Population distribution of metastable states of neodymium atoms produced by electron beam heating

The metastable states' population of neodymium atoms produced by electron beam heating was measured with the laser induced fluorescence method. The atomic excitation temperature derived from the metastable state distribution was lower than the temperature of evaporation surface (about 2000 K). With increasing deposition rate, the atomic excitation temperature decreased to about 1500 K. This excitation temperature is about three times higher than that of gadolinium atoms produced by electron beam heating. Near the evaporation surface the collisional relaxation of neodymium and gadolinium atoms occurs through inelastic collisions between fine structures. The gadolinium and neodymium atoms have ten valence electrons of 4f75d6s2 and six valence electrons of 4f46s2, respectively. The orbital radius of 5d electron is relatively larger than that of 4f electron. Low collisional relaxation of neodymium is considered to be due to small orbital radius of 4f electron and no existence of 5d electron. (author)