RADIATION PROTECTION
TRAINING
Charles F. Reindl, M.S., C.H.P.
Certified Diagnostic Radiological Physicist
Radiation Safety Officer
Tulane University
Office of Environmental Health & Safety
Table of Contents:
Section 1
Radiological Fundamentals:
A.
Matter
B.
Radioactive Decay & Types of
Ionizing Radiation
C.
Radiation Interactions
D.
Radiation Exposure Units
E.
External Exposure Measurement
F.
Biological Effects of Radiation
G.
Federal Limits for Occupational
Exposure to Ionizing Radiation
Section 2
Instrumentation & Radiation/Contamination
Monitoring:
A.
Gas-Filled Detectors
B.
Radiation Monitoring
C.
Contamination Monitoring
D.
Survey Frequency
E.
Other Laboratory Rules
Section 3
Exposure Reduction:
A.
Inverse Square Law
B.
Time
C.
Shielding
Section 4
Radioactive Decay & Specific Hazards:
A.
Decay Equation
B.
Radioiodine
C.
Tritium
D.
Phosphorus-32
Section 5
Radioactive Materials Disposals:
A.
Decay to Background Levels
B.
Sewer Disposal
C.
Incineration
D.
Transfer to a Licensed Disposal Firm
Radiological Fundamentals
Section 1
Radiological Fundamentals
A.
B.
C.
D.
E.
F.
G.
Matter
Radioactive Decay & Types of Ionizing Radiation
Radiation Interactions
Radiation Exposure Units
External Exposure Measurement
Biological Effects of Radiation
Federal Limits for Occupational Exposure to
Ionizing Radiation
Section 1-A
Matter
A. Matter
1.
All matter is composed of atoms, and each atom is made up of
three fundamental particles.
Symbol
Name
Mass
Charge
p+
Proton
1 amu
+1
e-
Electron
0.0005 amu
-1
n
Neutron
1 amu
0
Section 1-A, continues
Matter
An amu (Atomic Mass Unit) is approximately equal to the mass of
a proton or neutron and numerically equal to 1.66 E-24 grams.
The mass of an electron is negligible in comparison. Any atom
can be symbolized by the following notation:
2.
AX
Z
•
where:
•
X = The chemical symbol of the element which is
determined by the number of protons in its nucleus.
•
Z = The Atomic Number, equal to the number of protons in
its nucleus.
•
A = The Mass Number, equal to the number of protons plus
neutrons in its nucleus.
Section 1-A, continues
Matter
There are three isotopes of the element hydrogen, symbolized "H.“
3.
4.
a.
The first isotope is H-1, the most common type of hydrogen with a
natural abundance of 99.985%.
b.
The second isotope is H-2, heavy hydrogen, also called deuterium
with a natural abundance of 0.015%.
c.
The final isotope is H-3, radioactive hydrogen, also called tritium.
All three are isotopes of hydrogen and H-3, since it is radioactive,
is also called a radioisotope or a radionuclide. In general,
isotopes are atoms with the same number of protons (same Z),
but different numbers of neutrons (different A).
Section 1-B
Radioactive Decay & Types of Ionizing Radiation
B. Radioactive Decay and Types of Ionizing Radiation
Radioactive atoms become more stable by emitting one or more of the
following most common types of ionizing radiation:
1.
Alpha (α): A high speed helium nucleus (4He2++) with no orbital
electrons and a resulting +2 charge overall.
2.
Beta (β): A high speed electron (e-) with a -1 charge overall.
3.
Gamma (γ): An electromagnetic wave with no mass and no
charge overall.
Section 1-C
Radiation Interactions
C. Radiation Interactions
1.
All ionizing radiations produce ion pairs as they travel through air, detection
devices, shielding, or body tissue. These ion pairs are simply target atoms
whose electrons have been stripped off by the ionizing radiation. If Y is any
target atom:
Y + ionizing radiation -----> Y+ + e- where the two products are the ion
pair. The formation of ion pairs may result in ionization of the air,
ionization causing a pulse in a detector, heating of shielding, or
biological damage depending on what the target atom is.
2.
Particles with electric charge such as alphas and betas pull or push target
electrons through charge-charge interactions (unlike charges attract while
like charges repel) as they lose energy slowing down.
3.
Ionizing electromagnetic waves such as gammas or X-rays (X-rays being
simply low energy gammas) produce ion pairs by photointeractions
producing recoil betas/electrons which go on to produce further ion pairs by
charge-charge interactions.
