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/T E = 1/T P + 1/T B

Introductory Video: Exposure to Radiation 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

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

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?

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

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?

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

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

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

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

 The effective half-life is the time for half of the radioactive nuclei to be removed by both decay and biological removal.

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/T E = 1/T P + 1/T B ?

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.

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