Brief History of Nuclear Physics

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Brief History of Nuclear Physics
1896 - Henri Becquerel (1852-1908) discovered
radioactivity
1911 - Ernest Rutherford (1871-1937), Hanz Geiger
(1882-1945) and Ernest Marsden (1888-1970)
conducted scattering of alpha particles on nuclei
1930 - John D. Cocroft (1897-1967) and Ernest
T.S. Walton (1903-1995) conducted the first
artificial nuclear reaction
1932 - James Chadwick (1891-1974) discovered the
neutron
1933 - Frederick Joliot (1900-1958) and Irene
Joliot-Curie (1897-1956) synthesized artificial
elements
1938 - discovery of nuclear fission by Otto Hahn
(1879-1968) and Fritz Strassman (1902-1980)
1942 - Enrico Fermi (1901-1954) builds a fission
reactor
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Properties of nuclei
Mass Number A
- number of nuclei
- number of protons (charge, element)
Atomic Number Z
Neutron Number N
- number of neutrons
A
X
A nucleus is represented by symbol
Z
Elements with different numbers of neutrons are
called isotopes.
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relativistic energy relativistic momentum
relativistic mass
relativistic energy
relativistic momentum
energy momentum relation
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attributes of selected particles
proton 1.67262?10-27 1.007276 938.28 e ½
neutron 1.67493?10-27 1.008665 939.57 0 ½
electron 9.1094 ?10-31 0.0005486 0.510999 -e ½
positron 9.1094 ?10-31 0.0005486 0.510999 e ½
photon 0 0 0 0 0
neutrino 0 0 0 0 ½
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the spin
Spin angular momentum like quantity
responsible for the magnetic moment of particles.
z
quantum numbers

• spin quantum number I

- the magnitude of the spin is

• magnetic quantum number mI -I, . I

- the z component of the spin is
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Nucleus size and shape
Rutherfords experiment
m
Ze
2e
d
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Nuclear Stability
Coulomb interaction - repulsive
Nuclear interaction - attractive
line of stability
magic numbers (very stable nuclei)
Z, N 2, 8, 20,
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Binding Energy
The total (relativistic) energy of a nucleus is
always less than the combined energy of the
separated nucleons.
The difference Eb (MeV) ( Zmp Zmn - MA )
931.491 MeV/a.u. is called the binding energy of
the nucleus.
Example (alpha particle)
Eb (2 1.0073au 2 1.0087au 4.0026au)
931.491 MeV/au ? 27.4 MeV
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Fission and Fusion
Fission heavy nuclei (Agt60) split releasing
energy
Fusion light nuclei (Alt60) combine releasing
energy
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Radioactivity
- spontaneous emission of radiation resulting
from disintegration (decay) of unstable nuclei.
Types of radioactive decay
lead shield
photographic plate
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Activity the decay rate
The number of disintegrated nuclei in a unit time
is proportional to the number of radioactive
nuclei in the source.
? the decay constant
Hence
N0 initial number of radioactive nuclei
Activity
R0 initial activity
units
1Ci 3.7 1010 Bq (curie)
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Half life time
The decay constant can be expressed in terms of
time T½, in which activity (the number of
radioactive nuclei) decreases by a factor of two.
t