Section 1-D
Radiation Exposure Units
D. Radiation Exposure Units
Radiation exposure can be measured by use of the following units, listed in
order from oldest to most modern:
1.
Roentgen (R) - The amount of gamma or X-radiation producing one esu
(electrostatic unit) of ion pairs in a cubic centimeter (cc) of dry air. This
amounts to about two billion ion pairs in a cc of air.
2.
This same amount of gamma or X-radiation produces approximately
one.
3.
Rad (Rad) - The amount of any type of radiation depositing 100 ergs of
energy per gram of any material. This amounts to about two trillion ion
pairs in a gram (g) of air, one gram of air being about a thousand cubic
centimeters, and about the same number of ion pairs in a gram of body
tissue.
Section 1-D, continues
Radiation Exposure Units
4.
Numerically, one Rad = 100 ergs/g of absorbed radiation.
5.
One Roentgen of gamma or X-radiation produces about one Rad
(100 ergs/g) of absorbed dose and also one.
6.
Rem (rem) - The amount of any type of radiation producing biological
damage equivalent to that deposited by 100 ergs of gamma or Xradiation per gram of body tissue. In other words, a rem of any type of
radiation will always produce the same amount of harm to living tissue
as would a Rad of gamma or X-radiation. The damage produced by
gamma or X-radiation becomes the standard by which all other types
of radiation are measured.
7.
Numerically, one rem = the dose equivalent to 100 erg/g of or X-rays.
Section 1-D, continues
Radiation Exposure Units
8.
Gammas and x-rays generally cause a spray of recoil electrons
(betas) when they interact with cells through photointeractions.
These recoil betas, because of their -1 charge and high speed,
then produce relatively dispersed damage among many cells.
Because (γ/Χ-radiation produces recoil betas, β/γ/Χ-radiation
produce the same number of Rads and rems.
9.
The Roentgen, Rad, and rem are relatively large units relative
to research laboratory work, so subunits in the milli (one
thousandth) range are frequently employed.
Note that: 1 R = 1000 mR
1 Rad = 1000 mRad
1 rem = 1000 mrem
Section 1-E
External Exposure Measurement
E. External Exposure Measurement
1.
Alphas will never penetrate the outer layer of dead skin if present in an external
radiation field and are therefore never counted as external exposure.
However, ingested or inhaled alpha sources will deliver their entire absorbed
radiation dose.
2.
Betas will penetrate as far as living skin if present in an external radiation field,
contributing to external skin/shallow dose.
3.
Gammas, having no charge to interfere with their progress, will penetrate living
skin, internal organs, and possibly re-emerge from the far side of the body
because of their great range. They are counted as part of the skin/shallow and
whole body/deep dose because their recoil betas can be produced anywhere
and impart biological damage at that location.
Note: An "M" reading under deep/whole body or shallow/skin exposure reported on a Landauer
Radiation Dosimetry Report means "Less than the Minimum Detectable Exposure."
Section 1-F
Biological Effects of Radiation
F. Biological Effects of Radiation
Cell sensitivity to radiation is determined by two primary factors:
1.
2.
a.
Level of cell activity resulting in increased rates of chemical
diffusion across the nuclear membrane.
b.
Rate of cell division resulting in more time spent with the protective
nuclear membrane dissolved.
Other factors apply but will be discussed later.
Section 1-F, Continues
Biological Effects of Radiation
These criteria can be used to list the body's cells and organs in
approximate order from most to least radiosensitive:
3.
a.
b.
c.
d.
e.
f.
g.
4.
Fetal tissue
Reproductive cells (for long term genetic reasons).
Red and white blood forming cells primarily located in the bone
marrow.
Lens of eye.
Most internal organs such as the lung and lower intestine.
Skin of the whole body, thyroid, nerve, etc.
Extremities such as hands and feet.
In order to put the rem into its proper biological perspective, it is useful to
compare it to the effects of large acute exposures which are received in
24 hours or less.
Section 1-F, Continues
Biological Effects of Radiation
5.
CAUTION: The exact boundary of each exposure range depends on
individual health and the availability of medical treatment after exposure.
rem
0 - 25
25 - 100
100 - 200
Immediate Effects
None
Small measurable changes in white blood cell count.
