AS Level Physics' Radioactivity group presentation in class. covers up the question on: -Why certain nucleus is radioactive -Radioactive process -Half-life -exponential decay curve with a very lil' detail explanation for each subtopic.

1. RADIOACTIVITY
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2. • Why certain nucleus is radioactive
• Radioactive process
• Half-life
• exponential decay curve
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3. Understanding the term
• Radioactivity refers to the particles which are
emitted from nuclei as a result of nuclear
instability
• Radiation is energy given off by some atoms in
the form of particles or rays
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4. Stable and Unstable Atom /Nuclei
• Atoms found in nature are either stable or unstable. An atom is
stable if the forces among the particles that make up the nucleus
are balanced.
• An atom is said to be unstable (radioactive) if these forces are
unbalanced, the nucleus is said to has an excess of internal energy
• Unstable atoms are called radionuclides. The instability of a
radionuclide’s nucleus may result from an excess of either neutrons
or protons
• The protons in a nucleus are all positively charged and so they repel
each other. This should push the protons apart but it doesn’t so
there must be another force which keeps the nucleus together. The
force is called the STRONG NUCLEAR FORCE
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5. Why certain nucleus is radioactive?
• Unstable nuclei cause radioactivity.
• Radioactivity is caused by unstable nuclei trying to
become stable by emitting particles and/or energy .
• The nuclei of radioactive substances are unstable due
to an unstable ratio of protons to neutrons.
• In stable atoms of relatively low atomic mass there are
approximately equal numbers of protons and neutrons
i.e. a proton to neutrons ratio of about 1:1.
• In stable atoms of higher atomic mass more neutrons
than protons are needed to keep the nucleus stable.
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6. Radioactive process
• In radioactive processes, particles or
electromagnetic radiation are emitted from the
nucleus. The most common forms of radiation
emitted have been traditionally classified as
alpha, beta and gamma radiation
• During the processes, a radionuclide tries to
attain stability
• Nuclear radiation occurs in other forms, including
the emission of protons or neutrons or
spontaneous fission of a massive nucleus
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7. Conservation of Laws
• Law of conservation of energy
• Law of conservation of mass
• Law of conservation of electric charge
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8. Law of conservation of mass
• States that
the total energy (mass energy + kinetic energy +
energy in other form) remains unchanged during
a radioactive process or nuclear transformation
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9. Law of conservation of mass number
• States that
The sum of mass numbers remains unchanged in
radioactive or nuclear processes
• The mass number of a neutron or proton is
assumed to be one and that of an electron
zero
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10. Law of conservation of electric charge
• States that
The total charge during a radioactive process or
nuclear transformation remains unchanged
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11. Half life
• Definition : Time taken for the number of radioactive
nuclide to disintegrate to half its initial value
• Radioactive substances will give out radiation all the
time, regardless of what happens to them physically or
chemically. As they decay the atoms change to
daughter atoms, until eventually there won't be any of
the original atoms left.
• Different substances decay at different rates and so will
last for different lengths of time. We use the half-life of
a substance to tell us which substances decay the
quickest. It is also the time it takes for the count-rate of
a substance to reduce to half of the original value.
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12. • We cannot predict exactly which atom will
decay at a certain time but we can estimate,
using the half-life, how many will decay over a
period of time.
• The half-life of a substance can be found by
measuring the count-rate of the substance
with a Geiger-Muller tube over a period of
time. By plotting a graph of count-rate against
time the half-life can be seen on the graph.
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13. Graph : Number of radioactive nuclei against time
taken to become half of its initial value
The longer the half-life of a substance the slower the
substance will decay and the less radiation it will emit
in a certain length of time.
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