Nicole Erdmann

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 potential. The first ionization potentials (IP) of Am, Cm, Bk, Cf and Es were determined for the first time as IPAm=5.9736(3) eV, IPCm=5.9914(2) eV, IPBk=6.1979(2) eV, IPCf=6.2817(2) eV, IPEs=6.3676(5) eV with samples of 1012 atoms. Furthermore, the ionization potentials of Th, U, Np and Pu were remeasured.

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

Abstract 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-spectroscopy. Various samples have been determined by RIMS with respect to their content and the isotopic composition of plutonium in the ultra-trace regime. A detection limit of 10 6 to 10 7 plutonium atoms has been achieved for all isotopes, independent of their half-life and decay mode. For 239 Pu, this value is distinctly below the radiometric detection limit.

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, neptunium and plutonium, yielding IPTh = 6.3067(2)eV, IPNp = 6.2655(2)eV and IPPo = 6.0258(2)eV. Plotted as a function of the number of electrons N, the actinide ionization potentials can be approximated by two straight lines joining at the half-filled shell when normalized to ionization from the lowest fN s2 level to the lowest fN s level.

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 characterized simultaneously in real time. The SPASS system has been installed inside a truck, creating a mobile unit. The performance of the SPASS in terms of mass resolution and sizing capabilities of the laser velocimeter has been evaluated. Positive and negative mass spectra from different types of particles have been obtained to identify “typical” peak patterns. The relative detection sensitivity depending on particle size and chemical composition was studied. Significant differences in detection sensitivities for different compounds were observed, demonstrating that the results obtained from ambient single particle measurements are strongly biased and dominated by “easy-to-detect” particles. The instrument performance is illustrated with results from a 24 h measurement period during winter in Milan, Italy. The period encompasses two meteorologically different episodes, a period of stagnant conditions, where regional background pollutants contribute significantly and the aerosol is dominated by ammonium nitrate and sulfate, and a North-Foehn event, where accumulation mode particles are scavenged and the urban aerosol population is dominated by organic matter due to local emissions.

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. The excitation scheme used included a previously unknown EsI level at 32 924.9 cm −1 . Furthermore, an autoionizing state at 51 447.3 cm −1 was also found. The first ionization potential of Es was determined to be 6.3676(5) eV (≡51 358(5) cm −1 ).

RIMS measurements for the determination of the first ionization potential of the actinides actinium up to einsteinium

The ionization potential is a fundamental property of an element. In order to determine the first ionization potential, a method based on the measurement of photoionization thresholds in the presence of a well-defined electrical field is used. By one or two step resonant laser excitation, the investigated atoms are promoted to a highly excited state. Ionization is obtained by scanning the wavelength of an additional tunable laser across the threshold Wth, which is detected by a sudden increase of the ion signal. Extrapolation of Wth to zero field strength yields directly the first ionization potential. Using this method the first ionization potentials of Ac, Am, Cm, Bk, Cf, and Es have been determined for the first time. Furthermore, the ionization potentials of Th, U, Np, and Pu were remeasured.

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.

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.3b,d, 4 Through measurement of the 230Th/234U 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 87Sr/86Sr ratio were measured. The results provide evidence that the uranium was mined in the Czech Republic. Trace amounts of 236U and 239Pu were detected at the level of their natural abundance, which indicates that the uranium fuel was not exposed to any major neutron fluence.

A high repetition rate solid state laser system for resonance ionization mass spectrometry of actinides

A new, high repetition rate solid state laser system consisting of three Titanium-Sapphire (Ti:Sa) lasers pumped by one Nd:YAG laser has been set up for resonance ionization mass spectrometry for routine trace analysis of actinides. Each Ti:Sa laser produces up to 4 W of laser light with a bandwidth of 2–6 GHz continuously tuneable in a range from 725 to 900 nm. Using a three step ionization scheme with λ1=420.76 nm, λ2=847.28 nm and λ3<760 nm for 239Pu, the overall detection efficiency of the setup has been measured to be e=8.0×10−6. Thus a detection limit of 1×107 atoms of 239Pu is derived and opens up the way to use a reliable and easy to handle laser system for routine applications of RIMS.

Resonance ionization mass spectroscopy for trace detection of plutonium

Trace amounts of radiotoxic elements are determined by means of resonance ionization mass spectroscopy (RIMS). An extremely high element-selectivity is obtained via resonant multiphoton excitation of the atoms leading to an autoionizing state. The ions produced are mass-selectively detected. This leads to good isotope-selectivity and efficient background suppression. These properties allow a simplification of the chemical separation. With RIMS the detection limit does not depend on half-life or decay mode of the determined isotopes as it is the case for radiometric methods. Two experimental approaches for trace detection of plutonium are described. An overall detection efficiency of 3 multiplied by 10-5 has been determined yielding a detection limit of 1 multiplied by 106 atoms of 239Pu. The practicability of those methods was demonstrated with environmental samples.