X-ray fluorescence and Moseley's law

Principle

The irradiation of iodine, barium (sulfat), silver and tin with soft gamma-radiations gives rise to Ka radiations characteristics of these elements. The X-ray spectra are recorded with a gamma spectrometer consisting of a scintillation counter, a pulse height analyser and a recorder. After calibration of the spectrometer, the Rydberg constant is determined from the energies of the X-ray lines, using Moseley's law.

Benefits

• A high ranking nuclear physics experiment can be performed by students within some hours
• The combination of multichannel analyzer (MCA), gamma detector and high precision HV power supply leads to precise results
• Fundamental Rydberg's constant and Mosley's law are easily determined

Tasks

1. Calibration of the gamma-spectrometer in the low energy range, using the Ba-resonance line Cs-137 emitter (32 keV) and the gamma-line of 241 Am at 59.6 keV.
2. Recording of the X-ray fluorescence spectra (Ka-lines) of different elements and determination of the corresponding energies.
3. Plotting of the measured X-ray energies according to Moseley's law against (Z-1) 2 and determination of the Rydberg constant R; from the slope of the resulting lines.

Learning objectives

• Binding energy
• Photoelectric eftect
• Shell structure of electron shells
• Characteristic X-ray radiation
• g-spectrometry
• X-ray spectral analysis