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Measurement of the first ionization potential of astatine by laser ionization spectroscopy


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The radioactive element astatine exists only in trace amounts in nature. Its properties can therefore only be explored by study of the minute quantities of artificially produced isotopes or by performing theoretical calculations. One of the most important properties influencing the chemical behaviour is the energy required to remove one electron from the valence shell, referred to as the ionization potential. Here we use laser spectroscopy to probe the optical spectrum of astatine near the ionization threshold. The observed series of Rydberg states enabled the first determination of the ionization potential of the astatine atom, 9.31751(8) eV. New ab initio calculations are performed to support the experimental result. The measured value serves as a benchmark for quantum chemistry calculations of the properties of astatine as well as for the theoretical prediction of the ionization potential of superheavy element 117, the heaviest homologue of astatine.
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Received 21 Aug 2012 |Accepted 27 Mar 2013 |Published 14 May 2013
Measurement of the first ionization potential
of astatine by laser ionization spectroscopy
S. Rothe1,2, A.N. Andreyev3,4,5,6, S. Antalic7, A. Borschevsky8,9, L. Capponi4,5, T.E. Cocolios1, H. De Witte10,
E. Eliav11, D.V. Fedorov12, V.N. Fedosseev1, D.A. Fink1,13, S. Fritzsche14,15,w, L. Ghys10,16, M. Huyse10, N. Imai1,17,
U. Kaldor11, Yuri Kudryavtsev10,U.Ko
¨ster18, J.F.W. Lane4,5, J. Lassen19, V. Liberati4,5, K.M. Lynch1,20, B.A. Marsh1,
K. Nishio6, D. Pauwels16, V. Pershina14, L. Popescu16, T.J. Procter20, D. Radulov10, S. Raeder2,19, M.M. Rajabali10,
E. Rapisarda10, R.E. Rossel2, K. Sandhu4,5, M.D. Seliverstov1,4,5,12,10, A.M. Sjo
¨din1, P. Van den Bergh10,
P. Van Duppen10, M. Venhart21, Y. Wakabayashi6& K.D.A. Wendt2
The radioactive element astatine exists only in trace amounts in nature. Its properties can
therefore only be explored by study of the minute quantities of artificially produced isotopes
or by performing theoretical calculations. One of the most important properties influencing
the chemical behaviour is the energy required to remove one electron from the valence shell,
referred to as the ionization potential. Here we use laser spectroscopy to probe the optical
spectrum of astatine near the ionization threshold. The observed series of Rydberg states
enabled the first determination of the ionization potential of the astatine atom, 9.31751(8) eV.
New ab initio calculations are performed to support the experimental result. The measured
value serves as a benchmark for quantum chemistry calculations of the properties of astatine
as well as for the theoretical prediction of the ionization potential of superheavy element 117,
the heaviest homologue of astatine.
DOI: 10.1038/ncomms2819 OPEN
1CERN, CH-1211 Gene
`ve, Switzerland. 2Institut fu
¨r Physik, Johannes Gutenberg-Universita
¨t Mainz, D-55128 Mainz, Germany. 3University of York, York YO10
5DD, UK. 4University of the West of Scotland, School of Engineering, Paisley PA1 2BE, UK. 5The Scottish Universities Physics Alliance (SUPA), Glasgow,
G12 8QQ UK. 6Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan. 7Department of Nuclear Physics and Biophysics,
Comenius University, 84248 Bratislava, Slovakia. 8Centre for Theoretical Chemistry and Physics, The New Zealand Institute for Advanced Study,
Massey University Auckland, Private Bag 102904, 0745 Auckland, New Zealand. 9Helmholtz Institute Mainz, D-55128 Mainz, Germany. 10 IKS KU Leuven,
Department of Physics and Astronomy, Celestijnenlaan 200D, B-3001 Leuven, Belgium. 11 School of Chemistry, Tel Aviv University, 69978 Tel Aviv,
Israel. 12 PNPI NRC KI, Orlova Roscha, 188300 Gatchina, Russia. 13 Ruprecht-Karls Universita
¨t, Seminarstrae 2, D-69117 Heidelberg, Germany.
14 GSI Helmholtzzentrum fu
¨r Schwerionenforschung, Planckstrae 1, D-64291 Darmstadt, Germany. 15Frankfurt Institute for Advanced Studies (FIAS),
D-60438 Frankfurt am Main, Germany. 16 Belgian Nuclear Research Centre SCK CEN, Boeretang 200, B-2400 Mol, Belgium. 17 High Energy Accelerator
Research Organization (KEK), Oho 1-1, Tsukuba 305-0801, Japan. 18 Institut Laue-Langevin (ILL), 6 rue Jules Horowitz, F-38042 Grenoble, France.
19 TRIUMF, Accelerator Division, 4004 Wesbrook Mall, Vancouver, BC, V6T2A3 Canada. 20 University of Manchester, School of Physics and Astronomy,
Manchester M13 9PL, UK. 21 Institute of Physics, Slovak Academy of Sciences (IP SASc), Du
´cesta 9, 845 11 Bratislava, Slovakia. wPresent address:
Helmholtz-Institute Jena, Fro¨belstieg 3, D-07743 Jena, Germany. Correspondence and requests for materials should be addressed to S.Ro
NATURE COMMUNICATIONS | 4:1835 | DOI: 10.1038/ncomms2819 | 1
&2013 Macmillan Publishers Limited. All rights reserved.
