M D Lunney

McGill University, Montréal, Quebec, Canada

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Publications (14)4.98 Total impact

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    ABSTRACT: Mass measurements with a relative precision of better than 1.5 à 10^â'8 were performed on 22Mg and its reaction partners 21Na and 22Na with the ISOLTRAP Penning trap mass spectrometer at CERN, yielding the mass excesses D(22Mg) = â '399.92(27) keV, D(21Na) = â'2184.71(21) keV, and D(22Na) = â'5181.56(16) keV. The importance of these results is twofold. First, a comparative half-life (Ft value)has been obtained for the superallowed β decay of 22Mg to further test the conservedvector-current hypothesis. Second, the resonance energy for the 21Na proton capture reaction has been independently determined, allowing direct comparisons of observable γ radiation in nova explosions with the yield expected from models. PACS: 21.10.Dr (Binding energies and masses), 23.40.Bw (Weak-interaction and lepton aspects), 26.30.+k (Nucleosynthesis in novae, supernovae and other explosive environments), 27.30.+t (20 ⤠A ⤠38).
    01/2004;
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    ABSTRACT: Mass measurements with the Penning trap mass spectrometer ISOLTRAP at ISOL\-DE/CERN are extended to non-surface ionizable species using newly developed ion beam bunching devices. % Masses of $^{179-197}$Hg, $^{196,198}$Pb, $^{197}$Bi, $^{198}$Po and $^{203}$At were determined with an accuracy of 1$\cdot$10$^{-7}$ corresponding to $\delta m$\,$\approx$\, 20\,keV. Applying a resolving power of up to 3.7$\cdot$10$^6$ ground and isomeric states of $^{185,187,191,193,197}$Hg were separated. First experimental values for the isomeric excitation energy of $^{187,191}$Hg are obtained. A least-squares adjustment has been performed and theoretical approaches are discussed to model the observed fine structure in the binding energy.
    01/2001;
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    ABSTRACT: The MISTRAL experiment has measured its first masses at ISOLDE. Installed in May 1997, this radiofrequency transmission spectrometer is to concentrate on nuclides with particularly short half-lives. MISTRAL received its first stable beam in October and first radioactive beam in November 1997. These first tests, with a plasma ion source, resulted in excellent isobaric separation and reasonable transmission. Further testing and development enabled first data taking in July 1998 on neutron-rich Na isotopes having half-lives as short as 31 ms.
    01/1999;
  • M. D. Lunney, R. B. Moore
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    ABSTRACT: A simulation is presented of a radiofrequency quadrupole rod system operated in the presence of He buffer gas for cooling a mass separated, decelerated ionic beam and thus, reducing its emittance. This system is being developed to benefit the sensitivity of on-line experiments using weak beams of radioactive isotopes. The numerical integration algorithm incorporates a viscous damping force modeled by a fit of mobility data of ions in a light neutral gas. Results indicate that an emittance reduction of almost 2 orders of magnitude in all coordinates is possible with near 100% transmission barring charge exchange and molecular formation.
    International Journal of Mass Spectrometry - INT J MASS SPECTROM. 01/1999; 190:153-160.
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    ABSTRACT: The MISTRAL project (Mass measurements at ISolde using a Transmission RAdiofrequency spectrometer on-Line) is scheduled to begin experiments towards the end of 1996. With high resolution (105), potentially high accuracy (510–7) and excellent sensitivity (10 s–1), the MISTRAL spectrometer promises to provide needed mass measurements in regions of very-short lived nuclei. The spectrometer operation principles are described and a discussion concerning the interest in using highly charged ions is presented.
    Hyperfine Interactions 01/1996; 99(1):105-114. · 0.21 Impact Factor
  • R. B. Moore, M. D. N. Lunney, F. Buchinger
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    ABSTRACT: The possibility of efficient collection of an ISOL-type beam in a Paul trap with buffer gas cooling [1] makes it a very useful device for increasing the sensitivity of laser observation of low production rate radionuclides. By using a trap to collect the radionuclides into a very small phase space volume and ejecting them for illumination by a pulsed laser beam, the probability of interaction of the available photons with the available radionuclides is greatly increased. Furthermore, the duration of the interaction can be greatly reduced, thereby reducing the background noise in the signals. For such usage, it is essential to know the size and shape of the phase space volume of a cloud of ions in a Paul trap. In particular, it is necessary to know it for small numbers of ions, the situation for which a possible increase in sensitivity becomes most important. This paper reports on an observation of the phase space density of ions under buffer gas cooling in a Paul trap and the ramifications of this for laser observation of extracted clouds. The technique used in this work involves time-of-flight observation of extracted clouds under variable extraction and transport conditions. An important feature of the apparatus is that it is adjustable so that the spread in the time of arrival of the ions at a detector can be made to be due to the initial spatial extent of the cloud at the center of the trap or to be due to its momentum spread. In comparison with the results of previously published work [2, 3] carried out on clouds containing much larger numbers of ions, the new results show a surprisingly small phase space volume. Apparently, the RF heating of the ions depends on the number of ions in the trap, the temperatures observed for the ion cloud being consistent with a model that predicts a 2/3 rds power dependence on this number [4]. A temperature of 0.3 eV was observed for 2  104 39K+ ions with 3 x 10 -2 Pa of He as a buffer gas and a trapping welt depth of about 60 eV. This would indicate a temperature equal to that of the buffer gas itself (room temperature or 0.025 eV) with 1000 ions or less. An extracted cloud at this temperature would have 90% of its ions within a phase space volume with dimensions of about 0.25 eV-/.ts in each of the three orthogonal coordinates. As an indication of the quality of the Paul trap as a cooling device, this corresponds to the phase space volume of a 1 mm diamcter sphere of