Possible symptoms of radiation sickness:
Blood changes including a white blood cell decrease
leading to decreased disease resistance, a red blood
cell decrease leading to fatigue, and a blood platelet
decrease leading to a decreased ability of blood to clot
over wounds. Intestinal wall damage leading to
nausea, vomiting, and diarrhea.
Section 1-F, Continues
Biological Effects of Radiation
6.
7.
Note: The severity of symptoms increases with increasing exposure
until the following approximate exposures are reached:
500
Lethal Dose to 50% if those exposed within 30 days
(LD50/30) along with epilation (loss of hair) within two
weeks.
1000
Additional symptoms include convulsions due to Central
Nervous System damage.
The American Cancer Society states that 25% of the 20 to 65 year old
age group develops cancer from sources such as errors in gene
duplication, smoking, air pollution, food, and natural background
radiation. An increased exposure of 1 rem would increase the risk of
cancer from about 25% to about 25.03%.
Section 1-F, Continues
Biological Effects of Radiation
8.
This assumed linear relationship between radiation exposure and the
risk of effects provides the rationale for Federal limits on radiation
exposure to the whole body including bone marrow, genetic material,
trunk and head.
9.
A "background" exposure rate exists naturally. In the U.S., the natural
background radiation exposure rate is about 100 mrem/year from
traces of naturally occurring Uranium and Thorium in soil and building
materials, traces of naturally occurring K-40 and C-14 in foods, and
cosmic radiation. Including an average number of medical and dental
X-rays, the total U.S. average increases to about 200 mrem/year.
Section 1-G
Federal Limits for Occupational Exposure to Ionizing Radiation
G. Federal Limits for Occupational Exposure to Ionizing Radiation
1.
The occupational limits set forth in Title 10, Code of Federal
Regulations, Part 20 (10 CFR 20) and Louisiana State Regulations
apply to those with a complete prior occupational radiation exposure
history.
2.
The limit for occupational exposure to ionizing radiation is 5,000
mrem/year.
3.
The Federal limit for pregnant women is based on exposure to the
fetus which is very radiosensitive.
4.
The limit for radiation exposure to the fetus is 500 mrem/term.
Instrumentation and
Radiation/Contamination Monitoring
Section 2
Instrumentation and
Radiation/Contamination Monitoring
A.
B.
C.
D.
E.
Gas-Filled Detectors
Radiation Monitoring
Contamination Monitoring
Survey Frequency
Other Laboratory Rules
Section 2-A
Gas-Filled Detectors
A. Gas-Filled Detectors
1.
Once again, radiation interactions produce ion pairs. Gas-filled
detectors generally consist of an outer container along with an
inner wire placed inside and along the long axis of the detector
probe. Container (outer electrode) and wire (inner electrode) are
electrically insulated while the outer container is generally given a
negative charge and the inner wire a positive charge.
2.
With voltage on the electrodes, an electric field is created which
attracts the negatively charged electrons to the positive inner
electrode and the positively charged ions to the negative outer
electrode. A voltage drop or current increase is produced in the
attached detector circuitry which is amplified and counted as a
pulse.
Section 2-B
Radiation Monitoring
B. Radiation Monitoring
Radiation levels must be measured in order to determine the rate at
which dose is being received. This can only be done by using
radiation survey meters.
Before performing a radiation survey, the following preoperational
checks of the survey meter are recommended:
1.
Battery check the instrument by turning the range selection switch to the
battery check position to see if the meter measures adequate voltage in
the "Battery O.K." region.
2.
Source check the instrument with a check source on contact with the
meter probe. The meter should respond to radiation.
Section 2-C
Contamination Monitoring
C. Contamination Monitoring
1.
Activity (amount of radioactive material) can be measured in units or subunits of
the Curie (Ci).
Note that: 1 Ci = 1,000 mCi = 1,000,000 μCi
Example: An incoming source vial contains 0.25 mCi of P-32.
How many μCi is this?
0.25 mCi X 1,000 μCi/mCi = 250 μCi
2.
Loose contamination can be picked up and spread to other areas. It is measured
by taking a "wipe" such as a piece of filter paper, cloth, or a cotton-tipped swab
and rubbing it over a specified area. Most frequently a 100 cm2 area which is
about 4 inches by 4 inches is used as a standard. The smear is then beta or
gamma counted. The loose activity is then calculated as in the following example:
Section 2-C, continues
Contamination Monitoring
3.
