Radioactivity and Radioactivity and Nuclear ReactionsNuclear Reactions

Ch 9.1-9.2, 9.4Ch 9.1-9.2, 9.4

Nucleus and the Nucleus and the Strong ForceStrong ForceProtons and neutrons are packed tightly Protons and neutrons are packed tightly

togethertogether

Two positives normally repel each other, so why Two positives normally repel each other, so why dondon’’t the protons in the nucleus repel?t the protons in the nucleus repel?

Strong force = one of four basic forces that Strong force = one of four basic forces that causes protons and neutrons to be attracted to causes protons and neutrons to be attracted to each othereach other

100 times stronger than electric force100 times stronger than electric force

Short-range force, so it weakens with distanceShort-range force, so it weakens with distance

Small vs Large Small vs Large NucleiNuclei

Protons and neutrons are held together Protons and neutrons are held together less tightly in large nuclei. Why?less tightly in large nuclei. Why?

Small nuclei have few protons, so the Small nuclei have few protons, so the repulsive force on a proton due to other repulsive force on a proton due to other protons is smallprotons is small

In a large nuclei, the attractive strong In a large nuclei, the attractive strong force is exerted only by the nearest force is exerted only by the nearest neighbors. All the protons exert neighbors. All the protons exert repulsive forces making the repulsive repulsive forces making the repulsive force large.force large.

RadioactivityRadioactivityIn many nuclei, the strong force keeps the In many nuclei, the strong force keeps the nucleus together (STABLE)nucleus together (STABLE)

When it canWhen it can’’t, the nucleus can decay and give off t, the nucleus can decay and give off matter and energy in a process of radioactivitymatter and energy in a process of radioactivity

Larger nuclei tend to be unstable – all nuclei Larger nuclei tend to be unstable – all nuclei containing more than 83 protons are radioactivecontaining more than 83 protons are radioactive

All elements with more than 92 protons are All elements with more than 92 protons are synthetic and decay soon after they are created synthetic and decay soon after they are created (UNSTABLE)(UNSTABLE)

Stable and Unstable Stable and Unstable NucleiNuclei

Smaller elements neutron to proton Smaller elements neutron to proton ratio is 1:1 to be stable isotopesratio is 1:1 to be stable isotopes

Heavier elements neutron to proton Heavier elements neutron to proton ratio is 3:2 to be stable isotopesratio is 3:2 to be stable isotopes

Nuclei of any isotopes that differ much Nuclei of any isotopes that differ much from these ratios are unstable, whether from these ratios are unstable, whether heavy or lightheavy or light

Nuclear Radiation When an unstable nucleus decays, particles When an unstable nucleus decays, particles and energy are emitted from the decaying and energy are emitted from the decaying nucleusnucleus

Alpha Particles – (2 p and 2 n lost) massive, Alpha Particles – (2 p and 2 n lost) massive, comparatively speaking; loses energy comparatively speaking; loses energy quickly; canquickly; can’’t pass through paper; changes t pass through paper; changes the element (transmutation); mass changes; the element (transmutation); mass changes; can damage the bodycan damage the bodyBeta Particles – (n turns into p and emits e) e Beta Particles – (n turns into p and emits e) e emitted from n; transmutation changes the emitted from n; transmutation changes the element; mass doesnelement; mass doesn’’t change; much faster t change; much faster and penetrating; damage bodyand penetrating; damage bodyGamma Rays – electromagnetic waves that Gamma Rays – electromagnetic waves that carry energy; most penetrating form; cause carry energy; most penetrating form; cause less damage to biological moleculesless damage to biological molecules

At a glance…At a glance…

Radioactive Half-Radioactive Half-LifeLifeSome radioisotopes decay in less than a Some radioisotopes decay in less than a

second, while others take millions of second, while others take millions of yearsyears

Half-life: the amount of time it takes Half-life: the amount of time it takes for half the nuclei in a sample of the for half the nuclei in a sample of the isotope to decayisotope to decay

Radioactive Half-Life Radioactive Half-Life contcont

Ch 21.3: Ch 21.3: Absolute-Age Absolute-Age

Dating of RocksDating of RocksRelative-age dating vs. Absolute-Age Relative-age dating vs. Absolute-Age DatingDating

