Selective Laser Ionization Research Articles

Decay modes of the 9/2− isomeric state in Tl183

The internal transition decay and α decay of the T1/2=53.3ms, 9/2− isomeric state in the neutron-deficient isotope, Tl183, have been studied using the Resonance Ionization Laser Ion Source and the Windmill detection setup at the ISOLDE facility at CERN. Clean samples of Tl183m were produced by selective laser ionization and subsequent mass separation. An internal transition cascade of 356.5–272.2 keV γ rays has been identified. Multipolarities of these transitions have been determined by means of simultaneous γ-ray and conversion-electron spectroscopy. Improved data for the fine structure of the Tl183m→Au179 decay were deduced. This involves a 6058 keV α-decay transition, which populates a previously unknown state in Au179, that is tentatively assigned as a (9/2−). It is interpreted as a coupling of the 1h9/2 proton-intruder with the excited 0+ state in the Pt178 core.1 MoreReceived 11 January 2022Accepted 3 March 2022DOI:https://doi.org/10.1103/PhysRevC.105.034338Published 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 AreasAlpha decayCollective modelsElectromagnetic transitionsEnergy levels & level densitiesIsomer decaysNuclear decayNuclear spin & parityNuclear structure & decaysRare & new isotopesShell modelProperties150 ≤ A ≤ 189Nuclear Physics

Highly selective two-step laser ionization schemes for the analysis of actinide mixtures

Resonance ionization mass spectroscopy has proven to be a very efficient and selective method for the spatially resolved ultratrace determination of actinide contaminations, and the analysis of specific element and isotopic distributions on surfaces and environment particles. We report on the identification of highly element-selective optical excitation schemes identified for this purpose, with a particular focus on the precise determination of the isobaric ratios of 235U to 239Pu as well as 243Am to 241Pu. The chosen two-step ionization schemes were characterized with respect to their element selectivity on synthetic multi-element actinide mixtures, with an element ratio Pu : Am : U of 1 : 10 : 104, a composition which is typical, e.g., for spent nuclear reactor fuels.

Transport channel of secondary ion beam of experimental setup for selective laser ionization with gas cell GALS

GALS is the experimental setup intended for production and research of isobaric and isotopically pure heavy neutron-rich nuclei. The beam line consists of two parts. The initial part is used for transport of the primary 136Xe ion beam with the energy of 4.5-9.0 MeV/amu from the FLNR cyclotron U-400M to the Pb target for production of the studying ion beams. These beams have the following design parameters: the charge Z = +1, the mass A = 180-270 and the kinetic energy W = 40 keV. The second part placed after the target consists of the SPIG (QPIG) system, the accelerating gap, the electrostatic Einzel lens, 90-degree spectrometric magnet (calculated value of the mass-resolution is equal to 1400) and the beam line for the transportation of the ions from the magnet focal plane to a particle detector. The results of simulation of the particle dynamics and the basic parameters of all elements of the beam line are presented.

β-delayed fission of180Tl

The detailed analysis of the β-delayed fission data of 180 Tl is presented. The experiment was performed by producing a pure beam of 180 Tl by means of highly selective resonance laser ionization followed by mass separation with the ISOLDE (CERN, Geneva) isotope separator. A surprising asymmetric mass distribution of fission fragments from 180 Hg, the daughter of 180 Tl β decays, was observed. Here, the energy calibration of the silicon detectors, which is crucial for a proper determination of the fission fragments’ energy and mass split, is presented and the total kinetic energy and its dependence on the mass split ratio is discussed. A more precise β-delayed fission probability PβDF( 180 Tl) = 3.2(2) × 10 −3 % was deduced.

Colloquium: Beta-delayed fission of atomic nuclei

This Colloquium reviews the studies of exotic type of low-energy nuclear fission, the $\ensuremath{\beta}$-delayed fission ($\ensuremath{\beta}\mathrm{DF}$). Emphasis is made on the new data from very neutron-deficient nuclei in the lead region, previously scarcely studied as far as fission is concerned. These data establish the new region of asymmetric fission in addition to the previously known one in the transuranium nuclei. New production and identification techniques, which emerged in the last two decades, such as the wider use of electromagnetic separators and the application of selective laser ionization to produce intense isotopically or even isomerically pure radioactive beams are highlighted. A critical analysis of presently available $\ensuremath{\beta}\mathrm{DF}$ data is presented and the importance of detailed quantitative $\ensuremath{\beta}\mathrm{DF}$ studies, which become possible now, is stressed, along with the recent theory efforts in the domain of low-energy fission.

