Transcript Unit C - Grand Junction High School

Unit C
RADIOACTIVITY: NATURAL AND ARTIFICIAL (HANK 9:57)
C.1 Half-Life: A Radioactive
Clock

It is useful to know what the
rate of decay of a
radioisotope is to predict:

The time a radioisotope
used for medical
purposes will remain in
the body.

the length of storage for
hazardous materials.

Ages of ancient
organisms/civilizations.
Carbon Dating


The use of radiocarbon
for dating began some
50 years ago and was
based on the
detection of the decay
of the isotope C-14
which is formed when
cosmic rays react with
nitrogen gas to form a
radioactive carbon
dioxide molecule.
There are one of these
for every million million
atoms of carbon 12.
Half-Lives

The rate of decay for
radioisotopes is measured in
half-lives.

A half-life is the amount of time
it takes for one-half of a
radioisotopic sample to decay
into something else.

For instance, if H-3 has a half-life
of 12.3 years, and you have a
100 gram sample of it, how
many grams would be left in
36.9 years?
Variable half-lives

Half-lives can vary from a few seconds to a few
billion years.

After 10 half-lives, only 1/10,000th or 0.1% will
remain.

If you are considering very large numbers of
atoms, ie: 6.02 x 1023 , then even after 10 half-lives
there is still a considerable amount of the
substance left.
C.3 Benefits of
Radioisotopes

Ionizing radiation given off by certain
radioisotopes can be used in nuclear
technology such as:

Tracer studies where the radiation is used
to track cellular abnormalities, locate
damaged areas and aid in therapy.

Irradiation, where the radiation is used as
an energy source to treat medical
conditions like tumors or leukemia and to
sterilize medical equipment/seal plastic
containers.
Tracers

Radioisotopes called
tracers can be used to
detect certain
elements that are
known to collect in
specific places in the
body.

Cesium-137 is used as
an external source to
treat shallow tumors.
Radiation Detectors

Liquid Scintillation Counters

Devices called
scintillation counters
detect entering
radiation as light
emitted by the excited
atoms when hit with
the radiation.
Solid-state detectors
monitor the movement
of electrons through
semiconductors like
silicon.

A cloud chamber is a
glass filled with
supersaturated water
vapor. As radiation
passes through the
chamber, the vapor
condenses on the ions
formed leaving a white
particulate trail.
Artificial Radioactivity

Also called
transmutation,
Rutherford was the
first to create an
element different
from the original by
bombarding helium
with nitrogen to
form oxygen and
hydrogen.


From 1940 to 1961
Glenn Seaborg and
coworkers discovered
10 new element;
numbers 94-103
None occur naturally.
All were made by highenergy bombardments
of heavy nuclei on
various particles.
Glenn Seaborg and John F Kennedy