Understanding
Radioactivity
The Basics
This Course
 This
course is intended to provide a very
basic understanding of radiation,
radioactivity, and interacting with
radioactive patients.
 This course is not intended to serve as
health physics training.
Environmental Health & Safety/
Radiation Safety
Radiation is:
 The
process in which energy is released in
the form of waves or particles from an
unstable atom.
 Naturally
 All
occurring and man-made
around us.
Naturally Occurring Radiation
 Can
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
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
come from many sources:
The ground that we walk on
The mountains we climb
The food we eat
The water we drink
The air we breathe
Outer space
And, even from ourselves
Man-Made Radiation

Below are a few examples:

X-ray machines

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Radiopharmaceuticals & Implanted sources

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CT scanner, Linear Accelerator (Radiation Therapy),
Mammography, etc.
Tc-99 and I-131 (Nuclear Medicine), I-125 and Cs-131
(Radiation Oncology)
Industrial sources

Co-60 and Ir-192 (weld evaluation)
Radiation Exposure Rate &
Radiation Exposure


As we progress through this course, you will
see mR/hr and mrem being referenced.
Note:


mR/hr refers to the rate of radioactivity
measured in air(in other words, how much
radiation is being released from the source)
mrem refers to the amount of radiation an
individual is exposed to.
Radioactivity




Can be described as the process in which an
unstable atom releases energy and/or particles in an
attempt to reach stabilization (non-radioactive form).
This process is referred to as radioactive decay.
This can take minutes or years to complete;
depending on the substance (isotope) in question.
Example:
Decays into..
Radioactive
Technetium 99
(Used in Nuclear Medicine)
Stable
Ruthenium 99
Stabilization takes approximately 60 hours
RadioactivityHalf-Life

All radioactive substances have a “Half-Life”.



Note that not all substances have the same “Half-Life”.
Radioactive “Half-Life” can be defined as the amount of time
for a radioactive substance to decay to half of its original
radioactivity.
Here is an example:
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Technetium-99 (Nuclear Medicine) has a “Half-Life” of 6 hours.
If we measure 10 mR/hr initially (At the source)
In 6 hours it would measure 5 mR/hr
In 12 hours it would measure 2.5 mR/hr
In 18 hours it would measure 1.25 mR/hr
As you can see, the amount of radioactivity diminishes over
time.
A general rule of thumb is that radioactive substances require
ten half-lives to decay almost entirely (1/1000th of original activity).
Radiation Exposure & Exposure
Limits



We are all exposed to certain amounts of radiation
every day.
The annual average natural radiation exposure in the
United States is approximately 310 mrem for
members of the general public.
Occupational radiation exposure limits are as follows
(18 yrs of age or older):




Whole body (deep dose)
Lens of eye
Extremities (hands, etc.)
5000 mrem
15,000 mrem
50,000 mrem
General public radiation exposure limit:

100 mrem
Radiation Exposure cont.
 Here
are two examples (for perspective)
of common medical procedures that
result in radiation exposure but, not a
“Radioactive” patient.

A single-view chest x-ray = 10 -15 mrem

A dental x-ray = 1.5 mrem
Radiation ExposureTaking it a Little Further

Radiation exposure rate:


Radiation exposure:


Lets assume that we have a radioactive source whose
measured activity is 10 mR/hr 3 inches from its surface
Now, we place our hand at the same distance (3 inches) from
the radioactive source and keep it there for one hour.
Radiation Exposure Rate & Radiation Exposure are
equivalent.
 10 mR/hr _ 10 mrem
However

If we take the same source but,
leave our hand over it (3 inches)
for 1 minute, we only get .17mrem
of radiation exposure.
10 mR/hr

It would take 500 hours at this exposure rate and distance
to meet the annual maximum whole body exposure limit of
5000 mrem.

And, it would take 10 hours to reach the maximum
allowable exposure (100 mrem) for the general public.
Radioactivity and Distance
Relationship

The Inverse Square Law teaches us that intensity at a
given point is reduced to ¼ of its value when the original
measured distance is doubled.

Example:
4 feet
2 feet
10 mR/hr
2.5 mR/hr
Radioactive & NonRadioactive Patients

A Nuclear Medicine patient having just completed a cardiac stress study
typically emits radiation at a rate of approximately 2mR per hour at one
meter (approximately 3 feet).

A Radiation Oncology patient with an eye plaque usually emits radiation at a
rate of approximately 2 mR per hour at one meter (from the eye plaque, not
the entire patient)

A patient having just completed a Radiation Therapy session (Linearaccelerator) is not radioactive.
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A patient having just completed a CT scan is not radioactive.

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They were exposed to radiation but, are not radioactive as a result.
They too, were exposed to radiation but, are not radioactive.
The majority of imaging procedures do not result in a patient being
radioactive.
Radioactive PatientsRadioactive Contamination

Radioactive contamination occurs when a radioactive
material is somewhere that it was not intended to be.

Here are some examples:
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Radioactive material spill
Radioactive material leakage
Radioactive material release from a patient (blood and excreted
waste)
Not all radioactive patients are considered to be a
contamination risk.

A select few procedures result in potential radioactive
contamination for a short period of time.


For those few; patients are given very specific instructions prior to their
procedure.
Those that pose the greatest risk are treated as in-patients and are
released once the risk has diminished.
Working Around RadiationShould I be Worried?

Absolutely not!

The MS State Department of Health sets all
radioactive standards.
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This includes both radiation exposures and specific
patient release requirements.
These standards are very conservative (Low levels).
They were put into place in order to ensure that no
one in the general public is in any danger of excessive
radiation exposure or radioactive contamination as a
result of being near radiation and/or radioactive
patients.
Our staff are diligent in adhering to these
standards.
What to Take Away From This?

We are around many different sources of radiation
every day.

Not all procedures involving radiation result in a
radioactive patient.

Most radioactive patients pose no exposure or
contamination threat.
Radiation Safety Contacts
 Robert
Nelson
 Mark Langston
 Dale Tallman
 Logan Cowart
984-1989
815-1993
815-1989
815-5128