University of Alaska Fairbanks September 2019 Training Contents Radiation safety fundamentals Types of radiation Terms and definitions The principle of ALARA Shielding Detection of radiation and contamination ID: 915638
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Slide1
Radiation Safety Training: Fundamentals
University of Alaska Fairbanks
September 2019
Slide2Training
Contents
Radiation safety fundamentalsTypes of radiation
Terms and definitions
The principle of ALARA
Shielding
Detection of radiation and contamination
Principles of radiation protection
Properties of common
radioactive materials
used in UAF research labs
Slide3Radiation 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
.
Slide4Radiation Safety Fundamentals (cont.)
There
are four main types of ionizing radiation.
Alpha emission/alpha particles
Beta emission/beta particles
Gamma emission/gamma rays or X-rays
Neutrons
Some isotopes decay by a process known as
electron capture
. For example, in
55
Fe, 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
.
Slide5Alpha 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
a c
harge of +2.
Slide6Beta 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.
Slide7Gamma 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.
Gamma emission
4
gamma rays
Slide8Neutrons
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).
Slide9The 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.
Slide10The Radioactive Games Parlor
Alpha particles are like
bowling balls
.
They crash into objects and are easily stopped by the atoms in the object (e.g., the bowling pins).
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.
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.
Slide11The Radioactive Games Parlor
Beta particles are like
pin balls. They are smaller than bowling balls, and may make it past some atoms in the object before finally striking an atom.
Some lower-energy beta particles (14C,
3
H) cannot penetrate very far into the dead skin layer, and thus do not pose much of an external hazard. Internally, they can cause damage.
Higher-energy beta particles (
32
P), can penetrate into the living skin layer, and can cause a great deal of damage internally.
Slide12The Radioactive Games Parlor
Gamma rays are like
lasers. 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).
They may pass completely through an object without striking a single atom.
If they do strike an atom, their high energy will dislodge an electron, thus ionizing the atom.
Gamma emitters can readily cause damage both externally and internally.
Slide13Radiation 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 10
10
dps
(disintegrations per second
)
One
millicurie
(
mCi
)
:
3.7
x 10
7
dps
= 1 x 10
-3
Ci
One
microcurie
(
µCi):
3.7
x 10
4
dps
or 2.22 10
6
dpm (1 x 10
-6
Ci
)
(dpm is disintegrations per minute)
Slide14Radiation Terms and Definitions (cont.)
Half-life
(T
½)
is the amount of time required for
radioactivity
to decrease by one half.
Each
radioisotope has a unique
half-life.
14
C: 5,730 years
3
H: 12.3 years
32
P: 14.28 days
Half-life is a FIXED number. It does not increase with temperature or pressure, and cannot be changed.
Slide15Radiation 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.
Slide16Radiation 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.
Slide17Radiation 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.
Slide18Radiation 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.
Slide19Radiation 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
Slide20The 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:
Minimizing and limiting use of ionizing radiation.
Shielding sources that emit radiation
Keeping work areas clean and free of contamination by practicing good lab hygiene.
Slide21Radiation Protection: Shielding
Placing material between the source of radiation and people working nearby is considered
SHIELDING.
Slide22Radiation 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
32
P. 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)
Slide23Detection of radiation and radioactive contamination: using a Ludlum Geiger counter
Turn switch to “BAT”. Needle
should go
into “BAT TEST” area.
Turn switch
to the lowest
scale and turn
on audio switch
.
Make sure switch is set to “fast” response mode (F) rather than “slow” (S).
Note meter “background” reading in a location away from radiation source.
Slide24Detection of radiation and radioactive contamination: using a Ludlum Geiger counter (cont.)
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.Survey
work area by slowly moving probe over surfaces, listen to audible “clicks” from survey meter speaker
.
Look for areas of contamination (higher than background readings).
NOTE: the exposure limit for the general public is 2
mrem
/hour.
NOTE: Geiger counters can be used for
32
P and
125
I. They will NOT detect
3
H,
14
C, or
35
S.
Slide25Radiation 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.
Slide26Radiation Protection: External Exposures to High-Energy Beta Radiation
The
main concern with high-energy beta radiation (i.e., 32P) is skin exposure, as it can penetrate the epidermis and reach the live cell layer. Low energy beta-emitters such as
14C and 3
H are mainly an internal hazard.
