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University of Illinois at Chicago Radiation Safety Section Environmental Health and Safety Office

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University of Illinois at Chicago Radiation Safety Section Environmental Health and Safety Office Radiation Safety Physics Lecture Physics 108, 244 – PowerPoint PPT presentation

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Title: University of Illinois at Chicago Radiation Safety Section Environmental Health and Safety Office


1
University of Illinois at Chicago Radiation
Safety Section Environmental Health and Safety
Office
Radiation Safety Physics Lecture
  • Physics 108, 244

2
Ionizing Radiation
  • Radiation that can cause ionization of the
    material through which it passes either directly
    or indirectly
  • Electromagnetic radiation
  • Particulate radiation

3
Electromagnetic Radiation
  • Electro-magnetic waves (uncharged packets of
    energy) propagated through space or a material
    medium

Wavelength, m
Frequency, s-1
Energy of one photon, eV
4
Particulate Radiation
  • Matter that that is propagated through space or
    through a material medium
  • Alpha Particles
  • Beta Particles (Electrons, Positrons)
  • Neutrons (uncharged)
  • Protons
  • Heavy Ions
  • Fission Fragments

5
Sources of Ionizing Radiation
  • Radioactive Materials
  • H-3, C-14, P-32, S-35, I-125, etc.
  • Radiation Producing Machines
  • X-Ray equipment
  • Accelerators
  • Computer Tomography, C.T.
  • Fluoroscopy
  • Mammography

6
Radioactive Decay
  • Atoms that have a neutron to proton ratio that is
    too high or too low undergo the process of
    radioactive decay
  • Radioactive decay is the spontaneous emission of
    matter and/or energy from the nucleus of the atom
  • Particles Alpha and/or Beta Particles
  • Energy Gamma Rays and X-Rays
  • As a result of radioactive decay the atom
    transforms into a different element, which can be
    either stable or also radioactive

7
Nature of Radioactive Decay
  • Decay is random, predicting when a given atom
    will decay is impossible
  • In sufficient numbers, the probability of decay
    becomes well defined
  • Decay Constant (?) The probability that any one
    atom will decay

8
Activity
  • Activity is the rate at which nuclear
    transformations occur in a radioactive material
    (rate of decay)
  • A ?N
  • Number of radioactive atoms and, as a result,
    activity decreases exponentially with time
  • N N0exp(-?t)
  • A A0exp(-?t)

9
1/2
1/4
1/8
T1/2
T1/2
T1/2
10
Units of Activity
  • Modern SI Unit
  • Becquerel (Bq)
  • 1 Bq 1 decay per second
  • Traditional Unit
  • Curie (Ci)
  • The number of radioactive decays occurring in
    one gram of pure Ra-226
  • 1 Ci 3.7 x 1010 Bq 37 GBq

11
Modes of Radioactive Decay
  • Alpha Decay
  • Lowers the n/p ratio
  • Usually occurs when atomic number is gt 83
  • Beta Decay (- or )
  • Negative Betas (Negatrons) - Lowers the n/p ratio
  • Positive Betas (Positrons) - Raises the n/p ratio
  • Electron Capture
  • Raises the n/p ratio

12
Beta Decay
  • A neutron transforms into a proton, an electron,
    and an anti-neutrino

H-3
He-3
13
Gamma Emission
  • After decay, some nuclei (called isomers) are
    left in an excited state (extra energy)
  • Excitation energy may be emitted as a gamma ray

14
Gamma Decay (Cs-137)
661 keV Gamma
Beta
Cs-137 T1/2 30 yr
Ba-137m T1/2 2.55 min
Ba-137 STABLE
15
Tl-204 Decay
Tl-204 (T1/2 3.779 yr)
97.4
2.6
Pb-204
Hg-204
16
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17
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18
Absorbed Dose
  • ABSORBED DOSE - The amount of energy imparted per
    unit mass at a given location within irradiated
    material
  • RAD (rad) - The traditional unit of dose,
    defined as the absorption of 100 ergs per gram
    (0.01 J / kg or 0.01 Gy)
  • GRAY (Gy) The SI unit of dose, defined as the
    absorption of 1 joule per kilogram (100 rads)

1 Gy 100 rad
19
Exposure
  • A measurement of the amount of ionization created
    by X-rays or gamma rays in a volume of air
  • Roentgen 2.58 10-4 Coulombs / kg air
  • Exposure to 1 R delivers a dose of 0.96 rad to
    tissue

20
Biological Effectiveness
  • Equivalent Dose A quantity that expresses the
    biological effect of exposure to the different
    types of radiation.
  • Radiation weighting factor (wR) - estimate of the
    effectiveness per unit dose of the given
    radiation relative a to low-LET standard (X-ray
    or gamma)
  • Equivalent Dose Absorbed Dose wR

