Uranium ionization potentials

We sincerely appreciate the contributions of our co-workers R. W. Solarz and J. A. Paisner in the determination of the lanthanide and uranium ionization potentials. 

Laser requirements. In order to utilize photons efficiently, absorption by should be selective. A absorption line should be found that (1) occurs at a frequency at which does not absorb, and (2) has a high absorption cross section, to reduce the light path needed for efficient use of photons. Because the isotope shift between U and 17 absorption frequencies is of the order of 1 in 50,000, the first requirement calls for use of a very narrow absorption line. Because the absorption lines for transitions in which uranium is ionized are very broad, it is necessary to ionize the atoms in two or more steps, in which the first step is selective excitation of to an energy level below the uranium ionization potential of... 

Being a valuable isotope analytical technique in routine work for high precision isotope ratio measurements, TIMS is applied in many laboratories worldwide for isotope ratio measurements especially for elements with ionization potentials < 7 eV,7 such as alkali and earth alkali elements, rare earth elements (REE), uranium and plutonium. It is advantageous that the interference problem occurs relatively seldom in TIMS, especially if the negative thermal ionization technique for elements and molecules with electron affinities > 2eV (Ir, W, Os, Re, Pt, Cl and Br) is applied. TIMS with multiple ion collectors achieves a precision of up to 0.001 % thus permitting the study... 

Of all the different mass spectrometric techniques for isotope analysis (such as ICP-MS, LA-ICP-MS, TIMS, GDMS, AMS, SIMS, RIMS and isotope ratio mass spectrometry of gases), the greatest proportion of pubhshed papers today concern ICP-MS with single and multiple ion collection.19 Due to its benefits, ICP-MS has now become a widely accepted method for isotope analysis and allows isotope ratios to be measured in a short time with good accuracy and precision.9,19,75 78 As discussed above, as a powerful and universal tool, ICP-MS has opened up new applications for isotope ratio measurements of elements with a high first ionization potential, which are difficult to analyze with TIMS (such as Mo, Hf, Fe). Of all the heavy metals studied, uranium was favoured by ICP-MS and LA-ICP-MS. 

I he atomic wcighi varies because of natural variations in the isotopic composition of the element, caused by the various isotopes having different origins - I h is the end product of the thorium decay scries, while Ph and " Pb arise Irom uranium as end products of the actinium and radium series respectively. Lead-204 has no existing natural radioactive precursors. Electronic configuration l.v 2s lfc22/j"3v 3//,3i/l"4v- 4/, 4l/" 4/ IJ5v- 5/ "5t/l"bv />-. Ionic radius Pb I.IX A. Pb 1 0.7(1 A. Metallic radius 1.7502 A. Covalent radius (ip i 1.44 A. First ionization potential 7.415 cV second. 14.17 eV. Oxidation... 

Ionization potentials of 6.1941(5) eV for uranium i and 6.2657(6) eV for neptunium ) have been derived from observed Rydberg series using laser techniques and the method described above. These are the most accurate ionization potentials available for actinide elements. Series converging to the first excited state and to the ground state of the ion were observed for both elements. In the case of neptunium, the presence of two series converging to limits 24 cm - - apart (see Fig. 6) helps to confirm the unpublished value. ) for the interval between the two lowest levels of neptunium. 

Discussion of Actinide Ionization Potentials. The ionization potentials of actinides determined by laser techniques are given in Table IV together with values determined by surface ionization, appearance potential and semi-emperical methods. For uranium, all values are low compared with the values determined by laser techniques with the exception of the surface ionization value by Smith and Hertel.(z ) The spectroscopic values by Sugar jL were obtained from the 5f 7s - 5f 7s8s intervals interpolated from intervals known for the higher actinides. Except for Sugar s value, all the neptunium ionization potential values are low relative to the more accurate values determined by laser methods. The Rydberg series values are the preferred ionization potentials. 

The table "Ionization Potentials of the Atoms" is taken from the well-known tables of Kaye and Laby [347], completed with a number of new data, in particular the ionization potentials of osmium, iridium, erbium, thorium, and uranium. 

The radioactive noble gas radon has been much publicized in recent years as a potential risk to health. Radon-222 is a product of fire nuclear disintegration series of uranium-238 (Figure 21.4) and is continually generated as uranium in rocks and soil decays. As Figure 21.23 indicates, radon exposure is estimated to account for more fhan half the 360-mrem average annual exposure to ionizing radiation. 

---