Die experimentelle Bestimmung der Ionisationsenergien von Berkelium und Californium

Nuclear Forensics: A methodology applicable to Nuclear Security and to Non-Proliferation

Nuclear Security aims at the prevention and detection of and response to, theft, sabotage, unauthorized access, illegal transfer or other malicious acts involving nuclear material". Nuclear Forensics is a key element of nuclear security. Nuclear Forensics is defined as a methodology that aims at re-establishing the history of nuclear material of unknown origin. It is based on indicators that arise from known relationships between material characteristics and process history. Thus, nuclear forensics analysis includes the characterization of the material and correlation with production history. To this end, we can make use of parameters such as the isotopic composition of the nuclear material…

Frequency tripling for resonance ionization spectroscopy (RIS) of Cd

To explore the nucleosynthesis of heavy elements in the rapid neutron-capture process, investigations on short- lived, very neutron-rich Cd isotopes are planned that require pure samples. These will be produced at the CERN-ISOLDE on-line mass separator in combination with a chemically se- lective laser ion source. The excitation scheme for resonance ionization of Cd was tested in Mainz with a copper-vapor- pumped dye laser system. Due to the high ionization potential of Cd, frequency tripling was required for the first excita- tion step.1D 228: 8n m/. Laser light with an average power of 2m Wwas obtained after frequency tripling and was suc- cessfully used for RIS test measurements on cadmi…

Determination of the content in uranium oxide particles by fission track analysis

Abstract One of the most important tasks of nuclear safeguards is to control the activities in nuclear facilities worldwide. These activities include the enrichment of 235 U . To identify enrichments above the maximum authorised level in commercial enrichment plants (usually 5% 235 U ) swipe tests are performed and the 235 U enrichment is determined in the sampled uranium oxide particles. A method is described that allows to measure the 235 U content in small particles (around 1 μm in diameter) by the use of fission tracks. It is based on the fact that in uranium fuel, only 235 U atoms are fissile with thermal neutrons and contribute to the amount of fission tracks counted for individual pa…

Resonance ionization mass spectrometry for trace analysis of long-lived radionuclides

Resonance ionization mass spectrometry (RIMS) is a sensitive and selective method for the determination of extremely low abundances of long-lived radionuclides. The detection limits are about 106 atoms per sample and an isotopic selectivity up to 1013 has been achieved. The potential of RIMS using different experimental arrangements is outlined for the determination of isotope ratios and lowest abundances of long-lived radioisotopes of interest like 238–244Pu, 90Sr, and 41Ca. Recent developments in improving detection limits and the spatial resolution of this technique are briefly discussed.

First Experimental Determination of the Ionization Potentials of Berkelium and Californium

Uran aus deutschen Nuklearprojekten der 1940er Jahre – eine nuklearforensische Untersuchung

Wir berichten hier uber eine nuklearforensische Analyse verschiedener Uranmaterialien aus deutschen Nuklearprojekten der 1940er Jahre, bei denen Uranmetall in verschiedenen Geometrien verwendet wurde. Mithilfe des 230Th/234U-Isotopenverhaltnisses konnte fur das Metall ein Produktionszeitraum von 1940 bis 1943 bestimmt werden. Die geographische Herkunft des Urans wurde anhand des Spurengehalts an Seltenerdelementen und der Strontium-Isotopenverhaltnisse bestimmt. Die Ergebnisse zeigen, dass das bei den deutschen Nuklearprojekten verwendete Uran aus Minen in der Tschechischen Republik stammt. 236U und 239Pu wurden in Spuren nachgewiesen. Diese entsprechen in etwa der Haufigkeit dieser Isotope…

Erste Messung der Ionisationsenergie von Americium und Curium

Trace analysis of plutonium in environmental samples by resonance ionization mass spectroscopy (RIMS)

Resonance ionization mass spectroscopy (RIMS) is well suited for trace analysis of long-lived radioisotopes in environmental, biological and technical samples. By multiple resonant laser excitation and ionization of the elemental atoms under investigation, an extremely high element selectivity can be achieved. In addition, isotope selectivity is obtained by subsequent mass analysis. The excellent sensitivity results from the large atomic cross-sections in the excitation–ionization process and the good detection efficiency for ions. The element selectivity of RIMS allows a simplified procedure for the chemical preparation of the samples compared to the requirements of thin sources for α-spec…

Resonance ionization mass spectroscopy for trace determination of plutonium in environmental samples

Resonance ionization mass spectroscopy (RIMS) is a sensitive and isotope selective method and well suited for trace analysis of plutonium in the environment. After the chemical isolation of plutonium from soil, air filters or urine, e.g., it is electrolytically deposited as hydroxide on a tantalum backing and covered with a thin titanium layer. By heating such a sandwich filament in the RIMS-apparatus under vacuum an atomic beam of plutonium is produced. The atoms are ionized by a three-step resonant excitation using pulsed dye lasers, and the ions are mass-selectively detected with a time-of-flight (TOF) spectrometer and a multi channel plate detector. RIMS yields a low detection limit of …

Instrument Characterization and First Application of the Single Particle Analysis and Sizing System (SPASS) for Atmospheric Aerosols