21
Equivalent Dose
  • REM (rem) - The traditional unit of dose of any
    radiation which produces the same biological
    effect as a 1 rad of absorbed dose of x- or
    gamma-rays
  • Sievert (Sv) The SI unit of dose of any
    radiation that produces the same biological
    effect as a 1Gy of absorbed dose of x- or
    gamma-rays

1 Sv 100 rem
22
Radiation weighting factors
Type of Radiation wR
X-Rays 1
Gamma-Rays 1
Beta Particles 1
Alphas 20
Neutrons 2-20
23
Stochastic Effects
  • Cancer
  • Radiation is a weak carcinogen
  • Genetic
  • Magnitude thought to be very small

24
Stochastic Risks
  • The PROBABILITY that an effect occurs is related
    to the magnitude of the radiation dose
  • No relation between magnitude and severity of the
    effect all or none response for an individual
  • Same effect can be seen in unexposed individuals

25
Radiation Risk Estimates
  • International Commission on Radiological
    Protection (ICRP) Publication 103 (2007)
  • Nominal Risk for Stochastic Effects After
    Exposure to 1 Sv at Low Dose Rates

Cancer 5.5 (0.055 per 1 rem)
Heritable Effects 0.2 (0.002 per 1 rem)
For acute exposures a factor of 2 is used for
risk estimates
U.S. Cancer death rate 21.20 (40.6
total) With exposure to 5 rem 21.48
26
Radiation Levels (mrem/year)
27
Radiation Levels (mrem/year)
28
Radiation Levels (mrem/year)
29
Radiation Levels (mrem/year)
PART OF BODY OCCUPATIONAL EXPOSURE OCCUPATIONAL EXPOSURE
PART OF BODY ADULTS MINORS
WHOLE BODY SKIN EXTREMITIES LENS OF EYE 5,000 mrem 50,000 mrem 50,000 mrem 15,000 mrem 500 mrem 5,000 mrem 5,000 mrem 1,500 mrem
EMBRYO/FETUS (Declared Pregnancies) 500 mrem N/A
INDIVIDUAL MEMBERS OF THE PUBLIC - 100 mrem INDIVIDUAL MEMBERS OF THE PUBLIC - 100 mrem INDIVIDUAL MEMBERS OF THE PUBLIC - 100 mrem
30
Radiation Levels (mrem/year)
28 mrem
Dental bitewing Chest Radiograph Mammogram Head CT Barium Enema Chest or abdomen CT Coronary CT angiography Abdomen and pelvis CT Thallium myocardial perfusion lt 10 mrem 10-20 mrem 30-60 mrem 100-200 mrem 300-600 mrem 500-700 mrem 500-1200 mrem 800-1100 mrem 3500-4000 mrem
31
Radiation Levels (mrem/year)
500
32
Radiation Levels (mrem/year)
500
50
33
Exposure Rate Constant How to calculate your
radiation dose if you know the isotope, the
activity the distance.
34
Exposure Rate Calculation From a 10µCi Cs-137
Point Source at 1 cm (3.287 is the Exposure Rate
Constant for Cs-137)
35
Exposure Rate at Various Distances From 10µci of
Cs-137
  • 0.1 cm 3287 mR/h
  • 1.0 cm 32.87 mR/h
  • 10 cm 0.3287 mR/h
  • 100 cm 0.003287 mR/h

36
Radiation Levels (mrem/year)
500
50
37
ALARA Policy
  • As
  • Low
  • As
  • Reasonably
  • Achievable

38
Standard Warning Sign For Radioactive Material
Use Areas
  • Used to indicate an area is authorized for
    radioactive material use BUT only by projects
    that have it listed in their authorization!

39
Lab Entrance Labeling
LOW
MEDIUM
HIGH
40
Basic Principles of Radiation Protection
  • Time
  • Distance
  • Shielding
  • Contamination Control

41
Time
  • Radiation dose is directly proportional to the
    time of exposure

42
Distance
  • Inverse Square Law
  • Radiation intensity is inversely proportional
    to the distance squared

I1
I2
d1
d2
43
Shielding
44
Rules for Handling Sources
  • DO NOT place your
    finger or any other part
    of your body directly
    over the face of the
    source
  • Handle the sources
    only by their edges
  • Minimize the time
    sources are handled
  • Increase distance to minimize exposure
  • Sign sources in and out with the T.A.

45
Lab Coats
  • You will be working with Sealed Sources only.
  • Lab coats and gloves are to be worn in the lab
    when handling UNSEALED radioactive material.
  • When working with SEALED radioactive sources, lab
    coats and gloves are NOT required.

46
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