Laser Ion Source Research Articles

Efficient two-color two-step laser ionization schemes of λ1∼ 250 nm and λ2 = 307.9 nm for heavy refractory elements-Measurements of ionization cross-sections and hyperfine spectra of tantalum and tungsten.

We demonstrated efficient two-color two-step laser ionization schemes in the combined use of λ1 ∼ 250 nm and λ2 = 307.9 nm, which are applicable to heavy refractory elements with an atomic number in the wide range of Z = 69-78. We investigated newly observed ionization schemes of tantalum and tungsten atoms in an argon-gas-cell-based laser ion source for the efficient ionization of atoms of unstable nuclei through the two-color two-step laser resonance ionization technique. We experimentally determined the ionization cross sections from the measured saturation curves by solving the rate equations for the ground, intermediate, and ionization continuum populations. Hyperfine structures of these elements were also studied to deduce the isotope-shift, pressure-shift, and pressure-broadening in the resonance spectra of the excitation transitions in the argon gas cell. The electronic factor F255 of the excitation transition λ1 = 255.2115 nm between the ground and intermediate states was deduced from the measured isotope shifts of stable 182,183,184,186W isotopes. The ionization schemes investigated here are applicable to extract any isotopes of these elements by considering the measured pressure shift and nuclear isotope shift in optimizing the wavelength λ1.

Conceptual study on parasitic low-energy RI beam production with in-flight separator BigRIPS and the first stopping examination for high-energy RI beams in the parasitic gas cell

Abstract An in-flight separator performs the important role of separating a single specific radioactive isotope (RI) beam from the thousands of RI beams produced by in-flight fission as well as projectile fragmentation. However, when looking at ``separation'' from a different viewpoint, more than 99% of simultaneously produced RI beams are just eliminated in the focal plane slits or elsewhere in the separator. In order to enhance the effective usability of the RIKEN in-flight separator BigRIPS, we have been developing an innovative method: parasitic laser ion source (PALIS), which implements parasitic low-energy RI beam production by saving eliminated RI beams during BigRIPS experiments. In this paper, we present the expected benefits and feasibility for the PALIS concept and the results of the first stopping examination for high-energy RI beams in the gas cell.

Developments towards the delivery of selenium ion beams at ISOLDE

.The production of selenium ion beams has been investigated at the CERN-ISOLDE facility via two different ionization methods. Whilst molecular selenium (SeCO) beams were produced at ISOLDE since the early 1990s, recent attempts at reliably reproducing these results have so far been unsuccessful. Here we report on tests of a step-wise resonance laser ionization scheme for atomic selenium using the ISOLDE Resonance Ionization Laser Ion Source (RILIS). For stable selenium an ionization efficiency of 1% was achieved. During the first on-line radioisotope production tests, a yield of approx 2.4 times 10^4 ions/μC was measured for 71Se+, using a ZrO2 target with an electron impact ion source. In parallel, an approach for extraction of molecular carbonyl selenide (SeCO) beams was tested. The same ion source and target material were used and a maximum yield of approx 3.6times 10^5 ions/μ C of 71SeCO+ was measured.

Resonance laser ionization spectroscopy of tellurium

Resonance ionization schemes for tellurium are investigated with a resonance ionization laser ion source and Ti:Sapphire lasers for fundamental research applications. We present the first three-step resonance ionization spectra of atomic Te. Several autoionizing Rydberg series converging to the first excited state of Te+ are observed and assigned to 5p3 (2Do3/2) ns and nd configurations. Our results include confirmation and significant expansion of the Rydberg series previously reported as well as observation of three new series. From the series convergence limits the ionization potential of tellurium is revised to be 72,669.006(42)stat(20)sys cm−1.