βdecay of61Mn to levels in61Fe

A detailed $\ensuremath{\beta}$-decay study of ${}^{61}$Mn is presented, yielding extended information on the level structure of ${}^{61}$Fe. Pure beams were obtained at ISOLDE, CERN, after selective laser ionization and mass separation of fission products from the bombardment of a UC${}_{x}$ target by 1.4-GeV protons. The $\ensuremath{\beta}$ and $\ensuremath{\gamma}$ information was detected by two MiniBall clusters and three $\ensuremath{\Delta}$$E$ plastic scintillators. The new ${}^{61}$Mn decay scheme reveals 48 $\ensuremath{\gamma}$ transitions, distributed over 20 excited states. A comparison to the decay scheme of ${}^{59}$Mn and excited states in ${}^{59}$Fe is made. Shell-model calculations with two different interactions are performed in order to compare the nuclear structure of the two neighboring odd-$A$ iron isotopes. Tentative spin and parities of several excited states in ${}^{61}$Fe are assigned on the basis of $\ensuremath{\beta}$-decay feeding patterns in both ${}^{59,61}$Fe and of results from the theoretical shell-model calculations.

A hot cavity laser ion source at IGISOL

A development program is underway at the IGISOL (Ion Guide Isotope Separator On-Line) facility, University of Jyvaskyla, to efficiently and selectively produce low-energy radioactive ion beams of silver isotopes and isomers, with a particular interest in N=Z 94Ag. A hot cavity ion source has been installed, based on the FEBIAD (Forced Electron Beam Induced Arc Discharge) technique, combined with a titanium:sapphire laser system for selective laser ionization. The silver recoils produced via the heavy-ion fusion-evaporation reaction, 40Ca(58Ni, p3n)94Ag, are stopped in a graphite catcher, diffused, extracted and subsequently ionized using a three-step laser ionization scheme. The performance of the different components of the hot cavity laser ion source is discussed and initial results using stable 107,109Ag are presented.

Dual chamber laser ion source at LISOL

A new type of gas cell for the resonance ionization laser ion source at the Leuven Isotope Separator On Line (LISOL) has been developed and tested under off-line and on-line conditions. Two-step selective laser ionization is applied to produce purified beams of radioactive isotopes. The selectivity of the ion source has been increased by more than one order of magnitude by separation of the stopping and laser ionization regions. This allows the use of electrical fields for further ion purification.

Low-energy Coulomb excitation of neutron-rich zinc isotopes

At the radioactive ion beam facility REX-ISOLDE, neutron-rich zinc isotopes were investigated using low-energy Coulomb excitation. These experiments have resulted in B(E2,21+→01+) values in Zn74−80, B(E2,41+→21+) values in Zn74,76 and the determination of the energy of the first excited 21+ states in Zn78,80. The zinc isotopes were produced by high-energy proton- (A=74,76,80) and neutron- (A=78) induced fission of U238, combined with selective laser ionization and mass separation. The isobaric beam was postaccelerated by the REX linear accelerator and Coulomb excitation was induced on a thin secondary target, which was surrounded by the MINIBALL germanium detector array. In this work, it is shown how the selective laser ionization can be used to deal with the considerable isobaric beam contamination and how a reliable normalization of the experiment can be achieved. The results for zinc isotopes and the N=50 isotones are compared to collective model predictions and state-of-the-art large-scale shell-model calculations, including a recent empirical residual interaction constructed to describe the present experimental data up to 2004 in this region of the nuclear chart.7 MoreReceived 25 August 2008DOI:https://doi.org/10.1103/PhysRevC.79.014309©2009 American Physical Society

Ultratrace Uranium Fingerprinting with Isotope Selective Laser Ionization Spectrometry

Uranium isotope ratios can provide source information for tracking uranium contamination in a variety of fields, ranging from occupational bioassay to monitoring aftereffects of nuclear accidents. We describe the development of isotope selective laser ionization spectrometry for ultratrace measurement of the minor isotopes (234)U, (235)U, and (236)U with respect to (238)U. The inherent isotopic selectivity of three-step excitation with single-mode continuous wave lasers results in measurement of the minor isotopes at relative abundances below 1 ppm and is not limited by isobaric interferences such as (235)UH(+) during measurement of (236)U. This relative abundance limit is attained without mass spectrometric analysis of the laser-created ions. Uranyl nitrate standards from an international blind comparison were used to test analytical performance for different isotopic compositions and with quantities ranging from 11 ng to 10 microg total uranium. Isotopic ratio determination was demonstrated over a linear dynamic range of 7 orders of magnitude with a few percent relative precision and detection limits below 500 fg for the minor isotopes.

