The Joint Institute for Nuclear Astrophysics
Strange Quarks
Applications of Gamma Spectroscopy
Gamma ray spectroscopy implies structure, excitation energy, half lives, spin and parity, as well as
deformation
Purpose: To use the known energy values of metals to identify the composition of the coins studied within the lab.
Background and Methods:
• Coins were exposed to an excited form of Carbon-13, which released neutrons by decay and would radiate the coins.
• These coins were placed into the Germanium detector, which would then emit two photons as a result of their decay (beta
and positron/electron annihilations)
• Genie was run to take energy measurements and the different peaks were compared to other metals
• Energy spectra from an unknown coin were used to identify its composition
Results and Graphs
T1/2 = ln2/λ
y=N0e-λt
The graphs above demonstrate the accepted gamma energy signatures for discreet isotopes. It would be expected that samples undergoing Gamma
As time progresses, the quantity of Aluminum decreases. The data was used to
Spectroscopy would match these discreet energy values if the samples contained large enough quantities of each isotope..
determine the half life of Aluminum-28 using the equations above.
Energy (keV)
Counts
Pre-1982 Pennies
512.7, 1346.9, 1041.9, 1420.3
305, 5, 13, 2
Post-1982 Pennies
442, 512.7, 1117.8
10, 8, 3
Mix of Both
514.9, 442.6, 1041.6, 1459.8
86, 7 5, 2
Unkown
2278, 1562, 1547
3, 1, 3
Error:
Despite calibrating the data, the energy spectra signatures differ from the accepted value. For
example, the 511keV accepted value of copper was less than the experimental value by 2keV.
The accepted value of Aluminum-28 is 2.2 minutes. This is off by 4 seconds due to its short half
life. It had to be carried quickly from the neutron activation source to the Germanium detector in
order to prevent it from decaying before taking measurements.. The average error is .26 counts.
The data was also used to calculate the number of pre-1982 and post-1982
pennies. By comparing the 511 keV peaks of the three pennies’ samples,
the proportion of pre-1982 pennies to post-1982 pennies was determined,
and calculations determined 15 pre-1982 pennies and 35 post-1982
pennies. There were actually 10 pre-1982 pennies and 40 post-1982
pennies, so there was error, but the method could be used to get an
estimate.
The energy spectra were measured for this dime, and then used to
determine its composition.
Analysis and Conclusion
•Pre-1982 pennies are made of mostly copper due to the higher number of counts in the 512.7keV values
•The post 1982 pennies contained energy spectra in both 512.7keV values as well as the corresponding
energy values for Zn-71 and Zn-69
•Composition of the mixed unknown stack of pennies was estimated to have 15 pre-1982 pennies and 35
post-1982 pennies.
•The mystery coin is made of mostly silver, but also contains copper
•The calculated half life of the Aluminum-28 is128 seconds.
•Copper’s energy spectrum was recorded in every coin, demonstrating that it was the most prevalent
element in the coins.
This project is funded by the NSF through grant PHY0822648