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RADIATION BIOLOGY

QuestionAnswer
Radiation protection is applied radiation physics and radiobiology
The acronym for as lo as reasonably achievable is ALARA
On average, the medical doses of ionizing radiation are not greater than natural background radiation
The annual average dose per person from all sources is about 360 mrems
The risk of 1 rad of radiation is equivalent to driving 220 miles on a freeway
Two common means of expressing risk are perceived risk and risk comparisons
Dr. John Cameron has recommended use of unit called the BERT, which stands for Background Equivalent Radiation Time
What is the loss of life expectancy associated with each of the following risks?
Smoking a cigarette 10 minutes
Home accidents 95 days
1mrad of ionizing radiation 1.5 minutes
Radiation work at 5rem/yr from age 20 yeard 68 days
Radiation protection guidelines usually assume that there is no threshold or level below which no effects will be seen
Most radiologic examinations carry a very small risk in relation to the potential benefit
GSD is the abbreviation for ___________________ which is a measure of the genetic exposure to the population from ionizing radiation genetically significant dose
CDRH is the abbreviation for the_____________________ which is a part of the U.S. Food and Drug administration Center for Devices and Radiological Health
The safe medical devices act went into effect in 1991 and authorized civil penalties to_______________________ who do not report defects and failures in medical devices technologists and other health care workers
The goal of state licensure is to_____________ from excessive ionizing radiation, not to raise professional standing of the practitioners protect the public
Most state licensures laws are an outgrowth of the Consumer-Patient Radiation Health and Safety Act of 1981 Title IX of Public Law 97-35
X-Rays are a form of electromagnetic Radiation similar to light but with a wavelength that is shorter. They have no mass or charge but behave as both waves and particles
X-rays are the most penetrating electromagnetic waves.
They are similar to light but can not be focused by a lens nor do they reflect off a surface. They are electrically neutral. They are heterogenous and polyenergetic. Any given photon travels in a straight line at the speed of light.
X-rays diverge from the source and are emitted isotropically.
They ionize all matter, including gases and can cause biologic changes
X-rays produce secondary and scattered radiation when interacting with matter
They cause certain crystals to fluoresce and affect photographic film
Approximately 99 % or greater of the kinetic energy of the projectile electrons in the x-ray tube is converted to heat, with less than 1 % of the energy going to the production of X-rays
The kVp set on the machine determines the maximum energy of the x-rays produced
The deceleration of electrons in the target material is called Bremsstrahlung or braking radiation
Radiation produced when projectile electrons knock orbital electrons free is called characteristic radiation
The radiation that passes through the window of the x-ray tube is called the useful or primary beam while radiation exiting the tube anywhere else is called leakage radiation
In general diagnostic radiography, filtration is used to remove the low energy long wavelength photons from the beam
As a filter, aluminum tends to absorb only low energy photons due to its low atomic number
Mammography filters are made of molybdenum or Rhodium. Which have a higher atomic number than aluminum
A HVL or half-value layer is a measure of the quality of a radiographic beam. As the measurement thickness of aluminum, for a HVL, increases the harder the beam and the lower the patient dose
With single-phase the room mean square RMS voltage is only 70.7% of the peak voltage. The RMS value for three-phase 6-pulse is as low as 92% and the three-phase 12-pulse is near 97%
Conventional fluoroscopy uses lower mA settings than conventional radiography, approximately 1-3 mA and kVp settings of 90-120
Conventional TV monitors display a resolution of about 1-2 lp/mm.
Radiographic film-screen combinations are capable of displaying 5-9 lp/mm
The brightness gain of image intensifiers tends to range from 5000-20000
A Linear accelerator is a device used to accelerate subatomic particles for radiation therapy
Electron beams are typically used to treat superficial tumors overlying cartilage and bone
In 1896 this person discovered that certain naturally ocurring substances emitted radiation Becquerel
An English physicist named _____________named the radiations identified by Becquerels as alpha, beta, and gamma radiations after the first three letters of the Greek alphabet Ernest Rutherford
Alpha radiation, symbolized by the Greek letter is made up of 4 particles and does not easily penetrate matter.
Alpha particles are very large and slow moving particles that carry a lot of energy.
Alpha particles have a mass of 4 amu and a charge of +2.
They are described as a helium atom nucleus and are produced by nuclear disentigration
They have a range in air of about 1cm for each meV of energy they posess.
