1 2 3 Energy in the form of particles or electromagnetic waves emitted from the nuclei of unstable atoms RADIATION 4.

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Energy•in the form of particles•or electromagnetic waves•emitted from the nuclei of unstable atoms

RADIATION

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The term really includes all forms of The term really includes all forms of electromagnetic radiationelectromagnetic radiation Radio Waves, Infrared, Visible LightRadio Waves, Infrared, Visible Light Ultraviolet, X-rays, Ultraviolet, X-rays, -rays-rays

Commonly used today to describe Commonly used today to describe particle radiationparticle radiation

RADIATION

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Protons and neutrons determine nuclear reactions

One must understand atomic structure to understand radiation

NUCLEAR REACTIONS PRODUCE RADIATION

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Protons and Neutrons are the two basic nuclear particles. Together they contain practically all the mass of an atom and are determinants of an atom’s nuclear characteristics.

NUCLEAR PARTICLES

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• Radioactive decay refers to the spontaneous emission of radiation from the nucleus of an unstable atomic nucleus

RADIOACTIVE DECAY

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“Radioactive decay is the process of spontaneous emission of radiation in the form of particles or photons from the nuclei of unstable atoms”

DEFINITION OF RADIOACTIVE DECAY

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CHARACTERISTICS OF RADIOACTIVE DECAY

• It is a natural process in our universe• It is spontaneous – we cannot predict when

an atom will undergo decay

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BASIC TYPES OF RADIOACTIVE DECAY

Alpha () decay• Occurs when atomic nuclei have too many

protons and neutrons (i.e., Are heavy)

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ALPHA PARTICLE

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• Consist of 2 protons and 2 neutrons• Mass of an alpha particle is 4 amu• Charge = +2• The isotope’s Atomic Mass goes down four;• The Atomic Number goes down two• Are highly ionizing• Have low penetrating abilities

(only cm in air and mm in water)

CHARACTERISTICS OF ALPHA PARTICLES

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• Easily shielded; common types of shielding are paper, cardboard, air, clothing; will not penetrate skin

• Health hazard when taken internally• Not commonly used in medicine• Common sources = smoke detectors

(Am-241) and lantern mantles (thorium nitrate)

MORE ABOUT ALPHA PARTICLES

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• Changes both the mass and identity of the nucleus of the parent radionuclide

• This means that the decay results in the formation of a new element as the daughter product

ALPHA PARTICLE DECAY

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??QUESTIONS?

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NEGATIVE BETA (ß-) DECAY

Occurs when atoms have too many neutrons (i.e., Are “neutron-rich”) and decay by emitting a negative beta particle (ß-)

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WHAT ARE NEGATIVE BETA PARTICLES?During negative beta decay, neutrons are converted into protons and electrons. The protons remain in the nucleus but the new electrons are emitted as negative beta particles (ß-) or negatrons. You may wish to think of them as “nuclear electrons.”

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CHARACTERISTICS OF NEGATIVE BETA DECAY• Less ionizing than alphas due to decreased mass

of negatrons• Changes the identity of the nucleus but not the mass• The Atomic Number is increased by one due to

conversion of neutrons into protons

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CHARACTERISTICS OF NEGATIVE BETA PARTICLES (NEGATRONS) Negatrons consist of nuclear electrons The mass is the same as electrons There is a charge of –1 in negatrons More penetrating than alpha particles;

~ 12 meters in air They can penetrate skin–

best shielding is wood, plastics, thick cardboard, etc.

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??QUESTIONS?

GAMMA () EMISSION

Is a form of pure electromagnetic radiation emitted from nuclei that have excess energy. It is sometimes called gamma photon radiation.

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GAMMA RAYS

Are photons emitted from unstable nuclei to rid themselves of excess energy. Gamma photons are subatomic packets of pure energy. They are higher in energy and more penetrating than thephotons that make up visible light.

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PROPERTIES OF GAMMA () RAYS Charge is 0 (no charge) Mass is 0 (no mass) Low ionization Penetration abilities can be extremely high; –

penetrating power is dependent upon the energy of the emitted photons

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??QUESTIONS?

What is a “packet” of light energy that behaves like a particle?

1. Positron

2. Negatron

3. Megatron

4. Photon

Which form of radiation penetrates the least?

1. Alpha Decay

2. Beta Decay

3. Gamma Decay

4. Delta Decay

Which radioactive particle increases the Parent Nucleus’s atomic number?

1. Alpha Particle

2. Beta Particle

3. Gamma Particle

4. Delta Particle

Which form of radiation penetrates the most?

1. Alpha Decay

2. Beta Decay

3. Gamma Decay

4. Delta Decay

Which particle drops the Parent Nucleus’s atomic number by two?