We describe here the instrumental setup and first experiments with the mobile single particle analysis and sizing system (SPASS) for the on-line characterization of single atmospheric aerosol particles. Aerosols are introduced into the SPASS via a differentially pumped particle inlet system using an aerodynamic lens that forms a narrow particle beam. The particles are sized with a two-laser velocimeter and subsequently desorbed and ionized with a high-power pulsed Nd:YAG laser operating at 266 nm. Positive and negative ions formed are simultaneously detected in a bipolar time-of-flight mass spectrometer. Thus, the size and chemical composition of single aerosol particles can be characterize…

Cover Picture: Uranium from German Nuclear Power Projects of the 1940s— A Nuclear Forensic Investigation (Angew. Chem. Int. Ed. 45/2015)

Determination of the first ionization potential of actinide elements by resonance ionization mass spectroscopy

Abstract Resonance ionization mass spectroscopy (RIMS) in the presence of an external static electric field has been used for the determination of photoionization thresholds. Extrapolation of the thresholds obtained with different electric field strengths to zero field strength directly leads to the first ionization potential (IP). The ionization potentials of the transplutonium elements americium, curium, berkelium and californium could be measured for the first time. Due to the high sensitivity of RIMS, samples of only 1012 atoms have been used. The results are: IPAm = 5.9738(2)eV, IPCm = 5.9915(2)eV, IPBk = 6.1979(2)eV and IPCf = 6.2817(2)eV. The same technique was applied to thorium, ne…

Selective laser ionization of radioactive Ni-isotopes

Abstract A chemically selective laser ion source based on resonance ionization of atoms in a hot cavity has been applied in the study of Ni-isotopes at the CERN-ISOLDE on-line isotope separator. Laser ionization enhanced the yields of long-lived Ni-isotopes almost four orders of magnitude when compared to the yields obtained with the surface ionization mode of the source. As a result, high yields of long-lived Ni-isotopes were obtained. Separation efficiencies of 0.3 and 0.8% were obtained for Ni produced in uranium-carbide, produced from uranium-di-pthalocyanine, and Ta-foil targets, respectively. Ni was found to be released very slowly from the present target and ion source combination.

Titelbild: Uran aus deutschen Nuklearprojekten der 1940er Jahre – eine nuklearforensische Untersuchung (Angew. Chem. 45/2015)

First Determination of the Ionization Potential of Americium and Curium

Uranium from German Nuclear Power Projects of the 1940s— A Nuclear Forensic Investigation

Here we present a nuclear forensic study of uranium from German nuclear projects which used different geometries of metallic uranium fuel. Through measurement of the (230)Th/(234)U ratio, we could determine that the material had been produced in the period from 1940 to 1943. To determine the geographical origin of the uranium, the rare-earth-element content and the (87)Sr/(86)Sr ratio were measured. The results provide evidence that the uranium was mined in the Czech Republic. Trace amounts of (236)U and (239)Pu were detected at the level of their natural abundance, which indicates that the uranium fuel was not exposed to any major neutron fluence.

Determination of the first ionization potential of einsteinium by resonance ionization mass spectroscopy (RIMS)

Abstract The first ionization potential of einsteinium (IP Es ) was determined by resonance ionization mass spectroscopy (RIMS) using samples with ≤10 12 atoms of 254 Es ( T 1/2 =276 days). This method is based on the measurement of photoionization thresholds as a function of applied electric field strength, followed by extrapolation to zero field strength to yield IP Es . An atomic beam of Es was created by heating a filament on which einsteinium was electrodeposited from an aqueous solution onto a tantalum backing and covered with titanium metal. Es atoms were ionized via a three-step excitation scheme, and the ions mass-selectively detected in a time-of-flight (TOF) mass spectrometer. Th…

Production of monodisperse uranium oxide particles and their characterization by scanning electron microscopy and secondary ion mass spectrometry

Abstract Secondary ion mass spectrometry (SIMS) can be confidently used to measure uranium isotopic ratios in single particles. Dense particles of known isotopic composition and size allow the precision and the accuracy of the applied procedure to be estimated. These particles can be obtained by dissolving standard reference uranium materials, nebulizing the solution in droplets of proper diameter and collecting the particles after the desolvation and calcination of the droplets. A new instrumental set up, based on a commercial vibrating orifice aerosol generator to generate monodisperse droplets of the solutions from four uranium oxide reference materials, is described. The droplets were d…

Determination of the first ionization potential of nine actinide elements by resonance ionization mass spectroscopy (RIMS)

The high sensitivity of RIMS enables the precise determination of the first ionization potential of actinide elements with a sample size of ≤1012 atoms. By multiple resonant laser excitation, the actinide atoms under investigation are ionized in the presence of an electric field, and the ions are mass-selectively detected in a time-of-flight spectrometer. The first ionization potential is obtained by scanning the wavelength of the laser used for the last excitation step across the ionization threshold Wth—indicated by a sudden increase of the ion count rate—at various electric field strengths. Extrapolation of Wth to electric field strength zero leads directly to the first ionization potent…

Comparative parallel characterization of particle populations with two mass spectrometric systems LAMPAS 2 and SPASS

Abstract Two transportable laser mass spectrometers, Single Particle Analysis and Sizing System (SPASS) and Laser Mass Analyzer for Particles in the Airborne State (LAMPAS 2), have been applied to investigate the dependence of spectra patterns on instrumental parameters and data evaluation procedures in an inter-comparison experiment. Laboratory experiments showed the spectral response of both instruments for mineral particles before and after heterogeneous reactions. During a period of 47 h, both instruments determined size and chemical composition of several thousand single particles of an ambient particle population. Time-resolved evaluation (1-h resolution) of specific ion signals, whic…