Actinium (Ac)
actinideSolid
Standard Atomic Weight
[227]Electron configuration
[Rn] 7s2 6d1Melting point
1050.85 °CBoiling point
3197.85 °CDensity
1.007e+4 kg/m³Oxidation states
+3Electronegativity (Pauling)
1.1Ionization energy (1st)
5.380235 eVDiscovery year
1899Atomic radius
195 pmDetails
Actinium is a radioactive actinide metal and the element that gives the actinide series its name. Natural actinium is present only in minute amounts, chiefly as ²²⁷Ac in uranium decay chains. Its chemistry is dominated by the +3 oxidation state and resembles that of lanthanum more than the later, more strongly 5f-influenced actinides. Because all isotopes are radioactive and scarce, most knowledge comes from tracer-scale chemistry rather than ordinary bulk handling.
Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha particles. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees C. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons.
In April of 2012, Los Alamos National Laboratory announced a new medical isotope project that shows promise for rapidly producing major quantities of a new cancer-treatment agent, actinium 225 (Ac-225). Both a press release and a video are available.
Actinium was discovered in 1899 by André-Louis Debierne, a French chemist, while experimenting with new methods of separating rare earth oxides. Friedrich Otto Giesel independently discovered actinium in 1902. Actinium is a rare element that is present in uranium ores in tiny amounts, but it is usually cheaper and easier to create actinium when it is needed by bombarding radium with neutrons in a nuclear reactor.
Actinium's most stable isotope, actinium-227, has a half-life of 21.77 years. It decays into francium-223 through alpha decay or into thorium-227 through beta decay.
From the Greek aktis, aktinos, meaning beam or ray. Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals.
A freshly prepared macroscopic sample has rarely been available. Metallic actinium is described as silvery, but its bulk appearance and many physical properties are not as well characterized as those of common metals. It is expected to tarnish rapidly in air and to be self-luminous in the dark from intense radioactivity exciting surrounding materials.
Actinium has no broad commercial use as an elemental material. ²²⁵Ac is important in research and limited clinical development for targeted alpha therapy, where it is attached to carrier molecules intended to deliver alpha-emitting decay products to diseased cells. ²²⁷Ac has been used as a source for generating ²²⁷Th and other decay-chain nuclides, and actinium isotopes are used in radiochemical research, detector calibration, and studies of actinide separation chemistry. Proposed neutron-source uses with light-element targets are historically noted but are not a major present application.
Actinium has no significant commercial applications, although it is used in the production of neutrons.
Isotopes in Earth/Planetary Science
227Ac (with a half-life of 21.77 years) has been used as a tracer of deep-sea mixing in the oceans. By determining concentrations of 227Ac in a water column, scientists can study the rates and patterns of mixing and other vertical exchange processes [583] W. Geibert, M. M. Rutgers van der Loeff, C. Hanfland, H. J. Dauelsberg. Earth. Planet. Sci. Lett.198, 147 (2002).. As a product of the 235U decay chain, 227Ac and other radioisotopes have been used to determine information about the movement of fluids in mid-oceanic ridges and basaltic melts [584] D. McKenzie. Chem. Geol.162, 81 (2000)., [585] W. S. Moore, W. Ussler III, C. K. Paull. Mar. Chem.109, 421 (2008)..
Isotopes in Medicine
225Ac (with a half-life of 10 days) can be used in cancer treatments (Fig. IUPAC.89.1). The isotope is attached to a chelating agent (a substance that can form multiple bonds to a single metal ion) and delivered to the problem site. The emissions of alpha particles from actinium and its daughter products cause tumor death [586] M. R. McDevitt, D. Ma, L. T. Lai, J. Simon, P. Borchardt, R. K. Frank, K. Wu, V. Pellegrini, M. J. Curcio, M. Miederer, N. H. Bander, D. A. Scheinberg. Science294, 1537 (2001).. 225Ac in a series of alpha decays produces 213Bi (with a half-life of 0.76 h), which is also used for radioimmunotherapy [587] D. Ma, M. R. McDevitt, R. D. Finn, D. A. Scheinberg. Appl. Radiat. Isot.55, 667 (2001)..
