Measurement of radiation energies and thickness of 252Cf source backing
– study the spectrum of fission fragments from californium-225,
– study the spectrum of alpha particles from radium-226 passing through the backing of the californium-252 source,
– calculate the energy loss of alpha particles passing through the backing of the californium-252 source,
– calculate the thickness of the backing of the californium-252 source.
– Radium-226 source
– Californium-252 source
– PIN-diode detector
– Crate CAMAC
– Intelligent controller
– High voltage power supply (HV)
– Charge-to-digital converter (QDC)
– Vacuum station
– Vacuum gauge
– Cables and accessories
Study the scheme of the experimental setup.
Set the same amplification that you used for the PIN diode calibration in the previous laboratory work.
Compare the energy spectrum of alpha particles from radium-226, obtained in the previous laboratory work, with the energy spectrum of alpha particles from radium-226 passed through the californium-252 source. Alpha particles lose their energy when passing through the backing of the californium source, that is why the second spectrum should be shifted to the left relative to the first spectrum. At the same time in the second spectrum we can distinguish one additive peak which corresponds to the alpha particles from californium-252 with the energy of 6.112 MeV.
To compare peak values, use the blue vertical guideline (move it with the mouse).
Define the centers of gravity of:
– the alpha particle peak from californium-252,
– the alpha particle peak from radium-226 with the highest energy.
To measure the center of gravity of a peak, select it using the bounding dashed lines and read the data from the cell “Mean value” (write down the value with an accuracy of 3 decimal places).
Determine the centers of gravity of the peaks of fission fragments of californium-252 (write down the value with an accuracy of 3 decimal places). For better peak separation, it is recommended to select a linear scale of the vertical axis (y).
Keep in mind that light fragments have more kinetic energy. This follows from the relation arising from the law of conservation of momentum:
ЕLF · mLF = ЕHF · mHF ,
where ЕLF — kinetic energy of a light fission fragment, ЕHF — kinetic energy of a heavy fission fragment, mLF — mass of a light fission fragment, mHF — mass of a heavy fission fragment.
Convert the obtained mean values of the centers of gravity into megaelectron-volts (round values to 3 decimal places) by using the calibration dependence obtained in the previous laboratory work:
Energy = 0.35288 + 0.02682·Channel number
Calculate the difference between experimental and reference values of energy of fission fragments of californium-252 (round values to 3 decimal places).
Calculate the difference between the reference value of energy of alpha particles with the highest energy from radium-226 and the calculated energy of the same alpha particles that passed through the californium source in our experiment.
After estimation of the energy loss of alpha particles of radium in the process of passing through the californium source, we can define a thickness of this source. The californium source consists of a thin backing of aluminum oxide (Al2O3) with a drop of radioactive californium. The source backing is much thicker than the layer of the radioactive californium. That is why the energy losses in the layer of the radioactive californium can be neglected.
Define the thickness of the source tacking into account that energy losses occur only in the aluminum oxide backing. Below there is a dependence of alpha particle energy losses from thickness of aluminum oxide layer obtained by using the SRIM program (The Stopping and Range of Ions in Matter).