Rad Bio 11/09 Test
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What are two groups of sources in a radiation therapy department?
External Beam (ie linear accerator, cobalt therapy unit)
Brachytherapy (ie cesium 137, iridium 192, iodine 125)
Radiation with sufficient energy to separate an electron from its atom:
What do alpha particles consist of?
2 protons and 2 neutrons (a helium nuclei)
Charge: +2 Atomic Mass: 4
What are alpha particles emitted from?
- Unstable heavy nuclei
- ie. radon, radium
High or Low LET?
- Alpha particles are High LET
- Can only travel short distances & can be stopped by a sheet of paper.
Alpha particles are hazardous if:
Ingested or Inhaled
Can alpha particles be used for external beam therapy?
- Beta Particles:
- Charge Atomic Mass
- Negatron (B-) -1 0
- Positron (B+) +1 0
What is the origin of beta particles?
- Beta particles are electrons emitted by the nucleus.
- Can carry one unit of negative charge Negatron (B-)
- carry one unit of positive charge Positron (B+)
Whenever beta particles are emitted, they are accompanied by a small, massless, chargeless particle known as a:
___________ are not stable and can only exist for short periods of time
Positrons are not stable and can only exist for short periods of time.
High energy (1MeV) Beta particles may have range as long as _______ in soft tissue.
What is Bremsstrahlung radiation more likely to occur with?
What are the most common types of ionizing radiation used in XRT?
X-rays, Gamma rays & Electrons
X-rays & gamma rays are both forms of:
Electromagnetic radiation (photons)
How much exposure comes from natural background sources?
How is the background radiation broken down?
- Radon 55%
- Cosmic 8%
- Terrestrial 8%
- Internal 11%
What is the secong leading cause of lung Ca in the US?
1 Gy = 100 cGy = 100 rad
100 rad = 1 Gy = 100 cGy
The amount of ionization produced by photons in air per unit mass of air:
- traditional: roentgen (R)
- SI: 2.58 x 10-4 C/kg
What is the traditional unit for absorbed dose?
- Radiation Absorbed Dose
What the units of measure for exposure?
Traditional: roentgen (R)
SI: C/kg (Coulomb of charge per kilogram of air)
1R = 2.58 x 10-4 C/kg
What are the units of measure for absorbed dose?
1Gy = 100 rad
What takes in to account the fact that different types of radiation produce different amounts of biologic damage?
Each type of radiation is assigned a _________ _________ to account for the different biologic effects & responses
Quality Factor (QF)
Quality Factor (QF) is also known as
What are the units of measure for dose equivalent?
SI: sievert (Sv)
100rem = 1Sv
What are the units of measure for activity?
Traditional: curie (Ci) 3.7x1010 disintegrations per second
SI: becquerel (Bq) 1 disintegration per second
1Ci = 3.7 x 1010 Bq
The rate at which a radioactive isotope undergoes nuclear decay:
1Ci = 3.7x1010 Bq
1 Ci = 1000 mCi
1 mCi = 1000 uCi
The energy absorbed per unit mass of any material:
1 Gy = 100 rad = 100 cGy
Quality Factor (QF) of x-rays & gamma rays:
Quality Factor (QF) of beta particles, positrons & muons?
Quality Factor (QF) of high energy external protons:
Quality Factor (QF) of protons, other than recoil protons & energy
Quality Factor (QF) of thermal neutrons:
Quality Factor (QF) of fast neutrons:
Quality Factor (QF) of alpha particles:
Quality Factor (QF) of fission fragments & other heavy nuclei:
What are two types of gas-filled detectors?
- Ionization Chamber
- Geiger-Muller Detecter (GM)
What is the sensitivity of a gas filled detector dependant upon?
The mass of the gas within the chamber (chamber volume) & the Applied Voltage
A type of detector that consists of two electrodes within a gas filled chamber, an applied voltage accross the electrodes & electronics and a meter to amplify & measure the electrical signal
- Ionization Chamber
- (the simplest kind)
When ionization chambers are properly calibrated, their accuracy approaches _____%, which makes them suitable for the measurement of radiation output of therapy machines.
What is a form of ionization chamber used for personnel monitoring?
Because of their sensitivity, are ionization chambers suitable for the detection of very low levels of radiation or comtamination?
Because of their sensitivity, are GM detectors suitable for detection of very low levels of radiation or contamination?
Should a GM detector be used to measure the high energies of a LINAC?
- The GM counter can overload & produce a reading of zero if placed in a high level radiation field
What kind of gas-filled detector can detect individual ionization events & responds defferently to different photon energies?
Geiger-Muller (GM) Detector
(strongly energy dependent)
What kind of detector gives off light when heated?
- Thermoluminescent Dosimeters
Because of ________, TLDs are ________ used to measure radiation in a number of applications
- their SMALL SIZE
- WIDELY used
What is the atomic number of Lithium Fluoride similar to?
- The atomic number of LiF is close to that of
What is the accuracy rate of TLDs?
If proper care is taken, doses can be measured with an accuracy of approx: 5%
TLDs: The more radiation absorbed by the crystal, the more _______ will be in the ______ & the more _______ will be released when the crystal is heated later.
The more radiation absorbed by the crystal, the more ELECTRONS will be in the TRAPS and the more CHARACTEISTIC PHOTONS will be released when he crystal is heated later.
The amount of ________ is a measure of the dose received by the crystal.
What kind of detector can store the dose info for hours, days, or even weeks?
all info is lost if heated in transit
What kind of detector can be used for mailed intercomparison of therapy unit calibration, in ring badges for personnel and/or for rmeasurements of environmental levels of radiation?
After development, x-ray film turns black. The level of blackness is called the:
Optical Density, or the amount of _______, is related to the ________ of _________ received by the film
Once calibrated, the film badge is a _____ and ______ way to provide info about the dose received by workers & visitors
A typical ________ has a slot in which the _______ may be placed & several thin metal filters that surround portions of the _______.
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