Download Câmara de bolhas - high school teachers at CERN

Photo of Particles Interacting within a Bubble Chamber
How does a bubble
chamber work ?
How can you
analyze
this image ?
Fermilab bubble chamber: 4.6 m in diameter in a 3 T magnetic field
How does a bubble chamber function ?
How can you analyze the image ?
Relate the movement of the Compton Electrons
with the direction of the magnetic field
Relate the movement of the deflected particles with their charge
and the direction of the magnetic field
Relate the materialization of particle pairs (matter & antimatter)
to the energy of the photon which preceded them
Apply the Conservation of Momentum to a head-on collision between
a positron and an electron
Relate the movement of the Compton Electrons
with the direction of the magnetic field.
Notice the trajectory of the spiraling lone electron, indicated by the arrow. This
electron was knocked away from the atom that originally held it by a high energy
photon.
Identify the other examples of this interaction in the picture above
What is the direction of the magnetic field?
Why isn’t the photon visible ?
Relate the movement of the deflected particles with their charge and the
direction of the magnetic field.
Notice the trajectory of the spiraling lone electron, indicated by the arrow.
This electron was knocked away from the atom that originally held it by a high energy photon.
What is the relationship between the movement of the
deflected particles with their charge and the direction of the
applied magnetic field.

B



F

B
y
Remember the Lorentz Force

 
F  qv  B
z

qv

F
x
Why isn’t the photon visible ?
• A photon does not possess an electric charge. Therefore, it does not transfer
energy to the medium. Hence, it does not cause the initiation of boiling along its
path, therefore you get no bubbles.
What other particles would not leave a track in a bubble chamber ?
• A charged particle travelling through the same medium interacts with it trough
Coulomb’s Force. In this way it transfers enough energy to initiate the liquid boiling
and leaving behind a trail of small bubbles.
Relate the movement of the deflected particles with their
charge and the direction of the magnetic field
B
A
An electron ( e - ) and a positron (e + )leave the tracks shown in the picture.
Which is which?

B

Relate the movement of the deflected particles with their
charge and the direction of the magnetic field
B
A
An electron ( e - ) and a positron (e + )leave the tracks shown in the picture.
The particle that deflects to the right ( track B) is an electron ( e- ).
The particle that deflects to the left ( track A) is a positron ( e+ ).

B

Explain the materialization of particle pairs (matter & antimatter)
to the energy of the photon which preceded them
ee+
D
C
One of the photons emitted at C travels to D where it interacts with a
nucleus from the liquid and materializes into an electron/positron pair.
To a good approximation, all of photon’s energy is shared by the e-/e+ pair.
Calculate the kinetic energy of the materialized system, knowing that the linear
momentum of the photon is 26531 MeV/c .
( me =0,511Mev/c2 )
Calculate the kinetic energy of the materialized system, knowing that the linear
momentum of the photon is 26531 MeV/c .
( me =0,511Mev/c2 )
E =h
p=h/
ee+
Eo= mc2
D
C
E = 2Eo + K(e-,e+)
Apply the Conservation of Momentum to a head-on collision
between a positron and an electron
E
At point E a rare event took place:the positron track changed
into a negative track. What happened was that the positron made
a head-on collision with an electron.
What is the linear momentum of the electron if the incoming
positron’s linear momentum was 54±15MeV/c?
(melecton=mpositron)