PURPOSE: Show nuclear spectra as evidence of nuclear shells.

DESCRIPTION: Two types of spectra can be seen: alpha, using Am-241 and gamma using Cs-137 or Co-60. These spectra are seen using a detector, an oscilloscope, and a computer-based multi-channel spectrum analyzer. The photographs above show the system set up for alphas (left) and for gammas (right).

The alpha spectrum is obtained using a small commercial spectroscope which houses the source and a silicon surface barrier detector in a small vacuum chamber and contains all of the analysis electronics.

The gamma spectrum is obtained using a sodium iodide scintillator detector with a phototube base, pulse shaping and amplifying electronics (in NIM bin at right of picture), and the same computer-based multi-channel analyzer.

Spectra are displayed as shown above. The spectrum obtained in each experiment is shown in the top (log scale) and the bottom (linear scale) graphs. The other three spectra are those for Co-60, Cs-137, and Na-22 respectively. The resolution abtained using our Na-I scintillator does not meet the rigid specifications of the standard spectra, which were obtained using a Ge(Li) solid state detector operating at LN temperature.

SUGGESTIONS: The surface barrier detector can be damaged if operated incorrectly, and the sodium iodide phototube uses a high voltage, so you must get instruction before using this equipment.

REFERENCES: (PIRA 7D10.10)

EQUIPMENT: Roll-around relay rack of components as described above, oscilloscope, and computer-based multi-channel analyzer.

SETUP TIME: 1 hour.