Periodicity
http://www.phy.bris.ac.uk/groups/particle/PUS/A-level/Standard_Model.htm
Nuclear Radiation
If there was any remaining doubt the discovery of nuclear radiation ended any consideration that
atoms were indivisible. Not only could electrons be removed, the nucleus itself could fall apart!
α Alpha radiation 42 𝐻𝑒 2+ emitted from the nucleus
β Beta radiation 𝑒 − emitted from the nucleus, or 𝑒 +
γ Gamma radiation E = hν
Antoine Becquerel accidentally discovered
Uranium salts because film placed next to the salts
became exposed without benefit of light.
In 1898, Marie Curie discovered that pitchblend, a uranium ore, emits more
radiation than uranium itself. She deduced that this ore contains, in very
small quantities, one or more elements much more active that uranium.
With the assistance of her husband Pierre Curie and after two years of effort,
she arrived at isolating two new elements: Polonium (named thus in tribute
to her homeland) and Radium. It was then that Marie Curie invented the
http://molaire1.perso.sfr.fr/e_radioactiv.html
word "radioactivity".
National Council on Radiation Protection &
Measurements (2009, March 5). Medical
Radiation Exposure Of The U.S. Population
Greatly Increased Since The Early 1980s.
ScienceDaily. Retrieved November 23, 2012,
from http://www.sciencedaily.com
/releases/2009/03/090303125809.htm
In alpha decay the nucleus
spontaneously splits into a daughter
particle and a helium nucleus.
4
2+
𝐻𝑒
2
Examples of alpha decay
To write the equation for alpha decay,
use the following formula:
Quiz
What is an alpha particle?
A helium nucleus: 42𝐻𝑒 2+
How do you write the greek letter for an
alpha particle?
α
Write the balanced nuclear equation
for an isotope of 238U which undergoes alpha decay.
Is alpha decay a chemical reaction or a nuclear reaction?
A nuclear reaction.
(http://abyss.uoregon.edu/~js/ast123/lectures/lec07.html
not in our text book)
Beta decay: In beta decay either an
electron or a positron are expelled from
the nucleus. A neutrino or antineutrino
is also expelled.
Notice that in beta decay the number of protons
increases. The electrons do not come from the electron
cloud, which is why the neutrino or antineutrino is also
expelled.
(gamma radiation may also be expelled)
Neutrinos have no charge and almost
no mass and were predicted by Wolfgang
Pauli to explain why beta decay didn’t
violate the law of conservation of matter
and energy.
http://curriculum.cna.ca/curriculum/cna_radia
tion/beta_decayeng.asp?bc=Beta%20Decay&pid=Beta%20De
cay A cool animation of beta decay.
http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino.html
Radioactive isotopes which emit beta particles are called beta emitters.
Below is list of some beta emitting radioactive isotopes.
•Carbon-14 is used in carbon dating artifacts and as a medical tracer
•Cesium-137 is used in brachytherapy to treat various types of cancer and to
measure the flow of oil in pipelines.
•Cobalt-60
•Hydrogen-3 (tritium)
•Iodine-129
•Iodine-131 is used as a medical tracer
•Nickel-63 is used to detect explosives, and in voltage regulators and
current surge protectors in electronic devices.
•Promethium-147 is used in electric blanket thermostats, and to gauge
thickness of thin plastics, thin sheet metal, rubber, textile and paper.
•Sodium-24 is used to locate leaks in industrial pipelines, oil well studies
and in medical diagnostics.
•Strontium-90 is used as a power source for weather satellites and navigation buoys
•Sulphur-35 is used in manufacturing sensors and medical treatments.
•Technetium-99m is used in nuclear medicine as a radioactive tracer
•Thallium-204 is used to measure the dust and pollutant levels on filter paper,
and in gauges used to measure the thickness of plastics, sheet metal, rubber,
textiles, and paper.
http://curriculum.cna.ca/
curriculum/cna_radiation
/beta_emitterseng.asp?bc=Common%2
0Beta%20Emitters&pid=
Common%20Beta%20E
mitters
Gamma radiation.
http://faculty.virginia.edu/metals/cases/prescott2.html Interesting article about technetium.
Penetrating power of alpha, beta, and
gamma radiation.
http://www.frankswebspace.org.uk/ScienceAndMaths/physics/physicsGCE/D1-3.htm
http://sciencecity.oupchina.com.hk/npaw/student/glossary/ionizing_power.htm
http://library.thinkquest.org/C006669/data/Chem/atomic/development.html
Review
1. Which type of radiation has no
charge, and is high energy?
2. Which type of radiation is the size of
an electron, is either positive or
negative?
1. gamma
2. beta
3. Which type of radiation is basically a
helium nucleus?
3. alpha
4. Which two types of radiation
normally occur together?
4. Beta and gamma, also neutrinos
Half- life
Radioactivity is spontaneous. It occurs regardless of the temperature,
surface area, or any of the usual things which make chemical reactions
occur. The rate depends only on the amount of “parent nuclide” present.
We report the rate as a “half life”
The half life depends upon the
stability of the nucleus. The
more stable the nucleus, the
longer the half life.
At the end of the period of time
called “half life” there is half as
much of the “parent isotope” as
at the beginning.
½ → ¼ → 1/8 → 1/16 → 1/37
0.5 → 0.25 → 0.13 → 0.06 → 0.03
T → 2T →
3T → 4T → 5T
Half life equations
•AE is the amount of substance left
•A0 is the original amount of substance
•t is the elasped time
•t1/2 is the half-life of the substance
Other variations on the half-life equation are as follows:
An example problem is if you originally had 157 grams of carbon-14 and the
half-life of carbon-14 is 5730 years, how much would there be after 2000
years?
There would be 123 grams left.
http://library.thinkquest.org/10429/low/nuclea
r/nuclear.htm
How can we predict which atoms will decay and
what type of decay they will experience?
Alpha decay
reduces the
atomic number
by two protons
and two
neutrons.
So much
energy is
released that
gamma
radiation is
frequently
given off as
well.
http://mail.rdcrd.ab.ca/~smoles
ky/physics30/5Matter/day_8%2
0objective.htm
http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Nuclear-Chemistry/chemprime/CoreChem3ANuclear_Stability-745.html
http://mail.rdcrd.ab.ca/~smolesky/physics30/5Matter/day_8%20objective.htm
How can we predict which atoms will decay and
what type of decay they will experience?
Beta decay will increase the atomic
number so the daughter nuclide
will be more stable than the parent.
http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/NuclearChemistry/chemprime/CoreChem3ANuclear_Stability-745.html
Small atoms with too many protons will
undergo electron capture or positron emission
to obtain stable nucleii
http://mail.rdcrd.ab.ca/~smolesky/physics30/5
Matter/MatterPics/formulas/positron.gif
Gamma radiation is thought to be a release of nuclear energy. No
apparent change to the number of protons or neutrons is necessary for
gamma radiation.
For the original images and explanations…
http://mail.rdcrd.ab.ca/~smolesky/physics30/5Matter/MatterPics/radioactive%
20decay/AlphaBetaGamma2.jpg
More practice
Example 1: 238-Uranium undergoes alpha decay
Example 2: 234-Pa is produced by a beta negative decay
Label where alpha and beta decay are most likely.