Canadian Nuclear SocietyIonising Radiation Workshop

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Be Aware of NORMShortest Version

2014-07-26

CNS Team

Doug De La MatterPeter Lang

Bryan WhiteJeremy Whitlock

Rolly Meisel

Radioactive

Occurring

Naturally

Material www.cns-snc.ca

If your table has a computer, please don’t disturb it -- we’ll get to it shortly.

The ionising radiation workshop kit…

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Computer

Geigercounter

USBInterface

www.cna.ca3

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http://www.nuclearconnect.org/

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So why does the CNS provide this workshop?

• We believe that students will benefit from simple, personal, practical demos / experiments that enrich their classroom experience.

• We’re convinced that investing in science teachers is the best way we can help improve public understanding of ionising radiation.

Program for Today:

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• Electromagnetic Radiation

• Particle Radiation

• Ionising vs Non-ionising Radiation

• Radioactive Decay and background

• Detecting Radiation

• Experiments with a Geiger Counter

• Energy emitted by a source travelling through space away from the source.

What is Radiation?

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• Most radiation we encounter is Electro-Magnetic radiation and behaves like visible light.

I’m a particle!(0 rest mass)

I’m a wave!

Just call me a photon.

• Radiation can also refer to sub-atomic particles:– most have finite “rest mass”– Electrons, protons, neutrons, alpha particles, muons,

pions, neutrinos, …?

• Particles may be released from an atomic nucleus undergoing radioactive decay, or fission, or by an interaction such as “scattering”.

• Particles may be produced by interactions of other particles -- or may be produced by a particle accelerator.

Particle Radiation

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Figure copied from “Radiation Awareness” PowerPoint File by Health Physics Society, crediting NASA/JPL-Caltech

Electromagnetic Radiation

non-ionising ionising

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Notice that cell phone radiation falls well into the

“non-ionising” region of electromagnetic radiation.

Radioactive Decay

• A radioactive atom has excess energy in its nucleus, but not quite enough to change to a lower energy state, and then...

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…spontaneously it changes to a lower energy state.

• It does this by emitting sub-atomic particles……and/or electromagnetic energy in the form of gamma radiation…

…through quantum-mechanical tunnelling and other mechanisms.• One decay per second is known as one becquerel (Bq) of activity.

neutrons

pro

tons

Radioactive Decay Half-life:after 1 half-life, half of starting number of atoms of an isotope remain undecayed

www.nndc.bnl.gov/chart/

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Online Interactive Chart of the Nuclideshttp://www.nndc.bnl.gov/chart/

• Heavy nuclei that have “2 too many protons” will emit particles made up of 2 protons and 2 neutrons.

Alpha Radiation

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• These are known as “alpha particles”(the nucleus of a helium atom, 4He+2)

• After alpha emission, there is a nuclide with a different atomic number (a different element): this is known as transmutation.

• The resulting nuclide may or may not be radioactive itself.

Atomic Number -2, Mass -4

• A nucleus that has “1 too many neutrons” will emit an electron – a beta-minus particle – A neutron changes into a proton, an electron and

an anti-neutrino– The electron and anti-neutrino are emitted – along

with a photon (gamma) in many cases

• After beta emission, there remains a nuclide with a different atomic number – a different element.

• The new nuclide may or may not be radioactive itself.

Beta Radiation - 1

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Atomic Number +1, Mass -

• A nucleus that has “1 too many protons” will capture an orbital electron, or emit an anti-electron – a positron – a beta-plus particle – A proton changes into a neutron by:

• combining with an electron and emitting a neutrino • OR by emitting a positron and a neutrino

– This form of beta decay also emits a photon (gamma) in most cases.

• There remains a nuclide with a different atomic number – a different element.

• The new nuclide may or may not be radioactive itself.

Beta Radiation - 2

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Atomic Number -1, Mass -

• Highest energy EM radiation

Gamma Radiation

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• Interaction with matter similar to X-rays• “Collision” with an electron can ionise the atom, breaking a chemical bond.

Gamma Radiation

• Easily penetrates the body

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• Intense sources (Co-60, Cs-137 and high energy electron accelerators) are used to irradiate tumors

• Absorbed by large thickness of water, lead metal or concrete

• The atmosphere over your head provides shielding equivalent to

10 m of water

• If we start with 100 atoms of a particular nuclide, after a certain time we will have 50 of those atoms left.

Radioactive Decay

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• This is known as the “half-life” of the nuclide.

• After another “half-life”, we will have 25 of those atoms left .

0 1 2 3 4 5 6 7 8

0.39%

• Does not displace electrons from atoms.

Non-Ionising Radiation

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• Can break chemical bonds due to heating effects.

• Includes radio waves, microwaves, infrared radiation, visible light, and some UV.

• Visible light couples to atomic electron quantum state transitions.

• Microwaves couple to molecular vibrations and rotation.

