CARIBU: a new facility for the study of neutron-rich isotopes

The Californium Rare Ion Breeder Upgrade (CARIBU) to the ATLAS superconducting linac facility is currently being commissioned. It provides low-energy and re-accelerated beams of neutron-rich isotopes obtained from ²⁵²Cf fission. The fission products from a ²⁵²Cf source are stopped in a large high-intensity gas catcher, thermalized and extracted through an RFQ cooler, accelerated to 50 kV and mass separated in a high-resolution separator before being sent to either an ECR charge breeder for post-acceleration through the ATLAS linac or to a low-energy experimental area. This approach gives access to beams of very neutron-rich isotopes, many of which have not been available at low or Coulomb barrier energies previously. These beams provide unique opportunities for measurements along the r-process path. To take advantage of these unique possibility, the reaccelerated beams from CARIBU will be made available at the experimental stations of ATLAS to serve equipment such as Gammasphere, HELIOS and the reaction spectrometers. In addition, the Canadian Penning Trap (CPT) mass spectrometer has been moved to the CARIBU low-energy experimental area and a new injection line has been built. The new injection line consists of a RFQ buncher sitting on a 50 kV high-voltage platform that will accumulate the mass separated 50 kV radioactive beams, cool and extract them as a pulsed beam of 3 keV. This beam can be sent either to a tape station for diagnostics and tuning, or a cryogenic linear trap for preparation before transfer to the high-precision Penning trap where the mass measurements will take place. Initial CARIBU commissioning is proceeding with a 2 mCi source that will be replaced by a 100 mCi source as the commissioning proceeds. Final operation will use a 1 Ci source and attain yield in excess of 10⁷ ions/sec for the most intense beams at low energy, an order of magnitude less for reaccelerated beams.     

Mass Measurements of 114–124,130Xe with the ISOLTRAP Penning Trap Spectrometer

The masses of the xenon isotopes with 114≤A≤123 were directly measured for the first time. The experiments were carried out at the ISOLTRAP triple trap spectrometer at the on-line mass separator ISOLDE/CERN. A mass resolving power of the Penning trap spectrometer of m/Δm≈500 000 was chosen and an accuracy of δm≈12keV for all investigated Xe isotopes was achieved. An atomic mass evaluation was performed and the results of this adjustment are compared with theoretical predictions. The new results for the xenon isotopes and their effects on neighboring nuclides are discussed within the two-neutron separation energy picture. This revised version was published online in July 2006 with corrections to the Cover Date.     

Penning trap mass measurements of rare isotopes produced by projectile fragmentation with LEBIT at NSCL

The Low-Energy Beam and Ion Trap facility LEBIT at the NSCL at MSU has demonstrated that rare isotopes produced by fast-beam fragmentation can be slowed down and prepared for precision experiments with low-energy beams. High-pressure gas-stopping was combined with advanced ion manipulation techniques to carry out these studies with a high-precision 9.4-Tesla Penning trap mass spectrometer. The spectrometer has been used for a series of high precision mass measurements of short-lived neutron- and proton-rich isotopes during the past year. This paper presents an overview of the LEBIT facility and summarizes the first mass measurement results. The mass measurements of ⁸¹Se, where ground and isomeric states have been resolved, and of ⁸⁰As will be discussed in detail.     

New Methods for Fully Automated Isotope Ratio Determination from Hydrogen at the Natural Abundance Level

Abstract

A variety of methods for measurement of ²H/¹H from H₂ are evaluated for their ability to be fully automated and for applicability to automated isotopic analysis of water and organic compounds. Equilibration of water with H₂ gas with the aid of a platinum catalyst has been commercialized into a fully automated sample preparation device. A second and newer technique, involving injecting water, methane, or other volatile organic compounds onto hot chromium in a reactor attached to the dual inlet system of a gas isotope ratio mass spectrometer, can be integrated with a conventional GC-autosampler to allow automated analysis of a variety of substrates. Both techniques result in precisions around 1‰ (δ notation) on the VSMOW scale, and are fast and accurate, and with appropriate mass spectrometers require only negligible scaling for the SLAP/VSMOW difference. Several experimental methods which show considerable promise employ “isotope ratio monitoring” (irm) inlet systems, in which a carrier gas is used for transport of H₂ to the mass spectrometer. Any such method has to address the problem of He ions corrupting the measurement of the H₂ ions. One such approach uses a heated palladium membrane for selective introduction of H₂ into the mass spectrometer, and a second involves modifications to the ion optics to control the stray helium ions. Both approaches have significant limitations that must be overcome before irm techniques can be used in routine applications, in particular for measuring hydrogen isotopes from GC effluents (irm-GCMS).     