Example: A cotton-tipped swab wiped over 100 cm2 area of a fume hood
surface produces 50,000 counts per minute (cpm) above background on
contact with a survey meter. The Conversion Factor on the calibration
sticker of the meter reads "1 μCi = 100,000 cpm". What is the loose surface
contamination level in the fume hood?
50,000 cpm X 1 μCi/100,000 cpm = 0.5 μCi/100 cm2
4.
A laboratory sample counter can be used to measure lower levels of
contamination more accurately, as long as a standard with a known number of
μCi is used to determine the conversion factor from μCi to cpm. This is the same
as determining the efficiency of the counter.
Section 2-D
Survey Frequency
D. Survey Frequency
1.
Laboratories which use radioactive materials continuously must
be surveyed weekly and the survey results recorded. Infrequent
use laboratories must be surveyed at the completion of the
procedure.
2.
A record of these surveys, even if negative, must be kept on file for
inspection by State or Federal regulators.
Section 2-E
Other Laboratory Rules
E. Other Laboratory Rules
1.
Decontamination of work areas must be performed when
contamination levels exceed twice background.
2.
Refrigerator/freezers that are used to store radioactive materials
must be labeled “Caution, Radioactive Materials.”
3.
Incoming radioactive material packages labeled White I, Yellow II, or
Yellow III must be wipe tested for radioactive contamination and the
results recorded. This requirement is not applicable if the packages
arrive at 333 South Liberty Street since the Radiation Safety Office
checks these packages for contamination on a daily basis.
4.
Radioactive materials must be secured when not in use by storing
them in a locked container or locking the laboratory door when
absent from the room.
Exposure Reduction
Section 3
Exposure Reduction
A.
B.
C.
Inverse Square Law
Time
Shielding
Section 3-A
Inverse Square Law
A. Inverse Square Law
1.
The Inverse Square Law for gamma point sources is:
D1 X r12 = D2 X r22
2.
Example: The dose rate one foot away from a point source is 100
mrem/hr. What is the dose rate after stepping back to a distance of
two feet?
D2 = (100 mrem/hr) X (1 ft)2/(2 ft)2 = 25 mrem/hr
3.
As can be seen from the previous example, doubling distance from a
point source of radiation decreases dose rate to one quarter of what it
was. This is the basis of the Inverse Square Law and dose reduction by
increasing distance.
Section 3-B
Time
B. Time
1.
The time equation, which is applied frequently in radiation
protection work, is:
Dose = D x T where:
D = Dose rate
T = Time of exposure
Example: A researcher stands in an area where a survey
meter reads 50 mrem/hr for a period of six hours. What is
their total exposure as a result?
50 mrem/hr X 6 hr = 300 mrem
Section 3-C
Shielding
C. Shielding
1.
The range of a beta is sufficient to penetrate living skin. Because of its -1 charge,
a few millimeters of plastic can stop all betas.
2.
Recall that gammas and X-rays are electromagnetic waves with no mass or
charge and very penetrating. One Half Value Layer (HVL) is the thickness of
shield material that will reduce exposure rate to one half of its initial amount. The
thickness that reduces the incident flux to one half will, if doubled in thickness,
reduce the original incident flux to one quarter of what it was.
3.
In equation form: D = D0 (1/2)n and n = x/HVL where:
D0 = Unshielded dose rate.
D = Shielded dose rate.
n = Number of Half Value Layers.
x = Shield thickness.
Section 3-C, continues
Shielding
Example: A source is producing a dose rate of 100 mrem/hr at the
side of a laboratory bench. Estimate the remaining dose rate from
the source if two 1/2 inch lead shields are placed over the source.
The HVL is 0.5 inch for the gamma energy involved.
The total thickness of lead shielding is 1.0 inch and
n = 1.0 in/0.5 in = 2
D = (100 mrem/hr) X (1/2)2 = 25 mrem/hr
Radioactive Decay and
Specific Hazards
Section 4
Radioactive Decay & Specific Hazards
A.
B.
C.
D.
Decay Equation
Radioiodine
Tritium
Phosphorus-32
Section 4-A
Decay Equation
A. Decay Equation
1.
The following is the decay equation:
A = A0(1/2)n where:
A0 = Activity initial.
A = Activity final.
n = t/t1/2 = Number of half-lives that have elapsed.
t = Time that has elapsed.
