The 3 s 1 2 neutron levels in nuclei of mass 85–135 ar located by angular distributions of protons from (d, p) reactions on nuclei with even neutron numbers. Where the proton number is even, alomost all of the single particle level is in one nuclear level, and where there is an odd proton of low j, it is in two levels with spin j + 1 2 and j− 1 2 which are separated by about 60 KeV. Both of these cases are in agreement with the simple single particle model with negligible configuration mixing, but where there is an odd proton of large j, the single particle levels has many components, indicating strong configuration mixing. The binding energy of the 3 s 1 2 neutron varies very smoothly from isotope to isotope of the same element, and when corrected for symmetry energy, its variation with A is very smooth. The variation with A decreases about by half when its major shell begins filling, and becomes negligible when ground states of odd-mass nuclei are s 1 2 . This is explained as due to the fact that the levels become partially “hole” states, and since the energy of particle and hole states shift in opposite directions as a function of mass number, the two effecrts tend to cancel. Since, according to pairing theory and experimental observations, all subshells in a major shell begin to fill when the major shell begins to fill, energy shifting og a single particle level decreases rapidly once its major shell begins to fill. The observed shifting is in at least semi-quantitative agreement with the theory. Some difficulties with the Wilkinson theory of the photonuclear giant resonance are pointed out, and strong evidence againts reduced mass efects in excited states of nuclei are presented.