SP5630EN/ENP – Enviromental Kit
Beta Radioactive Source
Purpose of the experiment:
Gamma radioactivity detection by using a system composed of a scintillating crystal coupled to a photon detector.
Gamma rays interact with matter by three processes: Compton Scattering, Photoelectric Effect and Pair Production (whenever the energy exceeds the 1.022 MeV threshold corresponding to the e+e– rest mass). The cross section of each process depends on the energy of the gamma ray.
The Compton Effect is the inelastic scattering between the incoming photon and an atomic electron. In the Photoelectric Effect, the incident gamma ray transfers all its energy to a bound electron which acquires a kinetic energy equal to the incoming gamma energy decreased by the binding energy.
These processes convert, totally or partially, the gamma ray energy into kinetic energy of electrons (or positrons, in case of pair production). The interaction of the charged particles with the atomic and molecular systems of the medium results in excited states whose decay, possibly mediated, leads to light in the visible or UV region, eventually detected by the light sensor. A wide range of scintillator products is available today, differing for the light yield, the material properties, the time characteristics of the scintillation light and, last but not least, cost. The choice of the scintillator is essentially dependent on the specific targeted application.
No other tool is needed.
Experimental setup block diagram.
Carrying out the experiment:
Put the i-Spector digital into the base. Power the i-Spector and connect the Ethernet cable. Wait until the temperature is stable from the web interface (it can take half an hour from power on). Check the waveform, modify the threshold and gate width, if needed, then start a spectrum acquisition. Save the result and compare it with a spetrum acquired in presence of a radioactive sample. Place the radioactive source, like, for example, the LYSO scintillating crystal which is provided as calibration source and start the measurement of the energy spectrum.
Take for example 10 minutes of acquisition with the LYSO crystal sample by setting the corresponding acquisition time. Repeat the experiment by modifying the threshold value.
The energy spectrum will appear in the MCA tab of the i-Spector web interface. Verify the implication of modify the trigger threshold into the energy spectrum. For example, decrease the threshold until the peak at zero appears (corresponding to noise), then slightly increase it until the peak at zero disappear.
Note: threshold value may vary from kit to kit, find the corresponding value for your own kit.
Example 1: Trigger Threshold = 49 LSB
Example 2: Trigger Threshold = 53 LSB
Energy spectra with different threshold value of the internal discriminator of i-Spector