Radiation Safety Training:
Fundamentals
University of Alaska Fairbanks
September 2013
Training Contents
1) Radiation safety fundamentals
•
Types of radiation
•
Terms and definitions
2) The principle of ALARA
•
Shielding
•
Detection of radiation and contamination
•
Principles of radiation protection
3) Properties of common radioactive materials
used in UAF research labs
Radiation Safety Fundamentals
 Radioactivity is a natural and spontaneous process
by which unstable radioactive atoms decay to a
different state and emit excess energy in the form of
radiation.
 Radioactive decay is a random process.
 The type of radiation emitted by radioactive
isotopes is known as ionizing radiation.
 Ionizing radiation has the ability to change the
physical state of atoms it interacts with,
causing them to become electrically charged or
IONIZED.
Radiation Safety Fundamentals (cont.)
 There are four main types of ionizing radiation.
o Alpha emission/alpha particles
o Beta emission/beta particles
o Gamma emission/gamma rays or X-rays
o Neutrons
 Some isotopes decay by a process known as
electron capture. For example, in 55Fe, the
nucleus absorbs an electron from the inner
orbital. The hole left in the inner orbital is filled
by an electron from an outer shell, resulting in an
energy loss. The energy loss is manifested in
the emission of auger electrons and x-rays.
Alpha emission 4alpha particles
 During alpha emission, a helium nucleus is ejected
from an atom
 Occurs when the neutron to proton ratio is too low
in a particular atom.
 The alpha particle is relatively large, slow-moving,
and has no charge.
Beta emission 4 beta particles
 During beta emission, a neutron is converted into a
proton, releasing an electron (the beta particle).
Occurs when neutron to proton ratio is too high in a
particular atom.
Beta particles can travel greater distances than
alpha particles and can penetrate some objects
to at least some degree.
Gamma emission 4gamma rays
 Gamma rays are emitted from the nucleus during
radioactive decay of some elements.
 X-rays are produced when electrons are removed
from atoms or the atom is rearranged.
 Gamma rays and x-rays have both electric and
magnetic properties (electromagnetic radiation).
 Gamma rays and x-rays can travel great distances,
and can readily penetrate the body.
Neutrons
 Neutrons are heavy, uncharged particles that
cause the atoms that they strike to become ionized.
 Typical sources are nuclear reactors or cyclotrons,
but neutrons can also generated from alpha emitters
mixed with beryllium (e.g., Radium-beryllium sources).
 Neutrons are dangerous mainly because they
create unstable atoms when they strike materials,
ionizing the atoms in the material (thus creating
radioactive isotopes in the material).
The Radioactive Games Parlor
 One way to think about the relative danger of
radioactive materials is to think of them as
being bowling balls, pin balls, or lasers.
The Radioactive Games Parlor
Alpha particles are like bowling balls.
o They crash into objects and are easily stopped by
the atoms in the object (e.g., the bowling pins).
o External to the body, this is not a problem, as the
outer layer of skin is dead. They can be stopped
by a piece of paper.
o Internally, alpha particles are very dangerous.
When they bombard an atom in a cell, they can
dislodge electrons, thereby ionizing the atom in
the cell.
The Radioactive Games Parlor
Beta particles are like pin balls.
o They are smaller than bowling balls, and may make it
past some atoms in the object before finally striking an
atom.
o Some lower-energy beta particles (14C, 3H) cannot
penetrate very far into the dead skin layer, and thus do
not pose much of an external hazard. Internally, they
can cause damage.
o Higher-energy beta particles (32P), can penetrate into the
living skin layer, and can cause a great deal of damage
internally.
The Radioactive Games Parlor
Gamma rays are like lasers.
o Gamma rays (and x-rays) are not particles. They
are wave energy, and can travel great distances
in air (much like a laser or other light beam).
o They may pass completely through an object
without striking a single atom.
o If they do strike an atom, their high energy will
dislodge an electron, thus ionizing the atom.
o Gamma emitters can readily cause damage both
externally and internally.
Radiation Terms and Definitions
Activity:
The curie is the unit of activity most often used in the United
States and expresses the rate of radioactive disintegrations per
unit time, based on the following:
One curie (Ci) :
3.7 x 1010 dps (disintegrations per second)
One millicurie (mCi) :
3.7 x 107 dps = 1 x 10-3 Ci
One microcurie (µCi):
3.7 x 104 dps or 2.22 106 dpm (1 x 10-6 Ci)
(dpm is disintegrations per minute)
Radiation Terms and Definitions (cont.)
Half-life (T½) is the amount of
time required for radioactivity
to decrease by one half.
