The University of Sydney
School of Physics
Quanta to Quarks
Measuring the Mass defect in radioactive
decay
Risk Analysis
A very important part of any experimentation in physics is the identification
of any risks, and the subsequent mitigation of those risks. As you can
imagine, scientists use some very cool, and technical pieces of apparatus
and equipment. Radioactivity falls into this category.
Before we begin, identify three risks
associated with radioactive materials.
Once these risks have been identified,
you must identify what might happen if
the risks were to eventuate, and of
course, what we can do to mitigate
against the risks. These would be our
safety rules.
Assign a number to each of your risks
using the table to the left.
Risk
Consequence
Precaution
In this experiment we measure this mass defect for two radioactive
elements.
The University of Sydney
School of Physics
Quanta to Quarks
Cs 137
and
Co 60
Photomultiplier tube
The energy of a Gamma ray can measured using a photomultiplier tube.
The first job is to calibrate the system. We do this by measuring the peak
from a known source Cs 137 (662 keV). Once we know which bin this
peak corresponds to we can calculate the energy for each bin and hence
deduce the energy of unknown spectra.
Peak Cs137 = Bin ____________
Energy per bin = 662 keV / Bin______ = ______________
The University of Sydney
School of Physics
Quanta to Quarks
Next measure the unknown spectrum of Co 60. This will give us an
experimental value for the energy defect
Experimental
Peak number
1
Bin Number
Calculated energy (keV)
2
Total
Now we can do the same thing, but this time Mathematically
Theoretical
The mass of a Co 60 Nucleus is 59.9338, and a Ni 60 nucleus weighs
59.9308 AMU. Calculate is the mass defect in the decay:
Mass defect: ___________________________________ AMU
From E = Mc2 mass can be converted to its equivalent energy. The
conversion factor from AMU to keV is 931,500. Calculate the energy
defect.
Energy defect: ___________________________________keV
Does it match up with the energy of the gamma ray emission? Where is
the rest of the energy?
Difference in Energy defect _________________________keV