Science Buddies: "Ask an Expert"

Hello!

Get ready for a long post. This is my question and hypothesis so far:

Question:

What trails do gamma rays and/or X-rays create in a thermoelectric cloud chamber?

Hypothesis:

Since both Gamma Rays and X-rays are forms of electromagnetic waves, they both follow the equations:

Ε = hC / λ
C = f λ

If a gamma ray and an X-ray have at least one electromagnetic property (wavelength, frequency, energy, etc.) in common, the two waves would be nearly identical. This is possible, considering that the energy range of an X-ray can overlap or even exceed* the energy range of a gamma ray created by nuclear gamma decay. The main differentiation between gamma decay and X-ray radiation is the source of the radiation. Gamma rays are emitted when a nucleus transcends from a higher energy state to a lower energy state. X-rays are formed when electrons from a cathode are struck against a metal target.

Although, gamma rays and X-rays are formed differently, the cloud chamber will not detect this difference, as the trails formed in the cloud chamber depend on the p article being emitted. Although gamma rays usually have higher energies than X-rays, both X-rays and gamma rays emit a photon, meaning both trails should be very similar.

Since a photon has no charge, it will not be able to directly ionize the particles in the cloud chamber. However, since gamma rays emitted by the uranium ore most likely have energy higher than 100 keV, Compton scattering can occur. When the photon collides with a free electron, a lower energy photon and the electron are emitted. The electron ionizes the vapor and creates a trail, while the photon may collide with another free electron to undergo Compton scattering once more. This process may repeat one or two times until the photon no longer has enough energy to induce Compton scattering.

Hypothesis Part 1: X-ray trails and Gamma ray trails should appear similar.

Hypothesis Part 2: X-rays and Gamma Rays should produce very short chain
reaction paths, with straight electron trails seen at short
distances from each other.


* Some X-rays created by linear accelerators, megavoltage cancer treatment, etc. can exceed the
energy range of “classical” X-rays and even surpass the energy created by nuclear gamma decay.


I've pretty much finished the typing portion of the project, and I'm getting ready to work on the display board. However,
it turns our I have more information than I have space on my display board. I was wondering if it would be okay to keep
my Abstract on a separate "buddy board" in front of the project.

I'm a bit of a procrastinator and this project is due day after tomorrow. Any help would be appreciated.

THank You,

Rk9109

Hello and welcome to the forums

The answer really depends on the rules for your science fair. Some students make larger boards (up to 6 feet tall), some staple multiple sheets in one notebook paper sized space, and some leave some of the information in a report in front of the display. What do your teachers and science fair guidelines say? What are the judges expecting? Considering how much time judges get with a project, they rarely can read long reports anyway. A background research report is usually separate from the display, but does help with judging the project. Do you have a good lab notebook? That's often more important than the report. Good luck!

Keith

Sorry to be the bearer of bad news, but X-rays and gamma rays are the same thing. They are both photons. The only difference is the energy. The names "X-ray" and "gamma ray" are purely historical in origin. These terms are used to describe lower and higher energy photons in the same sense that "red" and "blue" are used to describe lower and higher energy photons in the range of energies that we perceive as light. Physically, there is a continuous range of energy from extremely low, which we choose to call "radio waves", then as the energy increases we give the photons various traditional names: "microwaves", "millimeter waves", "far infrared", "near infrared", "optical (red,yellow,...,blue)", "ultraviolet", "soft xrays", "hard xrays", and finally "gamma rays" for the most energetic; the names, however, are arbitrary and also overlapping. For example photons of energy around 500 KeV can be called either "xrays" or "gamma rays" although there may be some precise definition for, say, a particular physics journal. The important thing is xrays and gamma rays are the same particles, with just a variation in energy. Nuclear transitions usually have greater energies than atomic transitions, but not in every case. Using the term gamma rays when discussing nuclear physics is to a degree just a matter of tradition. The same goes for xrays. Both photons will produce more or less the same results in a cloud chamber. Since photons are not charged, they do not produce any tracks at all directly. They cruise along invisibly, then "bam!' they ionize an atom to produce a high energy electron ("beta ray") that does create a track. They can also create positrons or if they are sufficiently energetic muons or even protons and neutrons via nuclear reactions -- but these are very rare in a cloud chamber.

Hello!

I believe I acknowledged that in my hypothesis, so you are not the bearer of bad news

In my hypothesis I wrote:

"If a gamma ray and an X-ray have at least one electromagnetic property (wavelength, frequency, energy, etc.) in common, the two waves would be nearly identical. This is possible, considering that the energy range of an X-ray can overlap or even exceed* the energy range of a gamma ray created by nuclear gamma decay. The main differentiation between gamma decay and X-ray radiation is the source of the radiation. Gamma rays are emitted when a nucleus transcends from a higher energy state to a lower energy state. X-rays are formed when electrons from a cathode are struck against a metal target.

Although, gamma rays and X-rays are formed differently, the cloud chamber will not detect this difference, as the trails formed in the cloud chamber depend on the p article being emitted. Although gamma rays usually have higher energies than X-rays, both X-rays and gamma rays emit a photon, meaning both trails should be very similar."

Since they are essentially the same thing, I included both in the science fair question, since the
trails are very similar. It provides me away to easily get more sources of information.

In the project, I did not say they are exactly the same, since there are several notable differences
between the two types (though they aren;t detected by the cloud chamber). IS this correct?

Thank You for the responses!

Your description of how gamma and x rays are formed is usually correct, but in fact they can be formed in different ways (for example, non-nuclear gamma rays can be formed by lightning, and x-rays can be produced by a lot of mechanisms, generally all involving electrons, but not all related to orbital transitions... c.f. x-ray lasers). So perhaps a "usually" could be added to make it more precise.

Hello!

Although it has been a long time since the project is over, I appreciate the information.
In the actual project I used that idea that X-rays and Gamma rays were very similar to
my advantage. Although I had a uranium sample that did produce Gamma-rays, it was harder
to see the Compton Scattering than the scattering produced by X-rays.

Now to try and think of a good project for next year. I hope to make it to ISEF this year,
and I live in a relatively small city, so I won't as hard of a time as kids would in a large
city like Los Angeles or New York.