Lu and Pr beam development for resonance ionization laser ion sources

Resonance Ionization Laser Ion Sources (RILIS) are efficient and element selective ion sources, which are well suited for radioactive ion beam facilities. Using TRIUMF's off-line laser ion source test stand with a system of tunable titanium sapphire (Ti:Sa) lasers, laser resonance ionization schemes for lutetium (Lu) and praseodymium (Pr) have been investigated with a particular focus on autoionizing states. New ionization schemes via Rydberg states and autoionizing states were found and compared at the off-line test stand. The data from on-line RILIS delivery of Lu radioactive isotopes is presented.

Measurement of the laser resonance ionization efficiency for lutetium

Abstract The development of a highly efficient resonance ionization scheme for lutetium is presented. A laser ion source, based on the all-solid-state Titanium:sapphire laser system, was used at the 30 keV RISIKO off-line mass separator to characterize different possible optical excitation schemes in respect to their ionization efficiency. The developed laser resonance ionization scheme can be directly applied to the use at radioactive ion beam facilities, e. g. at the CERN-MEDICIS facility, for large-scale production of medical radioisotopes.

Atom beam emersion from hot cavity laser ion sources

Ion sources exploiting laser resonance ionization offer efficient and element-selective radioactive ion beam production at the leading isotope separation on-line facilities worldwide. Most commonly, laser resonance ionization takes place inside a resistively heated atomizer tube directly coupled to the production target, where the element of interest is evaporated and provided as atomic vapor. While naturally the majority of atoms is ionized inside this hot cavity, a fraction of the neutrals effuses towards the high voltage beam extraction system of the subsequent mass separator.We report on several systematic investigations on this phenomenon regarding its significance and implications on the operation of resonance ionization laser ion sources. Experiments suggest a less sharply directed atom cone than expected from theoretical model, up to a lateral opening angle of 45°. Inside the tubular volume defined by the laser beam diameter around the central axis behind the source exit, more than 90% of potentially ionizable atoms are found within the first 2 cm. Geometrical constraints for the construction of devices based on ionization in the effusing atom beam directly downstream of the hot cavity are derived, and causes for cross-mass beam contamination are identified. Counter measures using laser repetition rate synchronized beam gating by fast electrostatic beam deflection to overcome these problems are presented.

MELISSA: Laser ion source setup at CERN-MEDICIS facility. Blueprint

The Resonance Ionization Laser Ion Source (RILIS) has become an essential feature of many radioactive ion beam facilities worldwide since it offers an unmatched combination of efficiency and selectivity in the production of ion beams of many different chemical elements. In 2019, the laser ion source setup MELISSA is going to be established at the CERN-MEDICIS facility, based on the experience of the workgroup LARISSA of the University Mainz and CERN ISOLDE RILIS team. The purpose is to enhance the capability of the radioactive ion beam supply for end users by optimizing the yield and the purity of the final product. In this article, the blueprint of the laser ion source, as well as the key aspects of its development and operation are presented.

New program for measuring masses of silver isotopes near the N = 82 shell closure with MLLTRAP at ALTO

The ISOL facility ALTO, located at Orsay in France, provides stable ion beams from a 15 MV Tandem accelerator and neutron-rich radioactive ion beams (RIB) from the interaction of a γ-flux induced by a 50 MeV 10 μA electron beam in a uranium carbide target. A magnetic dipole mass separator and a resonance ionization laser ion source allow to select the ions of interest. New setups are under preparation to extend the fundamental properties measured at ALTO of ground and excited states of exotic nuclei. For example, high-precision mass measurements for an accurate determination of the nuclear binding energy. To perform these measurements two devices will be hosted at ALTO: a radio frequency quadrupole to cool and bunch (RFQCB) the continuous radioactive beam and the double Penning trap mass spectrometer MLLTRAP, commissioned off-line at the Maier-Leibnitz Laboratory (MLL) in Garching, Germany. The unique production mechanism using photo-fission at the ALTO facility allows for mass measurements in a neutron rich area of nuclides of major interest around 132Sn with less isobaric contamination than using proton drivers. In this context, we plan to measure neutron-rich silver isotopes (Z = 47, A > 121) to explore the possible weakening of the shell gap for Z < 50 and its impact on the A = 130 r- process nucleosynthesis. The ground-state light silver masses (A < 121), known with a precision below 20 keV, will be used for the on-line commissioning of MLLTRAP and to characterize the performance of the detection system. The status and timeline of the novel setup is presented.