Isotopes Used as a Source of Radioactive Isotope(s)
225Ac, which is a pure alpha emitter, is used to produce 213Bi with an 225Ac/ 213Bi radionuclide generator (Fig. IUPAC.89.2). 213Bi is a mixed alpha and beta emitter. The primary mode of decay is by beta emission to the very short-lived, alpha emitter 213Po. The 8.4 MeV alpha particle emitted by 213Po has a path length of 76 μm in human tissue and is responsible for its cytotoxic effects.
Actinium chemistry is almost entirely trivalent, with Ac³⁺ forming colorless or pale salts in the absence of colored counterions. Representative compounds include actinium oxide, Ac₂O₃, actinium fluoride, AcF₃, actinium chloride, AcCl₃, and actinium hydroxide, Ac(OH)₃. The ion is large and hard, so it favors oxygen- and fluorine-donor ligands and forms sparingly soluble fluorides, phosphates, oxalates, and hydroxides. Higher oxidation states are not established for ordinary actinium chemistry.
See more information at the Actinium compound page.
All actinium isotopes are radioactive, and safety depends strongly on isotope, activity, chemical form, and route of exposure. ²²⁷Ac is long-lived enough to persist and produces a chain of radioactive daughters, while ²²⁵Ac is a potent alpha emitter used only under controlled radiochemical conditions. Internal uptake is the principal concern because alpha particles cause severe local ionization in tissue. External gamma radiation from daughter products can also require shielding and remote handling.
Natural actinium occurs at trace levels in uranium-bearing minerals as part of decay chains and is continuously formed and lost by radioactive decay. In the environment Ac³⁺ is expected to bind strongly to mineral surfaces, organic matter, and phosphate- or carbonate-containing solids, limiting mobility under many conditions. It has no known biological role. Releases outside specialized nuclear or radiochemical settings are uncommon, and environmental behavior is inferred largely from tracer studies and analog chemistry.
Actinium is not traded as a bulk commodity. Usable quantities are obtained by radiochemical separation from decay products or by accelerator and reactor routes, depending on the isotope required. ²²⁵Ac supply is especially constrained because it must be isolated from suitable parent nuclides or produced by irradiation, followed by difficult purification from chemically similar actinides and radioactive daughters. Costs and availability are therefore governed by nuclear infrastructure, isotope purity, licensing, and short logistical timelines rather than mining demand. Recycling is mainly recovery from radiochemical processing streams.
Extremely rare, found in all uranium ores. Usually obtained by treating radium with neutrons in a reactor.
Actinium has no stable isotopes, so any primordial actinium has long since decayed. In nature and in planetary materials it exists only as a transient member of heavy-element decay chains, especially those derived from uranium and thorium. The heavy nuclei that ultimately feed these chains were produced by neutron-capture processes in earlier stellar events, but actinium itself is not a significant cosmic reservoir.
- Actinium was discovered through its radioactivity before its chemistry could be studied in ordinary amounts.
- The name comes from the Greek word for a ray or beam.
- ²²⁷Ac is a decay product in the ²³⁵U series.
- The element is usually handled at tracer scale, where carrier chemistry is often needed.
- Ac³⁺ is among the largest tripositive actinide ions.
- Separating actinium from lanthanum is chemically difficult because their ionic behavior is similar.
