Materials Radioactive II
Radiation Protection
Major Types of Ionizing Radiation Alpha, Beta, Gamma
Alpha Particle Helium Nucleus that has a +2 charge
He +2
Large Mass (nuclei) Range 1-2 centimeters in air
Beta Particle electron that originates from inside the nucleus
Small Mass (subatomic particle) Range 0-2 meters in air
Gamma Photon and X-Rays
Electromagnetic Radiation No mass; Range of meters in air
Ionizing Radiation interacts with matter and produces a dose that is absorbed by that matter
He +2
Gamma and xray
RAD and REM
Rad is an acronym that stands for
"Radiation Absorbed Dose". It is a measurement of the amount of energy deposited by any type of radiation in any material.
It does not account for the interaction with biological molecules and potential for biological damage.
Rem stands for "Radiation Equivalent
Man" or "Roentgen Equivalent Man"
RAD and REM
Rem = Rad x Q, where Q is a "quality" factor related to the probability of damage caused by the particular type of radiation.
Q factors
X or gamma ray 1 Beta particles 1 Neutrons (low E) 5 Neutrons (hi E) 10 Alpha particles 20
Radiation Risk
High Dose (acute)
100400 rem effects blood cell counts, but people usually recover 4001400 rem GI track, and epithelial cells effected. Lower end survive,. Upper end don't Above 1400 rem..death likely Atomic Bomb Victims Chernobyl nuclear meltdown
Low Dose
Primary risk is induction of cancer
Risk related to chance of mutation Above 50 rem, risk proportional to dose Below 50 rem, risk assessment less clear. Effects below 10 rem unknown.
Acute Radiation Syndromes
(Very high radiation doses) Between 0 and 100 rads Generally there are no clinically observable changes Some nausea at the high end of range in more susceptible persons Some blood changes above 25 rads 100 400 rads The hematopoietic system is affected Blood cell precursors are very radiosensitive Gradual depression in blood count over days or weeks Increased susceptibility to infection and hemorrhage Most recover at lower end of range with some medical care
Acute Radiation Syndromes
(Continued) 4001400 rads Gastrointestinal system is affected Cells lining the intestinal track are radiosensitive Bacteria and toxic material gain entry into the bloodstream Diarrhea, dehydration, infection, toxemia Survival is unlikely at the upper end of range Above 1400 rads Cardiovascular and Central Nervous System is affected Blood supply is impaired leading to nausea, vomiting, convulsions, or unconsciousness. There is no hope for survival
LD
is approximately 450 rads with modest medical treatement
High Dose Radiation?
How likely?
Chernobyllike explosion..a catastrophe
134 persons received over 70 rem exposure 28 deaths from Acute Radiation Sickness
Approximately 100x the radioactivity released as combined Hiroshima/Nagasaki bombs
Atomic Blast
Hiroshima
So even in the worst case scenario...acute radiation sickness is not the big worry
90140,000 persons died within 4 months, but that includes all causes of death. Estimate that 25000 of these died of Acute Radiation Sickness
What this means
Very few deaths have ever been tied in a clear cut correlation to radiation. It can only be done with acute radiation exposure. Many, many more people were exposed to low level radiation from these incidents.
5.5 million people continue to live in areas contaminated by the Chernobyl incident Longest running studies are of Hiroshima/Nagasaki survivors: Of 52,000 survivors who received 0.5 rem doses, 420 deaths due to radiation exposure observed, out of a total of 8100 cancer deaths.
LowDose Radiation Effects
Nonstochastic
Cataracts
Severity related to dose Threshold dose
Stochastic effects
Random, delayed effects Possibility related to dose Severity not related to dose
Mutation vs. no mutation
Low Dose Radiation Injury
At low doses, radiation injury is a statistical probability of interaction of the radioactive emission and biological molecules. Low dose radiation injury is primarily due to mutagenesis. Primary somatic biological effect caused by mutagenesis is cancer. Radiation damage to DNA in eggs or spermatocytes can lead to heritable mutations.
What factors influence probability of radiation damage?
Type of Target Cell
Law of Bergonie and Tribondeau
The radiosensitivity of a population of cells is directly proportional to their mitotic rate and inversely proportional to their degree of differentiation.
