www.medlinkstudents.com

2. What are the
Elementary
Constituents of
Matter?
What are the forces that
control their behaviour at the
most basic level?

3. History of Constituents of
Matter
AD

5. •In Nuclear Reactions momentum and mass-
energy is conserved – for a closed system the
total momentum and energy of the particles
present after the reaction is equal to the total
momentum and energy of the particles before the
reaction
•In the case where an alpha particle is released
from an unstable nucleus the momentum of the
alpha particle and the new nucleus is the same as
the momentum of the original unstable nucleus

6. 0
0
0
1
1
1
1
0  epn
•Large variations in the emission velocities of the 
particle seemed to indicate that both energy and
momentum were not conserved.
•This led to the proposal by Wolfgang Pauli of another
particle, the neutrino, being emitted in  decay to carry
away the missing mass and momentum.
•The neutrino (little neutral one) was discovered in 1956.
Wolfgang Pauli
__

7. 0
0
0
1
1
1
1
0  epn
1.008665 u 1.007825 u 0.0005486 u
27
10660.1 
1 u =
1 J =
19
106.1 

__
kg
eV

8. 0002914.0
)0005486.0007825.1(008665.1

Mass difference
27
10660.10002914.0 

31
1083724.4 

kg
kg
u

9. It has been found by experiment that the emitted beta particle
has less energy than 0.272 MeV
Neutrino accounts for the ‘missing’ energy
2
mcE 
2831
)100.3)(1083724.4(  
14
10353516.4 

271755
10602.1
10353516.4
19
14



 

J
J
eV
272.0 MeV

11. +
+

12. •First artificial splitting of
nucleus
•First transmutation using
artificially accelerated
particles
•First experimental verification
of E = mc2
Irish Nobel Prize
E.T.S. Walton 1951
Cockroft and Walton
Ernest WaltonJohn Cockcroft

14. EnergyHeHeLiH 4
2
4
2
7
3
1
1 
Proton + Lithium Two alpha particles + Energy
1 MeV 17.3 MeV
Experimental verification of E = mc2

16. • Ancient Greeks:
Earth, Air, Fire,
Water
• By 1900, nearly 100
elements
• By 1936, back to three
particles: proton, neutron,
electron

18. CERN LEP APPLET
http://www.hep.ucl.ac.uk/masterclass/Acc_sim2/simulator.html

21. The Four Fundamental Forces

22. 20
Instituteof Physics Peter Kalmus Particles and the Universe
Forces
Gravity
falling
objects
planet
orbits
stars
galaxies
inverse
square law
graviton
inverse
square law
photon
short
range
W
±
, Z0
Electro-
magnetic
atoms
molecules
optics
electronics
telecom.
Weak
beta
decay
solar
fusion
Strong
nuclei
particles
short
range
gluon

24. Particle
zoo
2
c
E
m 

25. 11
Instituteof Physics Peter Kalmus Particles and the Universe
Neutrinos
Antiparticles
1950s, 1960s
> 200 new “elementary” (?) particles
Feel weak force
“predicted”  later discovered
100,000,000,000,000 per second pass
through each person from the Sun
Equal and opposite properties
“predicted”  later discovered
Annihilate with normal particles
Now used in PET scans
Many new particles created
in high energy collisions
Convert energy to mass. Einstein E = mc2

26. mx 10
101 
mx 15
101 
mx 15
107.0 
mx 18
107.0 

Thomson (1897): Discovers electron

27. 0
0
0
1
60
28
60
27   eNiCo
Q = -1e almost all trapped in atoms
Q= 0 all freely moving through universe
_

30. Just as the equation x2=4 can have two
possible solutions (x=2 OR x=-2), so
Dirac's equation could have two
solutions, one for an electron with
positive energy, and one for an electron
with negative energy.
Dirac interpreted this to mean that for
every particle that exists there is a
corresponding antiparticle, exactly
matching the particle but with opposite
charge. For the electron, for instance,
there should be an "antielectron" called
the positron identical in every way but
with a positive electric charge.

31. 1928 Dirac predicted existence of antimatter
1932 antielectrons (positrons) found in
conversion of energy into matter
1995 antihydrogen consisting of antiprotons and
positrons produced at CERN

 ee
In principle an antiworld can be built from
antimatter
Produced only in accelerators and
in cosmic rays

32. 
 eerays

33. hfee 2 

35. 3
1
Q
3
2
Q
1Q
0Q

36. James Joyce
Murray Gell-Mann

37. 3
1

3
1

3
1

3
2

3
2

3
2


38. 12
Today’s building blocks
Leptons
(do not feel strong force)
electron e- -1
e-neutrino e 0
Quarks
(feel strong force)
up u +2/3
down d -1/3
proton = u u d
+2/3 +2/3 -1/3 = +1
neutron = u d d
+2/3 -1/3 -1/3 = 0
4 particles very simple
multiply by 3 (generations)
multiply by 2 (antiparticles)
First generation
1
3
1
3
2
3
2

0
3
1
3
1
3
2

3
2

3
1


39. http://lectureonline.cl.msu.edu/~mmp/applist/q/q.htm