Accurate masses of unstable rare-earth isotopes by ISOLTRAP

Direct mass measurements of neutron-deficient rare-earth isotopes in the vicinity of ¹⁴⁶Gd were performed with the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. This paper reports on the measurement of more than 40 isotopes of the elements praseodymium, neodymium, promethium, samarium, europium, dysprosium and holmium, that have been measured with a typical accuracy of m 14 keV. An atomic mass evaluation has been performed taking into account other experimental mass values via a least-squares adjustment. The results of the adjustment are discussed. Received: 18 April 2000 / Accepted: 12 July 2000     

Improvement of the Applicability, Efficiency, andPrecision of the Penning Trap Mass Spectrometer ISOLTRAP

With the Penning trap mass spectrometer ISOLTRAP, close to 200 nuclides have already been investigated and their masses determined with a typical relative precision of δm/m=10⁻⁷. Recently, ISOLTRAP's beam preparation system was replaced by an RFQ ion beam cooler and buncher. The principle and the characteristics of this new beam preparation system will be presented. It is planned to use ions of various carbon clusters C⁺ _n (n>1) as reference ions for mass measurements. Apart from negligible molecular binding energies, these clusters have masses that are exact multiples of the unified atomic mass unit. This will allow ISOLTRAP to carry out absolute mass measurements as well as to investigate possible mass-dependent systematic errors. The results of tests of the production, transport, and trapping of such carbon clusters will be presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

The LEBIT facility at MSU

The low-energy beam and ion trap facility LEBIT at the NSCL at MSU has demonstrated that rare isotopes produced by fast-beam fragmentation can be slowed down and prepared such that precision experiments with low-energy beams are possible. For this purpose high-pressure gas-stopping is employed combined with advanced ion manipulation techniques. Penning trap mass measurements on short-lived rare isotopes have been performed with a 9.4 T Penning trap mass spectrometer. Examples include ⁶⁶As, which has a half-live of only 96 ms, and the super-allowed Fermi-emitter ³⁸Ca, for which a mass accuracy of 8 ppb (280 eV) has been achieved. The high accuracy of this new mass value makes ³⁸Ca a new candidate for the test of the conserved vector current hypothesis.      

Isotopieverschiebung der natürlichen geraden und ungeraden Sm- und Nd-Isotope

The isotope shift of the natural isotopes of Sm and Nd was investigated by a digital recording Fabry-Perot spectrometer using highly enriched samples. By the accuracy achieved in the measurements it was possible to verify earlier results indicating different relative isotope shifts for lines with positive and negative displacements, and to show that also lines with the same sign of the displacement may have different relative isotope shifts. It is shown that these non-constant relative isotope shifts can be explained for the even isotopes by the different contributions of the mass and volume effect to the isotope shifts in the different lines, but this explanation seems only to be partly valid for some distances between even and odd isotopes. The size of the mass effect is estimated and its influence especially on the results of the odd-even staggering is considered. The odd-even staggering is compared to earlier results for Hg. The estimation of the mass effect shows that the results forδ〈r ²〉 determined from the measured isotope shifts without correcting for the mass effect may be considerably wrong. Nevertheless it is possible by a suitable combination of the measured distances to calculate a quantity which only depends on nuclear properties and which therefore enables to check the known theories of the volume dependent isotope shift also without calculating the probability density of thes-electrons at the nucleus.     

Penning-trap mass measurements on <Superscript>92, 94-98, 100</Superscript>Mo with JYFLTRAP

Penning-trap measurements on stable ^{92, 94-98, 100}Mo isotopes have been performed with relative accuracy of \(\ensuremath 1\cdot 10^{-8}\) with the JYFLTRAP Penning-trap mass spectrometer by using ⁸⁵Rb as a reference. The Mo isotopes have been found to be about 3keV more bound than given in the Atomic Mass Evaluation 2003 (AME03). The results confirm that the discrepancy between the ISOLTRAP and JYFLTRAP data for ^101-105Cd isotopes was due to an erroneous value in the AME03 for ⁹⁶Mo used as a reference at JYFLTRAP. The measured frequency ratios of Mo isotopes have been used to update mass-excess values of 30 neutron-deficient nuclides measured at JYFLTRAP.     