Optimization of a laser ion source for 163Ho isotope separation.

To measure the mass of the electron neutrino, the "Electron Capture in Holmium-163" (ECHo) collaboration aims at calorimetrically measuring the spectrum following electron capture in 163Ho. The success of the ECHo experiment depends critically on the radiochemical purity of the 163Ho sample, which is ion-implanted into the calorimeters. For this, a 30 kV high transmission magnetic mass separator equipped with a resonance ionization laser ion source is used. To meet the ECHo requirements, the ion source unit was optimized with respect to its thermal characteristics and material composition by means of the finite element method thermal-electric calculations and chemical equilibrium simulation using the Gibbs energy minimization method. The new setup provides an improved selectivity of laser ionization vs interfering surface ionization of 2700(500) and an overall efficiency of 41(5)% for the ion-implantation process.

Nuclear spectroscopy of r-process nuclei using KEK Isotope Separation System

We developed KEK Isotope Separation System (KISS) in RIKEN Nishina center to produce neutron-rich isotopes around N = 126 for the study of β-decay properties from astrophysical interests. The KISS is an argon-gas-cell-based on laser ion source with ISOL, and, therefore, allows us to extract heavy refractory elements and investigate neutron-rich isotopes around N = 126. We extracted the laser-ionized unstable nuclei in the vicinity of 198Pt, and performed β-γ spectroscopy and in-gas-cell laser ionization spectroscopy successfully.

In-source laser spectroscopy of dysprosium isotopes at the ISOLDE-RILIS

A number of radiogenically produced dysprosium isotopes have been studied by in-source laser spectroscopy at ISOLDE using the Resonance Ionization Laser Ion Source (RILIS). Isotope shifts were measured relative to 152Dy in the 4f106s25I8 (gs) →4f106s6p(8,1)8o (418.8nmvac) resonance transition. The electronic factor, F, and mass shift factor, M, were extracted and used for determining the changes in mean-squared charge radii for 145mDy and 147mDy for the first time.

First demonstration of Doppler-free 2-photon in-source laser spectroscopy at the ISOLDE-RILIS

Collinear Doppler-free 2-photon resonance ionization has been applied inside a hot cavity laser ion source environment at CERN-ISOLDE. An injection-seeded Ti:sapphire ring laser was used to generate light pulses with a Fourier-limited linewidth for high-resolution spectroscopy. Using a molybdenum foil as a reflective surface positioned at the end of the target transfer line, rubidium was successfully ionized inside the hot cavity. The results are presented alongside previously obtained data from measurements performed at the RISIKO mass separator at Mainz University, where collinear and perpendicular ionization geometries were tested inside an RFQ ion guide. This work is a pre-cursor to the application of the Doppler-free 2-photon in-source spectroscopy method at ISOLDE. This approach aims to take advantage of the unmatched sensitivity of in-source spectroscopy, without the disadvantage of Doppler broadening.

