Discovery of the astatine, radon, francium, and radium isotopes

doi:10.1016/j.adt.2012.05.003

Atomic Data and Nuclear Data Tables

Volume 99, Issue 5, September 2013, Pages 497-519

https://doi.org/10.1016/j.adt.2012.05.003 Get rights and content

Abstract

Thirty-nine astatine, thirty-nine radon, thirty-five francium, and thirty-four radium isotopes have so far been observed; the discovery of these isotopes is described. For each isotope a brief summary of the first refereed publication, including the production and identification method, is presented.

Introduction

The discovery of astatine, radon, francium, and radium isotopes is described as part of the series summarizing the discovery of isotopes, beginning with the cerium isotopes in 2009 [1]. Guidelines for assigning credit for discovery are (1) clear identification, either through decay-curves and relationships to other known isotopes, particle or $γ$ -ray spectra, or unique mass and $Z$ -identification, and (2) publication of the discovery in a refereed journal. The authors and year of the first publication, the laboratory where the isotopes were produced as well as the production and identification methods are described. When appropriate, references to conference proceedings, internal reports, and theses are included. When a discovery includes a half-life measurement the measured value is compared to the currently adopted value taken from the NUBASE evaluation [2] which is based on the ENSDF database [3]. In cases where the reported half-life differed significantly from the adopted half-life (up to approximately a factor of two), we searched the subsequent literature for indications that the measurement was erroneous. If that was not the case we credited the authors with the discovery in spite of the inaccurate half-life. All reported half-lives inconsistent with the presently adopted half-life for the ground state were compared to isomer half-lives and accepted as discoveries if appropriate following the criteria described above.

The first criterion is not clear cut and in many instances debatable. Within the scope of the present project it is not possible to scrutinize each paper for the accuracy of the experimental data as is done for the discovery of elements [4]. In some cases an initial tentative assignment is not specifically confirmed in later papers and the first assignment is tacitly accepted by the community. The readers are encouraged to contact the authors if they disagree with an assignment because they are aware of an earlier paper or if they have found evidence that the data of the chosen paper were incorrect.

The discovery of several isotopes has only been reported in conference proceedings, which are not accepted according to the second criterion. One example, from fragmentation experiments, why publications in conference proceedings should not be considered is ¹¹⁸Tc and ¹²⁰Ru, which had been reported as being discovered in a conference proceedings [5] but not in the subsequent refereed publication [6].

The initial literature search was performed using the databases ENSDF [3] and NSR [7] of the National Nuclear Data Center at Brookhaven National Laboratory. These databases are complete and reliable back to the early 1960’s. For earlier references, several editions of the Table of Isotopes were used [8], [9], [10], [11], [12], [13]. A good reference for the discovery of the stable isotopes was the second edition of Aston’s book “Mass Spectra and Isotopes” [14]. For the isotopes of the radioactive decay chains several books and articles were consulted, for example, the 1908 edition of “Gmelin-Kraut’s Handbuch der anorganischen Chemie” [15], Soddy’s 1911 book “The chemistry of the radio-elements” [16], the 1913 edition of Rutherford’s book “Radioactive substances and their radiations” [17], and the 1933 article by Mary Elvira Weeks “The discovery of the elements. XIX. The radioactive elements” published in the Journal of Chemical Education [18]. In addition, the wikipedia page on the radioactive decay chains was a good starting point [19].

The isotopes within the radioactive decay chains were treated differently. Their decay properties were largely measured before the concept of isotopes was established. Thus we gave credit to the first observation and identification of a specific activity, even when it was only later placed properly within in the decay chain.

Fig. 1 summarizes the isotopes of the three natural occurring radioactive decay series with their original nomenclature. These notations for the original substances introduced by Rutherford during his Bakerian lecture, presented on May 19th 1904 and published a year later [20], are shown by grey squares and connected by the grey arrows representing $α$ and $β$ decay. The decay from actinium to actinium X and from thorium to thorium X was later shown to be more complex. These isotopes are shown as black squares with the corresponding decays shown by black arrows.

