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

Abstract

Currently, 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 discussed. For each isotope a brief summary of the first refereed publication, including the production and identification method, is presented. Contents IntroductionThe discovery of astatine, radon, francium, and radium isotopes is discussed 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 discussed. 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 criterium described above.The first criterium 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 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 criterium. One example from fragmentation experiments why publications in conference proceedings should not be considered is 118 Tc and 120 Ru which had been reported as being discovered in a conference proceeding [5] but not in the subsequent refereed publication [6]. 2 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 Iso...

2014 update of the discoveries of nuclides

“…20 The second reassignment involves 12 Li which was initially assigned to Yu. Aksyutina et al 21 In this work, 12 Li was populated in the reaction 1 H( 14 Be,2pn) 12 Li simultaneously with the discovery of 13 Li which was produced in the one-proton knockout reaction. However, it was recently pointed out 22 that the 12 Li data could have been contaminated by misidentified low energy two-neutron decay events from 13 Li invalidating the extracted scattering length for 12 Li.…”

“…Aksyutina et al 21 In this work, 12 Li was populated in the reaction 1 H( 14 Be,2pn) 12 Li simultaneously with the discovery of 13 Li which was produced in the one-proton knockout reaction. However, it was recently pointed out 22 that the 12 Li data could have been contaminated by misidentified low energy two-neutron decay events from 13 Li invalidating the extracted scattering length for 12 Li. This interpretation is also supported by the analysis of two-neutron events from the decay of 26 O which was performed with the same setup as the 12 Li experiment.…”

Newly identified energy levels and calculated transition rates in astatine atom, the rarest element on Earth

“…This element was discovered in 1940 by Corson et al [2] by bombarding a bismuth target with α particles. As described by Fry and Thoennessen [3] , thirty-nine astatine isotopes with atomic masses ranging from A = 191 to A = 229 have been discovered so far and, according to the Hartree-Fock-Bogoliubov (HFB-14) mass model [4] , about 37 additional astatine isotopes could exist. All of these isotopes are characterized by very short half-lives, the most stable species being 210 At with a half-life time of only 8.1 h. This isotope's primary decay mode is positron emission to the relatively long-lived and very toxic 210 Po.…”

Nuclear Data Evaluation for Mass Chain A=217:Odd-Proton Nuclei

“…Fry and Thoennessen [ 4 ] reported that thirty–nine isotopes of Astatine (At) have been discovered based on the Hartree-Fock-Bogoliubov model (HFB-14). Meanwhile, the discovery of 217 At was reported in 1947 by Hagemann et al, [ 5 ] and English et al, [ 6 ], by studying the decay series (4n+1) of 233 U.…”