Mosdt naturally occurring Alpha particles travel 4-8 cm
Beta radiation is symbolized by the Greek letter for Beta and consists of high speed electrons with a charge of -1 or +1
They are produced by nuclear disentigration
Beta particles can travel approximately 3 meters/MeV of energy in air and up to several mm in tissue
Positron emission tomography abbreviated PET employs the use of positrons which are positively charged electrons
All electromagnetic waves travel with the same velocity 3.0x10(^8) meters per second
The higher the energy of an electromagnetic wave, the shorter the wavelength and the higher the frequency
X-rays are produced outside the nucleus by accelerating electrons and having them strike a metal target
Gamma Rays are produced in the nucleusand are identical to x-rays in energy, wavelength and frequency
Like x-rays gamma rays have no mass, and no charge
The traditional unit used to measure exposure in air is the Roentgen, abbreviated R
The SI Unit is coulombs per kilogram, abbreviated C/kg It is a measure of ionization in air produced by x-radiation or gamma radiation below 3 MeV
The SI Unit of electric charge is the Coulomb
Disadvantages of the pocket ionization chamber include: Charge can leak on the dosimeter, causing a false reading
Mechanical trauma can change the reading. Easy to misread
The SI unit used to express absorbed dose is the Gray (Gy) while the traditional unit is the rad
The rad is defined as an energy transfer of 100 ergs.
1 rad is equal to 0.01 gray.
The ratio between the number of roentgens (exposure) and the number of rads (energy transfer) is called the f-factor.
The rem is an acronym for radiation equivalent mean
The Si unit of biologic effect is the Seivert abbreviated Sv
Rems are determined by multiplying the absorbed dose in rad times a quality factor
The results are expressed as dose equivalence
The most common use of rems is for personal radiation monitoring
The traditional unit of radioactivity is the curie abbreviated Ci
The SI Unit of radioactivity is the Becquerel abbreviated Bq
Both units Curie, and Becquerel measure the rate of nuclear disentigration (decay) of a material
The Curie is defined as 3.7 x 10 (^10) disentigrations per second (dps)
The Becquerel is defined as one dps of any radioactive substance
The time is takes for any radioactive material to decay to 50% of its original activity is known as the half life
Roentgens measure exposure and are used for measuring intensity of the radiation
Rads are used to measur absorbed energy and are used to talk about dose from radiation
Rems are used in dosimetry and measure biologic effects
1 milliroentgen is equal to 0.001 roentgen
1 millirad is equal to 0.001 rad
1 microCurie is equal to one millionth (10(^-6)) of a Curie
One centigray, abbreviated cGy is equal to 0.01 (10(^-2)) Gray or 1 Rad
Dosimetry is the determination by scientific methods of the amount, rate and distribution of radiation emitted from a source of ionizing radiation
Three types of field survey instruments inculde ionization chamber, GM detector and portable scintillation detectors
The ionization chamber determines the amount of radiation by collecting ions in a chamber filled with gas, usually helium or argon
Ionization chambers are most widely used in measuring either the dose total amount of radiation) in milliroentgens or the exposure rate in milliroentgens per hour
ionization chambers are good at detecting x-rays, gamma rays and high energy beta radiation. They are not well suited for ALPHA radiation
GM detector probes have a very thin window that allows for the detection of alpha, beta and gamma radiation. They are not sensitive to very low energy alpha, beta and gamma radiation
GM counters are most useful in the detection rather than the measurement of radiation sources and low level radioactive contamination
The scintillation counter uses a sodium iodide or cesium iodide crystal that produces small light flashes of light called scintillations upon exposure to radiation Light from the scintillation crystal is detectable by a photomultiplier tube which converts the light flashes into electrical impulses which can be measured
The three basic types of personnel monitoring devices include: film badges,TLD's and pocket ionization chambers
Film badges are sensitive down to about 10 mrem (=0.1mSv)
Film badges have an upper sensitivity in the range of 700-2000 rem
The range of stated accuracy for film badges is between +/- 25% to +/- 50%
Advantages of film badges include inexpensive, easy to handle, easy to process, permenant record of exposure, wide range of sensitivity
Thermoluminescent dosimeters use lithium flouride (LiF)
TLD's can be worn up to 3 months, can be reused, and are more sensitive than film badges
TLD's are sensitive down to about 5 mrem or 0.05 mSv and show accuracy of around +/- 7%
TLD;s show the advantage of absorbing radiation approximately in the same way human tissue absorbs radiation
The biggest disadvantage of TLD's is that they do not provide a permenant record
A pocket ionization chamber is similar to other ion chambers and consists of two electrodes in an air filled chamber
Advantages of the pocket ionization chamber include: can be used for short periods of time, can give immediate readings, useful for monitoring personnel that are not normally monitored
Disadvantages of the pocket ionization chamber include: charge can leak on the dosimeter, causing a false reading. Mechanical trauma can change the reading. Easy to misread.
Created by: ABIGAILDRAKE1984