Determining Half-Life of Element X from Gamma Spectrum: Tips and Challenges

In summary: All I can say is that you should use the same method for each gamma line and see if the values are compatible within the uncertainties. In summary, the conversation revolves around calculating the half-life of an element (X) using gamma peak areas and time information. However, there is a discrepancy in the values obtained from different peaks (800 keV, 1000 keV, and 1200 keV). It is suggested to find an estimate of the uncertainties and use a weighted average if the values are compatible. There is also a discussion about the reliability of the values and the importance of understanding the experiment and potential decay products. The conversation ends with the realization that consistent and accurate information is needed to provide a proper analysis method.
  • #1
sakkoyun
10
0
Hello,
I have a gamma spectrum of one element (X). There are several gamma peak in the spectrum. For example,

800 keV peak, 1000 keV peak and 1200 keV.

I have an information about the peak area changing with time. Namely, I know the peak area in different times. So I can calculate the half life of the element by using the area and time information.

But I have a problem.

I got 15 hours from 800 keV peak.
14 hours from 1000 keV.
16 hours from 1200 keV peak.

Which half-life is correct. What should I do? Which is the most reliable? Should I get average value?

Best wishes
 
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  • #2
The widths of different peaks will be different.
Calculate the half-life, by measuring only the height of each peak.
These should all decrease at the same rate.
 
  • #3
Meir Achuz said:
The widths of different peaks will be different.
Sure, but the widths should not vary with time. And if they did, you could use the height of the peak. There is no absolute value mentioned here, all values are relative.

sakkoyun said:
I got 15 hours from 800 keV peak.
14 hours from 1000 keV.
16 hours from 1200 keV peak.

Which half-life is correct. What should I do? Which is the most reliable? Should I get average value?
You should find some estimate how precise your values are. For example, is your first value "15 hours plus/minus 2 minutes" or "in the range of 13 to 17 hours"? If those three values are compatible within the uncertainties, calculate the average. If the uncertainties differ significantly, a weighted average is better.
If the values are incompatible, it would be interesting to know more about the experiment. Do some lines come from decay products? That can give an activity that deviates from an exponential decay.
 
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  • #4
Thank you very much.
With the errors, 15 +-0.3
14+-0.1
16+- 0.5

The 1200 keV peak is more intense. The others are small peaks. Will I get an average of all them? Namely, (15+14+16)/3=15. Or, will I get the half-life as 16 due to the fact that 1200 keV is more intense. Or, will I get 14 for half-life due to the fact that this value is smallest error?

Best wishes
 
  • #5
sakkoyun said:
Will I get an average of all them?

--->

mfb said:
If the uncertainties differ significantly, a weighted average is better.
 
  • #6
14+-0.1 and 16+- 0.5 are a bit far apart. It would be interesting to see the decay scheme. If there is a physical reason for them to have the same half-life, something went wrong, you were really unlucky (>3 standard deviations) or the uncertainties are non-gaussian.
 
  • #7
mfb said:
14+-0.1 and 16+- 0.5 are a bit far apart. It would be interesting to see the decay scheme. If there is a physical reason for them to have the same half-life, something went wrong, you were really unlucky (>3 standard deviations) or the uncertainties are non-gaussian.

Zn68 was created after reaction. 3 gamma peak are clear in gamma spectra. 805, 1077 and 1260 keV. After analyzing each three peaks individually, I got three different half-life values. (Analyzing is performed by investigating the peak area with time. And obtaining decay (growth) curve). Which one is more reliable? Or ?
 
  • #8
Zn68 was created after reaction.
And what did you have before?

Did you identify the gamma energies in a decay scheme?

(Analyzing is performed by investigating the peak area with time. And obtaining decay (growth) curve)
How exactly did you do this?
 
  • #9
Ga69 was bombarded by 10 MeV photon. A neutron was emiited from Ga69. The unstable Ga68 decayed to Zn68.
 
  • #10
None of those are near the half life of Ga-68. Are you sure you are measuring what you think you are?
 
  • #11
I was choosen the numbers randomly for an illustration. Actually the half lives that I measured are 65 min, 67 min and 66 min.
 
  • #12
I'm afraid by asking people to help you with made up, inconsistent numbers, you ended up wasting people's time. Perhaps it would be better to show us the real numbers.
 
  • #13
My aim is to know the technique with a basic examples. It is not do an article all together. I have no realistic data. Again, I would like to know the technique. Because of someone, I made up an element, a realistic peaks and a realistic half life.
I do not have any of them. Just technique I wonder. A dream I had about this problem. So I ask to get an answer. Thats all.
 
  • #14
sakkoyun said:
Actually the half lives that I measured are 65 min, 67 min and 66 min.

sakkoyun said:
I have no realistic data.

It's difficult to help you if you don't provide consistent information.
 
  • #15
sakkoyun said:
My aim is to know the technique with a basic examples. It is not do an article all together. I have no realistic data. Again, I would like to know the technique. Because of someone, I made up an element, a realistic peaks and a realistic half life.
I do not have any of them. Just technique I wonder. A dream I had about this problem. So I ask to get an answer. Thats all.
The right analysis method depends on all those details you refuse to give.
 

1. What is half life determination?

Half life determination is a scientific process used to calculate the amount of time it takes for a substance to decrease by half of its initial amount. It is commonly used in radioactive decay and pharmaceutical studies.

2. How is half life determined?

Half life is determined by measuring the rate of decay of a substance over time. This is typically done by using specialized equipment, such as a Geiger counter, to track the amount of radiation emitted from the substance.

3. What factors can affect half life determination?

The factors that can affect half life determination include temperature, pressure, and the chemical properties of the substance being studied. Additionally, the accuracy of the equipment used and any external influences, such as contamination, can also impact the results.

4. Why is half life determination important?

Half life determination is important because it allows scientists to understand the stability and behavior of a substance over time. This information can be used in various fields, including medicine, environmental science, and nuclear energy.

5. What are some common applications of half life determination?

Half life determination has many practical applications, such as determining the expiration date of medications, studying the effects of radiation on the environment, and calculating the remaining lifespan of nuclear waste. It is also used in fields like archaeology and geology to date ancient artifacts and rocks.

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