Dianionic tin clusters Sn_34^2- stored in a Penning trap are excited by nanosecond laser pulses with photon energies ranging from 2.0 to 4.7 eV , resulting in delayed decays. Time-resolved measurements with varying delays between laser irradiation and fragment analysis from a few ten microseconds to a second reveal matching exponential appearance constants of several singly charged dissociation products. This indicates that the dianions undergo fission into competing pairs of Sn_10^- + Sn_24^- and Sn_15^- + Sn_19^- . Furthermore, matching decay constants for high photon energies of twice the low-energy values indicate that the decay observed at the low energies results from two-photon excitation.The delayed photodecay of dianionic tin clusters shows competing dissociation pathways by fission into two singly charged product clusters. Further sequential decay processes are investigated.

Many experiments with pulsed ion beams benefit from or even require ion bunches with both small temporal width as well as small energy spread. To achieve optimal ion-beam preparation, a buffer-gas filled cryogenic Paul trap is being developed in the context of the Multi Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS). There, ion bunches of short-lived radionuclides are trapped in a Multi-Reflection Time-of-Flight (MR-ToF) device. Thus, the ions can be repeatedly probed by a laser beam compared to only once in conventional, single-passage collinear laser spectroscopy. To fulfill MIRACLS’ opposing requirements of a small temporal ion-bunch width and small energy spread, a buffer-gas filled cryogenic Paul trap is envisioned. Ion-optical simulations confirm the advantages of cryogenic temperatures and the linear scaling of the beam emittance as a function of the buffer-gas temperature. Beyond MIRACLS, high-quality ion beams from a cryogenic Paul trap will be beneficial for other precision experiments at radioactive ion beam facilities.

In preparation of space-change studies a MagneTOF detector is evaluated for bunches with a wide range of ion numbers. The detector is calibrated based on the comparison between single-ion counting and ion-bunch-signal integration. This allows to determine up to several ten thousands of ions in a bunch with a FWHM of about 700 ns, the integrated signal of which increases linearly with the ion number. Furthermore, this detector limit can be circumvented using transmission-limiting elements in front of the detector. Based on this, ion bunches are investigated up to several million ions, which are prepared with a linear Paul trap. Thus, in addition to the MagneTOF detector this trap is characterized with respect to its space-charge limits at low potential-well depth.

The Greifswald multi-reflection time-of-flight setup has been extended with a magnetron sputtering gas aggregation source for the production of atomic cluster ions with sizes ranging from a single to thousands of atoms. This source, combined with a newly added quadrupole mass filter and a linear Paul trap, opens up the possibility of many new atomic-cluster studies not feasible with the setup before. The new components and their interfacing with the previous setup are described, and benchmarking as well as the first experimental results are presented. The capability of the system to handle singly charged ions with masses of several ten thousand atomic mass units is demonstrated.

The radioactive nuclide 225Ac is one of the few promising candidates for cancer treatment by targeted- α -therapy, but worldwide production of 225Ac faces significant limitations. In this work, the Isotope Separation On-Line method was used to produce actinium by irradiating targets made of uranium carbide and thorium carbide with 1.4-GeV protons. Actinium fluoride molecules were formed, ionized through electron impact, then extracted and mass-separated as a beam of molecular ions. The composition of the mass-selected ion beam was verified using time-of-flight mass spectrometry, α - and γ -ray decay spectrometry. Extracted quantities of ^225Ac^19F_2^+ particles per C of incident protons were 3.9(3)× 10^7 from a uranium carbide target and 4.3(4)× 10^7 for a thorium carbide target. Using a magnetic mass separator, the long-lived contamination 227 Ac is suppressed to <5.47× 10^-7 (95 A ^-1 h ^-1 of directly produced ^225Ac^19F_2^+ .

