The performance of the cryogenic buffer-gas stopping cell of SHIPTRAP

Abstract

Direct high-precision mass spectrometry of the heaviest elements with SHIPTRAP, at GSI in Darmstadt, Germany, requires high efficiency to deal with the low production rates of such exotic nuclides. A secondgeneration gas stopping cell, operating at cryogenic temperatures, was developed and recently integrated into the relocated system to boost the overall efficiency. Offline measurements using 223 Ra and 225 Ac recoil-ion sources placed inside the gas volume were performed to characterize the gas stopping cell with respect to purity and extraction efficiency. In addition, a first online test using the fusion-evaporation residue 254 No was performed, resulting in a combined stopping and extraction efficiency of 33(5)%. An extraction time of 55(44) ms was achieved. The overall efficiency of SHIPTRAP for fusion-evaporation reaction products was increased by an order of magnitude to 6(1)%. This will pave the way for direct mass spectrometry of heavier and more exotic nuclei, eventually in the region of superheavy elements with proton numbers Z 104.

High-precision ab initio calculations of the spectrum of Lr+

“…This in turn allows to reduce collisional broadening and thus to increase the experimental resolution [1,3]. Previous experiments proved that the gas mixture contains both atomic species, neutral as well as singly ionised Lr, wherein the fraction of the ions substantially dominates the sample composition under typical experimental conditions [4,5]. For both species, due to the extremely low production yields, highly precise theoretical predictions of the spectral lines are required to develop excitation schemes and to narrow down the search window to be able to pinpoint the ground-state transitions.…”

Simulation studies of the laser ablation ion source at the SHIPTRAP setup

“…More details on the operation and the recent optimizations of the cryogenic cell can be found in Ref. [10]. By using a combination of electrostatic and radio-frequency fields in addition to the gas-flow, the ions are extracted from the gas cell into a radio-frequency quadrupole (RFQ) section at low-vacuum (∼ 10 −2 mbar) and then guided towards the RFQ buncher.…”

“…1 Schematic view of the SHIPTRAP setup and its major components (modified from Ref. [10]): the cryogenic-gas stopping cell, the extraction RFQ and the buncher for ion preparation, the reference ion sources and the Penning traps. The triangles indicate detector positions single ion bunches are injected into the double Penning-trap system located inside a 7 T superconducting magnet.…”

Laser Resonance Chromatography of Superheavy Elements

“…This is best done by stopping them in gas catchers, preferably in inert gases like helium (He) to avoid formation of chemical compounds [10]. The ions are thermalized typically in 1+ and 2+ states [11][12][13][14]. Thus far, it has been necessary to neutralize them for resonance ionization spectroscopy (RIS) as in the nobelium studies [3].…”

“…The cell incorporates a radio-frequency (rf) funnel and is isolated from the detection part by an extraction nozzle [13,14]. The detection part comprises, sequentially, a rf quadrupole in a bunch-mode operation (called a buncher), a cryogenic drift tube, a second rf quadrupole as an ion guide, a quadrupole mass spectrometer (QMS) for charge-to-mass selection, and a particle detector.…”