In other words, the more frequently cells divide, the more sensitive they are to radiation injury. The more specialized the cells are, the less sensitive they are to radiation injury.
What factors influence probability of radiation damage?
Radiation Dose
Type Activity (how much) Time of exposure
DOSE LIMITS
If risk of injury is stochastic, how do we know how much radiation is required to increase the risk? As with any statistical, stochasitic process, you can't know for sure. Models are developed. Most are very conservative. This primary risk models have been developed by the National Academy of Sciences, the National Council on Radiation Protection and others.
Models for risk estimation
New evidence from National Academies of Science BIER VII, 2005 suggests that the Linear No Threshold model is supported.
Additional cancer risk due to radiation
Range of estimated effects at low dose
Range of known effects at high dose
1 = Linear model 2 = Linear Quadratic model 3 = Threshold dose effect model 4 = Increased effect at low dose
0
Dose (REM)
100
DOSE LIMITS
What's my risk of getting cancer from a radiation exposure? This is hard to determine. The most quoted estimate is that an exposure of 10000 workers to 1 rem of radiation would produce 4 cancers = 0.04%. Consider that in the US as a whole risk the of cancer is about 25%
Regulatory Premises
Competing and mostly unsupported
models for risk require using a conservative approach
LNT (linear, no threshold) assumes any dose is harmful. ALARA (as low as reasonably acheivable)
Do better than the regulatory limits on dose Provides a margin of safety
Regulatory limits
Nuclear Regulatory Commission
Sets the dose limits
States and other agencies may set more
Radiological workers Members of the Public Neither limit is zero.
stringent limits All expect ALARA
What are the regulatory limits?
Members of the Public
Radiological Workers
5 Rem in one year 50 Rem to one organ or tissue 15 Rem to eye 50 Rem to skin or extremity These are referred to as occupation dose limits.
100 mRem in year 2 mRem in one hour
Why are these limits different? Are members of the public less sensitive to Radiation?
Types of exposure
External Exposure High energy Betas Gammas
Internal exposure requires intake of radioisotope Alpha, Beta and Gamma
External Exposure Reduction
Time: reduce time spent in radiation area Distance: stay as far away from the radiation source as possible Shielding: interpose appropriate materials between the source and the body
Reducing Exposure Time
Training: Rehearsal of procedures prior to using radionuclide. Improves efficiency, reduces handling time. Equipment Shakers rather than hands! Lab/Workplace design Easy access to the equipment and components Task modifications from ALARA review
Controlling Distance
Remote operation manipulating devices forceps not fingers! Move away from sources remain near a source only when it is being used Removal of other radiation sources waste containers unnecessary sources
Shielding
Basic principle: Place materials between the source and person to absorb some or all of the radiation radiation: no shield required for external exposures; dead skin layer stops 's radiation: ranges of meters in air; some can penetrate dead skin layer; thin plexiglass shields adequate X and radiation: highly penetrating, best shields are high atomic number materials (lead)
Low Z shielding reduces Bremsstrahlung
INTERNAL RADIATION EXPOSURE
Entry paths
Dust inhalation, fume or mist inhalation Ingestion of contamination Injection (puncture wounds, accidental hypdermic needle injection, broken pipets, etc) Absorption through skin
Food, water, or from contaminated hands
Rarely any method to reduce exposure once in the body Length of exposure depends on the physical and biological halflife Dose estimates are very difficult
Usually don't know the amount of intake Biological variability in elimination from and concentration in tissues and in energy deposition.
INTERNAL RADIATION EXPOSURE
PREVENT INTAKE!
Controlling Internal Exposure
removable surface contamination airborne contamination
Safe Handling Practices! Contamination Control
Standard Procedures help!
Personal Procedures
No eating, drinking, smoking, makeup application, etc when working with RAM Work in hood Wear PPE Clean up contamination Survey to make sure no contamination exists Monitor Air, to make sure procedure doesn't release dust or volatiles
Exposures in perspective
You are exposed to ionizing radiation all
the time. This is called background radiation.
Nuclear Medicine 4% Rocks and Soil 7% Cosmic 8% Internal Radionuclides 9% Medical X-rays 10% Consumer Products 3% Nuclear Power 0.1%
Radon 59%
Exposures in perspective
E...