devil physics the baddest class on campus ib physics...
TRANSCRIPT
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DEVIL PHYSICSTHE BADDEST CLASS ON CAMPUS
IB PHYSICS
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TSOKOS OPTION I-3RADIATION IN MEDICINE
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IB Assessment Statements
I.3.1. State the meaning of the terms exposure, abosorbed dose, quality factor (relative biological effectiveness) and dose equivalent as used in radiation dosimetry.
I.3.2. Discuss the precautions taken in situations involving different types of radiation.
I.3.3. Discuss the concept of balanced risk.
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IB Assessment Statements
I.3.4. Distinguish between physical half-life, biological half-life and effective half-life.
I.3.5. Solve problems involving radiation dosimetry.
I.3.6. Outline the basis of radiation therapy for cancer.
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IB Assessment Statements
I.3.7. Solve problems involving the choice of radio-isotopes suitable for a particular diagnostic or therapeutic application.
I.3.8. Solve problems involving particular diagnostic applications.
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Objectives
Outline the effects of ionizing radiations on living things
Describe how radiation is measured
Solve problems involving absorbed dose (D = E/m), dose equivalent (H = QD), and exposure (X = Q/m)
State the meaning of half-life, biological half-life and effective half-life and solve problems using 1/TE = 1/TP + 1/TB
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Transition
Chapter 7 – Atomic and Nuclear Physics
Radioactive Decay
Types of Radioactive Particles
Option I – Radiation in Medicine
Option I-2, Radiation in Medical Imaging
Option I-3, Radiation in Medical Therapy
Radiation in the Closet Lab
Let’s take a look
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Biological Effects
Natural Sources of Radiation
Radon gas
Unstable isotopes in food
Gamma radiation from the earth
Cosmic rays from space
Greenhouse Effect???
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Biological Effects
Artificial Sources of Radiation
Nuclear weapons
Nuclear power plants
Medical diagnostics
Medical Therapy
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Biological Effects
What makes radiation bad?
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Biological Effects
What makes radiation bad?
Radiation on the order of 1 eV or greater carries enough energy to break molecular bonds
Molecules break apart causing enzymes which control cell functions to operate incorrectly
Damage to genes (as well as jeans)
Teenage Mutant Ninja Turtles
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Biological Effects
What makes radiation bad?
Irradiation can produce free radicals which induce changes in molecules with biological implications
HOHOHe
HOOHOHOH
eOHOH
2
322
22
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Biological Effects
What makes radiation bad?
Bone marrow is particularly susceptible to radiation
Blood cell production
Immune system
Causes leukemia and other cancers
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Safeguards
Keep as far as possible from the source
Keep exposure as short as possible
Use shielding whenever possible
Take food with you during a lockdown with Nick
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How to know when you’ve had too much
Absorbed dose (D) is defined as the amount of energy (E) absorbed by a unit of mass of the irradiated material,
The unit for absorbed dose is the gray (Gy) which is 1 J/kg
1 Gy equal to 100 rads
m
ED
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How to know when you’ve had too much
Damage from radiation is not only dependent on the amount of exposure, but also on the type of radiation
High school classes that cause large amounts of brain damage are identified by quality points
Radiation that causes the most amount of brain damage is identified by quality factors
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How to know when you’ve had too much
Dose Equivalent (H) is defined as the product of the absorbed dose (D) and a dimensionless quality factor (Q),
What then, is the unit for dose equivalent?
QDH
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How to know when you’ve had too much
Dose Equivalent (H) is defined as the product of the absorbed dose (D) and a dimensionless quality factor (Q),
What is the unit for dose equivalent?
Yeah, you’d think so
Even though it has the same composite units as absorbed dose (1 J/kg = 100 rads), we use sievert(Sv) as the unit for dose equivalent to distinguish it from absorbed dose
QDH
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How to know when you’ve had too much
Quality Factors
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Sample Problem: A person of mass 70-kg receives a whole-body dose equivalent of 30 mSv. Half of this amount is of quality 1 and half quality 10. How much energy did they receive?
Q
mHE
Q
H
m
E
m
ED
Q
HD
QDH
JEEE
Jx
Q
mHE
Jx
Q
mHE
Q
mHE
T 16.1
105.0102
103070
2
05.112
103070
2
21
3
2
2
3
1
1
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Another Term for Radiation Received
Relative Biological Equivalent (RBE)
Absorbed dose to produce an effect with 250 keV X-rays
RBE = ----------------------------------------
Absorbed dose to produce same effect with radiation used
Consider Q and RBE to be the same
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How bad is a sievert?