Isomers close to doubly magic _{28}^{78}Ni_{50} provide essential information on the shell evolution and shape coexistence near the Z=28 and N=50 double shell closure. We report the excitation energy measurement of the 1/2^{+} isomer in _{30}^{79}Zn_{49} through independent high-precision mass measurements with the JYFLTRAP double Penning trap and with the ISOLTRAP multi-reflection time-of-flight mass spectrometer. We unambiguously place the 1/2^{+} isomer at 942(10) keV, slightly below the 5/2^{+} state at 983(3) keV. With the use of state-of-the-art shell-model diagonalizations, complemented with discrete nonorthogonal shell-model calculations which are used here for the first time to interpret shape coexistence, we find low-lying deformed intruder states, similar to other N=49 isotones. The 1/2^{+} isomer is interpreted as the bandhead of a low-lying deformed structure akin to a predicted low-lying deformed band in ^{80}Zn, and points to shape coexistence in ^{79,80}Zn similar to the one observed in ^{78}Ni. The results make a strong case for confirming the claim of shape coexistence in this key region of the nuclear chart.

Millisecond-delayed photodissociation of gas-phase Sn-22(-) clusters stored in a Penning trap is investigated as a function of excitation energy. Sn-15(-) is the only significant charged fragment, indicative of the break-off of neutral heptamers. Fits of the time-resolved fragmentation require a distribution of decay constants, caused by the finite width of the internal energy distribution of the cluster ensemble prior to photoexcitation. A lower limit for the dissociation energy for the loss of Sn-7 is determined to be 2.1(1) eV, a factor of two above literature quantum chemical calculations.

Cationic and anionic clusters of the group-14 elements carbon, silicon, germanium, tin, and lead are produced by high-vacuum laser ablation and studied with a multi-reflection time-of-flight mass spectrometer. In-trap photodissociation is performed for cluster species in the size range n = 2–10. The clusters’ production rates as well as their dissociation pathways are used to probe the nonmetal–metal transition throughout the group. Carbon clusters show neutral-trimer break-off, while those of the other elements evaporate neutral monomers and, in some cases, form specific charged fragment sizes.

The combination of a linear quadrupole ion-filter and linear Paul trap operated with a rectangular guiding field for the filtering and accumulation of ions within the M ass S pectrometry for S ingle P article I maging of D ipole O riented protein C omplexes (MS SPIDOC) prototype [T. Kierspel et al., Anal. Bioanal. Chem. , published online] is characterized. Using cationic caesium-iodide clusters, the ion-separation performance, ion accumulation, cooling, and ejection via in-trap pin electrodes is evaluated. Furthermore, proof-of-principle measurements are performed with 64 kDa multiply-charged non-covalent protein complexes of human hemoglobin and 804 kDa non-covalent complex of GroEL, to demonstrate that the module meets the criteria to handle high-mass ions which are the main objective of the MS SPIDOC project. The setup's performance is found to be in line with previous results from ion-trajectory simulations [F. Simke et al., Int. J. Mass Spectrom. 473 (2022) 116779].

Isomers close to doubly magic 78 28Ni50 provide essential information on the shell evolution and shape coexistence near the Z = 28 and N = 50 double shell closure. We report the excitation energy measurement of the 1/2+ isomer in 79 30Zn49 through independent high-precision mass measurements with the JYFLTRAP double Penning trap and with the ISOLTRAP multi-reflection time-of-flight mass spectrometer. We unambiguously place the 1/2+ isomer at 942(10) keV, slightly below the 5/2+ state at 983(3) keV. With the use of state-of-the-art shell-model diagonalizations, complemented with discrete nonorthogonal shell-model calculations which are used here for the first time to interpret shape coexistence, we find low-lying deformed intruder states, similar to other N = 49 isotones. The 1/2+ isomer is interpreted as the bandhead of a low-lying deformed structure akin to a predicted low-lying deformed band in 80Zn, and points to shape coexistence in 79;80Zn similar to the one observed in 78Ni. The results make a strong case for confirming the claim of shape coexistence in this key region of the nuclear chart.

