The following information comes from The University of Chicago Office of Radiation Safety (AMB, M-031A, Ext. 2-6299, Fax 2-4008).
Information also available as a powerpoint presentation:
Radiation Doses Training.ppt .
Radiation basics
What is radiation?
Energy radiated from an object in the form of waves or particles which travel through space.
Ionizing radiation
Non-Ionizing radiation
Microwaves
Visible Light
Heat
Radio waves
Effects of radiation
Radioactive material
For our purposes, “Radioactive material” will refer to any substance which spontaneously emits ionizing radiation.
Naturally-occurring radiation
Radiation is a part of our everyday environment. Both natural and artificial radiation contributes to an average American’s yearly exposure of 360 mRem.
Cosmic Radiation
Exposure rates at:
Sea Level ……………………………. 26 mRem/year
Atlanta, Georgia (1,050 feet) ………. 31 mRem/year
Denver, Colorado (5,300 feet) …….. 50 mRem/year
Terrestrial Radiation
Exposure rates:
United States (avg.) ……………. 26 mRem/year
Denver, Colorado ………………. 63 mRem/year
Paris, France …………………….. 350 mRem/year
Pacos De Caldas, Brazil …….. 7,000 mRem/year
Other sources of radiation
Radon
Food and Water
Medical Treatments
Consumer Goods
Nuclear Fallout
Units of Measurement
Curie – quantifies the intensity of radioactive material decay (activity)
Rem – quantifies the amount of radiation absorbed in human tissue (exposure)
•yearly exposure limit to radiation workers = 5000 mRem
mR/hr – quantifies the equivalent rate of exposure (Dose Rate)
•Exposure rate at the surface of a package = 1.0 mR/hr
cpm – counts per minute
dpm – disintegrations per minute
Half-life
A half-life is the fixed period of time it takes for the activity of a radioactive substance to naturally decay to 1⁄2 its original value.
Basic Safety Principles
Modes of Decay
The natural decay of radioactive material results in one of four types of “radiation” being emitted:
Alpha particles
Beta particles
Gamma rays
Neutrons
Alpha particles, α
Helium nuclei with a +2 charge
Relatively large and energetic
Dangerous to cell nucleus
Easily shielded
Not commonly found in research settings
Beta particles, β
Electrons with a –1 charge
Ionizations occur as the particle penetrates matter
The ability of a Beta particle to penetrate matter is a function of its energy
Commonly used Beta emitters : H-3, C-14, P-32, P-33, S-35
Properties of commonly used β -emitters
Isotope | H-3 | C-14 | S-35 | P-33 | Ca-45 | P-32 |
Half-life | 12.4 Years | 5730 years | 87.4 days | 25.3 days | 162.7 days | 14.3 days |
Energy (β - maximum) | 18.6 keV | 156 keV | 167 keV | 249 keV | 258 keV | 1709 keV |
β Range in air | 6 mm | 24 cm | 26 cm | 49 cm | 50 cm | 790 cm ( 20 ft.) |
Gamma rays, γ
X-ray having no charge or mass
Ionization occurs as it passes directly through matter
Greatest penetrating ability of all
Commonly used γ emitters: Cr-51, I-125
Neutrons, N0
Shielding (in a laboratory setting)
Shielding different particles
All Beta emitters used in the laboratory can be safely shielded by 1cm thick Plexiglas.
Gamma emitters must be shielded by lead.
Neutron emitters may be shielded by low density material like paraffin wax or water.
Shielding guidelines
Shield all four sides when necessary
Check integrity of shielding material
Waste and source material may also require shielding!
General Rules for Safe Use of RAM in the laboratory
Personal Protective Equipment
Lab coat, disposable gloves are MANDATORY!
No exposed skin when handling RAM (shorts, skirts, open-toed shoes)
Must be worn when handling any samples or equipment bearing a RAM label.
Dosimetry
Dosimetry program monitors the amount of radiation exposure
Submit a “Radiation Badge Service Card” to order or cancel badge
A dosimetry badge must be worn by those who:
May receive over 10% of the annual exposure limits
Use more than 1 mCi per month of P-32 or S-35
Exemptions: H-3 and C-14 users
Radiation badge worn at the highest area of exposure (lapel)
Store your badge away from areas of potential exposure!
Note: Workers who use > 10mCi of a high-energy β-emitter or > 1 mCi of a γ-emitter must also wear a ring badge.
Prohibited substances and activities
Eating, drinking, smoking, chewing gum,
Application of cosmetics
Storage of food or drink
Preparation of food (microwave, coffee maker, etc.)
Unauthorized repair or removal of labeled equipment
Security
Areas where RAM is stored or used must be locked or attended at all times!
An empty room with a “Radioactive Materials” sign on the door is still a RAM use area!
Visitors must adhere to all radiation safety guidelines.
Required Postings / Labels
RAM workspaces must be clearly identified (with a sign or tape) and protected by absorbent coverings.
RAM must be labeled with a radioactive trifoil, isotope, activity, and date. This includes stock vials, stored radioactive samples, and all radioactive waste.
