Lecture 6Lecture 6

• Opening Packages of Radioactive MaterialsOpening Packages of Radioactive Materials

• Records of Radioactive Materials UsesRecords of Radioactive Materials Uses

• Radioactive Waste DisposalRadioactive Waste Disposal

• Units used in Radiation Safety and Units used in Radiation Safety and Radiation BiologyRadiation Biology

Measure of

Amount ofradioactive material Ionization in air

Absorbed energy per mass

Absorbed dose weighted by type of radiation

Radiation UnitsRadiation Units

*Note: For most types of radiation 1 R 1 rad = 1 rem

Quantity

Activity

Exposure

Absorbed Dose

Dose Equivalent

Unit

curie (Ci)

roentgen (R)

Rad(mRad)

Rem(mRem)

In some cases, SI units have In some cases, SI units have replaced conventional units.replaced conventional units.

Sources of Average Radiation Dose to the U.S. Population

Radon, 20055%

Internal, 3910%

Terrestrial, 288%

Cosmic, 278%

Nuclear Medicine, 144%

Medical x-rays, 3911%

Consumer Products, 103%

Other, 30.8%

Source: BEIR V Report, 1990

Background RadiationBackground Radiation360 millirem per year360 millirem per year

Radiation Exposures at AMHRadiation Exposures at AMH

• The average occupational radiation exposure to all The average occupational radiation exposure to all personnel, who do not handle radioactive material or personnel, who do not handle radioactive material or perform invasive radiology/cardiology procedures, is perform invasive radiology/cardiology procedures, is less than 100 millirem per year.less than 100 millirem per year.

• For radiation workers, the federal and state For radiation workers, the federal and state annualannual radiation exposure limits are set to safe levels radiation exposure limits are set to safe levels (negligible risk of biological effects). The annual (negligible risk of biological effects). The annual whole body radiation exposure limit is 5000 millirem.whole body radiation exposure limit is 5000 millirem.

Radiation ExposureRadiation Exposure

• Roentgens still used.Roentgens still used.

• One Roentgen = 2.58 Coulomb/KG of airOne Roentgen = 2.58 Coulomb/KG of air

• Therefore, Roentgen is measured as Q/mTherefore, Roentgen is measured as Q/m

• Q/m = Charge/MassQ/m = Charge/Mass

• Useful in the range of photon energies used in Useful in the range of photon energies used in radiological sciences.radiological sciences.

Radiation Exposure Continued,Radiation Exposure Continued,

• Devices expressly designed to measure Devices expressly designed to measure exposure are called air ionization chambers.exposure are called air ionization chambers.

Exposure Exposure • Must be able to assess the intensity of radiation in Must be able to assess the intensity of radiation in

an environment.an environment.

• Devices can measure the magnitude of electrical Devices can measure the magnitude of electrical charge produced in a detector.charge produced in a detector.

• Radiation Exposure means the quantity of Radiation Exposure means the quantity of electrical charged produced per unit mass of air in electrical charged produced per unit mass of air in a detectora detector

Exposure Exposure • Mathematical Definition:Mathematical Definition:

• X = Q/mX = Q/m

• where X = Exposurewhere X = Exposure

• Q Q = charge (in Coulombs) = charge (in Coulombs)

• mm = mass of air = mass of air

Units used for Exposure Units used for Exposure

• Roentgen: 2.58 x 10**-4 C/kg.Roentgen: 2.58 x 10**-4 C/kg.

• Still widely used.Still widely used.

• Most survey meters have scales in units of R, and Most survey meters have scales in units of R, and in cpmin cpm

What is a “Dose” of RadiationWhat is a “Dose” of Radiation??

• When radiation’s energy is deposited into our body’s When radiation’s energy is deposited into our body’s tissues, that is tissues, that is a dosea dose of radiation. of radiation.

• The more energy deposited into the body, the higher the The more energy deposited into the body, the higher the dose.dose.

• Rad Rad is a unit of measure foris a unit of measure for radiation dose.radiation dose.

• Small doses expressed inSmall doses expressed in mrem mrem = 1/1000 rem= 1/1000 rem..