ISOL Technique for the Production of 225Ac at CERN-MEDICIS

Over the last few years, several studies have proven the effect of targeted alpha therapy using 225Ac and 213Bi[1,2,3]. One of the crucial bottlenecks in upscaling current studies and moving to clinical trials is the availability of these isotopes. The current production methods cannot provide sufficient quantities of 225Ac or its daughter 213Bi. Furthermore, some of these production techniques result in batches of 225Ac with a lot of impurities which require advanced radiochemical separation techniques to be purified. Therefore, a new technique for the production of 225Ac and other radioisotopes is proposed. The new CERN-MEDICIS facility, which is under development, uses the Isotope Separation On-Line (ISOL) technique to produce a range of medical radioisotopes, e.g. 225Ac, 149Tb, etc [4]. This technique uses a combination of element selective and mass selective processes which result in a very pure, carrier-free batch of the isotope of interest. First a target material, e.g. UCx or Ta, is irradiated with high energy protons of 1.4 GeV. Afterwards, the target it heated to extract the produced isotopes. These isotopes are selectively ionized using a resonant ionisation laser ion source[5]. This allows to selectively ionize Ac isotopes. This ion beam passes through a mass separating magnetic field to result in an ion beam which is very pure in mass. As a final step this ion beam will be collected in a metallic foil or a salt. Afterwards, the radioisotopes can be separated from the collection material using dissolution and simple radiochemical purifications. Resonant laser ionisation of actinium has recently been achieved during a proof-of-concept experiment at CERN while the upscaling towards routine production is under investigation. In this contribution, we shall introduce the ISOL technique and its possible application in the production of alpha-emitting radioisotopes for medical applications. The CERN-MEDICIS facility will be introduced and the recent results on the production of 225Ac at CERN will be presented.[1]M. Sathekge et al. 225Ac-psma-617 in chemotherapy-naive patients with advanced prostate cancer: a pilot study. European Journal of Nuclear Medicine and Molecular Imaging, Sep 2018.[2]L. Finn et al. A phase 2 study of actinium-225 (225Ac)-lintuzumab in older patients with previously untreated acute myeloid leukemia (aml) unt for intensive chemotherapy. Blood, 130(Suppl 1):2638-2638, 2017.[3]L. Krolicki et al. Prolonged survival in secondary glioblastoma following local injection of targeted alpha therapy with 213Bi-substance p analogue. European Journal of Nuclear Medicine and Molecular Imaging, 45(9):1636-1644, Jul 2018.[4]R. dos Santos Augusto et al. CERN-MEDICIS (Medical Isotopes Collected from ISOLDE): A New Facility. Applied Sciences, 4(2):265-281, may 2014.[5]V. Fedosseev et al. Resonance laser ionization of atoms for nuclear physics. Physica Scripta, 85(5):058104, 2012.

β decay of In133 : γ emission from neutron-unbound states in Sn133

Excited states in Sn-133 were investigated through the beta decay of In-133 at the ISOLDE facility. The ISOLDE Resonance Ionization Laser Ion Source (RILIS) provided isomer-selective ionization for In-133, allowing us to study separately, and in detail, the beta-decay branch of In-133 J(pi)= (9/2(+)) ground state and its J(pi) = (1/2(-)) isomer.Thanks to the large spin difference of the two beta-decaying states of In-133, it is possible to investigate separately the lower and higher spin states in the daughter, Sn-133, and thus to probe independently different single-particle and single-hole levels. We report here new gamma transitions observed in the decay of In-133, including those assigned to the deexcitation of the neutron-unbound states.

Approaching Standardless Quantitative Elemental Analysis of Solids: Microsecond Pulsed Glow Discharge and Buffer-Gas-Assisted Laser Ionization Time-of-Flight Mass Spectrometry.

Among various ionization sources for mass spectrometry, microsecond pulsed glow discharge (MP-GD) and buffer-gas-assisted laser ionization (BGA-LI) sources have the potential for direct quantitative elemental analysis of solids without the requirement of standard reference materials. The analytical potential of these two ionization sources has been evaluated by coupling them to orthogonal time-of-flight mass spectrometry (MS). A straightforward method was proposed to achieve the quantitative result: if a spectrum contains little interference and elemental peak currents are proportional to their concentrations, then the molar concentration of each element is equal to its ion current proportion in the total ion current. Two series of metal standards were applied for the evaluation. Explicit spectra with little interference can be acquired by both techniques. The interferences contribute only a very small portion to the total ion current for MP-GD-MS and BGA-LI-MS; therefore, their influence on the quantitative result can be ignored. All metal elements can be determined quite accurately by the proposed quantitation method, while gaps exist for nonmetal elements due to the high ionization potentials or gas species interference. Between the two techniques, BGA-LI-MS offers a more accurate quantitative result, primarily due to its higher plasma temperature.