Astatine (At) is the rarest naturally occurring element on
earth with an estimated total abundance of 0.07 g (ref. 1).
There is significant interest in the pharmaceutical use of
the isotope 211At because its decay properties make it an ideal
short-range radiation source for targeted alpha therapy in cancer
treatment2–5. As only ultra-trace quantities can be used for
experimental chemical studies, computational chemistry is an
invaluable resource for improving our understanding of At
chemistry6,7. Such computations benefit greatly from validation
provided by experimental measurements, as summarized in
Brown8and Nefedov et al.9One of the most important properties
is the binding energy of the outermost valence electron which
determines the chemical reactivity of an element and, indirectly,
the stability of its chemical bonds in compounds. This energy is
also referred to as the first ionization potential (IP). Of all the
naturally occurring elements, At is the only one whose IP has not
been experimentally deduced. However, the IP(At) had been
calculated through the use of various theoretical treatments10–15.
Early extrapolations from the IP data for neighbouring
elements gave values of IP(At) from 9.2 to 10.4 eV10–13,
however, recent, more precise theoretical treatments14,15 cluster
around 9.3 eV (Table 1). Regarding the prediction of IPs of
heavier elements and in particular the superheavy elements,
the inclusion of relativistic and correlation effects are of major
importance. A measurement of the IP for At, the nearest lighter
homologue of the recently discovered element with Z¼117
(ref. 16), therefore provides an experimental basis for developing
theoretical methods which incorporate these effects.
The most precise method for determining IPs is the analysis of
the converging series of atomic energy levels with a high principal
quantum number n, known as Rydberg states. The Rydberg series
of an atom can be observed most easily in the ionization spectrum
of the final transition of a step-wise resonant ionization scheme.
Before this work, the only available data on the optical spectrum
of At came from absorption spectroscopy of a 70 ng sample
of the artificially produced, longest living (up to 8.1 h) isotopes
209–211At. Two optical lines at 216.225 and 224.401 nm were
observed17. This rudimentary knowledge of the atomic spectrum
and the lack of a suitable spectroscopic setup in proximity of an
isotope production facility limited the feasibility of a
measurement of the IP of At.
In this article, we report on in-source laser resonance
ionization spectroscopy studies of At isotopes using the resonance
ionization laser ion source (RILIS)18,19 of the ISOLDE radioactive
ion beam facility20 at CERN. As an initial step, the first
experimental value of the IP of the At atom is derived from a
direct measurement of the photoionization threshold. This result
facilitates the search for additional atomic transitions during the
development of an efficient three-colour resonance laser
ionization scheme, necessary for the production of pure and
intense Atþion beams at ISOLDE. The use of a suitable second-
step atomic transition enables resonance ionization spectroscopy
of high-lying Rydberg states, resulting in a more precise
determination of the IP(At). The extracted value serves as an
important benchmark for ab initio calculations in atomic physics
and quantum chemistry. New calculations of the IP of At are
performed in this work which compare well with the
experimental value.
First step transitions. The tentative assignments of the two
spectral lines at l
¼216 and 224 nm to transitions from the At
atomic ground state, as reported in McLaughlin17, were
confirmed by resonance ionization laser spectroscopy in a two-
colour laser scheme denoted as {l
; 273}, cf. Fig. 1a.
Figures 2a,b show laser scans across both of the two first step
transitions. The photo-ion rate of 199At, obtained from a-decay
rates, measured by the silicon detector of the Windmill system
(see Methods section), was recorded for successive laser scanning
steps of l
while l
was fixed at 273 nm, chosen such that the total
photon energy is higher than most of the theoretical expectations
of the IP of At (cf. Table 1).
Ionization threshold. The two-colour ionization schemes
{216; l
} and {224; l
}, as illustrated in Fig. 1b, were applied for
scanning the second-step laser wavelength within the range
¼312–335 nm, which encompasses the most recent published
Table 1 | Calculated and experimental values (last two rows)
for the first IP of astatine.
Author Year Method IP (eV)
Finkelnburg et al.10 1950 Extrapolation 9.5(2)
Varshni et al.11 1953 Extrapolation 10.4
Finkelnburg et al.12 1955 Extrapolation 9.2(4)
Kiser et al.13 1960 Extrapolation 9.5
Mitin et al.14 2006 DFT 9.24
Chang et al.15 2010 MCDF, up-shift 9.35(1)
This work MCDF 9.24(15)
This work DC CCSD(T) 9.307(25)
This work Expt. (threshold) 9.315(12)
This work Expt. (Rydberg) 9.31751(8)
Abbreviations: CCSD, Coupled-cluster single and double excitation; DC, Dirac-Coulomb; IP,
ionization potential; DFT, density-functional theory; MCDF, multi-configuration Dirac-Fock.