• RemRem & & RR (Roentgens) are similar units that are often (Roentgens) are similar units that are often equated to the Rad.equated to the Rad.

Radiation Absorbed Dose (RAD)Radiation Absorbed Dose (RAD)

• Absorbed dose is measured as E/mAbsorbed dose is measured as E/m

• Where E=energy, m = mass of absorber Where E=energy, m = mass of absorber material.material.

• 1 joule = 1.0 x 101 joule = 1.0 x 1077 ergs ergs

• 1 RAD = 100 ergs of energy deposited /gram 1 RAD = 100 ergs of energy deposited /gram of absorbing material.of absorbing material.

• One Rad = 1.0 x 10One Rad = 1.0 x 105 5 ergs/kilogramergs/kilogram..

Radiation Absorbed Dose (Gray)Radiation Absorbed Dose (Gray)

• One Gray = 1 Joule/kgOne Gray = 1 Joule/kg

• 1 joule = 1.0 x 101 joule = 1.0 x 1077 ergs ergs

• And one Rad = 1.0 x 10And one Rad = 1.0 x 105 5 ergs/kilogram.ergs/kilogram.

• Therefore, one Gray = 100 rads.Therefore, one Gray = 100 rads.

• 1 rad = 0.01 Gray1 rad = 0.01 Gray

Absorbed Dose MeasurementsAbsorbed Dose Measurements

• We want to be able to quantify the amount We want to be able to quantify the amount of damage to a unit mass of tissue. of damage to a unit mass of tissue.

• RAD: Radiation Absorbed DoseRAD: Radiation Absorbed Dose

• SI Unit: GraySI Unit: Gray

• 1 Gray = 100 Rads1 Gray = 100 Rads

• 1 Gray = 1 joule/kg of tissue. 1 Gray = 1 joule/kg of tissue.

• 1 rad = 100 ergs/gm.1 rad = 100 ergs/gm.

Dose EquivalentDose Equivalent

• Different biological effects results from the Different biological effects results from the same dose of different types of radiation.same dose of different types of radiation.

• DE = DQNDE = DQN

• Where, D = absorbed dose in Grays or rads, Q Where, D = absorbed dose in Grays or rads, Q = quality factor for the type of radiation, N = = quality factor for the type of radiation, N = product of all other modifying factors that product of all other modifying factors that apply in a given situation.apply in a given situation.

Equivalent to What?Equivalent to What?

The dose of one type of radiation that The dose of one type of radiation that produces the same amount of biological produces the same amount of biological

damage as the dose of a reference damage as the dose of a reference radiation which produces the radiation which produces the

equivalentequivalent amount of damage. amount of damage.

Effective Dose EquivalentEffective Dose Equivalent

• HHEE = = ΣΣwwii x H x Hii

• Where: HWhere: HEE = Effective dose equivalent, = Effective dose equivalent,

• Σ Σ wwii x H x Hi i Means “the sum of” the product of Means “the sum of” the product of

individual dose equivalents and weighting individual dose equivalents and weighting factor for the particular organ. factor for the particular organ.

Effective Dose EquivalentEffective Dose Equivalent

• The effective dose equivalent for the whole-The effective dose equivalent for the whole-body is the sum of dose-equivalents for body is the sum of dose-equivalents for various organs in the body weighted to various organs in the body weighted to account for different sensitivities of the organs account for different sensitivities of the organs to radiation. It includes the dose from radiation to radiation. It includes the dose from radiation sources internal and/or external to the body. sources internal and/or external to the body. The effective dose equivalent is usually The effective dose equivalent is usually expressed in units of millirem (mrem). expressed in units of millirem (mrem).

Q FactorQ Factor

• Dose is influenced by LET: ionization per unit Dose is influenced by LET: ionization per unit path length. path length.

• LET measured as keV/mm or micron.LET measured as keV/mm or micron.• RBE: Relative Biological Effectiveness, RBE: Relative Biological Effectiveness,

determines the dose equivalent. determines the dose equivalent. • RBE defined: The ratio of the absorbed dose RBE defined: The ratio of the absorbed dose

that produces the same damage as the that produces the same damage as the reference dose.reference dose.