• Able to displace electrons from atoms, often breaking chemical bonds.

Ionising Radiation

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• Includes ultraviolet light, x-rays, and gamma rays from the electromagnetic spectrum.

• Includes alpha particles, beta particles, neutrons, protons and (extremely rarely) neutrinos.

Sudbury Neutrino Observatory (SNO)

Transmutation of Elements

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Rn22286 Po218

84decays tovia α-emission

Po22084 At220

85decays tovia β-emission

Atomic number 2 Mass number 4

Atomic number 1 Mass number is unchanged

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Background Radiation

We are all exposed to ionising radiation – and most of that is natural background radiation

Natural Background 73%Medical Sources 25% Living at the boundary of a nuclear station 1% Other Sources 1 %

Inhalation (Radon) - 1.2 mSv

External Terrestrial - 0.48 Cosmic Radiation - 0.4 Ingestion - 0.3

The dose we absorb each year in Sieverts (Sv) from background varies with geology & geography by a factor of 100

• Photochemical films

Detecting X-rays, Gamma Rays and Particles

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• Gas discharge (Geiger detector)

• Cloud Chambers (track detectors)

• Scintillators (NaI – Li, liquid)• Solid state detectors (GeLi, thermoluminescent)

PLEASEDon’t Break the Window!

• Ionising radiation scatters off atoms in the detector, removing electrons from their atoms.

The Geiger Detector

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• Free electrons are accelerated toward a positively charged anode (~500V DC).

• These electrons ionise additional atoms in the gas space, leading to an avalanche discharge.• Electronics detect the discharge current pulse.• The counter can detect ONE event at a time.• It cannot distinguish between one ionising event and many events occurring within the dead-time interval.

Experiment 1: Background Radiation

• Ionising radiation is everywhere.

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• Background “measurements” can be tricky and time consuming.

• Short counting intervals give small average numbers of counts leading to unreliable statistics.• Long counting intervals can be tedious.

• The effect of shielding is easy to show.

• A container of water provides shielding to reduce background count

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Find the background running average on your screen

Workstation Running Average

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Average for 6

Counting for 10 minutes may not produceconsistent results

Experiment 1: Background and Shielding

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The CNS has launched a YouTube Channel for the Ionising Radiation Workshop

So far there are only 2 videos up:

There will be many more when I get around to it.

The Hot Balloon Experiment

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Experiment 4: The balloon experiment NEW• The balloon is an electrostatic precipitator

collecting dust particles from the air.

• The α decay of 222Rn (3.82 day) to:

7. 218Po (3.1 min) – α

8. 214Pb (26.8 min) – β-

9. 214Bi (19.9 min) – β-

10. 214Po (164 µs) – α

11. 210Pb (22.2 year) – β-

12. 210Bi (5.012 day) – β-

13. 210Po (138.4 day) – α

14. 206Pb (stable)

These dominate the balloon data

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Experiment 2

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• You can make a simple set of measurements with weak sources such as NoSalt®

• Potassium chloride (KCl) is a convenient source of K-40 available in any grocery store

• Note the jump in counts per minute

• Place the KCl near the Geiger window

5 kBq of 40K for $5.99 in grocery stores everywhere

Experiment 3: Th-232 in vintage camera lenses

From about 1950 through to 1980, several consumer cameras were made using thorium oxide in the glass lens to:

• enhance the refractive index of the glass

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• keep the dispersion low

Such “bright” sources provide counting rates at or above 5000 counts per minute.

• many measurements can be made in a short time• acceptable level of statistical errors• students are more likely to remain engaged• cameras can be found on sources such as EBay

• For high school demonstration experiments, these lenses are a conveniently “bright” source of particles.

Experiment 3: Th-232 in vintage camera lenses

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• The radioactive material is embedded inside the glass of the lens, and most of the particle emissions are absorbed by air. Kodak

Signet 40 camera lens

To get a Geiger Kit donated to your school you must ask the CNS. You might borrow one?

Check the list on the CNS website to find a school nearby.

Vintage Vaseline Glass: a uranium source

• Uranium compounds added to glass give it a green-yellow hue and it fluoresces under UV light.

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• It provides alpha, beta, and gamma radiation, but is not as intense as the vintage camera lenses.

Vintage Fiestaware: a uranium source

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•Uranium compounds added to the ceramic glaze give these saucers a red-orange hue (and no they don’t fluoresce under UV light)

•The maximum count rates at minimum separation with an RM-80 are about 30000 cpm and 20000 cpm for these two samples

40Online video experiments

Canadian Nuclear SocietyIonising Radiation Workshop

Be Aware of NORM

CNS Team

Bryan WhiteDoug De La Matter

Peter LangJeremy Whitlock

Rolly Meisel

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Thanks for Your Attention

www.cns-snc.ca Additional photographs copyright R. Meisel used with permission

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