Precision Atomic Mass Measurements Research Articles

Status of CHIP-TRAP: The Central Michigan University High-Precision Penning Trap

Precise and accurate atomic mass data provide crucial information for applications in a wide range of fields in physics and beyond, including astrophysics, nuclear structure, particle and neutrino physics, fundamental symmetries, chemistry, and metrology. The most precise atomic mass measurements are performed on charged particles confined in a Penning trap. Here, we describe the development, status, and outlook of CHIP-TRAP: the Central Michigan University high-precision Penning trap. CHIP-TRAP aims to perform ultra-high precision (∼1 part in 1011 fractional precision) mass measurements on stable and long-lived isotopes produced with external ion sources and transported to the Penning traps. Along the way, ions of a particular m/q are selected with a multi-reflection time-of-flight mass separator (MR-TOF-MS), with further filtering performed in a cylindrical capture trap before the ions are transported to a pair of hyperbolic measurement traps. In this paper, we report on the design and status of CHIP-TRAP and present results from the commissioning of the ion sources, MR-TOF-MS, and capture trap. We also provide an outlook on the continued development and commissioning of CHIP-TRAP.

Updated evaluation of potential ultralow Q -value β -decay candidates

"Ultra-low" Q value $\beta$ decays are referred to as such due to their low decay energies of less than $\sim$1 keV. Such a low energy decay is possible when the parent nucleus decays into an excited state in the daughter, with an energy close to that of the Q value. These decays are of interest as potential new candidates for neutrino mass determination experiments and as a testing ground for studies of atomic interference effects in the nuclear decay process. In this paper, we provide an updated evaluation of atomic mass data and nuclear energy level data to identify potential ultra-low Q value $\beta$ decay candidates. For many of these candidates, more precise and accurate atomic mass data is needed to determine if the Q value of the potential ultra-low decay branch is energetically allowed and in fact ultra-low. The precise atomic mass measurements can be achieved via Penning trap mass spectrometry.

Present status of HIRFL complex in Lanzhou

Heavy Ion Research Facility in Lanzhou (HIRFL) is a cyclotron, synchrotron and storage ring accelerator complex, which accelerates ions of hydrogen to uranium from low to medium energy. Since the complete of HIRFL-CSR project in 2008, under the support from CAS, efforts have been put to improve the infrastructure for machine performance, including improvement of EMC environments, power distribution stations, PS stations, cooling water system, RF system of cyclotrons and adoption of EPICS control system, etc. New generation SC ECR source (SECRAL-II) with high performance is put into operation. Experiments of electron cooling with pulsed electron beam are performed for the first time. Stochastic cooling and laser cooling are realized in CSRe. The performance of RIBLL2 and CSRe are gradually improved. The isochronous mode of CSRe for precise atomic mass measurements is well studied and reaches state-of-art mass resolution of storage rings. The operation status and enhancement plan of HIRFL will be briefly reported in this paper.

Identification and investigation of possible ultra-low Q value β decay candidates

Among the wide energy range of β decays, there can exist decays with Q values as low as a few hundred eV. These decays can occur when the parent decays to a excited state in the daughter nucleus. Such decays have been called “ultra-low” Q value β decays. Their application is mainly twofold: (1) they are of interest as potential candidates for neutrino mass determination experiments, and (2) they provide a testing ground for theoretical studies of atomic interference effects in the nuclear decay process. In this work we have identified a number of such potential candidates by analyzing the most recent atomic mass and nuclear energy level data. To determine if an ultra-low Q value β decay branch is energetically allowed for these candidates, more precise and accurate data for the Q value of the ultra-low decay branch is needed. In most cases, this requires more precise atomic mass measurements for the parent and/or daughter atoms. These requirements can be met using Penning trap mass spectrometry.

High-Precision Atomic Mass Measurements for Fundamental Constants

Atomic mass measurements are essential for obtaining several of the fundamental constants. The most precise atomic mass measurements, at the 10−10 level of precision or better, employ measurements of cyclotron frequencies of single ions in Penning traps. We discuss the relation of atomic masses to fundamental constants in the context of the revised SI. We then review experimental methods, and the current status of measurements of the masses of the electron, proton, neutron, deuteron, tritium, helium-3, helium-4, oxygen-16, silicon-28, rubidium-87, and cesium-133. We conclude with directions for future work.

Precision Mass Measurements on Neutron-Rich Rare-Earth Isotopes at JYFLTRAP: Reduced Neutron Pairing and Implications for r-Process Calculations.

The rare-earth peak in the r-process abundance pattern depends sensitively on both the astrophysical conditions and subtle changes in nuclear structure in the region. This work takes an important step towards elucidating the nuclear structure and reducing the uncertainties in r-process calculations via precise atomic mass measurements at the JYFLTRAP double Penning trap. ^{158}Nd, ^{160}Pm, ^{162}Sm, and ^{164-166}Gd have been measured for the first time, and the precisions for ^{156}Nd, ^{158}Pm, ^{162,163}Eu, ^{163}Gd, and ^{164}Tb have been improved considerably. Nuclear structure has been probed via two-neutron separation energies S_{2n} and neutron pairing energy metrics D_{n}. The data do not support the existence of a subshell closure at N=100. Neutron pairing has been found to be weaker than predicted by theoretical mass models. The impact on the calculated r-process abundances has been studied. Substantial changes resulting in a smoother abundance distribution and a better agreement with the solar r-process abundances are observed.

