Transcript B: Radioactive Decay - Grand Junction High School

B: Radioactive Decay
There are about 350
isotopes of 90
elements found in our
solar system.
Of these, about 70 are
radioactive.
Naturally occurring
radioisotopes
(elements with atomic
nos. of 83 or less)
emit background
radiation in relatively
small amounts.
B.2 Natural Radioactive Decay
Alpha particles have
two protons and two
neutrons.
They are massive—
8000 x heavier than
beta particles, but can
only cause damage
over very short
distances.
They are easily
blocked, even by skin.
Radium-226 loses
two protons, so it’s
atomic number
drops from 88 to
86.
Atoms of 2
elements, He and
Rn can be formed.
Beta particles are fastmoving negatively charged
particles released during
radioactive decay.
During beta decay, a
neutron changes into a
proton and an electron.
The proton remains in the
nucleus but the electron
(beta particle) is ejected at
high speed.
A third particle called an
antineutrino is also
released.
A beta particle has a mass number of 0
and an atomic number (nuclear charge) of
-1.
The overall result of beta emission is that
a neutron is converted into a proton.
Notice that the atomic number increases
and Radium turns into Actinium.
v
Gamma emissions
do not change the
mass or charge
balance in a
nuclear equation
because the rays
have no mass or
charge.
Of the three
emissions: alpha, beta
and gamma, alpha
radiation is the most
damaging at short
range but easy to
protect against. Beta
and gamma do less
damage over a long
range but it’s harder
to protect against
them.
New isotopes created
from radioactive decay
can also be
radioactive and
undergo further
decay.
Eventually, the result
will be a stable atom.
In this case Uranium
decays into stable
lead—it just takes 14
steps to do so.
B.3 Ionizing Radiation—How Much
is Safe?
Radiation can be measured with a Geiger
counter in counts per minute (cpm).
It can also be measured in rems when
evaluating its effect on humans. Rems
stand for Roentgen equivalent man and
measures the ability of radiation to cause
ionization in human tissue.
A third way to measure radiation levels is
in Becquerels.
1986 Nuclear Meltdown at
Chernobyl
The accident released 1.1 x 10
19 Becquerels of radioactive
material (one Becquerel is one
molecule undergoing radioactive
decay per second).
About 116,000 people were
evacuated from the area around
the plant, and 134 were
hospitalized for acute radiation
sickness. The 31 deaths were
mainly among fire fighters who
fought the first fire without
radiation protection.
The major health hazards came
from iodine 131 (I-131) , which
accumulates in the thyroid gland,
and cesium 137 (Cs-137), which
gathers in bone. The accident
released 1,760 * 10 15
Becquerels of I-131 and 85 * 10
15 Becquerels of Cs-137.
Radiation Damage Now and Later
Ionizing radiation
tears molecules apart
by breaking chemical
bonds.
Damage to proteins
and nucleic acids are
particularly
detrimental because
of their importance in
body functions and
structures.
Nucleic acids in DNA
can be damaged in
two ways:
Mutations result in the
synthesis of altered
proteins. Can result
in killing the cell or if
it’s a sperm or ovum,
cause birth defects.
If the exposure is high
enough and proteins
cannot be
synthesized, death
follows.
Sources of Radiation
Cosmic rays
Radioisotopes from rocks and soils
Radioisotopes from the atmosphere
Fallout from nuclear weapons testing
Increased exposure to cosmic rays
through air travel.
Radioisotopes released from nuclear
power technologies.
Radioisotopes in the Environment
On average, people in
the U.S. receive above
360 mrem per year, of
which 82% is naturally
occurring.
Radiation standard by
fed. Gov. is 500 mrem
per year.
Maximum exposure
recommended by
federal government is
5000 mrem (.5 rem)
per year.
Radioisotopes in the Human Body
Thyroid I-131
Lungs
Rn-222 U-238
Muscles K-40
Pt-239
Kr-85
P-32
C-14
Cs-137
Liver
Co-60
Bones
Ra-226 Sr-90
Radon in Homes
Radon is a decay
product of uranium
and is always present
in the atmosphere.
Some radon dissolves
into groundwater from
the soil.
Inhaled radon gas
goes through
radioactive decay
causing health
problems such as lung
cancer.
The Discovery of Radioactivity
Use with worksheet (9:10)
Becquerel Rays (9:10)