    Hyperfine Interactions 01/1992; 74(1):321-322. · 0.21 Impact Factor
  • R MOORE, M LUNNEY, G ROULEAU, G SAVARD
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    ABSTRACT: The collection of an ISOL beam in a Penning trap using implantation on a surface that is subsequently manipulated so as to become part of an end electrode of a Penning trap and reionization of the implanted material by heat has already been very productive for high-precision nuclear-mass measurements, even though it is limited to elements that are surface ionizable and the collection efficiencies are never better than about 0.1%. More recently, in 1990 a Paul trap system for electric collection of ions was installed at the ISOLDE-3 facility and collection was demonstrated for a 60 kV beam of 132Xe ions. The purpose of this test setup was to determine the relationship between phase space volume of a typical trap and the collection efficiency that could be obtained in direct capture. For the modest trap used, collection efficiencies of up to 0.2% were achieved. A beam of negative bromine ions was collected by simply reversing the polarities of all voltages used. From the experience with this system it appears feasible to build a Paul trap which is about three times as large in linear dimensions as the existing one and which could be driven at up to 10 kV peak at 1 MHz using a modest rf amplifier (300 W). With moderate prebunching of the injected beam at 1 MHz, this system should achieve collection efficiencies approaching 100%. Based on these results, preliminary design work is being carried out on the collection system to be installed at the ISOLDE Booster facility. Suggestions for other uses of a Paul trap collection system for ISOL beams are presented.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 01/1992; 70:482-489. · 1.19 Impact Factor
  • M. D. N. Lunney, F. Buchinger, R. B. Moore
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    ABSTRACT: A measurement of the temperature of a typical ion cloud in a Paul trap with buffer gas cooling has been made using time-of-flight of the extracted ion cloud. A temperature of 0·3 ± 0·1 eV was obtained for 20 00039K ions in a trap of potential well depth 60 eV with helium buffer gas at 3 × 10−2 Pa. This value is intermediate by a factor of about 10 in each direction between that of other published works using different observational methods on Paul traps operated under similar conditions. Explanations for the discrepancies are suggested. In any case, the present work indicates that sub-electronvolt temperatures can be achieved, at least for small trap loadings. The result considerably eases the design of transport systems for such ion clouds and greatly enhances the possible uses of a Paul trap collection device for highly sensitive precise experiments.
    Journal of Modern Optics 01/1992; 39:349-360. · 1.16 Impact Factor
  • M. David N. Lunney, J. P. Webb, R. B. Moore
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    ABSTRACT: A radio‐frequency quadrupole ion trap is an axisymmetric arrangement of electrodes used to contain charged particles. The field between the electrodes must be calculated using numerical techniques, as practical implementations of the trap cause the potential distribution to deviate from the closed form. The finite‐element method has been used to compute the electric field and a fourth‐order numerical integration has been written to compute ion trajectories inside the trap. Together, these computations were used to study the injection of ions into traps. Results from injection simulations are compared with experimental observations.
    Journal of Applied Physics 05/1989; · 2.21 Impact Factor
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    ABSTRACT: Mass measurements of high precision have been performed on sodium isotopes out to $^{30}$Na using a new technique of radiofrequency excitation of ion trajectories in a homogeneous magnetic field. This method, especially suited to very short-lived nuclides, has allowed us to significantly reduce the uncertainty in mass of the most exotic Na isotopes: a relative error of 5\audi was achieved for $^{28}$Na having a half-life of only 30.5 ms and 9\audi for the weakly produced $^{30}$Na. Verifying and minimizing binding energy uncertainties in this region of the nuclear chart is important for clarification of a long standing problem concerning the strength of the $N~=~20$ magic shell closure. These results are the fruit of the commissioning of the new experimental program Mistral.
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    ABSTRACT: The MISTRAL experiment for measuring masses of very short-lived nuclides at ISOLDE has been installed during the summer of 1997 and has had its first radioactive beam in November 1997. Tests are presently been carried out to study all possible systematic effects. This paper recalls the basic principles of the Smith-type radio-frequency spectrometer, gives its present characteristics and limitations, and describes the methods used to improve its performances.
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    ABSTRACT: The MISTRAL experiment (Mass measurements at ISOLDE with a Transmission and Radiofrequency spectrometer on-Line), conceived for very short-lived nuclides, has reached the end of its commissioning phase. Installed in 1997, results have been obtained consistent with all aspects of the projected spectrometer performance: nuclides with half-lives as short as 30 ms have been measured and accuracies of 0.4 ppm have been achieved, despite the presence of a systematic shift and difficulties with isobaric contamination. Masses of several nuclides, including $^{25-26}$Ne and $^{32}$Mg that forms the famous island of inversion around $N$~=~20, have been significantly improved.
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    M D Lunney, R B Moore
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    ABSTRACT: A simulation is presented of a radiofrequency quadrupole (RFQ) rod system operated in the presence of He buffer gas for cooling a mass separated, decelerated ionic beam and thus, reducing its emittance. This system is being developed to benefit the sensitivity of on-line experiments using weak beams of radioactive isotopes. The numerical integration algorithm incorporates a viscous damping force modeled by a fit of mobility data of ions in a light neutral gas. Results indicate that an emittance reduction of almost two orders of magnitude in all coordinates is possible with near 100% transmission barring charge exchange and molecular formation.