Radioactive Materials Safety Training
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Transcript of Radioactive Materials Safety Training
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Radioactive Materials Safety Training
Massachusetts Institute of Technology
Radiation Protection Program
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Outline
1. Introduction
2. Delegation of Authority
3. Radiation Physics
4. Units and Quantities
5. Background and Occupational Radiation Doses
6. Biological Effects of Ionizing Radiation
7. Minimizing Radiation Exposures - ALARA
8. General Radiation Safety and Surveys
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Radiation
• Radiation: Energy in the form of particles or electromagnetic waves
• Ionizing Radiation: Radiation with sufficient energy to remove an electron from an atom or molecule.
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Radioactivity
• The process by which unstable atoms spontaneously transform to new atoms* and in the process emit radiation.
-
* The “new atom” may be the same atom in a lower energy state.
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Units of Activity
• Curie (Ci): 37 Billion transformations per second. (2.22 trillion per minute)
• Bequerel (Bq): 1 transformation per second.
mCi and uCi are common quantities used in the lab (10 uCi up to 50 mCi).
0.0013 uCi (48 Bq) - Ra-226 in a 1 kg rock0.12 uCi (4400 Bq) - K-40 in your body330 pCi - C-14 in ¼ lb of beef
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Half-Life
• Half-life is the amount of time needed for the activity to reach one half of the original amount.
f1
2
tT1/2
f e t ln ( )2
T1/2
0 20 40 60 80 1000 .00
0 .20
0 .40
0 .60
0 .80
1 .00
One half-life
Two half-lives
0.007
Days
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Definitions• Exposure R (roentgen): Amount of charge produced per
unit mass of air from x-rays and gamma rays.
• Absorbed Dose rad: Amount of Energy deposited per unit mass of material. 1Gy = 100 rad.
• Dose Equivalent rem: Risk adjusted absorbed dose. The absorbed dose is weighted by the radiation type and tissue susceptibility to biological damage. 1 Sv = 100 rem.
• Radiation weighting factors: alpha(20), beta(1), n(10).
• Tissue weighting factors: lung(0.12), thyroid(0.03), and gonads(0.25).
For whole body x or gamma-ray exposure 1 R 1 rad 1 rem
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Alpha Decay
• Helium Nucleus – Very massive and doubly ionized• Only a hazard via ingestion or inhalation of alpha emitter• Not usually an external radiation hazard• Stopped by paper and dead layer of skin• Uranium, Thorium, Radon and radon daughters
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Beta Decay
• Energetic electron – singly ionized• External hazard to skin and eyes• Internal hazard via ingestion or inhalation of beta emitter• Produces bremsstrahlung radiation• A 1 MeV beta can travel up to 12 feet in air and 1 cm in plastic• Phosphorus, Tritium, Carbon, Sulfur
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Gamma Decay
• X-rays and gamma rays are photons – no charge
• External radiation hazard to deep organs and tissues
• Internal hazard via ingestion or inhalation of gamma emitter
• Lead (high electron density) is good for shielding x and gamma rays
• Iodine 125 gammas (30 keV) can be easily stopped with 1/8 inch of lead
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paper plastic lead
alpha particle
beta particle
gamma ray
x-ray
e-
e-
e-
He++
photon
Neutron shielding material depends on the energy of the neutrons
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Bremsstrahlung X-Rays
• Bremsstrahlung x-ray intensity increases with increasing atomic number of absorber, and the average x-ray energy increases with increasing electron energy. (activity of the source is also a factor)
x-ray
e-
plastic
lead
electrons
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Shielding for beta emitting material
90Srplastic lead
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Low energy gamma or x-ray
High energy gamma or x-ray
Shielding for gamma emitting material
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Typical background is 0.03 mR/hr or 100 cpm
GM pancake probe
NaI probe
Range selector
Batterycheck
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Sources of Average Radiation Dose to the U.S. Population
Radon, 20055%
Internal, 3910%
Terrestrial, 288%
Cosmic, 278%
Nuclear Medicine, 144%
Medical x-rays, 3911%
Consumer Products, 103%
Other, 30.8%
Source: BEIR V Report, 1990
Background Radiation360 millirem per year
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Annual Occupational Dose Limits
Whole Body 5,000 mrem/year
Lens of the eye 15,000 mrem/year
Extremities, skin, and individual tissues
50,000 mrem per year
Minors 500 mrem per year (10%)
Embryo/fetus* 500 mrem per 9 months
General Public 100 mrem per year
* Declared Pregnant Woman
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Biological Effects
• Many groups exposed to ionizing radiation at high levels resulted in adverse effects.
• Somatic effects– Prompt - skin burns and cataracts– Delayed - cancer
• Genetic effects
• Teratogenetic effects
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X-Ray Burns
5,000+ rad
500+ rad
P-32 - 6.5 rad/hr/uCi
S-35 - 2.5 rad/hr/uCi
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Cancer
• Radiation can damage cells through two methods;– Production of free radicals and– Direct damage to the DNA.
• Risk factor for radiation dose:– 4% increase in risk of dying of cancer for
every 100 rem of dose.– Normal cancer risk is 20%.
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0 10 20 30 40 50 60 70Committed Lifetime Dose (rem)
0.00
0.01
0.02
0.03
Ris
k of
dea
th fr
om c
ance
r
Dose Response Relationship
Predictable EffectsRisk Is not
Predictablebelow 20 rem
Effect is Detrimentalrisk level is uncertain
Occupational dose – above background
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ALARA
• ALARA - As Low As Reasonably Achievable
• Time
• Distance (inverse square law)
• Shielding
• Contamination Control
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Inverse Square Law
5 mrem/hr @ 10 cm
50,000 mrem/hr @ 0.1 cm
45 mrem/hr @ 3.3 cm
D2
.D1
x1
x2
2
D - Dosex - distance
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Radioactive Sealed Sources
• Sealed sources used as a source of radiation– Alpha particles– Beta particles– Gamma ray– Bremsstrahlung– Neutron sources
• Permanently enclosed in either a capsule or another suitable container designed to prevent leakage or escape of the radioactive material
• Inventory and Use records are required
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• Tested for surface contamination and leakage – Sources may leak radioactive material – Tested usually once every 6 months for beta &
gamma emitters that are > 100 uCi– Tested every 3 months for alpha emitters > 10 uCi– Allowable limit is less than 0.005 uCi
• A leaking source shall immediately be removed from use– Action to be taken to prevent contamination– Source to be repaired or disposed of
• RPP has a shielded storage facility for sources that are not in use.
Radioactive Sealed Sources
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Security and Transportation
• All radiation sources must be kept locked up when not in use.• Experiments left unattended should be labeled “Experiment in
Progress.”• An up-to-date use log of all sources must be kept at the storage
location.• All radiation laboratories will be locked when unattended for extended
periods.• When you are the means for security, you must challenge unknown
persons entering the lab.
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General Radiation Safety
• NoNo food or beverages in the lab
• Keep a survey meter conveniently close by
• ALARA - time, distance, and shielding
• Label radioactive materials and equipment
• Never remove sources from the Jr Physics Lab