In the book we study the single term energy formula also called the power index, for the ground band energies of Xe-Gd nuclei. We study the variation of constant parameters a and b with J to check the constancy. We also compare the results of the power index with other two parameters formulae such as ab, pq, Ejiri and soft rotor formula (SRF) to chekck the accuracy of the power index. The comparative study is carried out for A = 120 - 200 mass region nuclei.The odd-even staggering (OES) and the gamma band energies of A = 120-200mass region are studied in Chapter 4. In this work the OES in the gamma band help todistinguish between its rigid triaxial rotor and gamma soft vibrator. The variation of S(J) with R42 signify a smooth shape e ect. The study of gamma band energiesis carried out with the help of SRF formula.