nuclear chemistry. what is radioactivity? what are the 3 types of nuclear radiation? 2

Nuclear Chemistry

• What is radioactivity?• What are the 3 types of nuclear

radiation?

2

Nuclear Chemistry • The study of changes that occur in the nucleus

of an ATOM!!!

• Radioactivity - the process in which an unstable atomic nucleus emits charged particles and/or energy (also called nuclear decay)

• During "nuclear decay", an atom of one element can change into an atom of a different element.

Chemical vs. Nuclear ReactionsChemical Reactions Nuclear Reactions

Occur when bonds are broken

Occur when nuclei emit particles and/or rays


Occur when bonds are broken Occur when nuclei emit particles and/or rays

Atoms remain unchanged, although they may be rearranged

Atoms often converted into atoms of another element





Involve only valence electrons

May involve protons, neutrons, and electrons





Involve only valence electrons May involve protons, neutrons, and electrons

Associated with small energy changes

Associated with large energy changes





Involve only valence electrons May involve protons, neutrons, and electrons

Associated with small energy changes

Associated with large energy changes

Reaction rate influenced by temperature, particle size, concentration, etc.

Reaction rate is not influenced by temperature, particle size, concentration, etc.

Radioactivity•An 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.

Radioactivity•Alpha Particle – Helium nucleus

•Beta Particle – electron•Gamma Ray – high-energy photon

Types of Nuclear Radiation

• Alpha particles • Beta particles• Gamma rays

• Nuclear Decay song

Types of Nuclear Radiation• Alpha particles - positively charged, made

up of 2 protons and 2 neutrons (same as a helium nucleus)

• Alpha decay - one product is ALWAYS a Helium nucleus 4

2 He • The mass and atomic numbers of the

reactant must equal the sum of the mass and atomic numbers of the products

• (ex) 22288Ra 4

2 He + 218 86 Rn

Mass #Atomic #

Look up element #86

Beta Particles• Beta particles – electron emitted by an

unstable nucleus, negatively charged particle

• Beta decay - one product is 0-1e (because of

it’s negative charge, it is assigned an atomic number of -1)

• (ex) 146C 0

-1e + 147N

• (once again, the sums of mass number and atomic number of the products must equal the reactant)

• Once you find the atomic number, you look for the element on your periodic table!!!

Alpha and Beta Decay Animation• http://library.thinkquest.org/27954/

dequ.htm

Gamma Decay• Gamma decay- penetrating ray of energy

emitted by an unstable nucleus• They have no mass and no charge• Like X-rays and visible light, gamma rays

travel at the speed of light• During gamma decay, the atomic number

and mass number of the atom remain the same, but the energy of the nucleus decreases

• X-rays are emitted by electrons outside the nucleus, while gamma rays are emitted by the nucleus.

Decay Particles Penetrating Ability

• alpha particle– Least penetrating (can be stopped by a sheet of paper or clothing)

• beta particle– More penetrating that alpha (pass through paper, but stopped by

a thin sheet of metal• gamma ray

– Much more penetrating that alpha and beta (takes several centimeters of lead or several meters of concrete to stop gamma radiation)

Effects of Nuclear Radiation• Background radiation – nuclear radiation that

occurs naturally in the environment– Examples – radioisotopes in air, water, rocks, plants and

animals

• Nuclear radiation can ionize atoms, so it can damage the cells and tissues of your body– Bonds holding proteins and DNA may be broken

• Examples – Alpha particles: radon gas (can be inhaled and causes

lung cancer)– Beta particles can damage tissues more than alpha

particles– Gamma rays can expose all organs to ionization damage

Detecting Nuclear Radiation• Geiger counters

• Film badges

Nuclear Chemistry on youtube

• http://www.youtube.com/watch?v=aEBGE1Nm7vc

Practice on Nuclear Decay:

• Let’s work on p. 1 of your Nuclear Chemistry packet!

• Homework – p. 2 of packet

29

Half-Life•Amount of time it takes for one half of a sample of radioactive atoms to decay

Medical 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

Half-Life Calculation #1•You have 400 mg of a radioisotope with a half-life of 5 minutes. How much will be left after 30 minutes?

