Bubble chamber

Bubble Chamber videos

What types of particles can you spot in these videos?

(click on the pictures to see videos)

A Cloud Chamber Shows Tracks from Cosmic Rays And Natural Radioactivity

Introduction
Visitors to the Niigata Science Museum (NSM) can see a large scale diffusion cloud chamber in action. A cloud chamber is an instrument which makes visible the trajectory of high energy cosmic rays from outer space. These fast moving charged particles produce visible white tracks or "clouds" in the chamber. Neutral particles, such as gamma rays, x-rays and neutrons do not produce tracks directly. If a neutral particle transfers energy to a charged particle, such as an electron or proton, we can then see the cloud track of this secondary particle.
Later you can watch videos of cosmic ray tracks in the cloud chamber. The videos you will see later were taken from the position of a person watching the cloud chamber. video shows how the cloud tracks fade rapidly permitting new tracks to be seen.

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The above picture shows the cloud chamber in the exhibition hall of NSM. The videos you will see later were taken from the position of a person watching the cloud chamber.
This large scale diffusion cloud chamber was made in Germany.

What kind of particles can we see in this cloud chamber?

The cloud chamber is capable of producing a visible track from any ionized particle that passes through the sensitive area of the chamber as we will explain later. High energy ionized particles have two major sources - cosmic rays from outer space and disintegration products from radioactive substances. The cloud chamber shows mostly cosmic rays as there is very little radioactivity inside the chamber. If a radioactive source is placed in the cloud chamber it would produce many cloud tracks produced by charged particles from the radioactive disintegrations.
Ionizing radiation is all around us. Much of it comes from natural radioactive atoms which give off radiation in an effort to become more stable. This is a nuclear-disintegration (or decay) process. In the process, unstable nuclei emit excessive energy in the form of alpha rays (α-ray), beta rays (β-rays) or gamma rays (γ-rays). These rays come from radioactive substances. The sun and stars in outer space produce high energy particles by mechanisms which are not yet understood. These are called cosmic rays. Many of them are absorbed in the large mass of air that surrounds the earth. If you fly in a jet plane the number of cosmic rays that hit you is much greater than on the ground because there is less air to shield you. People who live in mountains also have more cosmic rays strike them.

Video1 Cosmic Rays 1
The trajectory marked "e" in the above picture originated from a low energy electron or positron. The heavier cloud marked a represents an alpha article. The parallel lines in the picture are wires of heater, which are attached back of the glass cover. The spacing of the wires is 4.0 cm. At the end we will explain how these heater wires are an important part of the mechanism that produces "cloud" tracks. Video2 Cosmic Rays2
The thick trail in the picture must be made by alpha particle. The thin long trail "e" must be originated from high energy electron, positron or muon.

Only charged particles can produce tracks in the cloud chamber. The following table lists the particles which can be seen in a cloud chamber.

Table of rays that can be seen in a cloud chamber and a brief description of the
appearance of their tracks.

Rays
Properties
Origin and appearance

Alpha rays It is identical to a doubly charged helium ion (He++), that is, the nucleus of a helium atom An alpha ray is emitted from a nucleus of an atom. In air, there exists a natural radioactive gas, radon. When radon decays it emits an alpha particle. The new nucleus is an atom of another radioactive element. Radon supplies most of alpha rays that we see in a the cloud chamber as thick tracks.

Beta rays (Electron beem) Beta rays can be either negative - a negative electron (e-) or a positive electron or positron (e+). High energy beta rays are electrons that come from radioactive sources. High energy electrons can also be produced by collisions of cosmic rays with electrons attached to atoms in the chamber. In the cloud chamber, high energy electrons produce thin, rather straight and long trajectories. Low energy electrons produce thin irregularly curved short paths.

Muons Muons are a type of elementary particle which are positively or negatively charged. They are unstable and decay into other particles in a very short time. Muons are a major component of cosmic rays at sea level. These particles are produced as reaction products of collisions of primary cosmic rays with atmospheric molecules. Muons have strong penetrating power. They can even be detected in deep underground. A low energy muon makes a thick track in the cloud chamber, similar to an alpha track. A high energy muon produces a thin track like an electron's.

Protons. Protons are very common as they are the nucleus of common hydrogen atoms. At sea level, high energy protons come from outer space as one type of cosmic ray. They are also produced in the atmosphere by other very powerful cosmic rays. Protons produce cloud tracks similar to alpha's.

Gamma rays
X-rays Gamma rays and X-rays are high energy electromagnetic waves or photons. Gamma rays originate from naturally existing radioactive substances or are produced secondarily by powerful cosmic rays. As they have no charge, they make no visible trails. However, they can interact with the molecules in the chamber to create energetic electrons or positrons which do produce cloud tracks.

Figure to illustrate the components of the diffusion cloud chamber

Alcohol evaporates from the warm top surface of the cloud chamber. The alcohol vapor diffuses toward the cold bottom surface. The stable temperature distribution from top to bottom includes a layer of supersaturated alcohol vapor near the bottom of the chamber. When a high speed charged particle passes through this layer produced ion pairs act as points for condensation of the alcohol vapor to make tiny alcohol droplets or fog. This produces a visible "cloud." The droplets are produced only in the supersaturated layer. The effect is similar to that seen when high-flying aircraft make fog trails (contrails) in the sky. In one minute many cosmic rays or alpha rays emitted from radon nuclei in the air, make visible tracks in the cloud chamber. You can see some of these "cloud" tracks in the following videos of the cloud chamber.

