Abstract
We achieve a considerable improvement in proposed schemes for the selective photoionization of odd mass zirconium isotopes. The technique implements intermediate-state alignment for isotope-selective laser excitation by broadband pulsed lasers, which incorporates the spectroscopic selection rules for the absorption of polarized light. The improvement includes newly found intermediate levels, where J = 0 character as a third excited-state intermediate, in cooperation with four-step photoexcitation (J = 2–1–1–0 scheme). Isotope selectivity (separation coefficient for 91Zr: >2400) has been identified in addition to a significant enhancement of ionization efficiency (30×) compared with previous research. A search for suitable third intermediate levels has covered over autoionizing Rydberg states in a singly ionized Zr II region (up to 58 000 cm−1). The measured autoionizing Rydberg states show high photoion yields but are not identified as favoured isotopic selectivity, as observed in the four-step photoionization. Prospects and future directions in laser even/odd-mass isotope separation are discussed.
Highlights
In this study, we employed an alternative approach using intermediate-state alignment for the isotope-selective laser excitation of atoms, which exploits the angular momentum selection rules for the absorption of polarized www.nature.com/scientificreports/
A newly found 3rd intermediate state, with J = 0 character, shows a high ionization efficiency and high isotopic selectivity. (c) The mass spectra of the naturally occurring Zr sample obtained in the two different configurations; In the selective condition, an exclusively isotopic selectivity is observed for 91Zr, where all laser polarizations of ω1, ω2, and ω3 are parallel
Since the naturally occurring odd mass isotope of Zr is 91 alone and the remaining isotopes are the even mass [90, 92, 94, 96], we focus on 91β by Eq 2 for an evaluation of the odd mass isotopic selectivity
Summary
We employed an alternative approach using intermediate-state alignment for the isotope-selective laser excitation of atoms, which exploits the angular momentum selection rules for the absorption of polarized www.nature.com/scientificreports/. (b) The mass-resolved, resonant photoionization spectra of Zr. A newly found 3rd intermediate state, with J = 0 character, shows a high ionization efficiency and high isotopic selectivity. Polarized, pulsed dye lasers are used to prepare aligned states from which further excitation of the even mass isotopes is prohibited by selection rules. Accompanied by the foregoing study of the laser isotope separation of palladium isotopes, we revisited the three-step resonant photoionization of Zr vapour and examined the isotopic selectivity for 91Zr from other naturally occurring even mass isotopes. The subsequent intermediate-state populations P(J′, M′), which are prepared by resonant transitions with linearly polarized light, are elaborated using the Wigner–Eckart theorem by
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