26 - particle and nuclear physics
TRANSCRIPT
-
8/18/2019 26 - Particle and Nuclear Physics
1/33
Modern Physics
Marline Kurishingal
Particle and Nuclear Physics
-
8/18/2019 26 - Particle and Nuclear Physics
2/33
The results of the α-particle
scattering experiment&
the existence and small size of the
nucleus
Rutherford Alpha Particle Scattering
Experiment
-
8/18/2019 26 - Particle and Nuclear Physics
3/33
Rutherford Alpha Particle Scattering Experiment
• Rutherford‘s alpha particlescattering experiment changed
the way we think of atoms.
• Before the experiment the
best model of the atom wasknown as the Thomsonor "plum pudding" model. Theatom was believed to consistof a positive material"pudding" with negative"plums" distributedthroughout.
-
8/18/2019 26 - Particle and Nuclear Physics
4/33
Rutherford Alpha Particle Scattering Experiment(continued from previous slide)
• Rutherford directed beams of alpha particles (which are the nuclei ofhelium atoms and hence positively charged) at thin gold foil to test thismodel and noted how the alpha particles scattered from the foil.
Note : Diagram
is only for your
reference, its
not in syllabus
-
8/18/2019 26 - Particle and Nuclear Physics
5/33
Rutherford Alpha Particle Scattering Experiment(continued from previous slide)
•
Rutherford made 3 observations:
Most of the fast, highly charged alpha particleswent whizzing straight through un-deflected. This
was the expected result for all of the particles ifthe plum pudding model was correct.
Some of the alpha particles were deflected backthrough large angles. This was not expected.
A very small number of alpha particles weredeflected backwards! This was definitely not asexpected.
-
8/18/2019 26 - Particle and Nuclear Physics
6/33
Rutherford Alpha Particle Scattering Experiment(continued from previous slide)
• To explain these results a new model of the atom was needed.
• In this model the positive material is concentrated in a small butmassive (lot of mass - not size) region called the nucleus. Thenegative particles (electrons) must be around the outsidepreventing the atom from trespassing on its neighbours space tocomplete this model.
• The diagram in next slide will help you to understand the results ofthe experiment.
-
8/18/2019 26 - Particle and Nuclear Physics
7/33
Rutherford Alpha Particle Scattering Experiment(continued from previous slide)
-
8/18/2019 26 - Particle and Nuclear Physics
8/33
-
8/18/2019 26 - Particle and Nuclear Physics
9/33
Particles in the Atom
-
8/18/2019 26 - Particle and Nuclear Physics
10/33
-
8/18/2019 26 - Particle and Nuclear Physics
11/33
2
-
8/18/2019 26 - Particle and Nuclear Physics
12/33
-
8/18/2019 26 - Particle and Nuclear Physics
13/33
-
8/18/2019 26 - Particle and Nuclear Physics
14/33
Recap…
-
8/18/2019 26 - Particle and Nuclear Physics
15/33
N
Note : This
equation is an
example for
balanced
equation. Do notconsider it for
alpha emission.
-
8/18/2019 26 - Particle and Nuclear Physics
16/33
-1
-
8/18/2019 26 - Particle and Nuclear Physics
17/33
• In alpha decay 2 protons and 2 neutronsare emitted. Notice that this reducesthe nucleon number by 4 and theproton number by 2. A new element isthus formed.
• In beta decay a neutron changes into aproton (which remains in the nucleus)and an electron (which is emitted asbeta radiation). The net effect is anincrease in proton number by 1, while
the nucleon number stays the same.Again a new element is formed.
• When a nucleus has undergone alpha orbeta decay it is often left in a high-energy (excited) state. This energy can
be lost in the form of an emitted agamma ray. Because the composition ofthe nucleus is unchanged no newelement is formed.
-1
-
8/18/2019 26 - Particle and Nuclear Physics
18/33
Recap…
-
8/18/2019 26 - Particle and Nuclear Physics
19/33
-
8/18/2019 26 - Particle and Nuclear Physics
20/33
-
8/18/2019 26 - Particle and Nuclear Physics
21/33
-
8/18/2019 26 - Particle and Nuclear Physics
22/33
-
8/18/2019 26 - Particle and Nuclear Physics
23/33
-
8/18/2019 26 - Particle and Nuclear Physics
24/33
Recap….
-
8/18/2019 26 - Particle and Nuclear Physics
25/33
-
8/18/2019 26 - Particle and Nuclear Physics
26/33
-
8/18/2019 26 - Particle and Nuclear Physics
27/33
-
8/18/2019 26 - Particle and Nuclear Physics
28/33
-
8/18/2019 26 - Particle and Nuclear Physics
29/33
-
8/18/2019 26 - Particle and Nuclear Physics
30/33
-
8/18/2019 26 - Particle and Nuclear Physics
31/33
-
8/18/2019 26 - Particle and Nuclear Physics
32/33
-
8/18/2019 26 - Particle and Nuclear Physics
33/33