Problems with cloud chamber project

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Problems with cloud chamber project

Postby Ssmiley » Thu Mar 20, 2014 3:27 pm

I am wondering if the time of day affects the number of radioactive particles I will see. When I do my experiment in the afternoon, I only see around 25. But, when I do it later at night around 9 p.m. I see over 100! I don't change anything. I just don't understand the big difference in the amount I am seeing.
Thanks.
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Project Question: I am trying to detect background radiation using a homemade cloud chamber
Project Due Date: 3/31/14
Project Status: I am conducting my experiment

Re: Problems with cloud chamber project

Postby Terik Daly » Fri Mar 21, 2014 8:47 am

Hi Ssmiley,

Which of these two projects are you doing?

Watching Nuclear Particles: http://www.sciencebuddies.org/science-f ... p087.shtml
Particles in the Mist: http://www.sciencebuddies.org/science-f ... p086.shtml

I can think of a few factors that might lead to variation in your findings, particularly if you are doing the Watching Nuclear Particles project. First, the background radiation in your location simply varies with time. This could be due to a number of things. If, for example, you live in an area with lots of granitic rocks, variations in how much air is flowing through the room your cloud chamber is sitting in might lead to changes in the number of tracks you observe. Another possibility is that it was easier to observe the tracks at one time. For example, was the room darker at one time than another? It is also possible that there was more alcohol vapor in the chamber during one of your tests due to differences in how soaked the felt was.

There will always be variability in your data. Some of that variability will be due to random fluctuations. Other variability may be systematic. Have you tried doing the experiment multiple times in the afternoon and multiple times at night (over a period of several days and nights)? This would assess the reproducibility of your observations. If not, try it and see if you consistently observe more particles at night. If you do, then the cause is something systematic, and we'll have to think about that in more detail. But, if the number of particles is not consistently higher at night, then the cause is likely random fluctuations.
All the best,
Terik
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Re: Problems with cloud chamber project

Postby Ssmiley » Fri Mar 21, 2014 9:48 am

Thank so much for your reply. It was helpful.
I am,in fact doing the Watching Nuclear Particles experiment. I have performed the experiment several times in the afternoon on different days and several times at night on different days. The results are consistent with the time of day - less particles in the daytime. The room in which I am doing the experiment is consistently dark. It is in the interior of our house and does not have any windows. There may be variations in the amount of alcohol,but I have rebuilt the chamber several times and the results are still consistent with my previous experiments done at the same time of day.
I appreciate any ideas you can share.
Thanks.
Ssmiley
 
Posts: 2
Joined: Thu Mar 20, 2014 2:36 pm
Occupation: Student 7th grade
Project Question: I am trying to detect background radiation using a homemade cloud chamber
Project Due Date: 3/31/14
Project Status: I am conducting my experiment

Re: Problems with cloud chamber project

Postby Terik Daly » Fri Mar 21, 2014 3:38 pm

Hi Ssmiley,

Thanks for clarifying the project you are working on! You have a repeatable pattern - you consistently measure more cloud tracks at night than during the day time. So, random chance or experimental errors are probably not the causes. Instead, for some reason the flux of cloud tracks really is higher at night. Based on your data, you know that much. (I'm assuming the cloud chamber was always placed in the same spot.) We don't know what causes the observed pattern, but the pattern is real.

What room of the house did you test? Is there something (a computer, for example) that is either on or in the room only in the afternoon but not at night (or vis versa)? Think about any differences at all between the conditions of the room in the afternoon and at night. Do you have an old cathode-ray TV in the room, by chance? Does anyone smoke in your house? Do you see the same afternoon/night pattern when the detector is in different rooms of your house? If the answer to that last question is no, then the cause must be something in the room. But, if you see the same pattern throughout the house, then the source of the pattern is something more widespread. Without being in your house, I can't pin down the answer precisely for you. But, the question of spatial variability (i.e., does the pattern hold for different rooms of the house) is interesting.

This process you are going through right now - getting a result that leads to more questions and the need for additional experiments - is how science works. We often don't know right off the bat what explains our results. Instead, we do additional experiments to get data that bring us closer and closer to pinning down the answer.
All the best,
Terik
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Re: Problems with cloud chamber project

Postby Ray Trent » Tue Apr 01, 2014 9:59 pm

That's an interesting result. In principle, the intensity of cosmic rays shouldn't be that different between the day and night, so I'm afraid I don't have any suggestions about what could be causing this effect.
../ray\..
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