First observation of medium-spin excitations in the <Superscript>138</Superscript>Cs nucleus

The Penning trap mass spectrometer JYFLTRAP, coupled to the Ion Guide Isotope Separator On-Line (IGISOL) facility at Jyv?skyl?, was employed to measure the atomic masses of neutron-rich ^70-73Ni and ^{73, 75}Cu isotopes with a typical accuracy less than 5keV. The mass of ⁷³Ni was measured for the first time. Comparisons with the previous data are discussed. Two-neutron separation energies show a weak subshell closure at ⁶⁸ ₂₈Ni₄₀ . A well established proton shell gap is observed at Z = 28 .     

Can an IR Diode Laser Spectrometer be Used for the Determination of Natural Isotope Ratios in Biological Samples?

Abstract

An IR diode laser spectrometer can detect the enrichment of stable isotopes (¹³C [1] and ¹⁵N[2]) in tracer studies. However our system cannot detect differences of the natural abundances of these isotopes. This problem is not a principal limitation of the IR diode laser spectroscopy, but is inherent to our standard system. A new isotope ratio IR diode laser spectrometer has an accuracy high enough for most biological applications. Some advantages like flexibility in measuring different isotopes, insensitivity against other gases in the sample and price are correlated to this system.     

Possibility of the use of the magnetic field for creating a quantum filter on the <Emphasis Type="Italic">D</Emphasis><Subscript>1</Subscript><Superscript>87</Superscript>Rb line

The possibility of the use of the F = 2?F = 1 transition of the D ₁ absorption line of the ⁸⁷Rb atom for creating of a single-photon quantum filter based on coherent population trapping (CPT) has been analyzed. It has been shown that the external magnetic field is necessary for ensuring the creation of the quantum filter on boson isotopes of alkali atoms. The field strength should be enough for the manifestation of the splitting of the Zeeman CPT resonances that is much larger than their spectral widths. The splittings of the CPT resonances, which characterize the nonlinearity of the Zeeman effect, have been measured for the ⁸⁷Rb atom and the possibility of the use of this system for the quantum filter is concluded.     

Towards direct mass measurements of nobelium at SHIPTRAP

The Penning-trap mass spectrometer SHIPTRAP allows precision mass measurements of rare isotopes produced in fusion-evaporation reactions. In the first period of operation the masses of more than 50 neutron-deficient radionuclides have been measured. In this paper the perspectives for direct mass measurements of rare isotopes around nobelium are discussed and the achievable precision is addressed. The temporal stability of the magnetic field, an important issue for the long measurement times resulting from the low production rates, was investigated and the time-dependent uncertainty due to magnetic field fluctuations was determined. Based on the present performance direct mass measurements of nobelium isotopes are already feasible. With several technical improvements heavier elements between Z=102–105 will be in reach.     

Mass-spectrometric measurements of exotic Rb,Cs and Fr isotopes

Direct mass measurements of exotic nuclei have been performed with a double-focussing mass spectrometer on line with an isotope separator. We report here on mass measurements with improved accuracy of exotic isotopes of Rb and Cs and on the first measurement of the masses of ¹¹⁶Cs and ¹⁴⁸Cs.     

High-precision masses of 29-33Mg and the N = 20 shell “closure”

High-precision mass measurements have been performed on the exotic magnesium isotopes ^29-33Mg using the MISTRAL radiofrequency spectrometer, especially suited for very short-lived nuclides. This method, combined with the powerful tool of resonant laser ionization at ISOLDE, has provided a significant reduction of uncertainty for the masses of the most exotic Mg isotopes: a relative error of 7×10^-7 was achieved for the weakly produced ³³Mg that has a half-life of only 90ms. Moreover, the mass of ³³Mg is found to change by over 250keV. Verifying and minimizing binding energy uncertainties in this region of the nuclear chart is important for understanding the lack of binding energy that is normally associated with magic numbers.     