Equipment that may be used with RAM (pipettes, centrifuges, water baths) must be labeled with a radioactive trifoil.
Transportation
All RAM must be transported in shielded, spill-proof containers.
Any RAM entering or leaving the University of Chicago must be facilitated by the Office of Radiation
Safety. Call ORS immediately if a radioactive package is delivered directly to your lab, or you intend to have a package shipped off-campus.
Transfer of RAM from one Private Investigator to another requires pre-approval by ORS.
Industrial Examples
Survey Instruments
Geiger-Mueller (GM) detectors
Probe types
| | |
Meter base | End-window probe | Pancake probe |
Detector Efficiency
RADIONUCLIDE | PANCAKE EFFICIENCY | END WINDOW EFFICIENCY |
H-3 | Not Detectable | Not Detectable |
C-14 | 3% | 1.5 to 2% |
S-35 | 4-5% | 2 to 2.5% |
P-32 | 28 to 30% | 14-15% |
Battery Test
Move switch on base to “BAT” position. - The indicator needle must deflect to the “BAT TEST” range. - If it does not pass, you may not use the instrument! Change the batteries or call ORS for assistance.
Instrument operational check
The display must read within the range limits on the “Checksource Measurement” sticker.
-
-
- Contact ORS if the reading falls outside the range. Do not use this instrument!
Effective use of a Geiger-Mueller detector
After battery check and operational check, set the dial switch to the lowest scale.
“Instrument Background” is the highest reading when no radioactive material is present.
Average Backgrounds (end window or pancake probe):
0.02- 0.04 mR/hr
30 – 100 cpm
0.3 – 1 cps
If your background is too high you must move to another area, re-perform the operational check, and try again. A short in the cable or a contaminated probe can cause elevated backgrounds!
Always remove red cap before surveying.
Proper survey distance is 1cm from the surface – don’t let the probe make contact with the object you are surveying!
Keep the probe face parallel to the area being surveyed.
You can never survey too slowly. Recommended survey speeds range from 2-5 cm/second. Keep in mind that the efficiency of your meter varies with the isotope you are trying to detect!
Survey with the audio “on”!
Sodium iodide (NaI) scintillation probe
Detection of gamma from I-125
Average background 100 to 500 cpm –Results in cpm only!
20-30% efficiency
Red cover is not removable!
Liquid scintillation counters
Detection of low energy β-emitters
Required whenever tritium (H-3) is used
Results measured in cpm
Average background < 50 cpm
Use small pieces of absorbent material (Kimwipe, filter paper, paper towel, cotton-tipped applicator)
Surface area wiped ~ 100 cm2
Wipe all potentially contaminated areas in an S-shaped pattern
Add appropriate type and volume of cocktail (4ml for a 5 ml vial)
“Blank wipe” must be counted to determine background readings.
1 minute count time per vial
LSC protocols must be programmed for detection of the appropriate isotope energies!
Decontamination
Remove the radioactive material by cleaning, shielding, or disposal of the offending item(s).
Threshold levels (when must I decontaminate?)
Required documentation
Corrective Actions
New survey results
Specific Hazards of Unsealed RAM sources
Absorption through gloves + skin
H-3, C-14 products – anything bound to lipids or cell membrane components can easily absorb through skin.
“Free” iodine-125 can penetrate latex gloves, so wear two pair!
Volatility
S-35 bound to amino acids (methionine) is easily volatilized. Opening the stock vial in a designated fume hood is mandatory!
Unbound I-125 such as NaI in NaOH must always be used in the fume hood. RIA kits and iodine bound to antibodies do not require special measures.
Exposure Rate
Your dosimeter badge detects exposure to the body, but not to the extremities! Limit the amount of time spent holding stock vials of high-energy β-emitters like P-32.
You aren’t working with radioactive material today, but someone else may be! Wear your badge on your lab coat whenever you are in a radioactive materials laboratory.
Difficulties in Detection
Occupational Exposure Limits
Whole body | 5 Rem/yr |
Lens of the eye | 15 Rem/yr |
Organs/Extremities | 50 Rem/yr |
Pregnancy (duration) | 0.5 Rem |
Specific Hazards and Risk Analysis
A comparison of hazards
Risk | Estimate of Days of Life Expectancy Lost (Average) |
Smoking 20 cigarettes/day | 2370 (6.5 years) |
Overweight by 20% | 985 (2.7 years) |
Alcohol consumption | 130 |
Teaching profession (US) | 30 |
1/5 of maximum permissible radiation dose (1 Rem) in a year for an occupation worker | 1 |
Chronic Effects resulting from small exposures over a long time (>1 year) period.
•Estimated increase in cancer risk
25% of all adults will develop cancer from all possible causes in a population.
At occupational limits of 5 rem/year, an individual working for 20 years would result in an lifetime exposure of 100 rem.
This level of exposure would result in a 3% INCREASE in incidence of cancer or a 28% chance vs a 25% chance.
Prompt Effects resulting from large exposures in a short (<1 day) period.