Discovery of tantalum, rhenium, osmium, and iridium isotopes

Abstract

Currently, thirty-eight tantalum, thirty-eight rhenium, thirty-nine osmium, and thirty-eight iridium, isotopes have been observed and the discovery of these isotopes is discussed here. For each isotope a brief synopsis of the first refereed publication, including the production and identification method, is presented.The discovery of tantalum, rhenium, osmium, and iridium 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 isomers half-lives and accepted as discoveries if appropriate following the criterium described above.Good examples why publications in conference proceedings should not be considered are 118 Tc and 120 Ru which had been reported as being discovered in a conference proceeding [4] but not in the subsequent refereed publication [5]. The initial literature search was performed using the databases ENSDF [3] and NSR [6] 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 [7-12]. A good reference for the discovery of the stable isotopes was the second edition of Aston's book "Mass Spectra and Isotopes" [13].

2014 update of the discoveries of nuclides

“…The assignments of early papers from the Institute of Physical and Chemical Research in Tokyo were incorrectly assigned to the University of Tokyo instead of RIKEN. [39][40][41][42] A total of 12 isotopes were reassigned ( 92 Y, 43 89 Zr, 44 92,94 Nb, 45 91,99 Mo, 44 102 Rh, 46 185,187 W, 47 186,188 Re, 48 and 237 U 49 ). Also, the assignment 2 of 169 Ho was changed from Tokyo to the Japan Atomic Energy Research Institute at Tokai.…”

Reexamining the half-lives of195Os and195Ir

“…The half-life of one specific N = 119 nucleus, 195 Os, which one would expect to be known, is still controversial. While the Table of Isotopes lists a half-life of 6.5 min [9], the majority of nuclear data bases and evaluations [10][11][12][13][14][15][16] do not accept this value and quote only an approximate theoretical value of ∼9 min from gross theory of beta decay [17]. In addition, the half-life of the daughter nucleus 195 Ir is also not well established.…”

Low-lying excited states in the neutron-deficient isotopes163Os and165Os

“…The osmium isotopes currently represent the best opportunity to probe the evolution of nuclear structure across the 82 N 126 neutron shell. The existence of the osmium isotopes in an uninterrupted sequence from 161 Os 85 [1] to 203 Os 127 [2] has been established [2,3], while excited states have been identified in these known nuclei below 200 Os 124 [4] with the exception of the odd-mass isotopes below N = 89. The excitation level schemes across the shell reveal the transitions between the single-particle and collective regimes as a function of neutron number.…”