Images
Properties
Physical
- Atomic radius (empirical)
- 195 pm Compare Atomic radius (empirical) of all elements →
- Covalent radius
- 215 pm Compare Covalent radius of all elements →
- Van der Waals radius
- 260 pm Compare Van der Waals radius of all elements →
- Density
- 1.007 × 104 kg/m³ Compare Density of all elements →
- Molar volume
- 0.02254 L/mol
- Phase at STP
- Solid Compare Phase at STP of all elements →
- Melting point
- 1050.85 °C Compare Melting point of all elements →
- Boiling point
- 3197.85 °C Compare Boiling point of all elements →
- Specific heat capacity
- 0.12 J/(g·K) Compare Specific heat capacity of all elements →
- Molar heat capacity
- 27.2 J/(mol·K) Compare Molar heat capacity of all elements →
- Crystal structure
- Face-centered cubic Compare Crystal structure of all elements →
Chemical
- Electronegativity (Pauling)
- 1.1 Compare Electronegativity (Pauling) of all elements →
- Electron affinity
- 0.35 eV
- Ionization energy (1st)
- 5.380235 eV Compare Ionization energy (1st) of all elements →
- Ionization energy (2nd)
- 11.75004 eV Compare Ionization energy (2nd) of all elements →
- Ionization energy (3rd)
- 17.43606 eV Compare Ionization energy (3rd) of all elements →
- Ionization energy (4th)
- 44.800154 eV Compare Ionization energy (4th) of all elements →
- Ionization energy (5th)
- 55.000189 eV Compare Ionization energy (5th) of all elements →
- Oxidation states
- +3 Compare Oxidation states of all elements →
- Valence electrons
- 3 Compare Valence electrons of all elements →
- Electron configuration
- [Rn] 7s2 6d1
Thermodynamic
- Heat of fusion
- 0.14510027 eV Compare Heat of fusion of all elements →
- Heat of vaporization
- 4.145722 eV Compare Heat of vaporization of all elements →
- Heat of sublimation
- 4.456651 eV
- Heat of atomization
- 4.456651 eV
- Atomization enthalpy
- 4.207908 eV
Nuclear
- Protons
- 89 Compare Protons of all elements →
- Neutrons
- 138 Compare Neutrons of all elements →
- Known isotopes
- 33 Compare Known isotopes of all elements →
- Stable isotopes
- 0 Compare Stable isotopes of all elements →
- Mass number (most stable)
- 227
- Most stable isotope
- Ac-227
- Discovery year
- 1899
Abundance
- Abundance (Earth's crust)
- 5.5e-10 mg/kg Compare Abundance (Earth's crust) of all elements →
Crystal Structure
- Lattice constant a
- 531 pm
Electronic Structure
- Electrons per shell
- 2, 8, 18, 32, 18, 9, 2 Compare Electrons per shell of all elements →
Identifiers
- CAS number
- 7440-34-8 Compare CAS number of all elements →
- Term symbol
- 2D3/2
- InChI
- InChI=1S/Ac
- InChI Key
- QQINRWTZWGJFDB-UHFFFAOYSA-N
Electron Configuration Measured
Ac: 6d¹ 7s²[Rn] 6d¹ 7s²1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹⁰ 6s² 6p⁶ 6d¹ 7s²Atomic model
Isotopes change neutron count, mass, and stability — not the electron configuration of a neutral atom.
Schematic atomic model, not to scale.
Atomic Fingerprint
Emission / Absorption Spectrum
Isotope Distribution
No stable isotopes.
| Mass number | Atomic mass (u) | Natural abundance | Half-life |
|---|---|---|---|
| 212 Radioactive | 212.007813 ± 0.000055 | N/A | 895 ms |
| 213 Radioactive | 213.006609 ± 0.000056 | N/A | 738 ms |
| 216 Radioactive | 216.008743 ± 0.000012 | N/A | 440 us |
| 210 Radioactive | 210.009436 ± 0.000062 | N/A | 350 ms |
| 211 Radioactive | 211.007732 ± 0.000057 | N/A | 213 ms |
Phase / State
Reason: 1025.8 °C below melting point (1050.85 °C)
Schematic, not to scale
Phase transition points
Transition energies
Energy required to melt 1 mol at melting point
Energy required to vaporize 1 mol at boiling point
Energy required to sublime 1 mol at sublimation point
Density
At standard conditions
At standard conditions
Atomic Spectra
Showing 10 of 89. Sorted by ion charge (ascending).