To calculate:• Start with 400 mg.• The half-life is 5 minutes, so how much will you

have after 5 minutes?– 200 mg

• Now, how much will you have at the 10 minute mark? (remember that after 5 minutes, you will half of what you started with at that particular time.)– 100 mg

• Keep going until you have reached 30 minutes!• You can also use fractions…you try it!

Half-Life Calculation #2•Suppose you have a 100 mg sample of Au-191, which has a half-life of 3.4 hours. How much will remain after 10.2 hours?

Half-Life Calculation # 3•Cobalt-60 is a radioactive

isotope used in cancer treatment. Co-60 has a half-life of 5 years. If a hospital starts with a 1000 mg supply, how many mg will need to be purchased after 10 years to replenish the original supply?

Half-Life Calculation # 4•A radioisotope has a half-life of 1 hour. If you began with a 100 g sample of the element at noon, how much remains at 3 PM? At 6 PM? At 10 PM?

Half-Life Calculation # 5•How many half-lives have passed if 255 g of Co-60 remain from a sample of 8160 g?

Half-Life Calculation # 6•Suppose you have a sample containing 400 nuclei of a radioisotope. If only 25 nuclei remain after one hour, what is the half-life of the isotope?

Half-Life Calculation # 7•If a radioactive element has diminished by 7/8 of its original amount in 30 seconds, what is its half-life?

Answers to Half-Life Calculations

•Half-Life Calculation #1– 6.25 mg

•Half-Life Calculation #2– 12.5 mg

•Half-Life Calculation #3– 750 mg


•Half-Life Calculation #4– 12.5 g, 1.5625 g, 0.09765625 g

•Half-Life Calculation #5– 5 half-lives


•Half-Life Calculation #6– 15 minutes

•Half-Life Calculation #7– 10 seconds

Video on Fusion and Fission

• http://www.youtube.com/watch?v=-Qliifidcuw

• Another one:• http://www.bbc.co.uk/schools/

gcsebitesize/science/add_aqa/atoms_radiation/nuclearact.shtml

Fission and Fusion

• Fission- splitting of atomic nuclei. Tons of energy produced from a small mass

• Fusion- combining atomic nuclei. Requires high temp, stars do this.

Fission vs. Fusion

• Look at my Physical Science notes under nuclear chemistry

Fission• NOT a natural process

• Occurs as a result of neutron bombardment

• heavy nucleus (mass# > 200) splits into two similar sized pieces

• wide range of nuclei produced

• releases lots of energy b/c smaller nuclei more stable

• 235U and 239Pu most important

Fission

• CONTROLLED: – Nuclear Power Plant

• UNCONTROLLED:– In reactor = meltdown!– Atomic bomb!

Fission and Fusion

Fusion• nuclei fuse together

• for very light elements, stability increases with increasing mass #

• energy released when two light nuclei combine to larger, more stable nucleus

• thermonuclear reaction - occurs only at very high tempslowest temperature required for fusion: 40,000,000 K

• occurs constantly in sun

• Plasma is an example (atoms have been stripped of their electrons)

• FusionHas it occurred on earth?

Hydrogen bomb

Comparing and ContrastingSection 10.4

a. is the splitting of a large nucleus into two smaller fragments

b. is widely used as an alternative energy source

c. is the fusing of two small nuclei into one larger nucleus

d. is still being researched and developed as an alternativeenergy source

Fission vs. Fusion

Radiation in our lives• Background radiation • cosmic rays in atmosphere• radon from granite rock (lung cancer)• Foods• bananas, Brazil nuts• Medical exposure• Dental x-ray• Cancer treatment (Cobalt-60)• Detecting art forgeries• Analyzing gunpowder residue• Agricultural research, diagnose disease• Smoke detectors (Americium-241)

What do we do with Nuclear Waste?

• Bury it underground in a spot that is geologically stable!!

• SC has a nuclear waste site.

Effects of Radiation Video Clips

• Gamma Radiation gone wrong

• Harmful effects of radiation

• Our radiation environment

• Chernobyl

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