Each radioisotope has a
unique half-life.
14C: 5,730 years
3H: 12.3 years
32P: 14.28 days
Half-life is a FIXED number. It
does not increase with
temperature or pressure, and
cannot be changed.
Radiation Terms and Definitions (cont.)
Radiation Exposure:
The Roentgen is the unit of radiation exposure in air
and is expressed as the amount of ionization per
unit mass of air due to X-ray or gamma radiation.
Absorbed Dose:
Radiation absorbed dose (rad) represents the
amount of energy deposited per unit mass of
absorbing material.
Radiation Terms and Definitions (cont.)
Dose Equivalent:
The measure of the biological effect of radiation requires a
variable called the quality factor (QF). Units are in rem or
millirem (mrem).
The quality factor takes into account the different degrees of
biological damage produced by equal doses of different types of
radiation.
The QF for beta, gamma, and x-ray radiation is 1.
The QF for neutron radiation is 10.
The QF for alpha radiation is 20.
Thus, alpha radiation is considered 20x more harmful than beta
or gamma radiation with regard to biological damage.
Radiation Terms and Definitions (cont.)
Damage from radiation depends on several factors such as
whether the exposure was from internal or external sources.
External Exposure comes from a source outside the body, such
as a medical x-ray. To do harm, the radiation must have enough
energy to penetrate the body.
If it does, three factors affect the radiation dose that the
individual will receive:
The amount of time the individual was exposed
The distance from the source of radiation
The amount of shielding between the individual and the
source of radiation.
Radiation Terms and Definitions (cont.)
Internal Exposure can occur when a radioisotope
enters the body by inhalation, ingestion, absorption
through skin, or through an open wound.
If this happens, any kind of radiation can directly
harm living cells.
Radioactive material inside human body
will cause an internal dose.
Radiation Terms and Definitions (cont.)
After internal exposure occurs, the damage caused
by the radiation depends on the following factors:
The amount of radioactive material deposited
into the body
The type of radiation emitted
The physical characteristics of the element
The half-life of the radioisotope
The length of time in the body
The Principle of ALARA
UAF is committed to the As Low As Reasonably
Achievable (ALARA) concept for working with
ionizing radiation.
Keeping exposures ALARA helps ensure that work
with ionizing radiation presents a very low risk to
faculty, staff, students and the general public.
The key components of ALARA are:
1. Minimizing and limiting use of ionizing radiation.
2. Shielding sources that emit radiation
3. Keeping work areas clean and free of
contamination by practicing good lab hygiene.
Radiation Protection: Shielding
Placing material
between the source
of radiation and
people working
nearby is considered
SHIELDING.
Radiation Protection: Shielding (cont.)
The following shielding guidelines can be used:
Alpha particles (α) stopped by paper
Beta particles (β) stopped by wood or Plexiglas
Gamma (γ) and X-rays (X) stopped by lead or
concrete
NOTE: do not use lead as shielding for 32P. When the
emitted beta particle strikes a high density material
such as lead, an x-ray is generated.
Neutrons (η) are absorbed by hydrogen-rich
materials (i.e. concrete, water, wax)
Detection of radiation and radioactive
contamination: using a Ludlum Geiger counter
1. Turn switch to “BAT”. Needle should go into “BAT TEST” area.
2. Turn switch to the lowest scale and turn on audio switch.
3. Make sure switch is set to “fast” response mode (F) rather
than “slow” (S).
4. Note meter “background” reading in a location away from
radiation source.
Detection of radiation and radioactive
contamination: using a Ludlum Geiger counter
(cont.)
4. Place probe (window face down) about ½ inch from surface
being surveyed. Do not let probe touch surfaces being
checked, as this can result in contamination of the probe.
5. Survey work area by slowly moving probe over surfaces,
listen to audible “clicks” from survey meter speaker.
6. Look for areas of contamination (higher than background
readings).
7. NOTE: the exposure limit for the general public is 2
mrem/hour.
NOTE: Geiger counters can be used for 32P and 125I. They will
NOT detect 3H, 14C, or 35S.
Radiation Protection: External Exposures to
Gamma Rays and X-rays
External exposure to gamma and x-ray radiation is controlled
by the following three factors:
Time:
Minimize exposure time by careful experimental design and
planning.
Do a “cold” run without isotopes in order to streamline your
protocol and become familiar with the steps involved.
Distance: Radiation intensity decreases as a the distance
from the source increases. Doubling the distance decreases
the radiation intensity by four-fold (inverse square law).
Shielding: Use lead as shielding material.
