Discovery of scandium, titanium, mercury, and einsteinium isotopes

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Abstract

Currently, 23 scandium, 25 titanium, 40 mercury, and 17 einsteinium 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.

Introduction

The discovery of scandium, titanium, mercury, and einsteinium 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.

Section snippets

Discovery of 39–61Sc

Twenty-three scandium isotopes from A = 39–61 have been discovered so far; these include 1 stable, 6 proton-rich, and 16 neutron-rich isotopes. Many more additional neutron-rich nuclei are predicted to be stable with respect to neutron emission and could be observed in the future. The mass surface towards the neutron dripline (the delineation where the neutron separation energy is zero) becomes very shallow. Thus the exact prediction of the location of the dripline is difficult and can vary

Discovery of 39–63Ti

Twenty-five titanium isotopes from A = 39–63 have been discovered so far; these include 5 stable, 7 proton-rich, and 13 neutron-rich isotopes. According to the HFB-14 model [4], 78Ti should be the last even–even particle-stable neutron-rich nucleus while the odd–even particle-stable neutron-rich nuclei should continue through 69Ti. The proton dripline has been reached and no more long-lived isotopes are expected to exist because 38Ti has been shown to be unbound with an upper limit for the

Discovery of 171–210Hg

Forty mercury isotopes from A = 171–210 have been discovered so far; these include 7 stable, 26 proton-rich, and 7 neutron-rich isotopes. According to the HFB-14 model [4], 268Hg should be the last bound neutron-rich nucleus (265Hg is predicted to be unbound). Along the proton dripline two more isotopes are predicted to be stable and it is estimated that seven additional nuclei beyond the proton dripline could live long enough to be observed [53]. Thus, there remain 66 isotopes to be discovered.

Discovery of the element einsteinium

Einsteinium is the first transuranium element covered in this series and thus it is appropriate to discuss the discovery of the element itself first. While the criteria for the discovery of an element are well established [91], [92], [93] the criteria for the discovery or even the existence of an isotope are not well defined (see, for example, the discussion in Ref. [53]). Therefore it is possible, as in the present case of einsteinium, that the discovery of an element does not necessarily

Discovery of 241–257Es

Seventeen einsteinium isotopes from A = 241–257 have been discovered so far; there are no stable einsteinium isotopes. According to the HFB-14 model [4], einsteinium isotopes ranging from 235Es through 328Es plus 330Es and 332Es should be particle stable. Thus, there remain about 80 isotopes to be discovered. In addition, it is estimated that 16 additional nuclei beyond the proton dripline could live long enough to be observed [53]. Less than 20% of all possible einsteinium isotopes have been

Summary

The discoveries of the known scandium, titanium, mercury, and einsteinium isotopes have been compiled and the methods of their production discussed.

The limit for observing long lived scandium isotopes beyond the proton dripline that can be measured by implantation decay studies has most likely been reached with the discovery of 40Sc and the observation that 39Sc is unbound with respect to proton emission by 580 keV. The discovery of especially the light scandium isotopes was difficult. Five

Acknowledgements

The main research on the individual elements were performed by DM (scandium, titanium, and mercury) and AB (einsteinium). AB acknowledges the support of the High School Honors Science Program at Michigan State University and would like to thank A. Fritsch, M. Heim, A. Schuh, and A. Shore for help during the project. This work was supported by the National Science Foundation under Grant No. PHY06-06007 (NSCL).

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