the abc's (or alpha, beta, gamma) of radioactivity

Science Park HS -- Honors Chemistry

The ABC's (or Alpha, Beta, The ABC's (or Alpha, Beta, Gamma) of RadioactivityGamma) of Radioactivity


ExpectationsExpectationsSWBAT state what radioactivity is, where

these rays come from, what each ray is made of and state why they are dangerous.

SWABT to explain the meaning of “half-life”.


Early Pioneers in RadioactivityEarly Pioneers in Radioactivity

Roentgen:

Discoverer of X-rays 1895

Becquerel:

Discoverer of Radioactivity

1896

The Curies:

Discoverers of Radium and

Polonium 1900-1908

Rutherford:

Discoverer Alpha and Beta

rays 1897


ReviewReview of Key Definitions of Key DefinitionsAtomic Number: It’s the Number of Protons in

the nucleus of an Atom.Nucleus: It’s where the Protons and Neutrons are

located in an Atom.Protons: Positively Charged Particles in the

Nucleus of the atom. Mass = (approx) 1 AMUNeutrons: Neutrally charged particles in the

nucleus of an atom Mass = (approx) 1 AMUMass Number of an atom: Number of Protons +

Number of Neutrons in the nucleus of an atom.

What do we mean by Radioactivity?What do we mean by Radioactivity?Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves.

~An unstable atomic nucleus emits a form of radiation (alpha, beta, or gamma) to become stable.

~A radioactive nucleus actually decays into a different atom. (= different # of protons ).


What do we mean by What do we mean by Radioactivity?Radioactivity?

But, why does radioactivity occur?

An unstable nucleus releases energy (emitting particles & Electromagnetic waves) to become more stable (and becomes a new type of atom)

What makes a nucleus unstable?A nucleus is unstable because of the ratio of protons to neutron in the nucleus of an atom. (Ratio outside of the Stability belt)


The Nuclear The Nuclear StabilityStability BeltBeltRatioRatio of neutrons to protons in the of neutrons to protons in the nucleusnucleus NeutronsNeutrons

ProtonsProtons

6 Neutrons6 Neutrons 6 Protons6 Protons

138 Neutrons138 Neutrons 92 Protons92 Protons


Kinds of RadioactivityKinds of Radioactivity

The three main decays are Alpha, Beta and Gamma

Three Common Types of Three Common Types of Radioactive EmissionsRadioactive Emissions

Alpha Beta

Gamma

241Am 237Np + 4He95 93 2

3H 3He + 0β1 -1 2


Three Common Types of Radioactive Three Common Types of Radioactive Emissions - PenetrabilityEmissions - Penetrability

Alpha particles may be completely stopped by a sheet of paper,

Beta particles by aluminum shielding.

Gamma rays, however, can only be reduced by much more substantial obstacles, such as a very thick piece of lead.

Radioactive Decay LawRadioactive Decay LawRadioactive decay is the spontaneous

release of energy in the form of radioactive particles or waves.

It results in a decrease of the original amount radioactive material over time -(the unstable nuclei become stable by releasing the particles & waves)

Radioactive Decay LawRadioactive Decay LawAny radioactive isotope consists of a

vast number of radioactive nuclei.Nuclei does not decay all at once.Decay over a period of time.We can not predict when it will decay,

its a random process but...

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... We can determine, based on probability, approximately how many nuclei in a sample will decay over a given time period, by asuming that each nucleus has the same probability of decaying in each second it exists.

RadioactiveRadioactive Decay Law Decay Law

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The equation for the radioactive decay law:

∆∆NN = - = - λλNN

∆ ∆ ttPOF!!!

What was that???What was that???

Nt = the number of nuclei present at a give time (t) N0 = the number of nuclei present at time (t = 0) e = is the natural expoentional (logarithms) t = time (years, days, hours, or seconds) λ = half life (a RATE of decay = amount/time)

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Half-Life (λ): The amount of time required for one-half or 50% of the radioactive atoms to undergo a radioactive decay.

Every radioactive element (isotope/nuclide) has a specific half-life associated with it.

Is a measure of how stable the nuclei is.

• Half-Life ranges from fractions of a second to billions of years.

• No operation or process of any kind (i.e., chemical or physical) has ever been shown to change the rate at which a radionuclide decays.

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238238U U λ = 4,510,000,000 Years= 4,510,000,000 Years

How long is the half-How long is the half-life of Sodium-24?life of Sodium-24?

Each half life is the Each half life is the SAMESAME time interval time interval

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RadioactivityRadioactivityAn unstable atomic nucleus

emits a form of radiation (alpha, beta, or gamma) to become stable.

In other words, the nucleus decays into a different atom.

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Half-LifeHalf-LifeAmount of time it takes for

one half of a sample of radioactive atoms to decay

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Half-Life CalculationHalf-Life CalculationYou have 400 mg of a

radioisotope with a half-life of 5 minutes. How much will be left after 30 minutes?

