How do you read a spectrum for a decaying source?

In summary, the spectrum of a 137Cs source decaying to 137Ba shows a high peak on the right representing directly absorbed photons, and a saddle-shaped peak on the left representing photons that underwent Compton scattering. The peaks on either side of the saddle are due to the different angles at which the photons interacted with electrons, resulting in different amounts of energy loss.
  • #1
jumbogala
423
4

Homework Statement


I have a 137Cs source which decays to 137Ba. When the Ba nucleus decays, it gives off a photon which can undergo Compton scattering.

Homework Equations


The Attempt at a Solution


The spectrum shows something that looks like a saddle on the left (it has two high peaks on either end and dips down in the middle). Then on the right there is a very high, sharp peak.

The high peak that shows the full energy of the photons is showing the photons that got absorbed directly by the device. Right? It says 91.1 % of photons have that energy.

So the other ~10% must undergo compton scattering, which is the saddle thing. But what causes the high peaks on both sides of it? It has something to do with photons giving up energy to electrons. Can anyone explain, I would like to understand. Thanks!
 
Last edited:
Physics news on Phys.org
  • #2


Hi there,

Yes, you are correct in your understanding of the two peaks in the spectrum. The high peak on the right represents the 91.1% of photons that were directly absorbed by the device. These photons have the full energy of the original 137Cs source.

The saddle-shaped peak on the left represents the photons that underwent Compton scattering. This is a process in which the photon interacts with an electron and loses some of its energy. The peak on the left side of the saddle represents the photons that lost a small amount of energy, while the peak on the right side represents the photons that lost a larger amount of energy.

The reason for these peaks is due to the different angles at which the photons interact with the electrons. When the photon loses a small amount of energy, it means that it interacted with an electron at a small angle. When it loses a larger amount of energy, it means that it interacted with an electron at a larger angle.

I hope this helps to clarify the peaks in the spectrum. Let me know if you have any further questions.
 

FAQ: How do you read a spectrum for a decaying source?

1. How do I interpret the x-axis of a spectrum for a decaying source?

The x-axis of a spectrum for a decaying source represents the energy levels of the particles emitted from the source. It is typically measured in electron volts (eV) or kiloelectron volts (keV).

2. What does the y-axis of a spectrum for a decaying source represent?

The y-axis of a spectrum for a decaying source represents the intensity or number of particles detected at each energy level. It is usually measured in counts or counts per second.

3. How do you determine the half-life of a decaying source from its spectrum?

The half-life of a decaying source can be determined by analyzing the shape and decay rate of the spectrum. The half-life is the time it takes for half of the radioactive material to decay, and it can be calculated by using the decay curve and the known characteristics of the source.

4. What are the key features to look for in a spectrum for a decaying source?

The key features to look for in a spectrum for a decaying source include the presence of characteristic peaks, the shape of the decay curve, and the presence of any background noise. These features can provide valuable information about the type of radiation emitted, the energy levels involved, and the intensity of the source.

5. How do you differentiate between a spectrum for a decaying source and a spectrum for a stable source?

A spectrum for a decaying source will exhibit a characteristic decay curve, with a peak at the highest energy level and a gradual decrease in intensity at lower energy levels. In contrast, a spectrum for a stable source will typically show a more uniform distribution of energy levels without a distinct decay curve. Additionally, a decaying source will show a decrease in intensity over time, while a stable source will maintain a consistent intensity over time.

Back
Top