New concepts for the ion guide technique

The technique of using noble gases to cool energetic beams offers fast extraction times, very little sensitivity to chemical properties of the ions and very low-energy spreads. A variant of this method is based on the selective laser ionization of radioactive species after they have been thermalized in gas as neutral atoms. The laser ion source in Jyväskylä is used to highlight the importance of buffer gas purity using yttrium, a particularly chemically reactive element. The time distribution profiles obtained on-line illustrate the competing factors that create and destroy the ion of interest during evacuation from the ion guide. A review of the extraction efficiencies of gas catchers of different volumes, buffer gases, projectile energies and electric fields all show a common decrease as a function of ionization-rate density. The reasons for this decline and possible solutions to tolerate higher primary beam intensities are discussed.

Characterization of the LISOL laser ion source using spontaneous fission of 252Cf

A spontaneous fission Californium-252 source was placed inside a gas cell in order to characterize the LISOL laser ion source. The fission products from 252Cf are thermalized and neutralized in the plasma created by energetic particles. Two-step selective laser ionization is applied to produce purified beams of radioactive isotopes. The survival of fission products in a single charge state has been studied in argon as a buffer gas for different elements.

Resonance-enhanced multiphoton ionization and VUV-single photon ionization as soft and selective laser ionization methods for on-line time-of-flight mass spectrometry: investigation of the pyrolysis of typical organic contaminants in the steel recycling process.

A newly conceived compact and mobile time-of flight mass spectrometer (TOFMS) for real-time monitoring of highly complex gas mixtures is presented. The device utilizes two selective and sensitive soft ionization techniques, viz., resonance-enhanced multiphoton ionization (REMPI) and single-photon ionization (SPI) in a (quasi)-simultaneous mode. Both methods allow a fragmentationless ionization. The REMPI method selectively addresses aromatic species, while with SPI applying vacuum ultaviolet light (118 nm) in principle all compounds with an ionization potential below 10.5 eV are accessible. This provides comprehensive information of the chemical composition of complex matrixes. The combustion and pyrolysis behavior of five organic materials typically used in steel processing in China was studied. The trace amounts of organic compounds in the gas phase during combustion and pyrolysis were monitored selectively and sensitively by real-time SPI/REMPI-TOFMS. The measurements were carried out at several constant temperatures in the range from 300 to 1190 degrees C in both synthetic air and nitrogen. Timely resolved mass spectra reveal the formation and subsequent growth of aromatic molecules. At lower temperatures, highly alkylated PAHs predominate, while at temperatures above 800 degrees C, the more stable benzene and PAHs without side chains prevail. Potential hyphenation of SPI/REMPI-TOFMS to methods of thermal analysis is discussed.

Detection and quantification of aromatic contaminants in water and soil samples by means of laser desorption laser mass spectrometry.

The combination of laser desorption of untreated soil samples and subsequent selective laser ionization followed by time-of-flight mass analysis results in an ultrafast technique for the quantitative detection of aromatic contaminants in soil samples. The method allows for high sample throughput, because the complete measurement is finished within about 1 min. Although the different types of soil investigated (sand, humus, clay) showed differences in the desorption efficiency, none of them produced mass spectrometric interferences when an ionization laser wavelength of 266 nm was used. Quantification was carried out by relative measurement with respect to an internal standard and gave satisfactory results over 4 orders of magnitude of analyte concentration. Although the detection of polycyclic aromatic hydrocarbons could successfully be carried out using nanosecond laser pulses, the quality of the mass spectra obtained for labile substances, for example, nitrotoluenes, could be greatly improved by the use of ultrashort pulses in the subpicosecond range. With the preliminary setup, detection limits in the low micrograms-per-gram range were achieved. The identical setup can be used for the analysis of liquids, in particular, water, when the soil sample is replaced by a solid, porous adsorber medium onto which the sample is applied. Activated carbon proved to be a useful adsorber for IR laser desorption, whereas for the UV, granular clay or lime/sand mixtures are preferable.

