Canadian Nuclear Society Ionising Radiation Workshop 1 Be Aware of NORM Short Version 2010-11-12 CNS Team Doug De La Matter Peter Lang Bryan White Jeremy.

Canadian Nuclear SocietyIonising Radiation Workshop

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Be Aware of NORMShort Version2010-11-12

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

Program for Today:

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• Electromagnetic Radiation

• Particle Radiation

• Ionising vs Non-ionising Radiation

• Radioactive Decay

• Nuclear Fission

• 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 light.

• Radiation can also refer to particles released from an atomic nucleus or produced by a particle accelerator.

Particle Radiation

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Click on the yellow area to start the simulation.

• Example: the electron gun in an “old” cathode ray tube television.

• Popular slang sometimes refers to cooking food in a microwave oven as “Nuking”.

How about a microwave oven?

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• Microwaves are electromagnetic radiation with photons having miniscule energies compared to nuclear radiation.

• You can’t “Nuke” anything in a microwave oven.

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.

• Heavy nuclei that have “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”.

• After alpha emission, the nucleus becomes a different isotope of a different element: this is known as transmutation.

• The resulting nuclide may or may not be radioactive itself. Click on the yellow area

to start the simulation.

• Nuclei that have “too many neutrons” will emit an electron, or beta-particle.

Beta Radiation

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• A neutron will spontaneously decay into a proton, an electron and an anti-neutrino.

• The proton stays in the nucleus.

• The other particles are emitted.

• After beta emission, the nucleus becomes an isotope of a different element.

• It may or may not be radioactive itself.

Click on the yellow area to start the simulation.

• 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 tumours

• 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 isotope, after a certain time we will have 50 of thoseatoms left.

Radioactive Decay

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

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

• 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.

• Visible light couples to electron quantum state transitions.

• Microwaves couple to molecular vibrations.

• 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)

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

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

• • The nucleus breaks into two new elements, as well as 2 or 3 free neutrons.

Fission and Neutrons

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• Some isotopes of uranium and thorium will split, or fission, spontaneously.

• • Most natural uranium consists of the isotope 238U, which is almost stable.

• • About 0.71% consists of the isotope 235U, which is fissile with thermal neutrons.• • There is also about 0.01% of the isotope 234U, too small to show on the chart.

• Beryllium is mixed with an alpha emitter such as radon 222.

Induced Fission

• Fission can be induced by “slow” neutrons.

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• The alpha particle transmutes the beryllium into carbon, releasing a neutron.

• If the neutron then strikes a fissile nucleus like uranium 235, it can induce fission.

>1 MeV

~107 m/s

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Induced Fission

Click on the yellow area to start the simulation.

• Energy is released in a variety of forms.

• U-235 typically fissions in one of two ways:

Fission Products

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• About 82% becomes Kinetic Energy of the fission products, or heat.• The heat can be used to run a steam turbine for the production of electricity.

• If the “fast” neutrons can be slowed down, perhaps using a moderator such as heavy water, they can induce additional fissions.

Nuclear Reactions

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• This results in a sustainable reaction, such as is used in the Canadian-designed and built CANDU nuclear reactor.

The first CANDU power reactor was built at Douglas Point on Lake Huron, and started operation in 1966. It is now decommissioned. The lastDarlington unit started operationin 1993.

• 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)

Don’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

Counting for 10 minutes may not produceconsistent results

Experiment 1: Background and Shielding

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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.

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

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

For more educational resources: visit the Canadian Nuclear Association Web Site

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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