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Friday, April 10th at 2:30pm

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Today: Radiation Dose Definitions, Medical Applications,

PET scan 3-D renderingSource: wikipedia

Small group exercise!

I place on the table a small piece of material and say, “this is radioactive.”

How many different properties of the material can you think of that you would want to characterize, in order to know everything about its radioactivity?

Form small groups, and brainstorm. Have a leader / spokesperson write down results.

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What kind of radiation is emitted? Alpha, beta, gamma.

Mass/weight“half-life” (time for ½ to decay)Color…?Temperature…What is the element?

Measuring the amount of radioactivity or dose

We can think about amount of radiation in two ways.

Describe the source of radiationPhysics-based, rigorous

Describe the absorbed radiation doseComplicated biology and other factors

There are rigorous ways to characterize the source of radiation

What type of radiation does the material emit?X-rays, gamma rays, beta radiation, alpha particles

How much radiation per second?curies, becquerels, counts per second

What is the half-life of the material?Minutes, days, years, …

What is the average energy per particle or ray emitted?

There are rigorous ways to characterize the source of radiation

What type of radiation does the material emit?X-rays, gamma rays, beta radiation, alpha particles

How much radiation per second?curies, becquerels, counts per second

What is the half-life of the material?Minutes, days, years, …

What is the average energy per particle or ray emitted?

There are two main units of radioactivity

The becquerel (Bq) is defined as one radioactive decay event per second

1 Bq = 1 reaction / second

The curie (Ci) is based on the radioactivity of about 1 gram of radium-226

1 Ci = 37 billion Bq = 37 billion reactions / second

Marie CurieNobel prizes in

Physics and Chemistry

Henri BecquerelNobel Prize in Physics

Example: 1 kilogram of “typical” soil has400 Bq of Potassium-40 -- or 11 nanocuries

There are rigorous ways to characterize the source of radiation

What type of radiation does the material emit?X-rays, gamma rays, beta radiation, alpha particles

How much radiation per second?curies, becquerels, counts per second

What is the half-life of the material?Minutes, days, years, …

What is the average energy per particle or ray emitted?

Radioactive decay is a random process

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Example: Phosphorus-32 decay into Sulfur-32

Half-life is the average amount of time for ½ of the atoms to decay

P-32 half life ~14 days

Decay rate is proportional to the number of radioactive atoms remaining

So, radioactivity of a sample decreases with the same half-lifeApplets: http://www.colorado.edu/physics/2000/isotopes/radioactive_decay3.html

http://lectureonline.cl.msu.edu/~mmp/applist/decay/decay.htm

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Radioactivity (becquerels) and Half-life are inversely related

Longer half-life = lower radioactivityStable isotope has an infinite half-life

Shorter half-life = higher radioactivityHighly radioactive isotopes will disappear

quickly

Clicker Question—Half life / radioactivity

Let’s say you have two samples, each with the same number of atoms in them.

Sample “A” has half-life of two weeks.Sample “B” has half-life of 4 billion years.

Which will have a higher radioactivity?

A or B

Clicker Question—Half life / radioactivity

Let’s say you have two samples, each with the same number of atoms in them.

Sample “A” has half-life of two weeks.Sample “B” has half-life of 4 billion years.

Which will have a higher radioactivity?

A or B

Shorter half-life = higher radioactivityIf the half-life is infinite, it is not radioactive

There are rigorous ways to characterize the source of radiation

What type of radiation does the material emit?X-rays, gamma rays, beta radiation, alpha particles

How much radiation per second?curies, becquerels, counts per second

What is the half-life of the material?Minutes, days, years, …

What is the average energy per particle or ray emitted?

The energy per emitted particle indicates how deeply it can penetrate materials and how much damage it can do

Examples:P-32 beta 1.7 megaelectronvolts (MeV)Ra-226 alpha 4.9 MeVRn-222 alpha 5.6 MeV K-40 beta 1.3 MeV

However, the type of radiation (alpha, beta, gamma, neutron) tends to be more important

Mega = 10^6 or 1 million

Clicker question—classifying radiation

If held 1 inch away from your body, which radiation source is more likely to cause cancer?

A) Source with radioactivity of 1 million becquerels (Bq)

B) Source with radioactivity of 1 billion becquerels (Bq)

C) Impossible to determine

Clicker question—classifying radiation

If held 1 inch away from your body, which radiation source is more likely to cause cancer?

A) Source with radioactivity of 1 million becquerels (Bq)

B) Source with radioactivity of 1 billion becquerels (Bq)

C) Impossible to determineThere are many other things you would need to know:What type of radiation do each emit? Is there any shielding in between?

Results of homework assignment

A few homework responses

Adrian: If I became a luddite and lived in a hut in the woods at sea level I might save myself 80 mrem or so.

Laura: Only 2.010 mrem or 0.6 % of my annual radiation exposure can be attributed to man made sources

David: Unavoidable background radiation is from food and water, there is absolutely nothing I can do to change that.

Measuring the amount of radioactivity or dose

We can think about amount of radiation in two ways.