75,151 cm–1
58,805 cm–1
57,277 cm–1
57,268 cm–1
57,157 cm–1
46,234 cm–1
44,549 cm–1
0 cm–1
J = 3/2
J = 5/2
J = 3/2
610–630 nm
532 nm
532 nm
312–335 nm
273 nm
710–915 nm
216 nm
224 nm
795 nm
Figure 1 | Schematic overview of the investigated ionization paths.
The assignments of the three lowest levels is according to17.(a) Verification
of the two transitions from the ground state at l
¼216 and 224 nm.
(b) Ionization threshold: scan of the ionizing laser wavelength l
(c) Development of a three-colour scheme: scan of l
in the infra-red
region for second excited states starting with l
¼216 nm first step.
(d) Verification of the levels found by exciting via the l
¼224 nm first step.
(e) Rydberg series: a wavelength scan of the ionizing laser (l
) in the visible
range using the {216; 795; l
} excitation path.
2NATURE COMMUNICATIONS | 4:1835 | DOI: 10.1038/ncomms2819 |
&2013 Macmillan Publishers Limited. All rights reserved.
theoretical predictions of the IP including the value from Chang
et al.15, privately communicated before publication. Figure 2c
reveals the onset of photoionization at a total excitation energy of
around 75,000 cm 1. The position of the photoionization
threshold, denoted as the vertical dotted line, was determined
as the intersection of the slope (blue tilted line) at the inflection
point of a fitted sigmoid curve (red line) and its upper level
(blue horizontal line). Using this method we obtain
(At) ¼75,129(95) cm 1, corresponding to 9.315(12) eV.
The quoted uncertainty arises from the low statistics.
Three-colour ionization scheme. The development of a three-
colour ionization scheme, which required a search for inter-
mediate atomic transitions, resulted in an increased ionization
efficiency and enabled high-resolution laser scans across the
ionization threshold. The search for new second-step transitions
) to higher lying atomic states, was performed at the TRIUMF-
ISAC radioactive ion beam facility with the TRILIS laser ion
source21. The fundamental output of a widely tunable grating-
based Ti:sapphire (Ti:Sa) laser22 was used to scan l
between 710
and 915 nm in a three-colour scheme {216; l
; 532}, see Fig. 1c.
Three new transitions were discovered. These transitions were
subsequently confirmed at ISOLDE where ionization routes via
both the l
¼224 nm and l
¼216 nm first steps were studied
by laser spectroscopy of the 205,196At isotopes. In total six
new transitions between excited states of At have been observed.
An overview is given in Fig. 1c,d, further details of these will be
published elsewhere.
Spectroscopy of Rydberg states. The {216; 795; l
} excitation
path was used for the scan of the third step (l
) across the
ionization threshold, as given in Fig. 1e. For this study, the
ISOLDE RILIS Ti:Sa laser system was arranged to produce the
two laser beams necessary to populate the E00 level (cf. Fig. 1). The
transition energies of the intermediate states are n0¼46,234.0(3)
cm1and n00 ¼12,571.5(3) cm1, obtained from Gaussian fits of
several laser scans across the 216 and 795 nm resonances of 205At.
From these we obtain E00 ¼n0þn00 ¼58,805.4(5) cm 1. A syn-
chronized dye laser provided the third step laser radiation and
was set to a tuning range encompassing the previously localized
region of the ionization threshold. The dye laser was scanned
whilst the 205At ion current was directly measured with a Faraday
cup (FC). A series of more than 30 Rydberg levels was observed in
the l
scan range of 15,000–16,300 cm 1, as shown in Fig. 3a.
The Rydberg atoms were ionized inside the hot cavity ion
source by the residual laser light, black-body radiation or by
collision processes. The Rydberg levels of lower principal quan-
tum numbers reveal resolved multiplet structures, attributed to
different fine structure components, with decreasing splitting as
the ionization limit is approached. A single-Gaussian fit was
applied to each resolved peak and for each unresolved multiplet.
The transition energies (n
) of each main peak are plotted
against their principal quantum number nas shown in the
Fig. 3b. These data are sufficient for precise determination of the
ionization limit E00
¼IP(At) E00 for this excited state using the
Rydberg formula: nn¼E00
ðndÞ2, where n
is the transition
Count rate (s–1)
75,000 76,000
Total photon energy (cm–1)
Sigmoid fit
Upper level
Ionizing threshold
44,548 44,552
Wavenumber (cm–1)
46,231 46,234
Wavenumber (cm–1)
Count rate (s–1)Count rate (s–1)
Figure 2 | Laser scans for the two-step ionization scheme. Panels aand bshow laser scans across the two optical transitions at l
¼216 and l
¼224 nm,
obtained using the ionization path shown in Fig. 1a and a-decay detection of the photo-ionized 199At. (c) Measurement of the ionization threshold.
The count rate of a-particles from the decay of 199At is registered for different total photon energies of the applied laser beams used in the
two-colour schemes {216; l
} and {224; l
} (cf. Fig. 1b).
