This element was isolated by A. von Welsbach in Vienna in 1885. The name comes from the Greek neos didymos (new twin).

Ionization energies
NdI 5.5 eV, NdII 10.7 eV, NdIII 22.1 eV, NdIV 40.4 eV.

Absorption lines of NdII
No lines of NdI have been observed in the sun. Gopka et al. (1990) observed a weak line of NdI 5676 in K 5 III (W = 0.016) and M OIII stars.

Absorption lines of NdII

Table 1. Equivalent widths of NdII

  4061(10)   5431(80)    

Group V Ib V III Ib

A1 0.005 0.035      
F0 0.075        
G0 0.072       0.017
G1         0 040
G2     0.002   0.043
G5 0.089       0.047
G6         0.067
G8         0.070
K0       0.018  
K2       0.013 0.081
K3         0.068
K5         0.085,0.120

NdII lines (for instance 4061 and 5431) appear in A-type spectra and strengthen toward later types. A positive luminosity effect is present (see for instance the line at 5431).

According to Smith and Lambert (1985), NdII is also visible beyond K 5. They quote that the line 7513 grows from 0.020 for K 5 III to 0.055 for M 6 III.

Behavior in non-normal stars
NdII lines are strong in the spectra of Ap stars of the Cr-Eu-Sr subgroup (Adelman 1973b). A typical value of W(4061) is 0.027 (Sadakane 1976). Cowley (1976) and Aikman et al. (1979) observed lines of Nd III in the spectra of several Ap stars with strong Nd II lines. Nd II and Nd III have also been observed in the spectrum of one Bp star of the Si subgroup (Cowley and Crosswhite 1978). Cowley (1984) calls attention to some Ap stars in which Nd and Sm are conspicuously absent, whereas other rare earths are strong.

Figure 34

NdII lines are also strong in Am stars. A typical value for late Am stars is W(4061) = 0.150 (Smith 1973, 1974).

NdII lines are enhanced in the spectra of Ba stars, which corresponds to large overabundances (Lambert 1985). Typical W values are twice as large as in normal giants of the same temperature (Danziger 1965). NdII lines are also enhanced in the subgiant CH stars (Luck and Bond 1991). In S-type stars NdII lines are prominent (Bidelman 1953), having W values larger by a factor of 2-3 than in normal giants. This leads to large overabundances (Smith and Lambert 1986, Smith et al. 1987). In MS stars the enhancements are less extreme.

Nd is strengthened in C stars later than C 3 (Utsumi 1984).

Nd II lines have been observed in G- and K-type metal-weak dwarfs by Gilroy et al.(1988). These authors found Nd to be overabundant with respect to iron (see also Part Two, section 2.2).

Nd occurs in the form of seven stable and nine short-lived isotopes and isomers. The stable ones are Nd 142,143,144,145,146,148 and 150. In the solar system their respective contributions are 27%, 12%, 24%,8%, 17%, 6% and 6%. For the use of Nd as a nuclear chronometer see Learner et al. (1991).

Nd 143, 144, 145 and 146 can be produced by either the r process or the s process. Nd142 is a pure s process product and Nd148 and Nd150 are both pure r process products.

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