Isotope Studies of Hydrogen and Oxygen in Ground Ice - Experiences with the Equilibration Technique

Abstract

Equilibration technique suitable for a large amount ofsamples is described for hydrogen and oxygen isotope analyses of ground ice, especially ice wedges, including the sampling strategy and the analytical procedure as well as the calibration of the Finnigan MAT Delta-S mass spectrometer in June, 1999. Since for future analyses of ice wedges, a higher sampling resolution with limited sample volume is required, the limit of the equliibration technique for small water samples size of between 0.05 and 5 ml was checked. For water samples smaller than 1ml, corresponding to a molar ratio [H₂O]/[H₂] of smaller than 0.994, a balance correction has to be applied. The experimental errors due to partial evaporation during evacuation, the balance calcultion of the isotope equilibration process, the linearity as well as memory effects of the mass spectrometer for smaples with large differences in δ¹⁸O and δD are tackled in this paper. In the polar regions of Northern Siberia without Late Pleistocene and Holocene glaciation, ground ice is used as an archive for paleoclimate studies. First results of stable isotope measurements on ice wedges clearly show a shift towards heavier isotopes and thus warmer winter temperatures as well as a change in the source of the precipitation between Late Pleistocene and Holocene. These results indicate the high potential of ground ice for paleoclimate studies.     

Shape Coexistence and the N=28 Shell Closure Far from Stability

A mass measurement experiment by a time of flight method with the SPEG spectrometer at GANIL has been performed to investigate the N=20 and N=28 shell closures far from stability. The masses of 31 neutron-rich nuclei in the range A=29–47 have been measured. The precision of 19 masses has been significantly improved and 12 masses were measured for the first time. The neutron-rich Cl, S and P isotopes are seen to exhibit a change in shell structure around N=28. Comparison with shell model and relativistic mean field calculations demonstrate that the observed effects arise from deformed prolate ground state configurations associated with shape coexistence. The evidence of an isomeric state in the ⁴³S and its interpretation by a shell model calculation confirm the analysis of the masses and constitutes the first evidence of the predicted shape coexistence around N=28. This revised version was published online in July 2006 with corrections to the Cover Date.     

High-resolution mass spectra of the residual gas in a metallic vacuum system

The mass spectra of the residual gas in a metallic vacuum chamber of capacity 3 l are studied with an MI-9303 high-resolution magnetic resonance mass spectrometer in the mass range 1–140 u. The experiments are carried out under four evacuation conditions in the pressure range P = 10⁻⁸–10⁻¹⁰ Torr, and almost all the mass peaks forming multiplets are resolved. It is shown that the multiplets with mass numbers M≤80 have, as a rule, a multicomponent structure and hydrogen is the basic component responsible for the total pressure in the chamber irrespective of evacuation conditions. Next in order of intensity in the mass spectra are, CH ₄ ⁺ , H²O⁺, CO⁺, and CO ₂ ⁺ peaks. Other lines in the residual gas spectra are largely due to various C-, H-, N-, and O-based compounds. In addition, the background mass spectrum involves Cl-and F-based compounds and noble gas isotopes. The multiplets with M > 80 often degenerate into a single hydrocarbon line.     

Hamiltonian formalism for non-invariant dynamics

In a completely Hamiltonian dynamical system, there will be a generating functionH _Y for each infinitesimal space-time transformationY. In the non-autonomous case, theH _Y depend on the observer. This dependence is here described by a system of commutation relations. It is also shown that these relations can be made to mirror exactly the commutation relations of theY's in the Lorentz-invariant case.The preparation of this paper was supported in part by NSF grant GP-33696X. It is a pleasure to acknowledge discussions with Professor H. Bacri, D. Kastler, J. M. Souriau and others at CNRS, CPT, Marseilles.     

Exploring new mass regions with the ISOLTRAP spectrometer

First direct mass measurements on rare earth isotopes around ¹⁴⁶Gd have been performed with the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. More than 40 isotopes of the elements Pr, Nd, Pm, Sm, Eu, Dy and Ho have been measured with an accuracy of typically 1 × 10^-7. In the case of ¹⁴¹Sm isomeric and ground state (ΔE = 175 keV) were resolved. Since isobaric contaminations are present in the ISOLDE beam, these measurements on rare earth isotopes became only possible after the installation of a new cooler trap which acts an isobar separator. This revised version was published online in August 2006 with corrections to the Cover Date.