25 30 35 40 45 50 55
16,200 16,250 16,300 16,350
Wavenumber (cm–1)
Principal quantum number, n
Ion current (pA)
Wavenumber (cm–1)
26 27 28 29 Principal quantum
Figure 3 | Determination of the ionization limit of the excited state. (a)
Laser scan of the ionizing laser across the ionization threshold of At. The
observed Rydberg resonances converge towards the ionization limit. The
indicated principal quantum numbers (n) are based on the assumption of
an nd series. (b) Analysis of the observed Rydberg spectrum. The top panel
shows the position of 31 high-lying Rydberg levels. The Rydberg formula is
fitted to the positions of the main peaks in the multiplets belonging to
different n. The residuals of the fit are shown in the bottom panel.
NATURE COMMUNICATIONS | 4:1835 | DOI: 10.1038/ncomms2819 | 3
&2013 Macmillan Publishers Limited. All rights reserved.
energy from the excited state E00 to a Rydberg level with principal
quantum number nof the valence electron, dis
the quantum defect and R
is the reduced-mass Rydberg
constant for 205At.
Following the trends of quantum defects of nd and ns series
of bromine and iodine23, we constrain the integer part bdcto 5 or
3 for ns or nd in At, respectively. The assumption of an nd series
allows us to assign principal quantum numbers to the Rydberg
levels. However, the result of the analysis is unaffected by this
choice. The obtained peak positions were fitted with the two free
parameters E00
and d. The result of the fit is shown as the solid
curve in the top panel of Fig. 3b. Residuals with error bars
accounting for the statistical error from the Gaussian fit of each
resonance and the uncertainties of the wavelength measurements
are shown in the bottom panel of Fig. 3b. This approach yields
¼16,345.4(2) cm1and d¼3.16. The sum E00 þE00
the first IP of At as IP
(At) ¼75,150.8(7) cm1, corresponding
to 9.31751(8) eV. Uncertainties arise from the statistical errors of
0.03 cm 1from the Rydberg series fit and 0.09 cm 1for the
determination of E00. The systematic error, covering the
wavelength measurements, unresolved hyperfine structure and
data acquisition, is estimated to 0.6 cm 1. This result is in perfect
agreement with the preparatory direct threshold measurement
but is two orders of magnitude more precise.
Ab initio calculations. Early predictions10–13 of the IP of At at
9.2–10.4 eV were based on known IPs of other neighbouring
elements and on spectroscopic data of other halogens.
A compilation of all predictions involving recent
calculations14,15, as well as theoretical and experimental values
obtained within this work, is given in Table 1. To strengthen this
work, the IP was calculated before the experiment with the use of
two relativistic methods, the multi-configuration Dirac-Fock
(MCDF) and the Dirac-Coulomb (DC) coupled-cluster
approach. The MCDF method provides a conceptually simple
approach for computing excitation energies and IPs of heavy
elements that can be improved systematically and is applicable to
quite different shell structures of the atoms and ions. Although
this method profits from a systematic enlargement of the active
configuration space, (deep) core-valence and core-core
correlations are usually not taken into account. Therefore, in
recent calculations by Chang et al.15, the (predicted) IP was
semiempirically up-shifted by 0.3 to 9.35 eV, based on similar
computations for the homologue elements and the comparison
with known IPs from experiment.
In a more systematic treatment, we now took into account all
triple excitations within the {6s,6p,6d,7s,7p} active space as well as
all single and double excitations to the {ns,np,nd,nf,ng;n¼7,8,9}
orbitals, starting from the 6s26p5and 6s26p4reference
configurations for neutral and singly charged At, respectively.
In addition, core-polarization contributions from the n¼4 and
n¼5 (fully) occupied shells were also incorporated. The most
precise value obtained using this method was IP(At) ¼9.24(15) eV
(see Table 1), in reasonable agreement with previous estimates.
The uncertainty quoted indicates that still further correlations are
expected to contribute to the IP.
An alternative approach was based on the solution of the DC
Hamiltonian24 in combination with the coupled-cluster approach
with single, double and perturbative triple excitations (CCSD(T))
for treatment of electron correlation. The IP was obtained by
taking the energy difference between the calculated energies of the
neutral element and its cation. The Dirac08 program package25
was used to perform the calculations. The uncontracted Faegri
basis sets26 were used for At as well as for iodine (I) as a
homologue, consisting of 26s24p18d14f7g4h2iorbitals
for I and 28s26p20d15f7g4h2iorbitals for At. The convergence
of the calculated IPs with respect to the size of the basis set was
verified. The outer 38 electrons of I and 54 electrons of At were
correlated; virtual atomic orbitals with energies higher than 50
Hartree (E1,360 eV) were discarded. The contribution of the
Breit term was assessed by performing Fock-space coupled-
cluster calculations, and was found to be small: 19 cm 1for I and
5cm1for At. Higher order QED effects should thus be
negligible. The final IPs, corrected for the Breit contribution, are
84,095 cm 1for I and 75,069 cm 1for At, corresponding to
9.307 eV. The IP value for I closely matches the experimental one
of 84,295 cm 1(ref. 23), and similar agreement is shown
between the newly measured and CCSD(T) values for At.