Biological EffectivenessBiological Effectiveness

• Not all types of radiation produce the same Not all types of radiation produce the same level of damage. level of damage.

• Higher LET, such as charged particles, will Higher LET, such as charged particles, will produce greater damage along a path produce greater damage along a path length/ amount of energy imparted to tissue.length/ amount of energy imparted to tissue.

• A quality factor (RBE) relative biological A quality factor (RBE) relative biological effectiveness, is applied to measurements to effectiveness, is applied to measurements to account for this.account for this.

Biological EffectivenessBiological Effectiveness

• REM: Roentgen Equivalent Man.REM: Roentgen Equivalent Man.

• REM takes dose measured in rads and REM takes dose measured in rads and multiplies by the QF to obtain the dose multiplies by the QF to obtain the dose equivalent. Equivalent to what?equivalent. Equivalent to what?

• Gamma and beta radiation are assigned 1.Gamma and beta radiation are assigned 1.

• Therefore, alpha, with QF of 20, is Therefore, alpha, with QF of 20, is equivalent to 20 times the damage from the equivalent to 20 times the damage from the same dose of gamma radiation. same dose of gamma radiation.

RBE ExamplesRBE Examples

• If 20 RADs of x-rays produce the same If 20 RADs of x-rays produce the same biological damage as one rad of neutrons, the biological damage as one rad of neutrons, the RBE is 20. The quality Factor for x-rays of RBE is 20. The quality Factor for x-rays of this type is therefore 20.this type is therefore 20.

• QF is really the only modifying factor used in QF is really the only modifying factor used in practice. Therefore N in the above equation practice. Therefore N in the above equation can be set to 1, giving:DE = DxQcan be set to 1, giving:DE = DxQ

Units of RadioactivityUnits of Radioactivity

• Curie (Ci): 3.7 x 10Curie (Ci): 3.7 x 1010 10 dpsdps

• milliCurie (mCi): 3.7 x 10milliCurie (mCi): 3.7 x 107 7 dpsdps

• microCurie (uCi): 3.7 x 10microCurie (uCi): 3.7 x 104 4 dpsdps

• Bequerel (Bq): 1 dpsBequerel (Bq): 1 dps

• kiloBequerel (kBq): 1.0 x 10kiloBequerel (kBq): 1.0 x 1033 dps dps

• megaBequerel (kBq): 1.0 x 10megaBequerel (kBq): 1.0 x 1066 dps dps

Half-LifeHalf-Life

• Half-life is the Half-life is the amount of time amount of time needed for the needed for the activity to reach one activity to reach one half of the original half of the original amount.amount.

f1

2

tT1/2

f e t ln ( )2

T1/2

Days

0 20 40 60 80 1000.00

0.20

0.40

0.60

0.80

1.00

One half-life

Two half-lives

0.007

Some Other TermsSome Other Terms

• Flux: # of neutrons, photons, etc, passing Flux: # of neutrons, photons, etc, passing through one cmthrough one cm22/instant of time/instant of time

• Fluence: # of neutrons, photons, etc, that Fluence: # of neutrons, photons, etc, that passed through one cmpassed through one cm2 2 over a period of time.over a period of time.

• Cross Section: a probability of interaction, and Cross Section: a probability of interaction, and thus transmutation after target bombardment.thus transmutation after target bombardment.

Measurement of RadioactivityMeasurement of Radioactivity

• Gas filled detectors.Gas filled detectors.

• Radiation ionizes gas molecules. The free Radiation ionizes gas molecules. The free electrons are attracted to the anode, positive electrons are attracted to the anode, positive charges to the cathode.charges to the cathode.

• This exists because there is a potential This exists because there is a potential difference across the electrodes.difference across the electrodes.