100 Sv – death in a few days
10 Sv – effects of radiation poisoning (nausea, vomiting, diarrhea) within a few hours, death within a few weeks
3 Sv is about the maximum dosage for radiation therapy
1Sv – increases probability of cancer by 1%
0.1 mSv – amount of a typical chest x-ray
2 µSv/hr – flight above 25,000 ft
How to know when you’ve had too much
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International Commission on Radiological Protection recommendations (yearly)
A person working with radioactive materials should not be exposed to more than 50 mSv
Other adults should not be exposed to more than 5 mSv
Children should not be exposed to more than 0.5 mSv
How to know when you’ve had too much
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International Commission on Radiological Protection recommendations (short-term)
No more than 10 µSv per hour for γ rays at a
distance of 10cm
No more than 50 µSv per hour for β particles at a
distance of 10cm
Particle sources with activity larger than 40 kBq
should be avoided
How to know when you’ve had too much
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Typical Annual Exposure
How to know when you’ve had too much
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Exposure to Ionization
Exposure (X) – total amount of produced charge (q) due to ionization in a given mass (m) of air
q is positive charges produced by
ionization
m is unit mass of air
Unit is C/kg (no special name)
Exposure rate – exposure per unit time
m
qX
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Exposure to Ionization Connection between exposure and absorbed
dose in other materials
In different materials, different energies required to produce an ion
f is a factor that accounts for the material and photon energy
f is about 40 for muscle tissue
f in bone drops from 150 at low photon energy to 40 at higher energies up to 0.1 MeV
)/( GykgJDfX
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Exposure to Ionization Connection between exposure and absorbed
dose in air
34 eV required to produce 1 ion
For a given exposure, X in C/kg
)/(34
1
106.134
106.1
1 19
19
GykgJDX
eV
Jxx
ionization
eVx
Cx
electronx
kg
CX
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Radiation Therapy
Radiation used for good, and not evil
Radiation kills healthy cells, but properly manipulated it can be used to kill bad cells
Targeted, narrow beams of X-rays or gamma rays, multiple angles
Radioactive material injected or implanted into cancerous tumors
Ingestion of radiation
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Radiation Therapy
How do you know how much is enough?
What is the proper dosage (dosimetry)?
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Physical and Biological Half-Life
Physical Half-Life - Radioactive isotopes decay according to the exponential decay law
Biological Half-Life - Radioactive isotopes are removed from the body as waste according to the same exponential decay law
Each process will have its own “decay” constant and each will have its own “half-life”
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Physical and Biological Half-Life
t
Tt
t
eAA
tNN
T
NN
eNN
0
2/1
/
0
0
693.0
2
12/1
bpE
bpE
E
bp
TTT
tNN
tNtNN
111
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Physical and Biological Half-Life
The effective half-life is the time for half of the radioactive nuclei to be removed by both decay and biological removal.
bpE TTT
111
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Physical and Biological Half-Life
In other words,
Physical half-life is the time for half of the radioactive nuclei to decay away
Biological half-life is the time for half of the radioactive nuclei to be removed from the body by biological processes
Effective half-life is the time for half of the radioactive nuclei to be removed by both processes
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Physical and Biological Half-Life
The proper dosage then is the amount needed to kill the targeted cells before the radiation is effectively removed from the body, but not so much that it remains to destroy good cells.
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Review Objectives
Can you outline the effects of ionizing radiations on living things?
Can you describe how radiation is measured?
Can you solve problems involving absorbed dose (D=E/m), dose equivalent (H=QD), and exposure (X=Q/m)?
Can you state the meaning of half-life, biological half-life and effective half-life and solve problems using 1/TE= 1/TP+ 1/TB?
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IB Assessment Statements
I.3.1. State the meaning of the terms exposure, abosorbed dose, quality factor (relative biological effectiveness) and dose equivalent as used in radiation dosimetry.
I.3.2. Discuss the precautions taken in situations involving different types of radiation.
I.3.3. Discuss the concept of balanced risk.
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IB Assessment Statements
I.3.4. Distinguish between physical half-life, biological half-life and effective half-life.
I.3.5. Solve problems involving radiation dosimetry.
I.3.6. Outline the basis of radiation therapy for cancer.
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IB Assessment Statements
I.3.7. Solve problems involving the choice of radio-isotopes suitable for a particular diagnostic or therapeutic application.
I.3.8. Solve problems involving particular diagnostic applications.
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QUESTIONS?
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#1-9
Homework