Laser spectroscopy of the 1001-nm ground-state transition in dysprosium

We present the first direct excitation of the presumably ultra-narrow $1001 \, \textrm{nm}$ ground state transition in atomic dysproium. By using resonance ionization spectroscopy with pulsed Ti:sapphire lasers at a hot cavity laser ion source, we were able to measure the isotopic shifts in the $1001 \, \textrm{nm}$ line between all seven stable isotopes. Furthermore, we determined the upper level energy from the atomic transition frequency of the $^{164} \textrm{Dy}$ isotope as $9991.004(1) \, \textrm{cm}^{-1}$ and confirm the level energy listed in the NIST database. Since a sufficiently narrow natural linewidth is an essential prerequisite for high precision spectroscopic investigations for fundamental questions we furthermore determined a lower limit of $2.9(1) \, \mu\textrm{s}$ for the lifetime of the excited state.

Radium ionization scheme development: The first observed autoionizing states and optical pumping effects in the hot cavity environment

This paper reports on resonance ionization scheme development for the production of exotic radium ion beams with the Resonance Ionization Laser Ion Source (RILIS) of the CERN-ISOLDE radioactive ion beam facility. During the study, autoionizing states of atomic radium were observed for the first time. Three ionization schemes were identified, originating from the 7s2 1S0 atomic ground state. The optimal of the identified ionization schemes involves five atomic transitions, four of which are induced by three resonantly tuned lasers. This is the first hot cavity RILIS ionization scheme to employ optical pumping effects. The details of the spectroscopic studies are described and the new ionization schemes are summarized.

Selective photoionization of lithium isotopes in a hollow cathode lamp: a feasibility study for a laser ion source and detector.

Two-step selective photoionization of lithium isotopes is carried out in a hollow cathode (HC) discharge lamp using a nitrogen-laser-pumped homemade tunable dye laser (∼0.2 cm-1, 7ns, 640-680nm). The HC lamp is developed in-house and used as a lithium ion source as well as a detector. The dark space region of HC discharge is illuminated by a dye laser exciting pulse followed by an ionizing radiation from the nitrogen laser. The high electric field (∼kV/cm) present in HC dark space is exploited for fast charge collection, produced by the simultaneous interaction of exciting and ionizing laser beams with sputtered lithium atoms, enabling the detection of photoionization signal. Photoionization signals with a high signal-to-noise ratio are obtained without using any amplifier. Effects of the ionizing laser pulse energy and the precise tuning of the dye laser on lithium photoionization signal, across 670.780nm (S1/22→P1/2,3/22) transition, are studied. The fine structure of lithium is clearly identified, and its two isotopes (Li7,6) are fairly resolved in the measured photoionization spectrum. Using a saturation technique, the photoionization cross section and the number density of lithium atoms for the Li7 (P3/22) excited level are also measured as 18.5±2.4 Mb, N0∼1.7×109 (atoms/cm3). The results obtained infer that HC-lamp-based photoionization is an easier and cost-effective way of selective photoionization of lithium atoms, and it can be applied for other elements also.

Enhancing the extraction of laser-ionized beams from an arc discharge ion source volume

Abstract The Versatile Arc Discharge and Laser Ion Source (VADLIS) is a recently established ion source for the CERN-ISOLDE radioactive ion beam facility. It offers either electron-impact ionization (VADIS-mode) or resonance laser ionization (RILIS-mode). The choice of operating mode depends on the element of interest or the required beam purity. Particle-in-cell simulations using the VSim software show that the ion extraction efficiency of the VADLIS in RILIS-mode can be improved if it is equipped with an insulated extractor plate, to which an optimal voltage can be applied. This enables optimization of the RILIS-mode ion extraction independently of the electron density. Experiments have been performed using a prototype VADLIS with an adjustable extractor plate voltage for the generation of gallium ion beams at the off-line separator as well as magnesium, molybdenum and mercury ion beams at ISOLDE. A factor >2 increase of the VADLIS efficiency in RILIS-mode has been achieved.