width. A hardware gate was set on the signal, suppressing the background by four orders of magnitude.

The level structures of 28 Mg and 29 Mg have been investigated by the β-decay of spin-polarized28 Na and 29 Na at ISAC, TRIUMF. The detailed β-γ and γ-γ coincidence measurements were performed. New γ rays and β transitions were observed both in 28 Mg and 29 Mg . We have succeeded in assigning spins and parities of many levels in 28 Mg and 29 Mg . Comparison with shell model calculations using USD Hamiltonian suggest that the structure of 28 Mg and 29 Mg are well explained in the sd-shell configurations, except for two levels at 1.095 and 1.430 MeV in 29 Mg . This suggests negative parity assignments for these levels. The evolution of sd-pf shell is discussed.

The low-energy collinear laser beam line at ISAC routinely produces highly nuclear-spin polarized beams of 8Li + for depth-controlled studies of thin films and near-surface phenomena. It also is used for nuclear structure and fundamental symmetry studies requiring other beams of polarized lithium and sodium isotopes. Further development of polarized 20F and 11Be beams is described, the latter in some detail. Laser fluorescence spectroscopy at high sensitivity using unpolarized bunched beams is briefly mentioned.

We report beta-detected NMR (β-NMR) measurements on a 50 nm thick platinum (Pt) film grown on a magnesium oxide (MgO) substrate. The frequency of the β-NMR resonance in Pt was compared to the MgO reference frequency to estimate the Knight shift at various temperatures (100-300 K). The Knight shift was found to be negative and strongly temperature dependent. The implications are discussed and compared to other transition metals that have been studied via β-NMR previously.

A low energy beam of spin polarized 8Li has been used to study the behaviour of isolated 8Li implanted into a 150 nm thick film of Al on an MgO substrate. The spin relaxation rate 1 / T 1 and β -NMR lineshape were measured as a function of temperature in a large magnetic field of 4.1 T. The resonances from different sites are unresolved due to the large nuclear dipolar interaction with the host 27Al magnetic dipole moments. Nevertheless the temperature variation of the site averaged 1 / T 1 and Knight shift show evidence for a transition between the octahedral O and substitutional S sites at about 150 K, as observed in other fcc metals.

The “cross-relaxation” method (also called “level-crossing resonance” or “avoided level-crossing”) is a powerful technique that can be used to provide detailed structural and site information on impurities in materials. In this paper, we report on the development of the cross-relaxation technique for Li + 8 at the β -detected nuclear magnetic resonance ( β -NMR) facility located in TRIUMF in Vancouver. The measurements were carried out on a 〈 1 1 0 〉 Cu single crystal where the relaxation rate of the Li 8 polarization was monitored as a function of the applied longitudinal magnetic field. The occurrence of cross-relaxation, at a particular magnetic field, between the Li 8 and the surrounding nuclei is evident as a resonant enhancement of the relaxation rate at the level crossing field. We discuss inferences about the site and structure of Li + 8 in Cu from this data.

A low energy beam of spin polarized 8 Li + has been employed to study the magnetic field distribution in an epitaxial thin film of 5.4% Mn doped GaAs(180nm) on a (100) GaAs substrate via beta-detected NMR. The spectrum is a strong function of the implantation energy in the range 28 keV to 3 keV. In the magnetic layer, there is no indication of a missing fraction, and even more remarkable, there is a broad negatively-shifted resonance. The spin lattice relaxation rate is, however, much faster in the Mn doped layer than in the substrate. A sharp peak characteristic of nonmagnetic GaAs is observed down to the lowest implantation energy, for which none of the Li should reach the substrate. This unexpected depth dependence is discussed.

