Download BC Example

EXAMPLE
DATA:
• Beam:
K - ; E = 4,2 GeV ; mK=mp/2
• Target:
Hydrogen atoms; Rnucleus=10-5Ratom
me = mp/2000
QUESTIONS
1.
Draw a diagram showing the tracks formed by different charged particles.
2.
What is the direction of the magnetic field in this picture?.
Notice: negative particles such as electrons turn clockwise and positive
particles such as protons turn anticlockwise in this magnetic field.
3.
Explain the interactions observed in the picture.
4.
What can we tell about the energy transferred in these interactions?.
5.
Consider the collision particle K- and proton. Compare the radius of curvature of
these particles’ trajectories.
ANSWERS
1. This coloured diagram
shows the paths
followed by these
charged particles.
Code:
green K- ;
red electron ;
blue proton.
2.
The direction of the
magnetic field is towards
axe X negative.
We use the formula of
Lorentz force to calculate
the value and direction of
the force exert on
charged particles by a
magnetic field.

 
F  q (v  B )
 
The orientation
of F , v

and B can be also found
using RHR right hand
rule or corkscrew rule.
Z
Y
X

F

v

v

F
3.
In point A, the K- particle hits an electron and this electron makes
its own characteristic curly track.

In point B, the K- strikes a proton. After the collision the proton
moves to the right causing the dark path shown on the picture.
4.



The charged particles passing along the Buble Chamber deposit
energy for ionization of Hydrogen atoms. This amount of energy
(13,6 eV) is negligible compared with the energy of the incoming
particles K- (4,2 GeV).
On the interaction referred in point A, there are more energy
transferred to the electron. This curly track requires an energy
about MeV’s.
On the collision between K- and proton, the proton takes some
energy from the K-. This proton loses its energy as it moves slowly
creating a short dark path.
•
We consider that the forces exert on charged particles by the magnetic
field inside a BC are centripetal forces. We use it to know the relation
between the momentum of the particle and the radius of curvature of its
trajectory.
m v2 / R = q v B
p=RqB
We can conclude that shorter radius (or more curvature ) indicates
lower momentum.
conclusion: Rp
< RK-
and
pp < pK-