We apply the technique of in-source laser spectroscopy to
artificially produced At isotopes. The discovered series of high-
lying Rydberg states enables us to deduce the IP with high
accuracy. This first experimental value of the binding energy
of the valence electron of At serves as a benchmark for
the prediction of the chemical properties of At as well as for
predictions of atomic physics properties of the superheavy
elements. The newly available, efficient three-step laser ionization
scheme for At enables further experiments on At isotopes at ISOL
Dipole magnet
Hot cavity ion source
Target material Reaction products Ions
Laser beams
60 kV
Po Tl
At Po
199At +
UAt At
Figure 4 | In-source laser spectroscopy at ISOLDE. Protons impinge on a thick target inducing nuclear reactions (for example, spallation) in which
different isotopes of various chemical elements are produced. The reaction products diffuse and effuse towards the hot cavity ion source, into which the
precisely tuned laser beams are focussed. Step-wise resonance laser ionization creates singly charged ions of the desired element. These photo-ionsare
extracted and accelerated by applying a high-voltage potential. The ion beam of the isotope of interest is selected by dipole magnets and guided to a
suitable detection setup.
4NATURE COMMUNICATIONS | 4:1835 | DOI: 10.1038/ncomms2819 |
&2013 Macmillan Publishers Limited. All rights reserved.
facilities world-wide. High-resolution in-source laser spectro-
scopy of isotope shifts and hyperfine structures27 as well as an
extension of the study of b-delayed fission28 to the At isotopes is
in preparation. Two theoretical methods are applied to calculate
the IP(At). The higher accuracy of the CCSD(T) result, compared
with the MCDF value is due to better treatment of dynamic
correlation within the former approach. The CCSD(T) approach
is particularly suitable in this case, as the ground states of both At
and Atþmay be approximated by single determinants. The
dynamic correlation, which is handled better by CCSD(T), is the
dominant effect.
In-source laser spectroscopy. Astatine isotopes were produced at the CERN
ISOLDE radioactive ion beam facility (see ref. 20) by directing a 1.4-GeV pulsed
proton beam of up to 2 mA from the CERN proton synchrotron booster (PSB) onto
a thick target of uranium carbide (UC
) or thorium dioxide (ThO
). Figure 4
illustrates the in-source laser spectroscopy method. The products of the proton-
induced nuclear reactions diffuse into a hot (E2,000 °C) metal tubular cavity
within which the neutral atoms are selectively photo-ionized by spatially over-
lapped beams of the RILIS lasers, wavelength tuned to the corresponding transi-
tions of a photoionization scheme. Ions are extracted and accelerated by an
electrostatic potential of up to 60 kV. The isotope of interest is selected by the
ISOLDE mass separator dipole magnets and transmitted to the detection setups.
The photo-ion signal is recorded as a function of laser frequency.
RILIS laser setup. The RILIS laser system comprises tunable nanosecond dye (type
Sirah Credo) and Ti:Sa lasers, pumped by the second harmonic output of Nd:YAG
lasers at a pulse repetition rate of 10 kHz. The wavelengths required for excitation
and ionization of the atoms were provided by the fundamental output of the lasers
or by the generation of their higher harmonics. A detailed description of the RILIS
laser system can be found in Fedosseev et al.29, Rothe et al.30and references therein.
Spectroscopy using the Windmill detector. For the initial laser spectroscopy
using the inefficient two-colour scheme (cf. Fig. 1a,b), a sensitive a-decay spec-
troscopy setup (Windmill detector), as described in Andreyev et al.28, was used to
detect photo-ion rates in the range of 0.1–1,000 s 1. The Windmill detector was
installed at the end point of one of the beam-lines of the ISOLDE general purpose
separator. The ion beam was implanted into one of ten carbon foils (20 mgcm2),
which are mounted on a rotating wheel. The carbon foil is surrounded by two
Si-detectors to acquire the a-decay spectrum of the implanted sample. The isotope
199At was chosen for its suitable half-life of 7.2 s and a well-sepa rated a-decay
energy of 6,643 keV. The number of 6,634 keV a-decays was counted for every
wavelength combination of the RILIS dye lasers. This measurement sequence
was synchronized to the PSB supercycle (E60 s), ensuring steady conditions.
Rydberg spectroscopy using FC detection. For the laser spectroscopy of Rydberg
states, the Ti:Sa lasers were used to generate wavelengths required for the first and
second-step transition. The laser powers measured on the laser table were 33 mW
(fourth harmonic) for the first step and 2 W (fundamental) for the second-step
transition. The dye laser (Sirah Credo with DCM dye dissolved in ethanol) was
scanned in the range of 16,599–15,523cm1in two sections at a speed of
0.251 cm1s1and 0.132 cm 1s1. The laser wavelengths were continuously
measured with a wavelength metre (HighFinesse-Ångstrom WS/7), calibrated with
a frequency stabilized HeNe laser. The three-colour ionization scheme has a higher
efficiency and the photo-ion signal was obtained from a direct ion current mea-
surement with a FC installed in the focal plane of the separator magnet. The best
signal to noise ratio was obtained with the separator magnet set to transmit mass
A¼205. This is because of the relatively high production cross section of the
isotope 205At, its slow component of release from the ISOLDE target and relatively
long half-life (26.2 min), which ensures quasi -independence from the PSB super-
cycle sequence. The continuous scanning method requires a correction for the
integration time of the FC and potential delays in the data acquisition. The cor-
rection factor was determined separately by spectroscopy of stable manganese
isotopes under the same conditions.