Detecting and Measuring RadiationDetecting and Measuring Radiation

Instruments:Instruments:• Verify presence of radiation or locate contamination Verify presence of radiation or locate contamination

- GM Survey Meter (Geiger counter)- GM Survey Meter (Geiger counter)- NaI Survey Meter (Sodium iodide detector)- NaI Survey Meter (Sodium iodide detector)

Personal Dosimeters: Personal Dosimeters: • Measure doses (radiation exposure) to staffMeasure doses (radiation exposure) to staff

– Radiation Badge: Luxel / Film / TLDRadiation Badge: Luxel / Film / TLD

Typical background is 0.03 mR/hr or 100 cpm

GM pancake probe

NaI probe

Range selector

Batterycheck

Review of Sample Dosimetry ReportReview of Sample Dosimetry Report

• Series code “F”Series code “F”

• Participant Number (Part. No.)Participant Number (Part. No.)

• Dosimeter (Badge) type – “chest” vs. “collar”Dosimeter (Badge) type – “chest” vs. “collar”

• 3 Categories of Exposure / Exposure Limits 3 Categories of Exposure / Exposure Limits (Deep/Eye/Shallow)(Deep/Eye/Shallow)

• Wear PeriodWear Period

• Quarterly exposuresQuarterly exposures

• Year to dateYear to date

• LifetimeLifetime

RegionsRegions

• Recombination: If the voltage is to low, the ions Recombination: If the voltage is to low, the ions recombine before reaching the electrodes.recombine before reaching the electrodes.

• Ionization (Ion Chambers) Size of pulse directly Ionization (Ion Chambers) Size of pulse directly related to energy deposited. Thus, can measure related to energy deposited. Thus, can measure exposure in Roentgens.exposure in Roentgens.

• Proportional Basically the same as Ion except Proportional Basically the same as Ion except stronger signal. Probably better in lower radiation stronger signal. Probably better in lower radiation areas where you still want exposure measurements. areas where you still want exposure measurements.

RegionsRegions

• Geiger-Mueller (The Geiger counter) Very Geiger-Mueller (The Geiger counter) Very sensitive to small amounts of radiation. Best sensitive to small amounts of radiation. Best calibrated for cpm and to locate radiation. calibrated for cpm and to locate radiation.

• Use ion chamber for exposure (hence dose)Use ion chamber for exposure (hence dose)

Scintillation Detectors.Scintillation Detectors.

• The most sensitive to radiation. Calibrated in The most sensitive to radiation. Calibrated in cpm.cpm.

• Can detect very small amounts.Can detect very small amounts.

• The type of survey meter that is used at The type of survey meter that is used at landfillslandfills

Multichannel AnalyzersMultichannel Analyzers

• It should be easy to differentiate between the types of It should be easy to differentiate between the types of radiation if there exists a relationship between energy radiation if there exists a relationship between energy deposited in a crystal, and size of pulse.deposited in a crystal, and size of pulse.

• Therefore, one can discriminate between various Therefore, one can discriminate between various energy levels.energy levels.

• Very useful for the identification of types of Very useful for the identification of types of radiation.radiation.

• In imaging, isolates the energy used for imaging, such In imaging, isolates the energy used for imaging, such as Tc-99mas Tc-99m

Image of the WeekImage of the Week

Neurological PET We will now examine the effects of various external stimuli on the PET scan image. The first stimulation Neurological PET We will now examine the effects of various external stimuli on the PET scan image. The first stimulation is auditory, i.e. the subject will listen to some music.is auditory, i.e. the subject will listen to some music.Notice the increased activity in the PET image containing the auditory cortex. Note that nonverbal stimuli (music) Notice the increased activity in the PET image containing the auditory cortex. Note that nonverbal stimuli (music) predominantly activates the nondominant (right) hemisphere. Simultaneous stimulation with language and music would predominantly activates the nondominant (right) hemisphere. Simultaneous stimulation with language and music would cause a more bilateral activation of the auditory cortex. cause a more bilateral activation of the auditory cortex.   

  

The subject now must perform a "thinking" task, The subject now must perform a "thinking" task, Notice the increased activity in the Notice the increased activity in the stimulated brain PET image (arrowhead). This region of increased activity corresponds to stimulated brain PET image (arrowhead). This region of increased activity corresponds to the frontal cortexthe frontal cortex