# Gamma ray pulse height spectrum

## Homework Statement

A radioactive source which is known to emit gamma rays only at a single energy is placed in front of a gamma ray detector. The gamma ray pulse height spectrum shows three distinct pulse heights of 7.38,6.49 and 5.60 volts. What is the energy of the gamma ray?

## The Attempt at a Solution

From what I know, the pulse recorded should be the energy of the gamma ray emitted from the source. If that is the case, how is it possible to record three pulse when the source can only emit gamma ray of one energy? Is there something wrong with my understanding of the pulse height spectrum?

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The source can emit photons of one energy, but it can emit any number of them.

rude man
Homework Helper
Gold Member
Volts? Obviously depends on the gain of the detector apparatus. What a weird question.

The source can emit photons of one energy, but it can emit any number of them.
I just learn this but from what I know one peak correspond to one energy with certain intensity. So what do you mean it can emit any number of them? If I have 5 gamma ray with energy E1 then I will only have a peak at position E1 is that correct?

Volts? Obviously depends on the gain of the detector apparatus. What a weird question.
I believe this is just a question to introduce the idea of pulse height spectrum so its not so complicated.

I just learn this but from what I know one peak correspond to one energy with certain intensity. So what do you mean it can emit any number of them? If I have 5 gamma ray with energy E1 then I will only have a peak at position E1 is that correct?
Not position. Height of the peak. It corresponds to the total energy of detected radiation. Which is proportional to the number of quanta of radiation (photons) detected.

Alright I see so the three values are the energy of the gamma energy? But I still don't understand why we have three peaks where the gamma ray emitted only has one energy. If the energy has only one energy then shouldn't we have only one peak?

If a single photon has energy E, and at times A, B and C you register k, m, n photons, what energies are you going to see?

Alright I get it now so those numbers are the total energy collected for x number of photons. So we have the total energy but how can we get the energy for the gamma ray?

What could differences in the energy values tell you?

Oh I get it now, using the difference we can get the equation to solve for the energy. Thank you so much!