Isomers close to doubly magic Ni502878 provide essential information on the shell evolution and shape coexistence near the Z=28 and N=50 double shell closure. We report the excitation energy measurement of the 1/2+ isomer in Zn493079 through independent high-precision mass measurements with the JYFLTRAP double Penning trap and with the ISOLTRAP multi-reflection time-of-flight mass spectrometer. We unambiguously place the 1/2+ isomer at 942(10) keV, slightly below the 5/2+ state at 983(3) keV. With the use of state-of-the-art shell-model diagonalizations, complemented with discrete nonorthogonal shell-model calculations which are used here for the first time to interpret shape coexistence, we find low-lying deformed intruder states, similar to other N=49 isotones. The 1/2+ isomer is interpreted as the bandhead of a low-lying deformed structure akin to a predicted low-lying deformed band in Zn80, and points to shape coexistence in Zn79,80 similar to the one observed in Ni78. The results make a strong case for confirming the claim of shape coexistence in this key region of the nuclear chart.Received 24 July 2023Revised 16 September 2023Accepted 25 October 2023DOI:https://doi.org/10.1103/PhysRevLett.131.222503Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBinding energy & massesNuclear structure & decaysNucleon-nucleon interactionsProperties59 ≤ A ≤ 89TechniquesMass spectrometryNuclear many-body theoryRadioactive beamsShell modelNuclear Physics

The heaviest actinide elements are only accessible in accelerator-based experiments on a one-atom-at-a-time level. Usually, fusion–evaporation reactions are applied to reach these elements. However, access to the neutron-rich isotopes is limited. An alternative reaction mechanism to fusion–evaporation is multinucleon transfer, which features higher cross-sections. The main drawback of this technique is the wide angular distribution of the transfer products, which makes it challenging to catch and prepare them for precision measurements. To overcome this obstacle, we are building the NEXT experiment: a solenoid magnet is used to separate the different transfer products and to focus those of interest into a gas-catcher, where they are slowed down. From the gas-catcher, the ions are transferred and bunched by a stacked-ring ion guide into a multi-reflection time-of-flight mass spectrometer (MR-ToF MS). The MR-ToF MS provides isobaric separation and allows for precision mass measurements. In this article, we will give an overview of the NEXT experiment and its perspectives for future actinide research.

Carbon-cluster ions are produced by laser irradiation of glassy carbon in high vacuum. In the case of positively charged species, a bimodal cluster distribution including fullerenes with cluster-size-to-charge ratios of up to a few hundred is observed. Resolving isotopologues by use of a multireflection time-of-flight mass spectrometer allows the detection and abundance determination of multiply charged clusters. It is found that mono-, di-, and tricationic fullerenes are produced, have similar size-over-charge-state ranges, and follow log-normal distributions known to be characteristic of an underlying coalescent growth. A statistical simulation is shown to reproduce the results.

At radioactive ion beam (RIB) facilities, ions of short-lived radionuclides are cooled and bunched in buffer-gas-filled Paul traps to improve the ion-beam quality for subsequent experiments. To deliver even colder ions, beneficial to RIB experiments' sensitivity or accuracy, we employ Doppler and sympathetic cooling in a Paul trap cooler-buncher. The improved emittance of Mg^{+}, K^{+}, and O_{2}^{+} ion beams is demonstrated by a reduced time-of-flight spread of the extracted ion bunches with respect to room-temperature buffer-gas cooling. Cooling externally-produced hot ions with energies of at least 7 eV down to a few Kelvin is achieved in a timescale of O(100 ms) by combining a low-pressure helium background gas with laser cooling. This is sufficiently short to cool short-lived radioactive ions. As an example of this technique's use for RIB research, the mass-resolving power in a multireflection time-of-flight mass spectrometer is shown to increase by up to a factor of 4.6 with respect to buffer-gas cooling. Simulations show good agreement with the experimental results and guide further improvements and applications. These results open a path to a significant emittance improvement and, thus, unprecedented ion-beam qualities at RIB facilities, achievable with standard equipment readily available. The same method provides opportunities for future high-precision experiments with radioactive cold trapped ions.

