Chapter 18: standard 11
• Nuclear processes are those in which an atomic
nucleus changes, including radioactive decay of
naturally occurring and human-made isotopes,
nuclear fission, and nuclear fusion. As a basis for
understanding this concept:
• Standard11. a. Students know protons and neutrons in
the nucleus are held together by nuclear forces that
overcome the electromagnetic repulsion between the
protons.
• Standard 11. b. Students know the energy release
per gram of material is much larger in nuclear fusion
or fission reactions than in chemical reactions. The
change in mass (calculated by E = mc2) is small but
significant in nuclear reactions.
Recap
• The atom is made up of Protons, Neutrons, and
Electrons. Protons and neutrons are located in
the nucleus while the electrons orbit on the
shells or orbital. Protons are positively charged
and neutrons have no charge.
• Standard 11 studies only the nucleus, that is,
protons and neutrons. The nucleus of an atom
(X) called nuclide is represented as AzX; where
A is the atomic mass (p + n) and z is atomic
number (number of protons only). Isotopes
have same atomic number, z but different A.
Electrostatic law
• The law of electrostatics states that like charges will
repel and unlike charges will attract each other. That
is
Proton-proton or electron-electron are like charges.
Proton-electron or anion - cation are unlike charges
• So, why should protons, that are like charges, stay
together in the nucleus?
• The neutrons have no charge so they function like
sandwich between the protons providing an opposing
force called the strong nuclear force which holds the
protons together in the nucleus
Helium atom
x
P+n 4 He
n p+ = 2
x
Stability of the nucleus
• What is nuclear stability? The ability of protons
and neutrons to stay together in the nucleus for
a long time.
• What factors promote nuclear stability?
- Strength of the nuclear force - the stronger
the nuclear force the more stable is the
nucleus.
- neutron/Proton ratio – atoms with atomic # s
1 – 20 favor a 1:1 ratio for the nucleus to be
stable. For atoms with atomic # more than 20, a
ratio of 3neutron to 2proton is favored. Or (3:2)
or Neutron/Proton = 3/2 =1.5
Nuclear binding energy
• The energy required to separate protons from neutrons in the
nucleus.
• When the nucleus of an atom is weighed, it will weigh less than
if the protons and neutrons were weighed separately and their
masses summed.
• Let us say the sum of individual masses of protons and
neutrons is A and the mass of the nucleus is B. The difference
in mass is A – B = m. m is called the mass defect.
A - B = m
Ex: Masses of (P+ + N + p+ + N ) - Pn = mass defect (m)
np
• Binding energy, E = mc2 where c is the speed of light.
• Assignment: If the sum of protons and neutrons is 20.000g and
the mass of the nucleus is 19.998g,What is the binding
energy? c = 300,000,000 m/s. (hint: convert mass difference to
kg)
Comparing Energy release
Chemical Fission Fusion
n + 235U → 143Ba +
Reaction C + O2 → CO2 91Kr + 2n
2H + 3H → 4He + n
UO2
(3%U-235 + 97% Deuterium + Tritium
Fuel Coal
U- 238)
700K 10,000K 100,000,000K
Temperature
Energy 3.3 x 107 2.1 x 1012 3.4 x 1014
J/Kg
Answer the following questions
1) What particles are found in an atom? State each
particle location within the atom.
2) Define the following words: a) atomic number;
b) mass number; c) isotope.
3) a) What is a nuclide? b) If nuclide of an atom X is
represented as AzX, what is i) A and ii) z called? c) if
the # of neutron is represented as n, what is the
relationship between A, z, and n?
4) a) What forces hold the nucleons together? b) what
is mass defect? c) What is the relationship between
mass defect and binding energy?
5) a) What is nuclear stability? b) What 2 factors are
responsible for nuclear stability? c) How can you
predict the stability of the nucleus of an atom?
11c. Students know some naturally occurring isotopes of elements
are radioactive, as are isotopes formed in nuclear reactions.
Name of isotope How it occurs Type of radiation Half-life uses
produced
radiometric dating:
determination of age
Carbon - 14 Natural Beta 5730 years of carbon-containing
artifacts up to about
70,000 years; also
used as a biological
tracer, for example,
in studies of
photosynthesis
Chlorine - 36 Natural beta 301,000 years measurement of
sources of chloride
and determining the
age of water up to
about 2 million years
old.
Sodiun-24 Nuclear reactor Beta & gamma 15 hours location of leaks in
water pipes, studies
of body electrolytes
Chromium-51 Nuclear reactor Alpha 27.7 days labeling of red blood
cells & quantifying
gastro-intestinal
protein loss
11d. Students know the three most common forms of radioactive
decay (alpha, beta, and gamma) and know how the nucleus
changes in each type of decay
Disintegration of the nucleus
• The spontaneous disintegration of the nucleus is called
radioactive decay. Radioactive decay is divided into Fission and
fusion. The energy or particles released during radioactive
decay is called radiation.
3 types of radiations produced are
• a) Alpha radiation = 42 He2+ ; symbol α (Helium nucleus)
• b) Beta radiation = o-1e ; symbol β (high speed electron)
• c) Gamma radiation = 00 γ ; symbol γ (photon – light)
Characteristics of each radiation
Radiation Charge mass also called in magnetic/electric field
• Alpha radiation +2 4 amu deflected
• Beta radiation -1 small high speed deflected
mass electron
• Gamma radiation 0 0 Electromagnetic wave Not deflected
Deflection of various radiations by magnetic or Electric fields
• Deflection by Magnetic field;
Magnetic field
N β
γ
α
S
• Deflection by Electric field Electric field
+ β
γ
_
α
How does the nucleus change with the production of
each radiation?
• When alpha radiation is produced, the atomic #
reduces by 2 and the atomic mass reduces by
4. Alpha particle
Ex: 22688Ra → 22286Rn + 24He
• When Beta radiation is produced, the atomic #
increases by 1 and that atomic mass stays the
same. Beta (electron)
Ex: 14 C → 14 N + 0 e
6 7 -1
• When gamma radiation is produced, the atomic
# and the atomic mass stay the same.
Gamma radiation
Ex: 13153I → 131
53I + γ
11e. Students know alpha, beta, and gamma radiation produce different
amounts and kinds of damage in matter and have different penetrations
• Penetration and damage caused by various radiations
• Alpha radiations are stopped by any thing made
of wood. Ex: a piece of paper. But they are very
damaging because of their high mass. They
ionize air as they move through.
• Beta radiations are stopped by Metal foil. Ex
Aluminum foil. They are not very damaging
since they have very little mass. They also
ionize air but to a lesser scale.
• Gamma radiation can only be stopped by a
thick block of lead or concrete. They are not
very damaging and will not ionize air.
Diagrammatic representation of Radiations penetration.
Aluminum Thick block of
paper foil Lead or concrete
Alpha radiation (α)
Beta radiation (β)
Gamma radiation (γ)
Answer the following questions
• 1) a) Define radioactivity. b) In what part of the atom does
radioactivity occur? c) What radiations are produced during
radioactivity? d) How is each radiation represented in a nuclear
equation?
• 2) In a tabular format, State the characteristics of each
radiation.
• 3) a) What do you need to know when balancing a nuclear
equation?
b) Balance the following nuclear equations
i) 22286Rn → 21884Po + _____, ii) 2813Al → ___ + 0-1e;
iii) 3718Ar + 0-1e → ____ ; iv) 94Be + ___ → 136C
• 4) name 2 types of nuclear reaction and give an example where
each occurs.
• 5) what is a) chain reaction, b) critical mass c) How are they
related.
• 6) Define nuclear waste. How is it disposed?