Lines Holdings ?
| Ion | Charge | Total lines | Transition probabilities | Level designations |
|---|---|---|---|---|
| Ac I | 0 | 153 | 95 | 113 |
| Ac II | +1 | 345 | 294 | 319 |
| Ac III | +2 | 11 | 11 | 11 |
| Ac IV | +3 | 6 | 0 | 0 |
Levels Holdings ?
| Ion | Charge | Levels |
|---|---|---|
| Ac I | 0 | 53 |
| Ac II | +1 | 84 |
| Ac III | +2 | 8 |
| Ac IV | +3 | 2 |
| Ac V | +4 | 2 |
| Ac VI | +5 | 2 |
| Ac VII | +6 | 2 |
| Ac VIII | +7 | 2 |
| Ac IX | +8 | 2 |
| Ac X | +9 | 2 |
Ionic Radii
| Charge | Coordination | Spin | Radius |
|---|---|---|---|
| +3 | 6 | N/A | 112.00000000000001 pm |
| +3 | 9 | N/A | 122 pm |
Compounds
Isotopes (5)
| Mass number | Atomic mass (u) | Natural abundance | Half-life | Decay mode | |
|---|---|---|---|---|---|
| 212 Radioactive | 212.007813 ± 0.000055 | N/A | 895 ms | α ≈100%β+ ? | |
| 213 Radioactive | 213.006609 ± 0.000056 | N/A | 738 ms | α ≈100%β+ ? | |
| 216 Radioactive | 216.008743 ± 0.000012 | N/A | 440 us | α =100%β+ ? | |
| 210 Radioactive | 210.009436 ± 0.000062 | N/A | 350 ms | α ≈100%β+ ? | |
| 211 Radioactive | 211.007732 ± 0.000057 | N/A | 213 ms | α ≈100%β+ ? |
Spectral Lines
Showing 50 of 213. Only spectral lines with measured intensity are shown by default.
| Wavelength (nm) | Intensity | Ion stage | Type | Transition | Accuracy | Source | |
|---|---|---|---|---|---|---|---|
| 391.4468 nm | 24000 | Ac II | emission | 6d.7s 3D → 5f.7s 3F* | Measured | NIST | |
| 417.99772 nm | 17000 | Ac I | emission | 6d.7s2 2D → 6d.7s.(1D).7p 2D* | Measured | NIST | |
| 481.2218 nm | 16000 | Ac II | emission | 6d.7s 3D → 7s.7p 3P* | Measured | NIST | |
| 438.64 nm | 15000 | Ac II | emission | 6d.7s 1D → 6d.7p 1D* | Measured | NIST | |
| 397.736 nm | 13000 | Ac II | emission | 6d2 3F → 6d.7p 3P* | Measured | NIST | |
| 445.2188 nm | 12000 | Ac II | emission | 6d.7s 3D → 6d.7p 3F* | Measured | NIST | |
| 388.55592 nm | 9000 | Ac I | emission | 6d.7s2 2D → 6d.7s.(3D).7p 2P* | Measured | NIST | |
| 401.9622 nm | 8700 | Ac II | emission | 6d2 3F → 5f.6d 1G* | Measured | NIST | |
| 544.6367 nm | 8700 | Ac II | emission | 6d2 3F → 6d.7p 3D* | Measured | NIST | |
| 435.9118 nm | 7300 | Ac II | emission | 6d.7s 3D → 7s.7p 3P* | Measured | NIST | |
| 446.27307 nm | 6900 | Ac I | emission | 6d.7s2 2D → 6d.7s.(1D).7p 2F* | Measured | NIST | |
| 471.65807 nm | 6900 | Ac I | emission | 6d.7s2 2D → 6d.7s.(1D).7p 2F* | Measured | NIST | |
| 495.8233 nm | 6800 | Ac II | emission | 6d.7s 1D → 6d.7p 1P* | Measured | NIST | |
| 384.304 nm | 6600 | Ac I | emission | 6d.7s2 2D → 6d.7s.(3D).7p 2P* | Measured | NIST | |
| 392.0101 nm | 6500 | Ac II | emission | 6d2 3P → 5f.6d 1D* | Measured | NIST | |
