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PeriodicityRadioactivity

http://www.phy.bris.ac.uk/groups/particle/PUS/A-level/Standard_Model.htm

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α Alpha radiation emitted from the nucleus

β Beta radiation emitted from the nucleus, or

γ Gamma radiation E = hν

Nuclear RadiationIf there was any remaining doubt the discovery of nuclear radiation ended any consideration that atoms were indivisible. Not only could electrons be removed, the nucleus itself could fall apart!

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In 1898, Marie Curie discovered that pitchblend, a uranium ore, emits more radiation than uranium itself. She deduced that this ore contains, in very small quantities, one or more elements much more active that uranium. With the assistance of her husband Pierre Curie and after two years of effort, she arrived at isolating two new elements: Polonium (named thus in tribute to her homeland) and Radium. It was then that Marie Curie invented the word "radioactivity".

Antoine Becquerel accidentally discovered Uranium salts because film placed next to the salts became exposed without benefit of light.

http://molaire1.perso.sfr.fr/e_radioactiv.html

National Council on Radiation Protection & Measurements (2009, March 5). Medical Radiation Exposure Of The U.S. Population Greatly Increased Since The Early 1980s. ScienceDaily. Retrieved November 23, 2012, from http://www.sciencedaily.com /releases/2009/03/090303125809.htm

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In alpha decay the nucleus spontaneously splits into a daughter particle and a helium nucleus.

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Examples of alpha decay

To write the equation for alpha decay, use the following formula:

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What is an alpha particle?

How do you write the greek letter for an

alpha particle?

Write the balanced nuclear equation

for an isotope of 238U which undergoes alpha decay.

Is alpha decay a chemical reaction or a nuclear reaction?

A nuclear reaction.

Quiz

α

A helium nucleus:

(http://abyss.uoregon.edu/~js/ast123/lectures/lec07.html not in our text book)

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Beta decay: In beta decay either an electron or a positron are expelled from the nucleus. A neutrino or antineutrino is also expelled.

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Notice that in beta decay the number of protons increases. The electrons do not come from the electron cloud, which is why the neutrino or antineutrino is also expelled. (gamma radiation may also be expelled)

http://curriculum.cna.ca/curriculum/cna_radiation/beta_decay-eng.asp?bc=Beta%20Decay&pid=Beta%20Decay A cool animation of beta decay.

Neutrinos have no charge and almostno mass and were predicted by WolfgangPauli to explain why beta decay didn’tviolate the law of conservation of matterand energy.

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino.html

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Radioactive isotopes which emit beta particles are called beta emitters. Below is list of some beta emitting radioactive isotopes. •Carbon-14 is used in carbon dating artifacts and as a medical tracer

•Cesium-137 is used in brachytherapy to treat various types of cancer and to

measure the flow of oil in pipelines.

•Cobalt-60 •Hydrogen-3 (tritium) •Iodine-129 •Iodine-131 is used as a medical tracer

•Nickel-63 is used to detect explosives, and in voltage regulators and

current surge protectors in electronic devices.

•Promethium-147 is used in electric blanket thermostats, and to gauge

thickness of thin plastics, thin sheet metal, rubber, textile and paper.

•Sodium-24 is used to locate leaks in industrial pipelines, oil well studies

and in medical diagnostics.

•Strontium-90 is used as a power source for weather satellites and navigation buoys

•Sulphur-35 is used in manufacturing sensors and medical treatments.

•Technetium-99m is used in nuclear medicine as a radioactive tracer

•Thallium-204 is used to measure the dust and pollutant levels on filter paper,

and in gauges used to measure the thickness of plastics, sheet metal, rubber,

textiles, and paper.

http://curriculum.cna.ca/curriculum/cna_radiation/beta_emitters-eng.asp?bc=Common%20Beta%20Emitters&pid=Common%20Beta%20Emitters

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Gamma radiation.

http://faculty.virginia.edu/metals/cases/prescott2.html Interesting article about technetium.

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Penetrating power of alpha, beta, and gamma radiation.

http://www.frankswebspace.org.uk/ScienceAndMaths/physics/physicsGCE/D1-3.htm

http://library.thinkquest.org/C006669/data/Chem/atomic/development.html

http://sciencecity.oupchina.com.hk/npaw/student/glossary/ionizing_power.htm

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1. Which type of radiation has no charge, and is high energy?

2. Which type of radiation is the size of an electron, is either positive or negative?

3. Which type of radiation is basically a helium nucleus?

4. Which two types of radiation normally occur together?

Review

1. gamma

2. beta

3. alpha

4. Beta and gamma, also

neutrinos

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Radioactivity is spontaneous. It occurs regardless of the temperature, surface area, or any of the usual things which make chemical reactions occur. The rate depends only on the amount of “parent nuclide” present.

We report the rate as a “half life”

Half- life

The half life depends upon the stability of the nucleus. The more stable the nucleus, the longer the half life.At the end of the period of time called “half life” there is half as much of the “parent isotope” as at the beginning.

½ → ¼ → 1/8 → 1/16 → 1/370.5 → 0.25 → 0.13 → 0.06 → 0.03

T → 2T → 3T → 4T → 5T

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Half life equations•AE is the amount of substance left•A0 is the original amount of substance•t is the elasped time•t1/2 is the half-life of the substance

Other variations on the half-life equation are as follows:

                    An example problem is if you originally had 157 grams of carbon-14 and the half-life of carbon-14 is 5730 years, how much would there be after 2000 years?

                    There would be 123 grams left. http://library.thinkquest.org/10429/

low/nuclear/nuclear.htm

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Alpha decay reduces the atomic number by two protons and two neutrons.

So much energy is released that gamma radiation is frequently given off as well.

How can we predict which atoms will decay and what type of decay they will experience?

http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Nuclear-Chemistry/chemprime/CoreChem3ANuclear_Stability-745.html

http://mail.rdcrd.ab.ca/~smolesky/physics30/5Matter/day_8%20objective.htm

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How can we predict which atoms will decay and what type of decay they will experience?

http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Nuclear-Chemistry/chemprime/CoreChem3ANuclear_Stability-745.html

Beta decay will increase the atomicnumber so the daughter nuclidewill be more stable than the parent.

http://mail.rdcrd.ab.ca/~smolesky/physics30/5Matter/day_8%20objective.htm

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http://mail.rdcrd.ab.ca/~smolesky/physics30/5Matter/MatterPics/formulas/positron.gif

Small atoms with too many protons willundergo electron capture or positron emissionto obtain stable nucleii

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Gamma radiation is thought to be a release of nuclear energy. No apparent change to the number of protons or neutrons is necessary for gamma radiation.

For the original images and explanations…http://mail.rdcrd.ab.ca/~smolesky/physics30/5Matter/MatterPics/radioactive%20decay/AlphaBetaGamma2.jpg

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Example 1: 238-Uranium undergoes alpha decay

Example 2: 234-Pa is produced by a beta negative decay

More practice

Label where alpha and beta decay are most likely.