Section snippets

^191–229At

Astatine was discovered in 1940 by Corson et al. by bombarding a bismuth target with $α$ particles [21]. A month later Minder reported the observation of element 85, naming it helvetium [22], which was later shown to be incorrect [23]. Also a later claim by Leigh-Smith and Minder, naming element 85 anglohelvetium [24], was not confirmed. An even earlier report of the discovery of element 85 by Allison et al. in 1931 [25], selecting the name alabamine, was incorrect [26]. The name astatine

^193–231Rn

Although it is generally accepted that the element radon was discovered by Dorn in 1900 the references to the original papers is not straightforward [60]. Also arguments have been made to credit Rutherford [61] or M. Curie and P. Curie [62] with the discovery of radon. In 1923, the IUPAC named the three known emanations–radium, actinium, and thorium–radon (Rn), actinon (An), and thoron (Tn), respectively. Ramsay and Gray had suggested the name niton for radium emanation [63] in 1910. Later

^199–233Fr

The element francium was discovered by Perey in 1939 by observing the $β$ decay of ²²³Fr in the natural actinium radioactive decay chain [96]. Earlier incorrect observations of francium are described and referenced in the 2005 article “Francium (atomic number 87), the last discovered natural element” on the occasion of the 30th anniversary of Marguerite Perey’s death in 1975 [97]. The name francium was officially accepted at the 15th IUPAC conference in Amsterdam in 1949 [27]. Perey had

^201–234Ra

The element radium was discovered in 1898 by P. Curie, M. Curie, and G. Bémont [108]. Thirty-four radium isotopes from $A = 201$ to 234 have been discovered so far and according to the HFB-14 model [28] about 50 additional radon isotopes could exist. Fig. 5 summarizes the year of first discovery for all radon isotopes identified by the method of discovery: radioactive decay, fusion–evaporation reactions, light–particle reactions, neutron-capture reactions, and spallation. In the following, the

Summary

The discoveries of the known astatine, radon, francium, and radium isotopes have been compiled and the methods of their production described. Only the following six isotopes were initially identified incorrectly: ^204,206,216At, ²¹⁴Rn, and ^202,230Ra. In addition, the half-lives of ^200,201,211At and ^205,212Ra were at first reported without definite mass assignments.

Acknowledgments

This work was supported by the National Science Foundation under grants No. 06-06007 (NSCL) and PHY10-62410 (REU).

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Discovery of the astatine, radon, francium, and radium isotopes

Abstract

Introduction

Section snippets

191–229At

193–231Rn

199–233Fr

201–234Ra

Summary

Acknowledgments

At. Data Nuclear Data Tables

Nuclear Phys. A

Phys. Lett. B

Nuclear Phys. A

J. Inorg. Nuclear Chem.

J. Inorg. Nuclear Chem.

Nuclear Phys. A

Phys. Lett. B

Nuclear Phys. A

J. Inorg. Nuclear Chem.

J. Inorg. Nuclear Chem.

J. Inorg. Nuclear Chem.

J. Inorg. Nuclear Chem.

Phys. Lett. B

J. Inorg. Nuclear Chem.

Pure Appl. Chem.

Proc. Int. Conf. on Exotic Nuclei Atomic Masses, ENAM’95, Arles, France 1995

Rev. Modern Phys.

Rev. Modern Phys.

Rev. Modern Phys.

Rev. Modern Phys.

Rev. Modern Phys.

Table of Isotopes

Mass Spectra and Isotopes

Gmelin-Kraut’s Handbuch der anorganischen Chemie, Siebente Auflage, Band III, Abteilung 2. herausgegeben von C. Friedheim

The Chemistry of the Radio-elements, F. Soddy

Radioactive Substances and their Radiations

J. Chem. Educ.

Philos. Trans. R. Soc. A

Phys. Rev.

Helv. Phys. Acta

Naturwissenschaften

Nature

Phys. Rev.

Phys. Rev.

International Union of Chemistry, Chem. Eng. News

Phys. Rev. C

Eur. Phys. J. A

Phys. Rev. C

Acta Phys. Polon. B

Phys. Rev. C

Eur. Phys. J. A

Phys. Rev.

Bull. Amer. Phys. Soc. II

Ark. Fysik

Phys. Rev.

^191–229At

^193–231Rn

^199–233Fr

^201–234Ra