New mass value for 7Li

Penning-Trap Mass Measurement of Helium-4

Light-ion trap (LIONTRAP), a high-precision Penning-trap mass spectrometer, was used to determine the atomic mass of ^{4}He. Here, we report a 12 parts-per-trillion measurement of the mass of a ^{4}He^{2+} ion, m(^{4}He^{2+})=4.001 506 179 651(48)  u. From this, the atomic mass of the neutral atom can be determined without loss of precision: m(^{4}He)=4.002 603 254 653(48)  u. This result is slightly more precise than the current CODATA18 literature value but deviates by 6.6 standard deviations.

Elucidation of the anomalous A=9 isospin quartet behavior

Recent high-precision mass measurements of 9Li and 9Be, performed with the TITAN Penning trap at the TRIUMF ISAC facility, are analyzed in light of state-of-the-art shell model calculations. We find an explanation for the anomalous isobaric mass multiplet equation behavior for the two A=9 quartets. The presence of a cubic d=6.3(17) keV term for the J(π)=3/2(-) quartet and the vanishing cubic term for the excited J(π)=1/2(-) multiplet depend upon the presence of a nearby T=1/2 state in 9B and 9Be that induces isospin mixing. This is contrary to previous hypotheses involving purely Coulomb and charge-dependent effects. T=1/2 states have been observed near the calculated energy, above the T=3/2 state. However, an experimental confirmation of their J(π) is needed.

A battery-based, low-noise voltage source

A highly stable, low-noise voltage source was designed to improve the stability of the electrode bias voltages of a Penning trap. To avoid excess noise and ground loops, the voltage source is completely independent of the public electric network and uses a 12 V car battery to generate output voltages of +/-15 and +/-5 V. First, the dc supply voltage is converted into ac-voltage and gets amplified. Afterwards, the signal is rectified, filtered, and regulated to the desired output value. Each channel can deliver up to 1.5 A. The current as well as the battery voltage and the output voltages can be read out via a universal serial bus (USB) connection for monitoring purposes. With the presented design, a relative voltage stability of 7 x 10(-7) over 6.5 h and a noise level equal or smaller than 30 nV/square root(Hz) is achieved.

Why is sideband mass spectrometry possible with ions in a Penning trap?

Many masses, particularly the masses of unstable nuclei, are measured with ions in Penning traps by determining the frequency of a driving force that most efficiently couples two of the three motions of trapped ions. A missing explanation of why such sideband mass spectroscopy works, contrary to simple estimates, begins with the established Brown-Gabrielse invariance theorem.

First Penning-trap mass measurement of the exotic halo nucleus 11Li

In this Letter, we report a new mass for 11Li using the trapping experiment TITAN at TRIUMF's ISAC facility. This is by far the shortest-lived nuclide, t_{1/2}=8.8 ms, for which a mass measurement has ever been performed with a Penning trap. Combined with our mass measurements of ;{8,9}Li we derive a new two-neutron separation energy of 369.15(65) keV: a factor of 7 more precise than the best previous value. This new value is a critical ingredient for the determination of the halo charge radius from isotope-shift measurements. We also report results from state-of-the-art atomic-physics calculations using the new mass and extract a new charge radius for 11Li. This result is a remarkable confluence of nuclear and atomic physics.

Direct mass measurement of the four-neutron halo nuclide 8He

A high-precision Penning trap mass measurement of the exotic 8He nuclide (T(1/2)=119 ms) has been carried out resulting in a reduction of the uncertainty of the halo binding energy by over an order of magnitude. The new mass, determined with a relative uncertainty of 9.2 x 10(-8) (deltam=690 eV) is 13 keV less bound than the previously accepted value. The mass measurement is of great relevance for the recent charge-radius measurement of 8He [P. Mueller, Phys. Rev. Lett. 99, 252501 (2007).10.1103/PhysRevLett.99.252501]. The 8He mass is the first result from the newly-commissioned Penning trap: TITAN (TRIUMF's Ion Trap for Atomic and Nuclear science) at the ISAC (Isotope Separator and Accelerator) radioactive beam facility at TRIUMF.

Isotope shift of the 32S 1/2 -22S 1/2 transition in lithium and the nuclear polarizability

High precision calculation of the isotope shift of the 3(2)S(1/2)-2(2)S(1/2) transition in lithium is presented. The wave function and matrix elements of relativistic operators are obtained by using recursion relations. Apart from the relativistic contribution, we obtain the nuclear polarizability correction for 11Li. The resulting difference of the squared charge radii 11Li-7Li based on the measurements of Sánchez et al. [Phys. Rev. Lett. 96, 033002 (2006)10.1103/PhysRevLett.96.033002] is deltar(ch)(2)=0.157(81) fm(2), which significantly differs from the previous evaluation.