| 418.31199 nm | 6400 | Ac I | emission | 6d.7s2 2D → 6d.7s.(3D).7p 2F* | Measured | NIST | |
| 439.67158 nm | 5800 | Ac I | emission | 6d.7s2 2D → 6d.7s.(3D).7p 2F* | Measured | NIST | |
| 419.43971 nm | 5300 | Ac I | emission | 6d.7s2 2D → 6d.7s.(1D).7p 2P* | Measured | NIST | |
| 494.5181 nm | 5300 | Ac II | emission | 6d2 3F → 6d.7p 3D* | Measured | NIST | |
| 496.0869 nm | 4900 | Ac II | emission | 6d2 3F → 6d.7p 3D* | Measured | NIST | |
| 461.39285 nm | 4000 | Ac I | emission | 6d.7s2 2D → 6d.7s.(3D).7p 2F* | Measured | NIST | |
| 527.15603 nm | 3800 | Ac I | emission | 6d.7s2 2D → 6d.7s.(1D).7p 2F* | Measured | NIST | |
| 406.31064 nm | 3700 | Ac I | emission | 6d.7s2 2D → 6d.7s.(1D).7p 2D* | Measured | NIST | |
| 407.8693 nm | 3700 | Ac II | emission | 6d.7s 3D → 6d.7p 1P* | Measured | NIST | |
| 403.4629 nm | 3500 | Ac I | emission | 6d.7s2 2D → 6d2.(3F).7p 4G* | Measured | NIST | |
| 420.9682 nm | 3500 | Ac II | emission | 6d.7s 3D → 5f.7s 1F* | Measured | NIST | |
| 669.5231 nm | 3300 | Ac II | emission | 6d2 3F → 6d.7p 3F* | Measured | NIST | |
| 474.0522 nm | 2600 | Ac II | emission | 6d2 1G → 6d.7p 1F* | Measured | NIST | |
| 515.6541 nm | 2100 | Ac II | emission | 6d2 3F → 5f.7s 3F* | Measured | NIST | |
| 383.53206 nm | 1900 | Ac I | emission | 6d.7s2 2D → 6d.7s.(1D).7p 2P* | Measured | NIST | |
| 488.9102 nm | 1800 | Ac II | emission | 6d2 3F → 5f.7s 3F* | Measured | NIST | |
| 480.7843 nm | 1700 | Ac II | emission | 6d.7s 1D → 6d.7p 3F* | Measured | NIST | |
| 534.47384 nm | 1700 | Ac I | emission | 6d2.(3F).7s 4F → 6d2.(3F).7p 4G* | Measured | NIST | |
| 400.5469 nm | 1500 | Ac II | emission | 6d2 1G → 5f.6d 3G* | Measured | NIST | |
| 536.2615 nm | 1400 | Ac II | emission | 6d2 3F → 6d.7p 1D* | Measured | NIST | |
| 522.8309 nm | 1300 | Ac I | emission | 6d.7s2 2D → 6d.7s.(3D).7p 4D* | Measured | NIST | |
| 454.408 nm | 1200 | Ac II | emission | 6d2 1D → 7s.7p 1P* | Measured | NIST | |
| 461.01055 nm | 1100 | Ac I | emission | 6d.7s2 2D → 6d.7s.(1D).7p 2D* | Measured | NIST | |
| 422.599 nm | 1000 | Ac I | emission | 6d2.(3F).7s 4F → 6d2.(3F).7p 4D* | Measured | NIST | |
| 387.7035 nm | 980 | Ac II | emission | 6d.7p 3P* → 5f.7p 3D | Measured | NIST | |
| 420.89072 nm | 960 | Ac I | emission | 6d2.(3F).7s 4F → 6d2.(3F).7p 4D* | Measured | NIST | |
| 469.05284 nm | 960 | Ac I | emission | 6d2.(3F).7s 4F → 6d2.(3F).7p 4F* | Measured | NIST | |
| 521.5399 nm | 960 | Ac II | emission | 6d2 3P → 6d.7p 3P* | Measured | NIST | |
| 486.88523 nm | 890 | Ac I | emission | 6d2.(3F).7s 4F → 6d2.(3F).7p 4F* | Measured | NIST | |
| 526.4481 nm | 890 | Ac I | emission | 7s2.7p 2P* → 7s2.8s 2S | Measured | NIST | |