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We thank the ISOLDE Collaboration for flexible allocation of beam time. We
acknowledge the support from TRIUMF, which receives federal funding via a con-
tribution agreement with the National Research Council of Canada and support through
an NSERC discovery grant, as well as beam time allocation for experiment S1237 at
TRIUMF. We thank the GSI Target Group for manufacturing the carbon foils.
We acknowledge support by the Wolfgang-Gentner-Programme of the Bundesminis-
terium fu¨r Bildung und Forschung (BMBF, Germany), by FWO-Vlaanderen (Belgium),
by GOA/2010/010 (BOF-KU Leuven), by the IUAP- Belgian Science Policy Office
(BriX network P7/12), by a grant from the European Research Council (ERC-2011-AdG-
291561-HELIOS), by the United Kingdom Science and Technology Facilities Council
(STFC), by the European Union Seventh Framework through ENSAR (contract no.
262010), by the Slovak Research and Development Agency (contract No. APVV-0105-10
and APVV-0177-11) and by the Reimei Foundation of JAEA. We acknowledge the Knut
and Alice Wallenberg Foundation (grant KAW 2005-0121) for funding the RILIS laser
NATURE COMMUNICATIONS | 4:1835 | DOI: 10.1038/ncomms2819 | 5
&2013 Macmillan Publishers Limited. All rights reserved.
Author contributions
This work constitutes the core of the PhD thesis by S.Ro. A.N.A., B.A.M., Y.K., J.L., S.Rae.,
V.F., K.D.A.W. and S.Ro. conceived the experiment with A.N.A. and V.F. spokespersons of
the At Collaboration. B.A.M., Y.K., N.I., D.V.F., D.A.F., R.E.R., V.F., M.D.S., A.M.S. and S.Ro.
set up the RILIS laser system. M.V., M.M.R., A.N.A., P.V.D., P.V.d.B., D.R., L.G., T.E.C., D.P.,
H.D.W., M.H. and V.L. set up the Windmill detector. B.A.M., T.J.P., M.M.R., Y.K. U.Ko
A.N.A., P.V.D., L.P., K.S., K.N., N.I., L.C., Y.W., D.V.F., D.R., L.G., D.A.F., R.E.R., J.L., S.Rae.,
S.A., V.F., M.D.S., A.M.S., T.E.C., K.D.A.W., D.P., H.D.W., M.H., K.M.L., V.L., J.F.W.L. and
S.Ro. performed the measurements. B.A.M., P.V.D., L.G., V.F., M.H., K.D.A.W. and S.Ro
analysed and interpreted the experimental data. S.F. performed the MCDF calculations. U.Ka.,
discussed and provided the theoretical results. U.Ka., P.V.D., A.N.A., V.F., K.D.A.W. and M.H.
supervised the project. S.Ro. wrote the paper with B.A.M., U.Ka., U.Ko
¨., A.B., A.N.A., P.V.D.,
J.L., S.Rae., S.A., V.F., T.E.C., K.D.A.W. and M.H. actively contributing to the manuscript.
Additional information
Competing financial interests: The authors declare no competing financial interests.
Reprints and permission information is available online at
How to cite this article: Rothe, S. et al. Measurement of the first ionization potential of
astatine by laser ionization spectroscopy. Nat. Commun. 4:1835 doi: 10.1038/
ncomms2819 (2013).
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6NATURE COMMUNICATIONS | 4:1835 | DOI: 10.1038/ncomms2819 |
&2013 Macmillan Publishers Limited. All rights reserved.
... Figure 1 shows a simple man's view upon the fine-structure of openshell elements with its overlapping configurations and strong relativistic contributions [3]. In particular, the actinides are known to exhibit very complex spectra owing to the presence of the open 5 f , 6d, 7s and 7p shells whose fine-structure can be resolved only by highresolution laboratory studies [4][5][6]. ...
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Open f-shell elements still constitute a great challenge for atomic theory owing to their (very) rich fine-structure and strong correlations among the valence-shell electrons. For these medium and heavy elements, many atomic properties are sensitive to the correlated motion of electrons and, hence, require large-scale computations in order to deal consistently with all relativistic, correlation and rearrangement contributions to the electron density. Often, different concepts and notations need to be combined for just classifying the low-lying level structure of these elements. With Jac, the Jena Atomic Calculator, we here provide a toolbox that helps to explore and deal with such elements with open d- and f-shell structures. Based on Dirac’s equation, Jac is suitable for almost all atoms and ions across the periodic table. As an example, we demonstrate how reasonably accurate computations can be performed for the low-lying level structure, transition probabilities and lifetimes for Th2+ ions with a 5f6d ground configuration. Other, and more complex, shell structures are supported as well, though often for a trade-off between the size and accuracy of the computations. Owing to its simple use, however, Jac supports both quick estimates and detailed case studies on open d- or f-shell elements.