5 min400200100

50

12.525

6.253.1251.5625

.78125

5 min5 min5 min

5 min5 min

5 min5 min

5 min

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Medical Applications of Half-LifeMedical Applications of Half-Life

Nuclide Half-Life Area of Body

I–131 8.1 days Thyroid

Fe–59 45.1 days Red Blood Cells

Sr–87 2.8 hours Bones

Tc–99 6.0 hours Heart

Na–24 14.8 hoursCirculatory

System


Sources of RadioactivitySources of Radioactivity Primordial - from before the creation of

the Earth (older than the earth) Cosmogenic - formed as a result of

cosmic ray interactions (from space) Human produced - enhanced or formed

due to human actions (minor amounts compared to natural)


Where are the Sources of Radioactivity?Where are the Sources of Radioactivity? Naturally Occurring Sources:

– Radon from the decay of Uranium and Thorium– Potassium -40 – found in minerals and in plants– Carbon 14 – Found in Plants and Animal tissue

Manmade Sources:

– Medical use of Radioactive Isotopes– Certain Consumer products –(eg Smoke detectors)– Fallout from nuclear testing– Emissions from Nuclear Power plants


Radiation Exposure to AmericansRadiation Exposure to Americans


Radioactivity – Is it a Health Problem?Radioactivity – Is it a Health Problem?

The Alpha, Beta and Gamma particles all add energy to the body’s tissues. The effect is called the Ionizing Energy. It can alter DNA.

Even though Alpha particles are not very penetrative if the decaying atom is already in the body (inhalation, ingestion) they can cause trouble.

The Time, Distance and Shielding principle


Summary/QuestionsSummary/QuestionsWhy does a nucleus decay?Order these emissions from least to greatest

penetrability: Gamma, Alpha, Beta.What is the greatest source of exposure to

radioactivity in our everyday lives?If I tell you that that the half-life of Fellmanium-

250 is 10 days, how much would be left after 30 days if I started with 1600 atoms?

FUSION AND FISSIONFUSION AND FISSION

Every second, the sun converts 500 Every second, the sun converts 500 million metric tons of hydrogen to million metric tons of hydrogen to helium. Due to the process of fusion, helium. Due to the process of fusion, 5 million metric tons of excess 5 million metric tons of excess material is converted into energy in material is converted into energy in each second. This means that every each second. This means that every year, 157,680,000,000,000 metric year, 157,680,000,000,000 metric tons are converted into energy. tons are converted into energy.

THE SUNTHE SUN

Nuclear FusionNuclear FusionNuclear fusion is the process by which multiple nuclei

join together to form a heavier nucleus. It is accompanied by the release or absorption of energy

depending on the masses of the nuclei involved..

FUSIONFUSIONDEUTERIUM

TRITIUMHELIUM

NEUTRON

http://fusioned.gat.com

Complete the Fusion Reactions

1H

2He1H

2He

2He

4Be

2He

2He

6C

6C

4Be8O

What process creates energy in the Sun? Fusion of hydrogen into helium in the Sun’s core generates

the Sun’s energy.

How long ago did fusion generate the energy we now receive as sunlight?

Fusion created the energy we receive today about a million years ago. This is the time it takes for photons and then convection to transport energy through the solar interior to the photosphere. Once sunlight emerges from the photosphere, it takes only about 8 minutes to reach Earth.

Fusion Changes Mass into EnergyFusion Changes Mass into Energy

H

He1kg Hydrogen

.993 kg Helium

E=mc2

What happened to the 0.007 kg?What happened to the 0.007 kg?

=(0.007kg) (3.0x108m/s)2

= 630,000,000,000,000 J

NUCLEAR FISSIONNUCLEAR FISSION Nuclear Fission - a reaction in which an

atomic nucleus of a radioactive element splits by bombardment from an external source, with simultaneous release of large amounts of energy.

(used for electric power generation & nuclear weapons)

Neutron induced in U235

Fission is Exothermic

The sum of the masses of the resulting nuclei is less than the original mass (about 0.1% less)

Nuclear FissionNuclear Fission

The “missing mass” is converted to energy according to E=mc2

Neutrons may:Neutrons may:1 - Cause another fission by colliding with a U235 nucleus

Each split (fission) is Each split (fission) is accompanied by a large accompanied by a large quantity of quantity of E-N-E-R-G-YE-N-E-R-G-Y

• Creates two smaller nuclides and free neutrons• The free neutrons potentially collide with

nearby U235 nuclei• May cause the nuclide to split as well

U.S. Electrical Power Production by Source

Source: EIA

(2004)

Nuclear Fuel CostsNuclear Fuel CostsNuclear Fuel Costs Include

– Uranium

– Enrichment

– Manufacturing

– Waste DisposalTotal Nuclear Fuel Cost is Only About 0.5 cents per kilowatt-

hour– Uranium accounts for only about 20% of this cost or 0.1 cents per

kilowatt-hour

– Increasing Uranium Cost has Minimal Impact

ReviewNuclear fission: - A large nucleus splits into several small nuclei when impacted by a neutron, and energy is released in this process

Nuclear fusion: - Several small nuclei fuse together and release energy.

Draw a Double Bubble Map of Draw a Double Bubble Map of Fusion and FissionFusion and Fission

fusion fission

Differences Similarities Differences


Where to Get More InformationWhere to Get More Information

http://www.physics.isu.edu/radinf/natural.htm

EPA (Environmental Protection Agency)Dept of Energy

THE END!!!THE END!!! Resources: http://cathylaw.com/images/halflifebar.jpg http://burro.astr.cwru.edu/Academics/Astr221/HW/

HW3/noft.gif http://www.chem.ox.ac.uk/vrchemistry/Conservation/

page35.htm www.gcse.com/ radio/halflife3.htm www.nucmed.buffalo.edu/.../ sld003.htm http://www.iem-inc.com/prhlfr.html http://www.math.duke.edu/education/ccp/materials/

diffcalc/raddec/raddec1.html http://www.mrgale.com/onlhlp/nucpart/halflife.htm

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