| 440.21056 nm | 860 | Ac I | emission | 6d2.(3F).7s 4F → 6d2.(3F).7p 4F* | Measured | NIST | |
| 447.18106 nm | 850 | Ac I | emission | 6d2.(3F).7s 4F → 6d2.(3F).7p 4F* | Measured | NIST | |
| 421.80204 nm | 740 | Ac I | emission | 6d2.(3F).7s 4F → 6d2.(3P).7p 2D* | Measured | NIST | |
| 462.16811 nm | 710 | Ac I | emission | 6d2.(3F).7s 4F → 6d2.(3F).7p 4F* | Measured | NIST | |
| 426.8209 nm | 570 | Ac II | emission | 6d2 3F → 6d.7p 3P* | Measured | NIST |
Extended Properties
Covalent Radii (Extended)
- Covalent radius (Pyykkö)
- 186 pm
- Covalent radius (Pyykkö, double)
- 153 pm
- Covalent radius (Pyykkö, triple)
- 140 pm
Van der Waals Radii
- Alvarez
- 280 pm
- UFF
- 347.8 pm
- MM3
- 308 pm
Atomic & Metallic Radii
- Atomic radius (Rahm)
- 293 pm
Numbering Scales
- Mendeleev
- 14
- Pettifor
- 48
- Glawe
- 33
Electronegativity Scales
- Ghosh
- 0
Polarizability & Dispersion
- Dipole polarizability
- 203 a.u.
- Dipole polarizability (unc.)
- 12 a.u.
Phase Transitions & Allotropes
| Melting point | 1323.15 K |
| Boiling point | 3473.15 K |
Oxidation State Categories
Advanced Reference Data
Crystal Radii Detail (2)
| Charge | CN | Spin | rcrystal (pm) | Origin |
|---|---|---|---|---|
| 3 | VI | 126 | from r^3 vs V plots, | |
| 3 | IX | — | 136 |
Isotope Decay Modes (56)
| Isotope | Mode | Intensity |
|---|---|---|
| 205 | A | 100% |
| 205 | B+ | — |
| 206 | A | 100% |
| 206 | B+ | — |
| 207 | A | 100% |
| 208 | A | 100% |
| 208 | B+ | — |
| 209 | A | 100% |
| 209 | B+ | — |
| 210 | A | 100% |
X‑ray Scattering Factors (516)
| Energy (eV) | f₁ | f₂ |
|---|---|---|
| 10 | — | 1.19484 |
| 10.1617 | — | 1.15672 |
| 10.3261 | — | 1.11982 |
| 10.4931 | — | 1.0841 |
| 10.6628 | — | 1.04952 |
| 10.8353 | — | 1.01604 |
| 11.0106 | — | 0.98234 |
| 11.1886 | — | 0.94669 |
| 11.3696 | — | 0.91233 |
| 11.5535 | — | 0.88152 |
Additional Data
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
5.5×10-10 milligrams per kilogram
References (1)
- [5] Actinium https://education.jlab.org/itselemental/ele089.html
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
Not Applicable
References (1)
- [5] Actinium https://education.jlab.org/itselemental/ele089.html
References
(9)
Data deposited in or computed by PubChem
The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.
Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.
The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.
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The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.
The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database
This section provides all form of data related to element Actinium.
The element property data was retrieved from publications.