This element was discovered by J. GaIisard in Geneva in 1880. The name alludes to the Finnish chemist J. Gadolin.

lonization energies
GdI 6.1 eV, GdII 12.1 eV, GdIII 20.6 eV, GdIV 44.0 eV.

Absorption lines of GdI

Table 1: Equivalent widths of GdI 5803

Group III

K5 0.010
M0 0.008

Source: Data from Gopka et al. (1990).

No GdI lines are seen in the solar spectrum.

Absorption lines of GdII

Table 2: Equivalent widths of GdII

  3101(12) 4342(15) 5952(95)


S 0.098    
K0   0.128  
K5     0.014
M0     0.021

Source: Data for 5952 are from Gopka et al. (1990).

GdII appears in late F-type stars and intensifies toward cooler types.

GdII is also seen in one F 0Ib star (Reynolds et al. 1988).

Emission lines of GdII
Some GdII lines, excited by fluoreseence from H epsilon, have been observed in emission in one Mira variable (Grudzinska 1984).

Behavior in non-normal stars
GdII is weakly present in some Bp stars of the Hg-Mn subgroup, with W(3850) = 0.005 (Adelman 1989).

GdII is strong in Ap stars of the Cr-Eu-Sr subgroup (Adelman 1973b).

Typical values are W(4251) = 0.04 (Sadakane 1976). There even exists a star in which, exceptionally of all rare earths, only GdII is strengthened (Cowley and Henry 1979). GdIII is seen in Ap stars of the Cr-Eu-Sr subgroup (Cohen et al. 1969).

GdII is also strong inAm stars. Typical values for W(4251) of early types are 0.020 and of late types, W = 0.100 (Smith 1973, 1974). Similar values are found in delta Del stars (Kurtz 1976).

GdI and GdII lines are enhanced in some Ba stars (Lambert 1985). In these stars the W values may be twice as large as in normal giants of the same temperature.

GdII lines are present in S-type stars (Merrill 1947).

Gilroy et al. (1988) observed GdII 4130(M.19,49) in a number of metal weak G- and K-type dwarfs. These authors find the element to be overabundant with respect to iron. See also Part Two, section 2.2.

Gd has seven isotopes - Gd 152, 154, 155, 156, 157, 158 and 160. In the solar system Gd 155,156, 157, 158 and 160 are present as 15%, 21%, 16%, 25% and 22% of all Gd. Furthermore, there exist ten other short-lived isotopes, among them Gd150, with a half life of 2 × 106 years.

Gd is made by several processes: Gd 155, 156, 157 and 158 by either the r or the s process, Gd152 by the p or the s process, Gd154 only by the s process and Gd160 only by the r process.

Published in "The Behavior of Chemical Elements in Stars", Carlos Jaschek and Mercedes Jaschek, 1995, Cambridge University Press.