We use radon gas as the alpha ray source, most of the alpha rays are from 220Rn and few are from 222Rn. The gas is injected in the cloud chamber and records the trails in videos. 220Rn's decay chain is shown in Fig1. As soon as the decay of a 220Rn-nucleus make an alpha ray trail, the daughter nucleus 216Po's decay occurs in succession. These successive two alphas make a pair of V-shaped trails. So you can observe many "V" in the chamber. Above mechanism is shown in the animation in this page. Animation in this page.
The lengths of alpha's trails or the angle between two trails of V-shape depend on the location, which the trail appears. Because the thickness of the supersaturated layer is 1 to 2 mm in length, we can see only the part of the alpha particles' trajectory as the trails, which belong to the very thin layer. For the structure of cloud chamber, see the page "A Cloud Chamber Shows Tracks from Cosmic Rays and Natural Radioactivity"

Particle tracks

The following videos show many kind of particle tracks in the the large scale
diffusion cloud chamber in NSM's exhibition hall.

Picture of electron track
This picture shows an enlarged view of thin tracks. The irregularly curved tracks "e" must have originated from low energy electrons or positrons.
Video Alpha Particle
This Video shows an enlarged view of thick tracks. In this video you can see how to a track appears, develops and then fades away. The tracks shown with "α" and "e" must have been made by an alpha ray and an electron, respectively.

Video5 High Energy Particle1
In this Video, you can see many thick tracks. Among them, a V-shaped track, T2, which must have been made by two high energy charged particles, that were simultaneously created by an at the point of the V by a very high energy cosmic ray particle colliding with a nucleus in an atom of the air or alcohol. "α" must be an alpha particle's track. The particle that created "T1" is unknown.
Video6 High Energy Particle2
A long track "HC" originated from some high energy particle, such as proton cosmic ray. "e" and "α" must be an electron (or positron) and an alpha particle track, respectively.

NEXT PAGE

We welcome your comments about these tracks. Please send an e-mail to Niigata Science Museum of the following address.

E-mail nsm@coral.ocn.ne.jp

Acknowledgement
We would like to thank Shinichi Wada, Professor of Niigata University , for helpful discussions and recommendation for making this page.
And we also thank John R. Cameron, Professor Emeritus of University of Wisconsin-Madison, (U.S.A) for assistance with the English explanation.

NIIGATA SCIENCE MUSEUM 〒950-0948　3-1-1 Meike Minami Niigata-Shi, Niigata-Ken, Japan
TEL: +81-25-283-3331　FAX: +81-25-283-3336
E-mail: nsm@coral.ocn.ne.jp

What kind of particles can we see in this cloud chamber?
The cloud chamber is capable of producing a visible track from any ionized particle that passes through the sensitive area of the chamber as we will explain later. High energy ionized particles have two major sources - cosmic rays from outer space and disintegration products from radioactive substances. The cloud chamber shows mostly cosmic rays as there is very little radioactivity inside the chamber. If a radioactive source is placed in the cloud chamber it would produce many cloud tracks produced by charged particles from the radioactive disintegrations. Ionizing radiation is all around us. Much of it comes from natural radioactive atoms which give off radiation in an effort to become more stable. This is a nuclear-disintegration (or decay) process. In the process, unstable nuclei emit excessive energy in the form of alpha rays (α-ray), beta rays (β-rays) or gamma rays (γ-rays). These rays come from radioactive substances. The sun and stars in outer space produce high energy particles by mechanisms which are not yet understood. These are called cosmic rays. Many of them are absorbed in the large mass of air that surrounds the earth. If you fly in a jet plane the number of cosmic rays that hit you is much greater than on the ground because there is less air to shield you. People who live in mountains also have more cosmic rays strike them.

Rays	Properties	Origin and appearance
Alpha rays	It is identical to a doubly charged helium ion (He++), that is, the nucleus of a helium atom	An alpha ray is emitted from a nucleus of an atom. In air, there exists a natural radioactive gas, radon. When radon decays it emits an alpha particle. The new nucleus is an atom of another radioactive element. Radon supplies most of alpha rays that we see in a the cloud chamber as thick tracks.
Beta rays (Electron beem)	Beta rays can be either negative - a negative electron (e-) or a positive electron or positron (e+).	High energy beta rays are electrons that come from radioactive sources. High energy electrons can also be produced by collisions of cosmic rays with electrons attached to atoms in the chamber. In the cloud chamber, high energy electrons produce thin, rather straight and long trajectories. Low energy electrons produce thin irregularly curved short paths.
Muons	Muons are a type of elementary particle which are positively or negatively charged. They are unstable and decay into other particles in a very short time.	Muons are a major component of cosmic rays at sea level. These particles are produced as reaction products of collisions of primary cosmic rays with atmospheric molecules. Muons have strong penetrating power. They can even be detected in deep underground. A low energy muon makes a thick track in the cloud chamber, similar to an alpha track. A high energy muon produces a thin track like an electron's.
Protons.	Protons are very common as they are the nucleus of common hydrogen atoms.	At sea level, high energy protons come from outer space as one type of cosmic ray. They are also produced in the atmosphere by other very powerful cosmic rays. Protons produce cloud tracks similar to alpha's.
Gamma rays X-rays	Gamma rays and X-rays are high energy electromagnetic waves or photons.	Gamma rays originate from naturally existing radioactive substances or are produced secondarily by powerful cosmic rays. As they have no charge, they make no visible trails. However, they can interact with the molecules in the chamber to create energetic electrons or positrons which do produce cloud tracks.