Ion trajectories have been simulated for an assembly of a linear quadrupole ion-filter and a linear Paul trap with additional pin electrodes for MS SPIDOC, a project in preparation for the study of biomolecules by single-particle imaging with X-ray pulses. The ion-optical components are based on digital RF guiding and trapping fields. In order to carefully handle biomolecules over a wide mass-over-charge range, the module presented consists of separate components for filtering and accumulation/trapping in order to select the ions of interest and to convert the beam from a continuous ion source to ion bunches, respectively, as required for the experiments downstream. The present analysis focuses on the transmission efficiency and mass resolving power of the filter, as well as the buffer-gas-pressure-dependent ion capture and thermalization in the trap for the example of a mass-to-charge ratio equivalent to hemoglobin 15 thorn ions. The resulting optimized ion bunch delivered by the assembly is characterized. (c) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

A series of multi-reflection time-of-flight (MR-ToF) spectra is recorded with increasing ion flight times and added up to a single transient. It shows periodic ToF-signal trains for each ion species revolving between the MR-ToF analyzer's mirrors. This is used to perform a "comb-sampling" evaluation previously devised for analysis of capacitive-pickup signals (Greenwood et al., Rev. Sci. Instrum. 82 (2011), 043103). The recording and evaluation focuses on simultaneously measuring the full range of trapped ions for wide-band mass spectrometry. The comb-sampling technique is revisited for the present transients, as it is the first time it is used for comparatively background-free single-ion-counting data. (c) 2021 Elsevier B.V. All rights reserved.

Collinear laser spectroscopy (CLS) has been combined with the multi-reflection time-of-flight (MR-ToF) technique. To this end, a photodetection system has been implemented at the drift region of a MR-ToF apparatus and a laser beam has been sent along the path of the ions that are stored between the two ion-optical mirrors. The main goal of the present proof-of-principle (PoP) experiments, is the confirmation of the expected increase in sensitivity compared to conventional fluorescence-based CLS due to the repeated probing of the trapped ion bunches. The novel method will be used for the precise measurement of nuclear ground- and isomeric-state properties of exotic nuclei with low production yields at radioactive ion-beam facilities. A significant sensitivity improvement of CLS is expected, depending on the half-life and mass of the nuclide of interest. The status of the PoP setup and future improvements are discussed.

The Multi-Ion Reflection Apparatus for Collinear Laser Spectroscopy (MIRACLS), currently under development at ISOLDE/CERN, aims to combine the high resolution of fluorescence-based collinear laser spectroscopy (CLS) with a high sensitivity. This will be achieved by confining 30-keV ion bunches in a Multi-Reflection Time-of-Flight (MR-ToF) device which allows laser spectroscopic probing for several thousand times. An MR-ToF setup operating at similar to 1.5 keV beam energy has been adapted for a proof-of-principle experiment. Thus, efforts had to be undertaken to reduce the laser stray light as the leading source of background of this apparatus, not originally designed for CLS. These measures enabled CLS of Mg-24,26(+) ions in single-path mode, i.e. without ion trapping, which is the reference point to gauge the gain in sensitivity of the MIRACLS technique.

The authors perform multi-reflection time-of-flight mass spectrometry of time-resolved photodissociation of indium clusters and observe a power-law exponent of the decay rate links cluster dissociation energy and ensemble temperature.

Repeated switching of electric potentials within a single experimental cycle is introduced for a multi-reflection time-of-flight mass spectrometer (also known as an electrostatic ion beam trap) in order to eject different ion species after different storage times. The method is demonstrated with two cluster ions with considerably different mass-to-charge ratios (the A = 624 and 832 isotopologues of Pb3+ and Pb4+, respectively) for the specific case where the sequential ejections result in an identical number of revolution periods. Thus, the ions' flight lengths are identical, and the resulting time-of-flight values allow single-reference mass determination. The requirements for the switching time window are studied in detail. For the present system and ion pair, the relative mass uncertainty is found to be 3 · 10-7 for short measurements (≈10 min) and 6 · 10-8 for longer ones (≈2 h).