1. Alpha Particle

2. Beta Particle

3. Gamma Particle

4. Delta Particle

Which particle resembles a Helium nucleus?

1. Alpha Particle

2. Beta Particle

3. Gamma Particle

4. Delta Particle

Which particle isn’t a particle but a photon?

1. Alpha Particle

2. Beta Particle

3. Gamma Particle

4. Delta Particle

Decay Systems

• Each radioactive element will undergo various forms of radiation until it becomes stable

• The particular elements that a “Parent Nucleus” changes into are always the same

• This “path” is a Decay System

Half-life• The amount of time it

takes for HALF of an amount of a radioactive material to decay

• One symbol for half-life is (lambda)

Original Amount

# of Current Amount

100g 1 50g

100g 2 25g

100g 3 12.5g

100g 4 6.25g

100g 5 3.125g

A Decay System showing half-

lives

Nuclear Processes

• Fission– The splitting of a large, unstable nucleus into two

or more stable nuclei– Scientists can cause fission by injecting a neutron

at high speed– These are the uses associated with nuclear fission:

• Power plants / reactors

• Bombs

• “Dirty bombs”

Nuclear Processes

• Fusion– The joining of two or more smaller nuclei into one

larger, more stable nucleus– Scientists are working on fusion using high

pressures, temperatures, and lasers– The only place that fusion occurs naturally is stars

Chernobyl Disaster

• April 26, 1986 – flawed reactor design was operated by inadequately trained personnel and w/o regard to safety

Chernobyl Disaster

• Result – steam explosion and fire released at least 5% of the radioactive reactor core into the atmosphere & downwind

• 28 people died within 4 months from radiation or thermal burns

• 19 subsequently died and 9 deaths from thyroid cancer

TERMS TO REVIEWRadiationRadiation Alpha decayAlpha decayAlpha particleAlpha particle Radioactive decayRadioactive decayNegatronNegatron Negative beta decayNegative beta decayX-rayX-rayGamma rayGamma ray PhotonPhotonHalf-LifeHalf-LifeDecay SystemsDecay SystemsMother NucleusMother Nucleus Daughter NucleiDaughter NucleiFissionFission FusionFusion

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Half-Life Problems

• 1. An isotope of cesium (cesium-137) has a half-life of 30 yrs. If 1.0 mg of cesium-137 disintegrates over a period of 90 yrs., how many mg of cesium-137 would remain?

Half-life

• 2. A 2.5 gram sample of an isotope of strontium-90 was formed in a 1960 explosion of an atomic bomb at Johnson Island in the Pacific Test site. The half-life of strontium-90 is 28 yrs. In what year will only 0.625 grams of this strontium-90 remain?

Half-life

• 3. Actinium-226 has a half-life of 29 hours. If 100 mg of actinium-226 disintegrates over a period of 58 hours, how many mg of actinium-226 will remain?

Half-life

• 4. Thallium-201 has a half-life of 73 hours. If 4.0 mg of thallium-201 disintegrates over a period of 6.0 days and 2 hours, how many mg of thallium-201 will remain?

Half-life

• 5. Sodium-25 was to be used in an experiment, but it took 3.0 minutes to get the sodium from the reactor to the laboratory. If 5.0 mg of sodium-25 was removed from the reactor, how many mg of sodium-25 were placed in the reaction vessel 3.0 minutes later if the half-life of sodium-25 is 60 seconds?

Half-life

• 6. The half-life of isotope X is 2.0 years. How many years would it take for a 4.0 mg sample of X to decay and have only 0.50 mg of it remain?

Half-life

• 7. Selenium-83 has a half-life of 25.0 minutes. How many minutes would it take for a 10.0 mg sample to decay and have only 1.25 mg of it remain?

Half-life

• 8. Element-106 has a half-life of 0.90 seconds. If one million atoms of it were prepared, how many atoms would remain after 4.5 seconds?

Half-life

• 9. The half-life of Po-218 is three minutes. How much of a 2.0 gram sample remains after 15 minutes? Suppose you wanted to buy some of this isotope, and it required half an hour for it to reach you. How much should you order if you need to use 0.10 gram of this material?

Half-life

• 10. Three grams of Bismuth-218 decay to 0.375 grams in one hour. What is the half-life of this isotope?

Half-life

• 11. The half-life of francium is 21 minutes. Starting with 4 x 1018 atoms of francium, how many atoms would disintegrate in 1 hour and 45 minutes? What fraction of the original sample remains?

Half-life

• 12. The half-life of a radioactive element is 30 seconds. In what period of time would the activity of the sample be reduced to one-sixteenth of the original activity?