1929 In August, Zheng Yanfen went to the Graduate School of Physics Department of Stanford University in the United States to study, and 1934 received her doctorate. His doctoral thesis is entitled "Polarization of X-rays produced by thick targets". Its main content was published in the August issue of Physical Review, 1934. He used 90 scattering method and bimetallic (Nb and Mo, Rh and Pd, Ta and W) foil filters to systematically measure and analyze the X-ray continuous spectrum polarization of different wavelengths generated by the target voltage of tungsten, copper and aluminum at 20- 100 kV, which further confirmed the relationship between the continuous spectrum polarization increasing with the decrease of voltage and the continuous spectrum polarization increasing with the decrease of wavelength. In addition, it is proved quantitatively that: (1) when extrapolated from the continuous spectrum generated by the above three targets to the short-wave limit, the degree of polarization is close to100%; (2) When the wavelength is constant, the X-ray produced by the low atomic number target has a high degree of polarization. This paper clarified some differences about X-ray polarization experiments at that time, which played a certain role in the development of X-ray spectroscopy.
Zheng Yanfen returned to China in July 1934 and became an associate professor in the Physics Department of Zhejiang University. A year later, he was appointed Professor Geng Zhongying and the head of the Department of Physics of Shanghai Datong University, and concurrently served as a professor of the Department of Physics of Tongji University until the summer of 1938.