This experiment guide is referred to the SP5600EMU educational kit. If you don’t have this kit, choose your own from the following list to visualize the related experiment guide:
SG6117A – Gamma / Premium Kit,
SG6117B – Emulation Kit,
SG6117C – Enviromental Kit
SP5640 – Backpack Detector
Additional Gamma Radioactive Source
Purpose of the experiment:
Determination of the ratio of the effective cross-sections due to Compton and Photoelectric effects as a function of photons energy.
In the energy range up to 2MeV, gamma rays interact with matter by two processes:
- Photoelectric Effect, dominant at energy less than 100 KeV. In this process the photon energy is completely transferred to atomic electron bounded
γ + atom -> ion + e–
- Compton Scattering, linked to the elastic collision between electrons and photons and relevant at 1MeV energy level
γ + e – -> γ’ + e-’
The predominant mode of interaction depends on the energy of the incident photons and the atomic number of the material with which they are interacting. From the acquired γ-spectrum, it is possible to estimate the fraction of events due to Compton scattering and those caused by the photoelectric. The ratio of the event fractions is used to determine the ratio of the two effective cross-sections that depends on the detector size.
Carrying out the experiment:
The experiment can be performed both by taking off the instrumentation from the backpack and using the backpack with the open zipper. To power ON γstream, press the ON/OFF button. Take care that the γstream internal battery is charged, otherwise use the external power system. Connect the Ethernet cable from γstream to the PC and configure the Ethernet network of your PC. Connect γstream to the MC2Analyzer software through Ethernet connection. Run the software and power ON the detector. Place the radioactive source close to the scintillator/under the central part of the backpack. Once the radioactive source is properly positioned, the spectrum can be recorded. Once done, change the radioactive gamma source and repeat the measurement.
By using several radioactive sources, the energy dependence of the ratio between the cross-sections of two phenomena can be examined, by verifying that the Photoelectric Effect cross section decreases with increasing energy compared to the Compton Scattering cross section for the used detector size.
Spectra of radioactive sources used to estimate the ratio of Photonuclear and scattering Compton cross sections
Behaviour of the ratio between Photo-Peack and Compton contributions as a function of energy