Describe the source of radiationPhysics-based, rigorous

Describe the absorbed radiation doseComplicated biology and other factors

Classifying the radiation dose is very complicated

Biological effects depend on acute versus chronic dose

Interaction of radiation with cells has a number of possible outcomes…depends on numerous factors

Characteristics of the radiation

Characteristics of the biological system (e.g. general level of health)

Nevertheless, attempts are made to define dose

Radiation doses

In terms of energy, absorbed dose is measured in grays (Gy)1 Gy = 1 joule per kilogram of material

Biological dose is measured in sieverts (Sv) or rem1 Sv = effect of 1 joule per kilogram1 Sv = 100 rem

1 sievert = Q * gray “Q” is some fudge factor

For photons (x-ray, gamma) Q = 1Beta rays, Q = 1Low energy neutrons, Q = 5; medium energy Q = 20; high energy

Q=5Alpha, Q = 20

Some relevant radiation dose values

Acute radiation doseAbout 3 Sv (whole body) will cause radiation poisoning and

50% chance of death.

Medical imaging procedures typically in the milli-sievert range

Chronic radiation doseNatural background about 2.4 milli-Sv per year

What dose will cause cancer? Difficult to determine and also random.

Medical applications of radiation

Destruction:Radiation Therapy

Imaging:X-rays

Imaging:Positron emission tomography

Imaging:Gastrointestinal imaging

Positron emission tomography (PET scanning)

Radiation Therapy

Extremely high but localized dose, meant to destroy tumor cells.20 or more localized grays

Also a “whole body” dose for killing immune system prior to bone-marrow transplant.~ 10 grays (3 usually lethal)

Some slides about cancer radiation therapy

http://youtube.com/watch?v=ZtENJI1K1hA&feature=related

Clicker Question—Acute Radiation Dose

I said earlier that a dose of about 3 sieverts (Sv) will kill someone about 50% of the time. Let’s say someone is exposed to 100 sieverts of radiation. Can you say almost certainly they will die?

A) YES!B) No!

Clicker Question—Acute Radiation Dose

I said earlier that a dose of about 3 sieverts (Sv) will kill someone about 50% of the time. Let’s say someone is exposed to 100 sieverts of radiation. Can you say almost certainly they will die?

A) YES!B) No!The information is not specific enough.

If it happens over the whole body in a short time, then probably YES…

However, if it happens over 100 years, then probably not.

Also if localized, also will not die

There is no easy way to put a concrete number on radiation dose

Ionizing radiation almost NEVER makes something turn radioactive!

In order for an object to become radioactive, the nuclei in the atoms must change…”nuclear reactions” required.

Typically:

Neutrons are the most effective at causing nuclear transmutation…

Radiactive decay very rarely releases neutrons

The person does NOT becomeradioactive … his nuclei are unchanged

Nuclear reactionReleases

ionizing radiationCauses

Chemical reactions

Clicker question--transmutation

Food irradiation or “cold pasteurization” often uses gamma rays to kill any microorganisms in the food. There are no neutrons involved.

Does the food then become radioactive (only mildly, though)?

A) YesB) No

Clicker question--transmutation

Food irradiation or “cold pasteurization” often uses gamma rays to kill any microorganisms in the food. There are no neutrons involved.

Does the food then become radioactive (only mildly, though)?

A) YesB) No

There are safety concerns, but NOT because of radioactive food! We can understand the physics

The risks need to be balanced against the benefits…In US:325,000 hospitalized per year from food poisoning!5,000 deaths / year!

Protons and neutrons are made of quarks

Quark model of a protonwww2.cnrs.fr/presse/communique/709.htm

“Up” quarks charge = + 2/3 each

“Down” quark-1/3 charge

Arpad Horvath

Quark model of neutron

Quarks and Leptons are the constituent parts of matter.

Murray Gell-MannNobel Prize 1969

There are six quarks

Up Charmed Top

Down Strange Bottom

Charge = +2/3

Charge = -1/3

Similarly, there are six leptons

Increasing mass

Electron Muon Tau

Electron neutrino

Muon neutrino

Tauneutrino

Antimatter consists of the 6 anti-particle quarks and

6 anti-particle leptons

Under normal conditions, quarks do not exist in free space.

Fermilab particle accelerator

Billion-dollar physics experiments were required to detect quarks for fleeting instants in time

Beta-decay can transform a neutron into a proton

Quarks

(Electron)

It is a decay of a “down quark” into an “up quark”

Clicker question--Quarks

An up quark has an electric charge of +2/3.A down quark has an electric charge of -1/3.Which of the following combinations would a proton

consist of?

A) Up, up, upB) Down, down, downC) Up, down, downD) Up, up, downE) Up, up, down, down

Clicker question--Quarks

An up quark has an electric charge of +2/3.A down quark has an electric charge of -1/3.Which of the following combinations would a proton

consist of?

A) Up, up, upB) Down, down, downC) Up, down, downD) Up, up, downE) Up, up, down, down

+2/3 +2/3

-1/3Take home message about quarks:Nucleons are composed of three quarks.Particle Physicists can predict a lot about matter from the quark / lepton models,Including some radioactive decay properties