The Leuven isotope separator on-line laser ion source

An element-selective laser ion source has been used to produce beams of exotic radioactive nuclei and to study their decay properties. The operational principle of the ion source is based on selective resonant laser ionization of nuclear reaction products thermalized and neutralized in a noble gas at high pressure. The ion source has been installed at the Leuven Isotope Separator On-Line (LISOL), which is coupled on-line to the cyclotron accelerator at Louvain-la-Neuve. 54,55Ni and 54,55Co isotopes were produced in light-ion-induced fusion reactions. Exotic nickel, cobalt and copper nuclei were produced in proton-induced fission of 238U. The b decay of the 68–74Ni, 67–70Co, 70–75Cu and 110–114Rh isotopes has been studied by means of β– γ and γ– γ spectroscopy. Recently, the laser ion source has been used to produce neutron-deficient rhodium and ruthenium isotopes ( 91–95Rh, 98Rh, 90,91Ru) near the N= Z line in heavy ion-induced fusion reactions.

ISOL techniques, present status and new developments

On-line mass separation has recently gained extra momentum due to two extremes of applications. On the one side, beams from on-line mass separators have been decelerated in order to inject them in ion traps for precise experiments. On the other side, beams from on-line mass separators have been post-accelerated in order to use the secondary beam for nuclear reaction studies. Both applications put stringent requirements on the ISOL beams. These requirements relate to: • the element range of the beam, including refractory elements; • to the time span of the separated isotopes, down to the millisecond region; • to the intensity of the beam, dealing with high-intensity targets; • to the charge state of the beam, breeding it up from 1 + to n +; • to the purity of the beam, in mass as well as element selection; • and to the ion-optical quality, related to energy as well as time. This contribution deals with the recent developments in each direction and will give an outlook for further studies. Special emphasis is put on the use of dense, noble gases for thermalization, storage and transport of short-living ions and on the use of selective laser ionization.

Beams of short-lived nuclei by selective laser ionization in a gas cell

Resonant laser ionization in a gas cell has been implemented at the Leuven Isotope Separator On Line facility to produce beams of short lived radioactive nuclei and to study their decay characteristics. A description of the laser ion source is presented together with technical details on the laser system, the gas cell and the gas purification system. Results from off line as well as on line measurements are discussed. The new laser ion source has allowed β decay studies of neutron deficient (54Ni, 92Rh) as well as neutron rich (up to 74Ni and 70Co) isotopes.

Decay of Neutron-Rich Mn Nuclides and Deformation of Heavy Fe Isotopes

The use of chemically selective laser ionization combined with beta-delayed neutron counting at CERN/ISOLDE has permitted identification and half-life measurements for 623-ms Mn-61 up through 14-ms Mn-69. The measured half-lives are found to be significantly longer near N=40 than the values calculated with a QRPA shell model using ground-state deformations from the FRDM and ETFSI models. Gamma-ray singles and coincidence spectroscopy has been performed for Mn-64 and Mn-66 decays to levels of Fe-64 and Fe-66, revealing a significant drop in the energy of the first 2+ state in these nuclides that suggests an unanticipated increase in collectivity near N=40.

Beta decay of the MT=-1 nucleus 58Zn studied by selective laser ionization

Beta decay of 58Zn has been studied for the first time. A new laser ion-source concept has been used to produce mass-separated sources for beta and gamma spectroscopy. The half-life of 58Zn was determined to be 86(18) ms. Comparisons are made with previous data from charge-exchange reactions. Our Gamow–Teller strength to the 1+ state at 1051 keV excitation in 58Cu agrees well with the value extracted from a recent (3He, t) study. Extensive shell-model calculations are presented.

Optical Emission Detection of Charged Particles after Selective Laser Ionization of Mercury Atoms in a Buffer Gas

A method for the optical detection of the resonance ionization signal of mercury atoms in a buffer gas is described that is based on the emission from buffer gas atoms that are collisionally excited by interactions with electrons in a strong electric field. The first observations of this phenomenon are reported here, along with comparisons between optical and electrical detection. Advantages of a pulsed electric field over a continuous field are described. A wide range of possible applications for this type of gas phase detector are suggested.