Radiation Protection: External Exposures
to Beta Radiation
The main concern with beta radiation is skin
exposure, as some beta particles can penetrate the
epidermis and reach the live cell layer.
Time and distance methods of exposure reduction
for x-rays and gamma rays listed above also apply to
beta radiation.
Shielding: use >½” thick Plexiglas. Do not use lead.
Some beta radiation produces x-rays
(Bremsstrahlung or “braking radiation”) when
interacting with lead.
Radiation Protection: Internal Exposures
to Radiation
Routes of internal exposure
1. Absorption
2. Inhalation
3. Ingestion
4. Injection
If you every suspect that you may have internal
contamination with radioactive materials, contact the
UAF Radiation Safety Officer immediately (474-6771).
Radiation Protection: Internal Exposures
to Radiation (cont.)
Prevent absorption :
1. Change gloves frequently.
2. Avoid touching your eyes, nose or mouth while
conducting experiments.
3. Monitor your work area with survey meter or regular
wipe testing.
4. Wash your hands after removing gloves and before
leaving the lab. If appropriate, check your hands and
lab coat with a survey meter (for 32P or 125I only).
Radiation Protection: Internal Exposures
to Radiation (cont.)
Prevent inhalation:
1. Use fume hood when you are using any volatile
sources of radioactivity.
Prevent ingestion:
1. Never eat or drink in the laboratory.
2. Never store food in refrigerators or freezers or other
areas designated for chemical or radioactive material
storage.
Radiation Protection: Internal Exposures
to Radiation (cont.)
Prevent injection:
1. Practice safe sharps handling. Do not recap needles
and dispose of sharps in a sharps container (labeled
with “Caution, Radioactive Materials” label or tape.
2. Be careful handling glass that is contaminated with
radioactive materials. Use plastic lab ware whenever
possible.
Radioactive materials used at UAF
Carbon-14 (C-14, 14C)
Half-life:
5730 years
Type of emission:
pure beta
Energy (average/maximum): 0.049/0.156 MeV
Max range in air:
24 cm
Max range in H2O:
0.28 mm
Hazard:
Internal
Detection method:
Wipe tests & Liquid Scintillation Counting (LSC)
(98% efficient); NO Geiger counter!
Radioactive materials used at UAF (cont.)
Hydrogen-3 (3H, tritium)
Half-life:
12.28 years
Type of emission:
pure beta
Energy (average/maximum): 5.7/18.6 keV
Max range in H2O:
6x10-3nm
Hazard:
Internal
Detection:
Wipe tests & LSC
(60-65% efficient); NO Geiger counter!
Radioactive materials used at UAF (cont.)
Sulfur - 35 (35S)
Half-life:
87.44 days
Type of emission:
pure beta
Energy (average/maximum): 0.049/0.167 MeV
Max range in air:
26 cm
Max range in H2O:
0.32 nm
Hazard:
Internal
Detection:
Wipe tests & LSC
(97% efficient); NO Geiger counter!
Radioactive materials used at UAF (cont.)
Iron- 55 (55Fe)
Half-life:
Type of emission:
2.7 years
X-rays, auger
electrons
6 keV/5.2 keV
0.15 cm
0 cm
Internal (blood)
Energy (gamma/electrons):
Max range in air:
Max range in tissue:
Hazard:
Detection:
Wipe tests & LSC (0-400)
(35% efficient); NO Geiger counter!
Radioactive materials used at UAF (cont.)
Phosphorus -32 (32P)
Half-life:
Type of emission:
14.28 days
pure beta
(but may generate x-rays if lead is used as shielding)
Energy (average/maximum):
Max range in air:
Max range in H2O:
Hazard:
0.695/1.71 MeV
790 cm
0.76 cm
External skin,
internal
Detection:
Survey meter, wipe tests & LSC
(100% efficient); Geiger counter is very useful.
Radioactive materials used at UAF (cont.)
Iodine -125 (125I)
Half-life:
Type of emission:
60.14 days
low-energy gamma,
x-rays
Energy (average/maximum): MeV
Max range in air:
cm
Max range in H2O:
cm
Hazard:
External, internal
(thyroid)
Detection:
Survey meter, wipe tests & gamma counter; Geiger
counter can be useful if it has a gamma probe.
Radioactive materials used at UAF
Relative toxicity ranking of radioisotopes is based upon
internal uptake through ingestion, inhalation, or
absorption of radioisotopes.
High toxicity
None
Medium-high
toxicity
125I
(gamma)
137Cs (gamma)
Low-medium
toxicity
32P
(beta)
35S (beta)
14C (beta)
Low toxicity
3H
(beta)
55Fe (x-rays, auger electrons)
Thank you!