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 occurring and man-made  All around us.

Naturally Occurring Radiation  Can 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  CT scanner, Linear Accelerator (Radiation Therapy), Mammography, etc.  Radiopharmaceuticals & Implanted sources  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: Radioactive Technetium 99 (Used in Nuclear Medicine) Stabilization takes approximately 60 hours Stable Ruthenium 99 Decays into..

Radioactivity- Half-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 :  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 ( 1/1000 th 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)5000 mrem  Lens of eye 15,000 mrem  Extremities (hands, etc.)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 = mrem  A dental x-ray = 1.5 mrem

Radiation Exposure- Taking it a Little Further  Radiation exposure rate :  Lets assume that we have a radioactive source whose measured activity is 10 mR/hr 3 inches from its surface  Radiation exposure:  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.  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. 10 mR/hr

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: 2 feet 4 feet 10 mR/hr2.5 mR/hr

Radioactive & Non- Radioactive 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 (Linear- accelerator) is not radioactive.  They were exposed to radiation but, are not radioactive as a result.  A patient having just completed a CT scan is not radioactive.  They too, were exposed to radiation but, are not radioactive.  The majority of imaging procedures do not result in a patient being radioactive.

Radioactive Patients- Radioactive Contamination  Radioactive contamination occurs when a radioactive material is somewhere that it was not intended to be.  Here are some examples:  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 Radiation- Should I be Worried?  Absolutely not!  The MS State Department of Health sets all radioactive standards.  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