This element was discovered by C. Perrier and E. Segre in Palermo, Italy, in 1937. Its name alludes to the Grcek technikos (artificial).
Ionization energies
TcI 7.3 eV, TcII 15.3 eV, TcIII 29.5 eV.
No Tc lines have been observed in the sun.
Behavior in stars
Tc I has its resonance lines at 4238, 4262 and 4297. It was identified
by Merrill (1952) in S-type stars. The interest of this element
lies in the fact that it is unstable. Its longest lived isotope has a
half life of
2.6 × 106 years. The element can be produced by a
neutron flux operating on iron-peak elements (Fe, Co, Ni).
Such a neutron flux can be either rapid (the r process) or slow (the s
process) and the isotopic form in which Tc is formed depends on the time
scale in which the neutron flux occurred. In any case, the presence of
Tc denotes that its formation occurred a short time ago, on the cosmic
time scale. The presence of Tc thus constitutes an indication of recent
element formation. Since element formation is
assumed to occur in the stars' interior, the material must have been
forcibly
circulated to the surface in a short time. Up to now Tc has been
observed in stars of types M, MS, S, SC, CS and C. All of the
stars having Tc show large-amplitude light variations. It should be
stressed that not all stars of the types quoted exhibit Tc
(Little-Marenin 1989). To be more specific, according to Smith and Lambert
(1988) 40% of a sample of MS- and S-type stars do not show Tc although they
exhibit enhanced lines of other elements formed by neutron capture.
There seems to exist a relation between Tc in S- and MS-type stars and the HeI 10830 line (in absorption, emission or both): when one is present, the other is absent (Brown et al. 1990).
Typical values for W(5924) of TcI in SC stars are 0.100-0.400 (Smith and Wallerstein 1983). Typically, in an S6 star, W(4297) = 0.490. This is almost double the value for a normal giant of the same temperature (i.e. M 6) (Wallerstein and Dominy 1988). For a recent analysis stressing the uncertainties involved, see Kipper (1992a,b).
Tc has been searched for but not found in Ba stars (Warner 1965).
Isotopes
Tc has three long-lived isotopes, Tc97 (2.6 ×
106 years), Tc98 (1.5 × 106 years)
and Tc99 (2.1 × 105 years half
life), as well as 20 short-lived isotopes and isomers.
Published in "The Behavior of Chemical Elements in Stars", Carlos Jaschek and Mercedes Jaschek, 1995, Cambridge University Press.