The most precise atomic mass measurements in Penning traps

A perspective is given of the motivations, methods and status of Penning trap atomic mass measurements of long-lived isotopes, with fractional uncertainties near and below 10−10.

Precision atomic mass spectrometry with applications to fundamental constants, neutrino physics, and physical chemistry

We present a summary of precision atomic mass measurements of stable isotopes carried out at Florida State University. These include the alkalis 6Li, 23Na, 39,41K, 85,87Rb, 133Cs; the rare gas isotopes 84,86Kr and 129,130,132,136Xe; 17,18O, 19F, 28Si, 31P, 32S; and various isotope pairs of importance to neutrino physics, namely 74,76Se/74,76Ge, 130Xe/130Te, and 115In/115Sn. We also summarize our Penning trap measurements of the dipole moments of PH + and HCO + .

Dipole moments and orientation polarizabilities of diatomic molecular ions for precision atomic mass measurement

In high precision Penning trap mass spectrometry the cyclotron frequency of a polarizable ion is perturbed due to the Stark interaction with the motional electric field. For polar diatomic molecular ions, which have adjacent rotational levels of opposite parity, these shifts can be particularly large---especially for the lowest rotational levels, which are those occupied by ions stored for many hours in cryogenic Penning traps. In order to provide corrections to precision atomic mass measurements, we consider the calculation of orientation polarizabilities of $\mathrm{C}{\mathrm{O}}^{+}$ and the positive ions of the first and second row diatomic hydrides, $\mathrm{Li}{\mathrm{H}}^{+}$ to $\mathrm{Ar}{\mathrm{H}}^{+}$. Dipole moments for these ions have been calculated using the restricted coupled cluster method with perturbative triples and large basis sets. Using these dipoles and an effective Hamiltonian, we have obtained rotational-state dependent polarizabilities of the open-shell diatomic ions $\mathrm{C}{\mathrm{O}}^{+}$, $\mathrm{N}{\mathrm{H}}^{+}$, $\mathrm{O}{\mathrm{H}}^{+}$, $\mathrm{F}{\mathrm{H}}^{+}$, $\mathrm{P}{\mathrm{H}}^{+}$, $\mathrm{S}{\mathrm{H}}^{+}$, and $\mathrm{Cl}{\mathrm{H}}^{+}$. Results are given for those rotational levels that are significantly populated at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, for magnetic fields up to $10\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. For the remaining first and second row hydride cations, polarizabilities at the magnetic fields of interest can be obtained from a simple formula valid for closed-shell molecules. Conversely, in cases where the polarizability shifts can be measured, our results enable experimental determination of dipole moments.

Precise atomic mass measurements by deflection mass spectrometry

Since its inception nearly 90 years ago by J.J. Thomson, the precise determination of atomic masses by the classical technique of deflecting charged particles in electric and magnetic fields has provided a large body of data on naturally occurring nuclides. Currently, such measurements on stable nuclides have frequently achieved a precision of better than two parts in 10 9 of the mass. A review of the technique, together with a brief summary of the important historical developments in the field of precise atomic mass measurements, will be given. The more recent contributions to this field by the deflection mass spectrometer at the University of Manitoba will be provided as illustrations of the culmination of the techniques used and the applications that have been studied. A brief comparison between this and newer techniques using Penning traps will be presented.

Fourier transform ion cyclotron resonance versus time of flight for precision mass measurements

Both Fourier transform ion cyclotron resonance and ICR time-of-flight mass spectroscopy have been applied to precision atomic mass measurements. This paper reviews the status of these approaches and compares their limitations.

Limits to fourier transform—ion cyclotron resonance mass spectrometry for atomic mass measurements

The application of Fourier transform—ion cyclotron resonance to precision atomic mass measurements is considered including a computer analysis of several facets of ion motion in an ion cyclotron resonance mass spectrometry cell. Numerical methods were used in conjunction with the analytical equations of motion to model cyclotron motion, including the effects of inhomogeneities in the electric and magnetic fields. Limits on mass accuracy are discussed and results are compared with those of several other studies.

Atomic mass measurements at Osaka university

The masses of H, D, 35Cl and 37Cl have been measured using the peak-matching technique with a double-focusing mass spectroscope operating with a mass resolution of 4–5 × 10 5. The accuracy of these measurements is estimated to be in the range, 1 part of slightly less in 10 8. Agreement with other measurements for H is good and for D not so good. The scattering of values for the chlorine isotopes is rather large. It appears that the investigation of systematic errors is still one of the most important things to do in the field of precise atomic mass measurements.