How can counting time be scheduled for a source with a high count rate?

In summary, the conversation discusses the need to determine the strength of a radioactive source using counting equipment that is only available for two hours. The net source counting rate is 7 times the background rate, suggesting that relatively short counting periods should be used. The net source count rate is calculated by subtracting the measured background rate from the measured count rate from the source. It is unclear if the source has a known half-life or if the goal is to determine a change in activity within the two hours. The textbook may provide guidance on counting statistics and the use of multiple counting periods to determine half-life. It is also mentioned that different types of radiation can be differentiated through attenuation measurements. A summary of a similar question is provided, where the counting equipment is
  • #1
Soilwork
102
0
It is necessary to determine the strength of a radioactive source. Counting equipment has been made available for only two hours. How should the time be schedule if:

The net source counting rate is 7 times the background rate.

I mean I would say that you would use relatively short counting periods since the count rate seems reasonably high.
But it sounds like you have say more than that.
Just to clarify as well the net source count rate is the
(measured count rate from source - measured background rate) right?
Any advice would be great
Thanks
 
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  • #2
Soilwork said:
It is necessary to determine the strength of a radioactive source. Counting equipment has been made available for only two hours. How should the time be schedule if:

The net source counting rate is 7 times the background rate.

I mean I would say that you would use relatively short counting periods since the count rate seems reasonably high.
But it sounds like you have say more than that.
Just to clarify as well the net source count rate is the
(measured count rate from source - measured background rate) right?
Any advice would be great
Thanks

Do you know the source and its half-life, or are you trying to determine if there is a change in the activity during the two hours?
 
  • #3
no you don't know anything at all.
All the information is there.
You just have to write down how you would schedule the the time given that you have the counter for 2 hours.
But all I can really think of is that since the number of counts seems high you would use short counting periods over the two hours.
Although that isn't really a schedule so I don't really know what is expected of me as such.
 
  • #4
Gross activity is net (source) activity + background. Seven times background is usually pretty low activity.

What does your textbook say about counting statistics?

Also, are you supposed to take several time periods during the 2 hr period in order to determine the half-life, so as to project activity outside the 2 hr period? Of course, low activity could mean 1) long half life, 2) very few atoms of the radionuclide, or 3) well shielded. Is this a confined or distributed source?

One would need at least 2 counting periods to determine half-life, but 3 would be better, and 4 even more so. If there would be a daughter radionuclide, more counting intervals might be needed.

One could also do attentuation measurements during this period. Can you think of how you would differentiate between {alpha, beta, gamma}?


Here is a nice little summary on counting in low activity with low background.
http://www.detectors.saint-gobain.com/Media/Documents/S0000000000000000003/tinlow%20background.pdf
 
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  • #5
yeah sorry what I meant when I said reasonably high was that it is high in relation to the other second situation which is the net source count rate is equal to the background rate.
Yes I think it is suggesting that you would need to break your measurements up into certain time periods that span over the two hours.
It doesn't actually say it is confined or distributed in the question.
alpha, beta and gamma have different attenuation curves so you could differentiate between them that way by taking measurements taken at various ranges.
 
  • #6
oh and I think it's just parent decay because it doesn't mention anything about daughters at all.
 
  • #7
Well I've found an answer to a similar sort of question to the one I was trying to understand here.
But it is just an answer and not a solution so I have no clue how they got it.
It is the same question above but with this one the counting device is only available for 1 hour.
(a) the net source count rate is about 5 times the background rate
(b)the net source count rate is 10 times the background rate.

ANS: Ts= source counting time in hours, Tb=background counting time in hours

(a) Ts = 0.711 and Tb= 0.289
(b) Ts = 0.586 and Tb = 0.414

So at least now I know that I got that question wrong when I did it :( but if someone has an idea of how they calculated that I would appreciate any hints on understanding how to do those sorts of questions :)
 
  • #8
didn't you post a thread about books on this course in the gen disc. forum? if this an the other thread you posted here are the kind of problems you have to solve have a look at knoll: radiation detection and measurement.
 
  • #9
yes I did and thanks a lot for recommending that book.
It really helps :)
 

1. How is radioactivity measured?

Radioactivity is measured using a device called a Geiger counter, which detects and counts the number of radioactive particles emitted from a substance. These particles are often alpha or beta particles, or gamma rays.

2. What units are used to measure radioactivity?

The units used to measure radioactivity are the Becquerel (Bq) and the Curie (Ci). The Becquerel is the International System of Units (SI) unit, and is equal to one disintegration per second. The Curie is a non-SI unit, and is equal to 3.7 x 10^10 disintegrations per second.

3. What is the difference between activity and exposure in terms of measuring radioactivity?

Activity is a measure of the rate at which a radioactive substance decays, while exposure is a measure of the amount of radiation that an object or person is exposed to. Activity is measured in units of disintegrations per second (Bq or Ci), while exposure is measured in units of radiation dose (such as Gray or Sievert).

4. What are some methods for measuring radiation in the environment?

There are several methods for measuring radiation in the environment, including using a Geiger counter, scintillation counter, or ionization chamber. These devices can be used to measure radiation in the air, soil, water, and other materials. Another method is through the use of dosimeters, which are worn by individuals to measure their personal exposure to radiation.

5. How accurate are measurements of radioactivity?

Measurements of radioactivity can be highly accurate when performed by trained professionals using calibrated equipment. However, there is always a margin of error due to background radiation and other factors. It is important to follow proper procedures and use reliable equipment to ensure the most accurate measurements possible.

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