Example: A radioactive sample has a half-life of 30 minutes. If the sample
initially contained 1 mCi, how much remains after 60 minutes?
n = 60 min/30 min = 2 elapsed half lives
A = 1 mCi X (1/2)2 = 0.25 mCi
2.
The example is simple but illustrates the point that one half-life of time will
decrease a given amount of radioactivity to one-half of what it was.
Section 4-B
Radioiodine
B. Radioiodine
Radioiodine is most commonly I-125 with a 60 day half-life. It
produces a relatively low energy 35 keV gamma/x-ray in only 7%
of the decays. When purchased as sodium iodide (NaI) in base
(NaOH) the radioiodine is relatively stable and water soluble.
Under acidic conditions, sodium iodide chemically partitions to
form volatile elemented iodine (I2) which can be inhaled. Due to
its rapid biological accumulation in the thyroid, thyroid monitoring
is necessary. Radioiodine is primarily an airborne thyroid
hazard.
Section 4-C
Tritium
C. Tritium
1.
Tritium, H-3, has a 12.3 year half-life.
2.
It produces a 19 keV beta and no gamma.
3.
Tritium is an internal exposure hazard.
a.
Rubber gloves must always be used when handling radionuclides.
b.
Including tritium since it can be absorbed through bare skin.
c.
Urinary monitoring, which is done by collecting a milliliter of urine to be
mixed with scintillation medium and counted, must be performed when
using large amounts of tritium.
Section 4-D
Phosphorus-32
D. Phosphorus-32
1.
Phosphorus-32 (P-32) has a 14.3 day half-life and emits a 1,710 keV
beta with no gamma.
2.
P-32 is an external skin/shallow exposure hazard, while not a
whole body/deep dose hazard.
3.
It can also deliver a large dose to the hand when handled in mCi
amounts.
Radioactive Materials Disposal
Section 5
Radioactive Materials Disposal
A.
B.
C.
D.
Decay to Background Levels
Sewer Disposal
Incineration
Transfer to a Licensed Disposal Firm
Section 5-A
Decay to Background Levels
A. Decay to Background Levels
1.
Radioactive waste may be discarded in the normal waste stream if the
following conditions are met:
a.
b.
c.
d.
The material has decayed 10 half-lives.
The waste produces no count rate above background on
contact with a radiation survey meter.
All "Radioactive" labels have been removed/defaced.
Notation is made on the "Radionuclide Receipt & Use Record"
that the waste has been defaced & discarded, ≤bkg, and date.
Note: Accurate Radionuclide Receipt and Use Records prove to
Federal and State auditors that radioactive material has been used
and disposed of in a safe and legal manner.
2.
After decay, the waste may still be hazardous or infectious and have to
be disposed of in one of these specialized waste streams.
Section 5-B
Sewer Disposal
B. Sewer Disposal
1.
Aqueous liquid radioactive waste may be disposed of in the
laboratory "hot sink" along with copious amounts of water
as long as the date, radioisotope, and activity disposed of is
recorded.
2.
Its very important to note that this method may only be used if the
sewer is connected to a municipal sewer system.
3.
A "Semi-Annual Radionuclide Inventory/Sewer Disposal" report is
requested of each licensee every six months. These are used by
the Radiation Safety Office to ensure that the activity
concentrations leaving each building are below drinking water
concentration limits and that the total activity discharged is less
than 1 Ci per year.
Section 5-C
Incineration
C. Incineration
1.
Contaminated laboratory trash and biodegradable liquid
scintillation vials can be taken to the Medical School waste
room, tagged with the radioisotope, activity amount in µCi,
date, and licensee name for eventual incineration.
2.
The Waste Room is located in room 1105 of the Medical School
and is open Tuesdays from 8:30 to 10:30 a.m.
3.
The Radiation Safety Office ensures that the amount of
radioactivity incinerated per hour does not cause effluent air
concentrations to exceed the limit for unrestricted air and that the
resulting incinerator ash does not exceed drinking water
concentration limits.
Section 5-D
Transfer to a Licensed Disposal Firm
D. Transfer to a Licensed Disposal Firm
1.
Organic liquid scintillation cocktail such as toluene containing
radioisotopes with long half-lives must be transferred to a
licensed radioactive/chemical waste disposal company.
2.
The Radiation Safety Office will arrange these shipments, but must bill
the licensee generating the waste because of the high price of such
disposal.
RADIATION PROTECTION
TRAINING
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