Mass measurements and evaluation around A = 22

Frequency ratio measurements with different combinations of the singly charged ions from ^{21, 22, 23}Na , ^{22, 24}Mg , and ^{37, 39}K were performed at the on-line Penning trap mass spectrometer ISOLTRAP, CERN, Geneva. The masses and mass differences were deduced with a relative uncertainty of about or even below one part in 10⁸ for the ions of interest using a least-squares analysis of all measured relations. The results have direct consequences for weak-interaction study as they give additional input to the test of CVC, and for nuclear astrophysics, because they help to establish the minimum observable signal for a NeNa cycle in a nova burst. We report here about the measurements and the detailed evaluation.     

From direct to absolute mass measurements: A study of the accuracy of ISOLTRAP

For a detailed study of the accuracy of the Penning trap mass spectrometer ISOLTRAP all expected sources of uncertainty were investigated with respect to their contributions to the uncertainty of the final result. In the course of these investigations, cross-reference measurements with singly charged carbon clusters ¹²C⁺ _n were carried out. The carbon cluster ions were produced by use of laser-induced desorption, fragmentation, and ionization of C₆₀ fullerenes and injected into and stored in the Penning trap system. The comparison of the cyclotron frequencies of different carbon clusters has provided detailed insight into the residual systematic uncertainty of ISOLTRAP and yielded a value of 8×10^-9. This also represents the current limit of mass accuracy of the apparatus. Since the unified atomic mass unit is defined as 1/12 of the mass of the ¹²C atom, it will be possible to carry out absolute mass measurements with ISOLTRAP in the future. Received 7 June 2002 Published online 6 November 2002 RID="a" ID="a"e-mail: a.kellerbauer@cern.ch RID="b" ID="b"Current address: Centre de Physique des Particules de Marseille, 13288 Marseille Cedex 9, France.     

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     

New mass data for the rp-process above Z = 32

High-accuracy mass measurements have been performed with the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN. The short-lived nuclides ^{70, 71, 72, 73}Se , ^{72, 73, 74, 75}Br , and ^{98, 99, 100, 101, 103}Ag have been measured with an average uncertainty of a few keV. The data are important input for nucleosynthesis calculations of the rp-process beyond Z = 32 .     

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.     

High-precision mass measurements of hydrogen-like <Superscript>24</Superscript>Mg<Superscript>11+</Superscript> and <Superscript>26</Superscript>Mg<Superscript>11+</Superscript> ions in a Penning trap

For the determination of the bound-electron g factor in hydrogen-like heavy ions the mass of the ion is needed at a relative uncertainty of at least 1 ppb. With the SMILETRAP Penning trap mass spectrometer at the Manne Siegbahn Laboratory in Stockholm several mass measurements of ions with even-even nuclei at this level of precision have been performed so far, exploiting the fact that the mass precision increases linearly with the ion charge. Measurements of masses of the hydrogen-like ions of the two Mg-isotopes ²⁴Mg and ²⁶Mg are reported. The masses of the hydrogen-like ions are 23.979011054(14) u and 25.976562354(34) u, corresponding to the atomic masses 23.985041690(14) u and 25.982592986(34) u, respectively. The possibility to use these two isotopes for the first observation of an isotope effect in the bound-electron g factor in hydrogen-like heavy ions is discussed.     

Study of Muon-Catalyzed Fusion in Ortho–Para Controlled Solid Deuterium

Recently, the applicability of Penning trap mass spectrometry has been extended to nuclides with a half-life of less than one second. The mass of ³³Ar (T _1/2=174 ms) was measured using the ISOLTRAP spectrometer with an accuracy of 4.2 keV. This measurement provided a stringent test of the Isobaric Multiplet Mass Equation (IMME) at mass number A=33 and isospin T=3/2. The fast measurement cycle that shows the way to other measurements of very-short-lived nuclides is presented. Furthermore, the results of the IMME test are displayed. This revised version was published online in July 2006 with corrections to the Cover Date.     

High-accuracy mass determination of unstable cesium and barium isotopes

Direct mass measurements of short-lived Cs and Ba isotopes have been performed with the tandem Penning trap mass spectrometer ISOLTRAP installed at the on-line isotope separator ISOLDE at CERN. Typically, a mass resolving power of 600 000 and an accuracy of δm ≈ 13 keV have been obtained. The masses of ^123,124,126Ba and ^122mCs were measured for the first time. A least-squares adjustment has been performed and the experimental masses are compared with theoretical ones, particularly in the frame of a macroscopic-microscopic model.     

Accurate mass measurements of very short-lived nuclei

Mass measurements of ³⁴Ar, ^73-78Kr, and ^74,76Rb were performed with the Penning-trap mass spectrometer ISOLTRAP. Very accurate Q _EC-values are needed for the investigations of the t-value of 0⁺ → 0⁺ nuclear β-decays used to test the standard model predictions for weak interactions. The necessary accuracy on the Q _EC-value requires the mass of mother and daughter nuclei to be measured with δm/m ⩽ 3 ^. 10^-8. For most of the measured nuclides presented here this has been reached. The ³⁴Ar mass has been measured with a relative accuracy of 1.1 ^. 10^-8. The Q _EC-value of the ³⁴Ar 0⁺ → 0⁺ decay can now be determined with an uncertainty of about 0.01%. Furthermore, ⁷⁴Rb is the shortest-lived nuclide ever investigated in a Penning trap. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: frank.herfurth@cern.ch     

Breakdown of the isobaric multiplet mass equation at A = 33, T = 3/2

Mass measurements on (33,34,42,43)Ar were performed using the Penning trap mass spectrometer ISOLTRAP and a newly constructed linear Paul trap. This arrangement allowed us, for the first time, to extend Penning trap mass measurements to nuclides with half-lives below one second ( 33Ar: T(1/2) = 174 ms). A mass accuracy of about 10(-7) (deltam approximately 4 keV) was achieved for all investigated nuclides. The isobaric multiplet mass equation was checked for the A = 33, T = 3/2 quartet and found to be inconsistent with the generally accepted quadratic form.     