... The design of optimal astatine-based radiopharmaceuticals has long been hampered by the elusive nature of this element. 11 For instance, the measurements of atomic ionization energy and electron affinity, which are fundamental quantities for understanding the subtle mechanisms of bond formation, were only reported in 2013 12 and 2020, 2 respectively. A number of astatine's properties remain thus far inaccessible because the radioelement is available from artificial production at the nanogram scale at best, making usual spectroscopic tools inapplicable to physical and chemical characterization. ...
Astatine-211 (²¹¹At, T1/2 = 7.21 h) emitting two α particles with energies of 5.87 and 7.45 MeV, can lead to a high linear energy transfer (LET = 98.84 keV/μm) and short tissue range (50 ∼ 90 μm). Since the 1950s, ²¹¹At had stepped into endoradiotherapy and has always been regarded as one of the most promising α-emitters for targeted-alpha therapy (TAT) in various malignancies. In the past two decades, ²¹¹At related radiopharmaceuticals have achieved great progress in the studies of basic physicochemical properties of astatine, ²¹¹At labelling strategies, preclinical and clinical studies, producing profound effects in nuclear medicine. This work will give a panorama of ²¹¹At-related researches in the recent 20 years, which will cover both the fundamental insights of ²¹¹At radiochemistry and applied labelling compounds. It can provide some important hints for the studies of TAT and other radiopharmaceuticals applied in tumor radiotherapy.
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The newly measured ionization potential of atomic astatine is discussed and compared with that of the recently determined value for polonium and for the other atomic halogens. Regularities in these atomic values are discussed and applied to the understanding of the energetics of diatomic halogens. Some surprises remain.
Thermodynamic properties including bond dissociation energies (BDEs), heats of formation, and gas-phase acidities for the hydrides and dimers of chalcogens and halogens, H2Y, HX, Y2, and X2 for Y = Se, Te, and At and X = Br, I, and At, have been predicted using the Feller-Peterson-Dixon composite-correlated molecular orbital theory approach. A full four-component CCSD(T) approach was used to calculate the spin-orbit effects on thermodynamic properties, except for Se2, where the AoC-DHF value was used due to strong multireference effects in Se2 for the SO calculations. The calculated results show that the At2 BDE is quite small, 19.5 kcal/mol, with much of the low bond energy due to spin-orbit effects. H2Po is not predicted to be stable to dehydrogenation to Po + H2 in terms of the free energy at 298 K. In the gas phase, HAt is predicted to be a stronger acid than H2SO4. The current results provide insights into potential difficulties in the actual experimental observation of such species for heavy elements.
The interest to perform laser spectroscopy in the heaviest elements arises from the strong impact of relativistic effects, electron correlations and quantum electrodynamics on their atomic structure. Once this atomic structure is well understood, laser spectroscopy also provides access to nuclear properties such as spins, mean square charge radii and electromagnetic moments in a nuclear-model independent way. This is of particular interest for the heaviest actinides around $N = 152$, a region of shell stabilized deformed nuclei. The experimental progress of laser spectroscopy in this region benefitted from continuous methodological and technical developments such as the introduction of buffer-gas-stopping techniques that enabled the access to ever more exotic nuclei far-off stability. The key challenges faced in this endeavor are small yields, nuclides with rather short half-lives and the need to search for atomic transitions in a wide spectral range guided by theoretical predictions. This paper describes the basics of the most common experimental methods and discusses selected recent results on the atomic and nuclear properties of the actinides up to nobelium where pioneering experiments were performed at the GSI Helmholtzzentrum f\"ur Schwerionenforschung in Darmstadt, Germany.
The near quantitative separation, purification, and recovery of 211At has been demonstrated through an extraction chromatography process which utilizes porous beads impregnated with 3-octanone, resulting in an elution yield of 92–95%. Moreover, the rapid nature of this process, less than 20 min, was achieved after dissolution of a Bi metal target in HNO3 following retrieval from the beamline after α–particle bombardment. The solution was directly loaded onto the column with no volume or acidity adjustment. The column was washed with HNO3 and H2O, and 211At was eluted with ethanol, collecting roughly 87–93% in 1 mL. This process of recovering high purity 211At, in near quantitative yields, represents a significant advance in At separations.
The potential energy curves (PECs) of all covalent states of Molecular Astatine (At2) have been investigated in this work within a four-component relativistic framework using the MOLFDIR program package. The ground state was determined using multireference configuration interaction with all single and double excitations including Davidson size-extensivity correction (MRCISD+Q) whereas the 22 excited states were treated by complete open shell configuration interaction (COSCI). Spectroscopic constants (Re,ωe,ωexe,ωeye, De,Be,αe,βe,Te ) are presented for all states as well as vertical excitations obtained at COSCI, MRCISD and MRCISD+Q levels. In addition, it is also presented accurate extended Rydberg analytical form for the ground state X: (1)0g⁺.
