Abstract: On basis of Fermi theory of β decay for nuclei, the momentum distribution of 990Sr-90YB radioactive source is measured by using the magnetic spectrometer in the modem physics experiment, then one studies its Kurie plot. The experimental data are considered the correction of shape factor S1 with the characters of Kurie plot for allowed transition and forbidden transition of ~ decay. The corrected data are in agreement with the transition character, the spin and parity of energy level for 90Sr-90Y source. It is helpful to deeply know the β decay of nuclei and expand the studied contents of the modem physics experiment for students.

Key words: magnetic spectrometer, Kurie plot, β ray, forbidden transition