Chap.18 Scott test 11/9 JQ
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The overall risk of exposure to radiation is approximately
7 in 10,000 persons per rem
What is the approximate single whole-body exposure for LD50/30
4.5 Gy (450 rads)
What does LD50/30 represent
Lethal for 50% of the exposed population within 30 days of event
Long term effects of rad exposure for which a threshold exists and for which the severity of the effect increases with dose
- Examples: erythema(red skin), epilation(hair loss), cataracts and infertility
- NOTE: Threshold doses for these effects are relatively high, which is reflected in the highter permitted doses to the specific organs involved.
Long term effects of rad exposure that have NO threshold and for which the probability of occurrence IS a function of dose.
- Examples: cancer induction, genetic effects, embryologic and teratogenic(defect) effects
- NOTE: In this case, the severity of the effect is NOT a function of the dose. It either occurs and does not.
Because stochastic effects have no threshold they are of more concern at low levels of radiation exposure.
The organizations that oversee the transportation of radioactive materials
- DOT(Department of Transportation) and
- NRC(Nuclear Regulatory Commission)
Oversees the use of machines that produce ionizing radiation, such as x-ray units and linear accelerators.
- FDA(Food and Drug Administration)
- state agencies
- EPA(Enviromental Protection Agency)
- OSHA(Occupational Safety and Health Admin.)
The role of regulatory agencies
to license users of radioactive materials and ratiation-producing equipment, inspect users and enforce the laws
Role of advisory agencies
to analyze existing data, to assess radiobiologic risks and develop recommendations for dose limits.
Leading federal regulatory agency in US
NRC(Nuclear Regulatory Commission)
use of isotopes produced in nuclear reactors
Isotopes produced in nuclear reactors are used for
- nuclear medicine departments
- teletherapy(external beam rad)
- brachytherapy(internal implants)
"agreement" states are
states that have entered into agreements concerning licensing, inspection and enforcement with the NRC
they must maintain a certain level of compatibility with NRC regulations
the two types of gas-filled detectors
- ionization chamber
- Geiger-Muller(G-M) detector
how a gas-filled detector functions
- it has a chamber filled with a gas that is inonized in part or whole when radiation is present
- it measures the quintity of electrical charge or the rate at which the charge is produced
- is the simplest
- it consists of 2 electrodes within a gas-filled chamber
- an applied voltage across the electrodes
- electronics and a meter to amplify and measure the electrical signal
accuracy of a ionization chamber
- when properly calibrated, their accuracy approaches 2%
- NOTE: Ionization chambers with large air volumes are suitable for environmental surveys around therapy rooms.
- are ionization chamber used for personnel monitoring
- NOTE: ionization chambers are not very sensitive, they are not suitable for detection of very low levels of rad or rad contamination
thermoluminescent dosimeters (TLDs)
are small in size and are widely used to measure radiation in a number of applications
TLDs give off
light when heated
are sensitive so they are best for finding contamination and low levels of radiation
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