Today: Inverse-square law, shielding, sources of radiation

Sources of annual ionizing radiation dose of typical human

Quiz results

Ouch!

Clicker question review—inverse square law

Let’s say we know that if we stand 1 meter from a source of radiation that in 1 hour we will receive a dose of radiation equal to our normal background for one year. How far should we stand (approximately) so we receive the same dose in 16 hours?

A) 1/16 of a meterB) ¼ of a meterC) 4 metersD) 16 meters

Clicker question review—inverse square law

Let’s say we know that if we stand 1 meter from a source of radiation that in 1 hour we will receive a dose of radiation equal to our normal background for one year. How far should we stand (approximately) so we receive the same dose in 16 hours?

A) 1/16 of a meterB) ¼ of a meterC) 4 metersD) 16 meters

The intensity of radiation follows the inverse square law

Force Charge1 * Charge2

distance2

Intensity of radiation Source intensity

distance2

Remember for electric charge:

If you double the distance,Intensity decreases by a factor of 4

Inverse-square law demo

Three pieces together are a “Geiger counter”

Geiger-Müller tube

High VoltagePower Supply

Counter

Radioactive Source Holder

Calibrated distance rail

Refresher on Geiger counter

Depending on the design:

Maybe detect alpha-radiationCAN detect beta-radiationMaybe detect gamma-radiation

Alpha particles difficulty passing through windowBut can make it through mica

Ionizing radiation (beta, gamma, some alpha)enter through window and create ions inside.

These events are detected via the electric current and turned into audible “clicks.”

Inverse-square law demo

Geiger-Müller tube

Radioactive Source Holder

Calibrated distance rail

Let’s try the experiment again from last week

Distance

Three kinds of radiation emitted via radioactive decaynamed before they were understood…alpha, beta, gamma

Alpha particles stopped by paperalpha particles are helium nuclei

Beta particles stopped by aluminumbeta particles are electrons (or positrons)

Gamma rays stopped by leadgamma rays are high energy photonsx-rays similar, but lower energy than gamma

Shielding demo

Geiger-Müller tube

Radioactive Source Holder

Calibrated distance rail

Let’s try experiments with different shielding materials

Place different shielding materials here

Ionizing radiation is radiation with enough energy per particle to knock an electron off an atom (ionize it)

Electromagnetic radiation (no charge):Gamma-rays, x-rays, UV radiation

Particle radiation (charged or uncharged):Beta-radiation (electrons / positrons)Alpha-radiation (helium nuclei)Protons, neutrons, other particles

You can see that many of these types of ionizing radiation are produced from nuclear decay reactions

Clicker Question—Ionizing radiation

Which of the following is not a type of ionizing radiation?

A) Microwave radiationB) High-energy alpha particleC) Gamma-rayD) High-energy protonE) X-ray

Clicker Question—Ionizing radiation

Which of the following is not a type of ionizing radiation?

A) Microwave radiationB) High-energy alpha particleC) Gamma-rayD) High-energy protonE) X-ray

Microwave photons DO NOT have enough energy to kick an electron out of an atom

Effects of ionizing radiation on living cellsWe care about ionizing radiation because it can induce chemical reactions

Cells have proteins that can repair damaged DNAVery successful at doing so (http://www.youtube.com/watch?v=te-

NQG8Negk)

When DNA cannot be repaired either:Cell deathPermanent mutation—This is what we usually worry about.

Ionizing radiation creates radicals (reactive chemicals) in the water

Radicals react with DNA to cause damage

DNA Damage

NOTE: Some ionizing radiation is essential!

Ultraviolet (UV) radiation is essential for the synthesis of vitamin D

It is becoming clear to many scientists that Vitamin D is essential for the body’s cancer defense mechanisms.

Many mainstream cancer biologists believe sun exposure has much more positive benefits than negatives (but still controversial)

7-dehydrocholesterol pre-vitamin D3

A)Less than 300 mrem (or don’t know)B)300-350 mremC)350-370 mrem (within 10 mrem of average)D)370-400 mremE)Greater than 400 mrem

From the homework for today, what is your annual radiation dose?

A) Natural (Radon, uranium, cosmic radiation)B) Medical (x-rays, therapy, ...) C) Man-made (smoke detectors, glow-in-the dark, ...)D) Participation in nuclear catastrophesE) Don’t know

For most people, what accounts for biggest fraction of annual radiation dose?

