DEVIL PHYSICSTHE BADDEST CLASS ON CAMPUS

IB PHYSICS

TSOKOS OPTION I-3RADIATION IN MEDICINE

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.

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.

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.

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

Introductory Video:Exposure to Radiation

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

Biological Effects

Natural Sources of Radiation

Radon gas

Unstable isotopes in food

Gamma radiation from the earth

Cosmic rays from space

Greenhouse Effect???

Biological Effects

Artificial Sources of Radiation

Nuclear weapons

Nuclear power plants

Medical diagnostics

Medical Therapy

Biological Effects

What makes radiation bad?

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

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

Biological Effects

What makes radiation bad?

Bone marrow is particularly susceptible to radiation

Blood cell production

Immune system

Causes leukemia and other cancers

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

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

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

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

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

How to know when you’ve had too much

Quality Factors

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

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

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

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

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

Typical Annual Exposure

How to know when you’ve had too much

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

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

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

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

Radiation Therapy

How do you know how much is enough?

What is the proper dosage (dosimetry)?

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”

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

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

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

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.

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?

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.

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.

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.

QUESTIONS?

#1-9

Homework