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.     

High-accuracy mass measurements in ion traps and storage rings

High-accuracy mass measurements have recently been performed on radioactive isotopes produced by proton-induced spallation at the on-line isotope separator ISOLDE at CERN and by heavy-ion projectile fragmentation at the fragment separator FRS at GSI. At ISOLDE, singly charged ions were injected into the Penning trap mass spectrometer ISOLTRAP and their masses determined by observing their cyclotron frequencies in the homogeneous magnetic field of the ion trap. At GSI, bare, hydrogen, or helium-like ions were injected into the experimental storage ring ESR, electron-cooled to the same velocity, and their masses determined by observing their revolution frequencies in the ESR. With ISOLTRAP and ESR, resolving power in the range of 4 × 10⁵< = m/Δ m(FWHM)< = 10⁷ and an accuracy up to \delta m/m~ 10^-7 were achieved for radioactive isotopes. Mass measurements of highly charged ions of stable isotopes were performed at Stockholm by use of SMILETRAP. In this case, a resolving power of about 10⁸ and an accuracy close to 10^-9 were obtained. This revised version was published online in August 2006 with corrections to the Cover Date.     

Accurate Mass Determination of Neutron-Deficient Nuclides Close to Z=82 with ISOLTRAP

The recent implementation of gas-filled radiofrequency traps for efficient ion beam bunching extended the applicability of the Penning trap mass spectrometer ISOLTRAP/CERN to non-surface ionizable species. In a first series of successful runs the masses of ^182–197Hg, ^196,198Pb, ¹⁹⁷Bi, ¹⁹⁸Po and ²⁰³At have been determined with an accuracy of 1⋅10⁻⁷. In order to unambiguously determine the ground state mass the ground and isomeric states of ^{185,187,191,193,197}Hg were separated applying a resolving power of up to 3.7⋅10⁶. First experimental values for the isomeric excitation energy of ^187,191Hg were obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

RF-coupling and cooling techniques of stored heavy ions

A tandem Penning trap system, the ISOLTRAP, is now used at the on-line mass separator ISOLDE at CERN, Geneva, for accurate mass measurements of short-lived nuclei. The mass of the stored ions is measured by the determination of the cyclotron frequency _c=qB/m in theB=6 T magnetic field of the trap. A new technique has been developed and implemented to allow reliable high-efficiency loading of the trap with radioactive heavy ions.     

Penning trap mass spectrometry for nuclear structure studies

High-precision mass measurements as performed at the Penning trap mass spectrometer ISOLTRAP at ISOLDE/CERN are an important contribution to the investigation of nuclear structure. Precise nuclear masses with less than 0.1 ppm relative mass uncertainty allow stringent tests of mass models and formulae that are used to predict mass values of nuclides far from the valley of stability. Furthermore, an investigation of nuclear structure effects like shell or sub-shell closures, deformations, and halos is possible. In addition to a sophisticated experimental setup for precise mass measurements, a radioactive ion-beam facility that delivers a large variety of short-lived nuclides with sufficient yield is required. An overview of the results from the mass spectrometer ISOLTRAP is given and its limits and possibilities are described.      

SMILETRAP?II

The new Penning trap mass spectrometer SMILETRAP II has been set up at the AlbaNova Research Center, Stockholm. Based on the former spectrometer SMILETRAP I, it uses the merits of highly-charged ions to achieve high precision in the mass measurements. Various improvements over the SMILETRAP I setup will allow to routinely perform mass measurements with relative uncertainties of 10^???10 and below. In this paper we will discuss the limitations of SMILETRAP I and present the corresponding improvements of SMILETRAP II. An overview on the SMILETRAP II setup is given.     

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.     

Preparing a journey to the east of 208Pb with ISOLTRAP: Isobaric purification at A = 209 and new masses for 211-213Fr and 211Ra

With the Penning trap mass spectrometer ISOLTRAP, located at ISOLDE/CERN, preparatory work has been performed towards mass and decay studies on neutron-rich Hg and Tl isotopes beyond N = 126 . The properties of these isotopes are not well known because of large isobaric contamination coming mainly from surface-ionised Fr. Within the studies, production tests using several target-ion source combinations were performed. It was furthermore demonstrated around mass number A = 209 that the resolving power required to purify Fr is achievable with ISOLTRAP. In addition, masses of several isobaric contaminants, ^211-213Fr and ²¹¹Ra , were determined with a three-fold improved precision. The results influence masses of more than 20 other nuclides in the ²⁰⁸Pb region.     

Extending and refining the nuclear mass surface with ISOLTRAP and MISTRAL

Through the nuclear binding energy, the atomic mass gives us important information about nuclear structure. Viewing the ensemble of mass data over the nuclear chart, we can examine the hills and valleys that form this surface and make hypotheses about the effects of certain nuclear configurations. To unveil these effects, mass measurements of very high precision (<10⁻⁶) are required. Two experiments at ISOLDE pursue this effort of nuclear cartography: the tandem Penning trap spectrometer ISOLTRAP and the radiofrequency transmission spectrometer MISTRAL. Between them, the masses of almost 150 nuclides have been measured from stable isotopes to those with half-lives as short as 30 ms. Both experiments rely on good optical properties of a low energy ion beam and are thus well suited to the ISOLDE facility. This revised version was published online in July 2006 with corrections to the Cover Date.