The periodic table provides a deep unifying principle for understanding chemical behaviour by relating the properties of different elements. For those belonging to the fifth and earlier rows, the observations concerning these properties and their interrelationships acquired a sound theoretical basis by the understanding of electronic behaviour provided by non-relativistic quantum mechanics. However, for elements of high nuclear charge, such as occur in the sixth and higher rows of the periodic table, the systematic behaviour explained by non-relativistic quantum mechanics begins to fail. These problems are resolved by realizing that relativistic quantum mechanics is required in heavy elements where electrons velocities can reach significant fractions of the velocity of light. An essentially non-mathematical description of relativistic quantum mechanics explains how relativity modifies valence electron behaviour in heavy elements. The direct relativistic effect, arising from the relativistic increase of the electron mass with velocity, contracts orbitals of low angular momentum, increasing their binding energies. The indirect relativistic effect causes valence orbitals of high angular momentum to be more effectively screened as a result of the relativistic contraction of the core orbitals. In the alkali and alkaline earths, the s orbital contractions reverse the chemical trends on descending these groups, with heavy elements becoming less reactive. For valence d and f electrons, the indirect relativistic effect enhances the reductions in their binding energies on descending the periodic table. The d electrons in the heavier coinage metals thus become more chemically active, which causes these elements to exhibit higher oxidation states. The indirect effect on d orbitals causes the chemistries of the sixth-row transition elements to differ significantly from the very similar behaviours of the fourth and fifth-row transition series. The relativistic destabilization of f orbitals causes lanthanides to be chemically similar, forming mainly ionic compounds in oxidation state three, while allowing the earlier actinides to show a richer range of chemical behaviour with several higher oxidation states. For the 7p series of elements, relativity divides the non-relativistic p shell of three degenerate orbitals into one of much lower energy with the energies of the remaining two being substantially increased. These orbitals have angular shapes and spin distributions so different from those of the non-relativistic ones that the ability of the 7p elements to form covalent bonds is greatly inhibited. This article is part of the theme issue ‘Mendeleev and the periodic table’.
Publisher Summary Astatine, the fifth and heaviest member of the Periodic Table Group VIIB (the halogens), is the earth's rarest naturally occurring element. Many aspects of the nuclear physics, and inorganic and organic chemistry, of the astatine radionuclides have been the subject of a number of excellent reviews. The possibility of their existence was predicted from the β -decay of polonium. The relationship between the emitted α -particle energy and mass number of the astatine isotope is presented. Preparation of the isotopes of astatine is more difficult than with most radionuclides, as they cannot be synthesized by neutron irradiation; this precludes the use of a nuclear reactor. Numerous nuclear reactions have been employed to produce astatine. Three of these are particularly suited for routine preparation of the relatively long-lived isotopes with mass numbers 209, 210, and 211. Astatine can be readily and routinely obtained in an inorganic form suitable for chemical and biomedical application from the α -irradiated bismuth target by either extractive or dry distillation techniques. Distillation of astatine from molten metallic bismuth is the most widely used technique for separation of the radionuclide. Astatine, regardless of its electronic state (vide infra), appears to possess many physiobiochemical properties similar to those of its nearest homolog iodine.
The range of isotopes available at the TRIUMF Isotope Separator Accelerator (ISAC) facility has been greatly enhanced by adding a Resonance Ionization Laser Ion Source (RILIS). A large wavelength range is accessible with the fundamental, second and third harmonic generation of titanium-sapphire laser light. In addition a dedicated laser is available for non-resonant laser ionization. The first on-line beam 62Ga was delivered in Dec. 2004. In general RILIS improves the intensity, purity and emittance of ion beams. 62Ga and 26Al and Be beams have been delivered so far on-line.
CONTENTS I. History of discovery 87 II. Isotopes of astatine 88 III. Astatine in nature 89 IV. Methods of obtaining and isolating astatine 89 V. Physical properties of astatine 90 VI. Chemical properties of astatine 91 VII. Astatine in organic compounds 95 VIII. Biological behaviour of astatine 96
Es wird eine Verbesserung derMatuyama-Clark-Beziehung über den Zusammenhang der Schwingungsfrequenzen zweiatomiger Moleküle vom Typ XX im Grundzustand mitgeteilt. Diese Beziehung lautet für die Zahlenwerte: logω e=g − h log n2V. n ist dabei die Hauptquantenzahl der Valenzelektronen,V das Ionisierungspotential undg undh sind Konstante. Die Ionisierungspotentiale von Polonium (9,44 eV), Astatin (10,4 eV) und Francium (3,83 eV) werden berechnet.
The ionization potential and dissociation energy are estimated for astatine from empirical correlations. From the /sub e values for the lighter halogens, the e/ for At/sub 2/ is estimated to be 160 cm/sup -1/, and a plot of these /sub e/ values on a log /sub e/ vs. log n/sup 2/I graph (n = principal quantum number)
A highly sensitive method of spectrographic detection of gases was used to detect the absorption of atomic astatine. Two lines were recorded whose wavelengths were 2244.01 and 2162.25 Å. These lines were tentatively assigned to the transitions 2P3/20-4P5/2 and 2P3/20-4P3/2between configurations 6p5 and 6p4 7s. The assignment of two resonant lines of polonium was confirmed.