A) Natural (Radon, uranium, cosmic radiation)B) Medical (x-rays, therapy, ...) C) Man-made (smoke detectors, glow-in-the dark, ...)D) Participation in nuclear catastrophesE) Don’t know

For most people, natural, unavoidable radiation is largest source.

For most people, what accounts for biggest fraction of annual radiation dose?

Some Sources of Radiation Discussed (by Katie Richardson-McDaniel)

Elevation: Albuquerque is at 5312 feet above sea level. How does this effect our exposure to radiation?

Why would there be less radiation at sea level?

This explains why plane flight hours matter, too

Solar wind as a source of radiation: http://www.youtube.com/watch?v=w1DfOYl857w

Earth's magnetic field protects us from charged radiation onlySo elevation still matters for gamma radiation

Space vehicles need to be built to withstand the radiationMars lost its magnetic field and consequently its atmosphere

Some Sources of Radiation Discussed (by Katie Richardson-McDaniel)

Colorado Plateau: Deposits of Uranium

Higher doses of Radon

30% of homes in ABQcontain indoor radon levels over the EPA action level,compared to 10-12%of homes for the entire US.

Indoor radon contributes about 100–300 mrem/yr.

Q:Is this why we don’t have basements in Albuquerque?

Some Sources of Radiation Discussed (by Katie Richardson-McDaniel)

We are always surrounded by significant natural sources of ionizing radiation

Interestingly, our own bodies are radioactive!

Counter-intuitively, the human impact on average background radiation is negligible.But of course, human events can cause huge local / acute doses

So: It is reasonable that humans could perform nuclear reactions while having negligible impact to the average radiation exposure

People in Ramsar, Iran have 100x the background dose that we do here!

Clicker question—Radioactive shielding

Based upon what you know about the types and sources of ionizing radiation and radiation shielding:

If you build a bunker out of lead 10 meters thick, and go inside the bunker, can you shield your body from all ionizing radiation?

A) YesB) No

Clicker question—Radioactive shielding

Based upon what you know about the types and sources of ionizing radiation and radiation shielding:

If you build a bunker out of lead 10 meters thick, and go inside the bunker, can you shield your body from all ionizing radiation?

A) YesB) No

For one thing, your own body is radioactive!

Parallel of electrical energy with nuclear energy

Electricity and radioactivity have existed since the beginning of time

So, the dangers have always been present, and always will be.

Humans have learned how to harness the powers of electricity and nuclear reactions…presenting new dangers along with great benefits

The task for society is to weigh the benefits against the dangers

Hey toddlers! I’m your friend!

How to read the short-hand summary of an isotope

C126

Number of protonsAtomic number (Z)

Total number of nucleons (protons + neutrons)Mass number (A) Element symbol

The atomic number and element symbol provide the same information.I.e., Carbon always has 6 protons. So, this isotope is also written:

12C or Carbon-12

In chemical reactions, these items do not change

C126

Atomic number (Z) is constant

Mass number (A) is constant Element does not change

If any of these values change, then it is a nuclear reaction!

Transmutation of an Element

Examples of nuclear reactions

U23892 Th234

90 He42

(Plus a lot of kinetic energy)Alpha-decay

n10 N14

7Neutron capture

p11 C14

6(This reaction happens in the upperatmosphere to produce Carbon-14)

Clicker question—Beta Decay

In one kind of beta decay, a neutron in a nucleus can transform into a proton, emitting an electron (beta radiation) and an electron neutrino. What kind of transmutation of the element occurs?

A) The remaining atom has an atomic number TWO LESS than before

B) The remaining atom has an atomic number ONE LESS than before

C) The remaining atom has an atomic number SAME as beforeD) The remaining atom has an atomic number ONE MORE than

beforeE) The remaining atom has an atomic number TWO MORE than

before

C126 C126

Number of protonsAtomic number (Z)

Total number of nucleons (protons + neutrons)Mass number (A)

Element symbol

Clicker question—Beta Decay

In one kind of beta decay, a neutron in a nucleus can transform into a proton, emitting an electron (beta radiation) and an electron neutrino. What kind of transmutation of the element occurs?

A) The remaining atom has an atomic number TWO LESS than before

B) The remaining atom has an atomic number ONE LESS than before

C) The remaining atom has an atomic number SAME as beforeD) The remaining atom has an atomic number ONE MORE than

beforeE) The remaining atom has an atomic number TWO MORE than

before

C126 C126

Number of protonsAtomic number (Z)

Total number of nucleons (protons + neutrons)Mass number (A)

Element symbol

Let’s understand beta-decay a little more by learning a bit about particle physics