Time
and
distance
methods of exposure reduction for x-rays and gamma rays listed above also apply to
high-energy 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.
Slide27Radiation Protection: Internal Exposures to Radiation
Routes of internal exposure
AbsorptionInhalation
Ingestion
Injection
If you every suspect that you may have internal
contamination with radioactive materials,
contact
the UAF
Radiation Safety Officer
immediately (474-6771).
Slide28Radiation Protection: Internal Exposures to Radiation (cont.)
Prevent
absorption :Change gloves
frequently. Avoid touching your eyes, nose or mouth while conducting
experiments.
Monitor
your work area with survey
meter or regular wipe testing.
W
ash
your
hands after removing gloves and before leaving the lab. If appropriate,
check your hands and lab coat with a survey
meter (for
32
P or
125
I).
Slide29Radiation Protection: Internal Exposures to Radiation (cont.)
Prevent
inhalation:Use fume hood when you are using any volatile sources of
radioactivity of if aerosols will be generated while working with it.Prevent
ingestion:
Never eat
or
drink
in the laboratory.
Never
store food in refrigerators or freezers or other areas designated for chemical or radioactive material storage
.
Slide30Radiation Protection: Internal Exposures to Radiation (cont.)
Prevent
injection:Practice safe sharps handling. Do not recap needles and dispose of sharps in a sharps container (labeled with “Caution, Radioactive Materials” label or tape.
Be careful handling glass that is contaminated with radioactive materials. Use plastic lab ware whenever possible.
Slide31Radioactive 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
H
2
O
: 0.28
mm
Hazard
: Internal
Detection method
:
Wipe
tests & Liquid Scintillation Counting (
LSC)
(98% efficient);
NO Geiger counter!
Slide32Radioactive materials
used at UAF (cont.)
Hydrogen-3 (3
H, tritium)
Half-life
:
12.28
years
Type of emission
: pure beta
Energy (average/maximum)
: 5.7/18.6
keV
Max
range in
H
2
O
: 6x10
-3
nm
Hazard
: Internal
Detection
:
Wipe
tests &
LSC
(60-65% efficient);
NO Geiger counter!
Slide33Radioactive 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
M
ax
range in
air
: 26 cm
M
ax
range in
H
2
O
: 0.32
nm
Hazard
: Internal
Detection
:
Wipe
tests & LSC
(97% efficient);
NO Geiger counter!
Slide34Radioactive materials
used at UAF (cont.)
Iron- 5
5 (55Fe)
Half-life
:
2.7 years
Type of emission
: X-rays, auger electrons
Energy (gamma/electrons)
: 6
keV
/5.2
keV
M
ax
range in
air
: 0.15 cm
M
ax
range in
tissue
: 0 cm
Hazard
: Internal (blood)
Detection
:
Wipe
tests &
LSC (0-400)
(35% efficient);
NO Geiger counter!
Slide35Radioactive materials
used at UAF (cont.)
Phosphorus -32 (32
P)
Half-life
:
14.28
days
Type of emission
: pure beta
(but may generate x-rays if lead is used as shielding)
Energy (average/maximum)
: 0.695/1.71
MeV
M
ax
range in
air
: 790
cm
M
ax
range in
H
2
O
: 0.76 cm
Hazard
: External skin, internal
Detection
:
Survey meter, wipe tests
&
LSC
(100% efficient);
Geiger counter is very useful.
Slide36Radioactive materials
used at UAF (cont.)
Iodine -125 (125
I)
Half-life
:
60.14
days
Type of emission
: low-energy gamma, x-rays
Energy (average/maximum)
:
MeV
M
ax
range in
air
:
cm
M
ax
range in
H
2
O
: cm
Hazard
: External, internal (thyroid)
Detection
:
Survey meter, wipe tests
&
gamma counter;
Geiger counter can be useful if it has a gamma probe.
Slide37Radioactive materials used at UAF
Relative toxicity ranking of radioisotopes is based upon internal uptake through ingestion, inhalation, or absorption of radioisotopes.
High
toxicity
Medium-high toxicity
Low-medium
toxicity
Low toxicity
None
125
I
(gamma)
137
Cs (gamma)
32
P (beta)
35
S (beta)
14
C (beta)
3
H (beta)
55
Fe (x-rays, auger
electrons)
Slide38Thank you!