On-line targets of silicon carbide have been used to produce radioactive ion beams (RIB) at TRIUMF’s ISAC facility. Surface ionized beams of Li, Na and Al from SiC targets have been delivered to a variety of experiments. While yields of Li and Na radionuclide beams have been high enough to meet experimental requirements, the yields of radio-aluminums have been very low in comparison to in-target production estimates. The properties of SiC relevant to radioactive Al ion beam production are reviewed and on-line measurements of radiogenic Li, Na and Al from SiC are presented. Diffusion, effusion and formation of stable phases are found to strongly affect the release of radio-aluminum from SiC, greatly reducing overall Al RIB production efficiency. In comparison, the production of radio-sodium beams from SiC is found to be relatively efficient.

An intense beam of 26gAl has been developed for accelerated beam experiments at TRIUMF’s ISAC facility. Studies of the on-line production of Al radionuclides from thick silicon carbide targets have been performed as part of a program of beam development for astrophysical reaction studies at ISAC. While the release of short-lived Al nuclides from SiC was found to be slow, development of new target material forms and high-power target containers has allowed operation of SiC targets with proton currents of up to 70 μA on target. In addition, operation with the TRIUMF resonant ionization laser ion source (TRILIS) has produced 26gAl beam intensities of 5.1 × 1010 s−1.

The feasibility of in-beam polarization of nuclear spin in F+ beams was studied. It was demonstrated that metastable atomic fluorine could be optically pumped on the closed transition (3s 4P5/2-3p 4D7/2) at 686 nm. The metastable production efficiency in sodium vapor was measured using optical depopulation pumping of the metastable on the (3s 4P5/2-3p 4D5/2) transition at 678 nm. At low helium density, 0.24 (+0.16/0.03) of the reionized beam was derived from metastables, implying an ion beam polarization of 24% would be feasible if the metastables were fully polarized. The hyperfine structures of the 3s 4P5/2, 3p 4D5/2 and 3p 4D7/2 states in 19F were measured via laser-induced fluorescence and modulated optical depopulation pumping. Based on these results, a scheme is suggested for polarizing 20F. Thesis work of Thomas E. Cocolios (M.Sc. 2005, McGill University, Montreal, QC) ispartof: Nuclear Instruments and Methods in Physics Research A vol:580 issue:3 pages:1571-1577 status: published

A measurement of the neutrino asymmetry is presented which represents the first search for new physics using polarized radioactive atoms initially cooled and confined in a magneto-optical trap. Optical pumping and photoionization techniques are used to generate and measure, in situ, a highly spin-polarized ( 96.5 ( 0.8 ) % ) sample of the short-lived β + -emitter 37 K. The angular distribution of neutrinos from this polarized decay, inferred from the daughter recoil asymmetry, is used to search for a hypothetical V + A current in the weak interaction. We find the ν asymmetry parameter to be B ν = − 0.755 ± 0.020 ( stat ) ± 0.013 ( syst ) , in agreement with the standard model's purely V – A interaction.

Many experiments carried out at radioactive beam facilities require the production of intense, isotopically clean and isobar free beams of a particular isotope. At TRIUMF the addition of a resonant ionization laser ion source (TRILIS) enables a multitude of new beams and therefore new experiments to be carried out. 26Al was one of the first radioactive ion beams delivered to an experiment using TRILIS. This paper outlines the development of the 26Al ion beam for nuclear astrophysics.

Reactions such as 25Al(p,λ)26Si are the key to understand the production of 26g Al and 26m Al in our galaxy. Experimental results could provide important constraints on nova nucleosynthesis and modelling where 26A1 is believed to be produced. To achieve such measurements, high-intensity and high-purity radioactive beams are required. However, production targets at ISOL-type facilities such as ISAC at TRIUMF produce high-intensity alkali beams by surface ionization on hot transfer tubes hampering the measurement of isotopes of interest. To overcome this issue, an ion source combining a segmented linear radiofrequency quadrupole (RFQ) to a laser ion source is being built. Its main function is to suppress alkali impurities whilst allowing for fast-release of short-lived isotopes. The beam production method, the RFQ/laser ion source and the removal of alkali contaminants are discussed in this paper.