Nuclear Physics I
Dr. Mohammed Hassen Abu-Sei’leek
CH 1: Basic Concepts
• In 1896, Henri Becqurel discovered that
radiation from uranium salt cast shadows of
opaque objects which could be recorded on a
photographic plates wrapped in black papers.
( this radiation is persisted even when the
excited light had been removed) ≡
radioactivity.
• Radiations have the ability to discharge an
electrified body by using of the current in an
ionization
chamber
for
quantitative
measurements.
• In 1898, Piece and Mary Curie separate
plutonium and radium from crude U ores.
• Bequeral’s work attracted Ernest Rutherford
who studied the conductivity of gases under J.
Thomson in Cambridge investigated the
radiation of Thorium.
• Experiments of Curie & Rutherford showed
that
radioactive
radiations
contained
components with different powers of
penetrating matter.
1. α - particles
2. β – particles {(e- & e+ ) internal conversion
electrons}
3. ϒ – rays
• Effect off a magnetic field
𝐵 into page
• Rutherford, Soddy and Monterial found
Radioactivity produced new chemical
substances.
• Some Introductory Terminology:
1. Z is atomic number gives number of protons
(p). In neutral atoms have Z protons & Z
electrons.
2. A is mass number of a nucleus.
A=Z+N where N is number of neutrons
Proton and neutron are form a family of
nucleons.
Nuclides
• A nuclide is a specific combination of a
number of protons and neutrons.
A
• Z X N is the complete symbol for a nuclide, but
A
the information is redundant and X is
sufficient.
• X is the chemical symbol of the element.
• Nuclides with the same atomic number Z are
called isotopes, same A isobars, same N
isotones (isos (gr.) - the same).
• We generally use the form ZA X N  2656Fe 30 , 238
92U 146
• Isotopes are nuclei with Z proton that can
have a variety of different mass number 1737Cl , 1735Cl
• Isotones are nuclei with the same N but
different Z such as: 12H , 23He
• Isobars are nuclei with the same A such as:13H , 23He
• Any nucleus contains Z protons & N neutrons.
• The present of electrons within the nucleus is
unsatisfactory for several reasons:
1. The nuclear electrons would need to be bound
to the protons by a very strong force, stronger
even than the Coulomb force. Yet no evidence
for this strong force exists between protons and
atomic electrons.
2. To confine electrons in a region of a nucleus
14
(x  10 m ),by using the uncertainty principle,
these electron have a momentum with a range
(p 
 20MeV / c ).Electrons that are emitted from
x
the nucleus in radioactive β decays have energies ˂
1 MeV; never do we see decay electron with 20
MeV energies.
3. The total intrinsic angular momentum (spin)
of nuclei for which A-Z is odd would disagree
with observed value if A protons and A-Z
electrons were present in the nucleus. For
2
example 1 H , according to p-e hypothesis
would contain 2 p and 1e.
s p  s e  1/ 2  s ( 12H )  2s p  s e  3 / 2 or 1/ 2
but the observed spin of the deuterium
nucleus is 1.
4. Nuclei containing unpaired electrons would
be expected to have magnetic dipole moments
far greater than those observed.
2
1
2
1
For example H -nucleus, if a single electron was
present in a H -nucleus, we would expected the
nucleus to have a magnetic dipole moment
about the same size as that of an electron, but
the observed magnetic moment of the
deuterium nucleus is about 1/2000 of the
electron’s magnetic moment.
• Neutron was discovered by Chadwick in 1932.
12
2
1
u

1/12
M(
C
)

931.502
MeV/c
• Atomic mass unit,
E  mc 2
c  931.502 MeV/u
2
m p  938.272 MeV/c 2