Relative-age dating: compares past Relative-age dating: compares past geologic events based on the observed geologic events based on the observed order of strata in rock recordorder of strata in rock record

Absolute-age dating: determines actual Absolute-age dating: determines actual age of a rock, fossil, or other objectage of a rock, fossil, or other object

Radioactive DecayRadioactive DecayRadioisotopes are found in igneous and Radioisotopes are found in igneous and metamorphic rocks, some fossils, and metamorphic rocks, some fossils, and organic remainsorganic remains

Emission of radioactive particles and the Emission of radioactive particles and the resulting change into other elements over resulting change into other elements over time is called time is called radioactive decayradioactive decay

This decay stays constant regardless of the This decay stays constant regardless of the environment, pressure, temperature, or environment, pressure, temperature, or any other physical changesany other physical changes

So, these atomic particles become accurate So, these atomic particles become accurate indicators of the absolute age of an objectindicators of the absolute age of an object

I love you I love you Mrs. Sjuts! Mrs. Sjuts!

Radioactive Radioactive DatingDating

Fossils and rocks can be dating using Fossils and rocks can be dating using radioactive isotopesradioactive isotopes

Amounts of the radioisotope and its Amounts of the radioisotope and its daughter nucleus are measured in a daughter nucleus are measured in a samplesample

Then, the number of half-lives that need to Then, the number of half-lives that need to pass to give the measured amounts of the pass to give the measured amounts of the isotope are calculatedisotope are calculated

The number of half-lives is the amount of The number of half-lives is the amount of time that has passed since the isotope time that has passed since the isotope began to decay AND usually is the same as began to decay AND usually is the same as the age of the object.the age of the object.

Carbon DatingCarbon DatingThe radioactive isotope C-14 is often used to The radioactive isotope C-14 is often used to find the ages of once living objectsfind the ages of once living objects

It is naturally found in most all living thingsIt is naturally found in most all living things

An atom of C-14 eventually will decay into N-An atom of C-14 eventually will decay into N-14 with a half-life of 5,730 years14 with a half-life of 5,730 years

By measuring the amount of C-14 in a By measuring the amount of C-14 in a sample and comparing it to the amount of C-sample and comparing it to the amount of C-12, scientists can determine the approx age 12, scientists can determine the approx age of plants and animals that lived within the of plants and animals that lived within the last 50,000 yearslast 50,000 years

Uranium DatingUranium DatingSome rocks contain uranium, which has Some rocks contain uranium, which has two radioactive isotopes with long half-two radioactive isotopes with long half-lives, both decaying into isotopes of leadlives, both decaying into isotopes of lead

By comparing the uranium isotope and the By comparing the uranium isotope and the daughter nuclei the number of half-lives daughter nuclei the number of half-lives since the rock was formed can be since the rock was formed can be calculatedcalculated

U-235 U-235 0.7 billion years 0.7 billion years

U-238 U-238 4.5 billion years 4.5 billion years

Ch 9.4 Nuclear Ch 9.4 Nuclear ReactionsReactions

Nuclear Fission – the process of splitting a Nuclear Fission – the process of splitting a nucleus into two nuclei with smaller massesnucleus into two nuclei with smaller masses

Chain reaction – ongoing series of fission Chain reaction – ongoing series of fission reactionsreactions

Critical mass – the amount of fissionable Critical mass – the amount of fissionable material required so that each fission reaction material required so that each fission reaction produce approximately one more fission produce approximately one more fission reactionreaction

Nuclear Fusion – two nuclei with low masses are Nuclear Fusion – two nuclei with low masses are combined to form one nucleus of larger masscombined to form one nucleus of larger mass

Nuclear FissionNuclear FissionLarge elements need a TON of energy in order to Large elements need a TON of energy in order to hold their nucleus together.hold their nucleus together.

When the large nucleus is split into smaller nuclei, When the large nucleus is split into smaller nuclei, those smaller nuclei donthose smaller nuclei don’’t require as much energy t require as much energy to stay together…to stay together…

So, that leftover energy is released!So, that leftover energy is released!

Atomic bomb – used in Hiroshima and NagasakiAtomic bomb – used in Hiroshima and Nagasaki

Fission - Chain Reaction Fission - Chain Reaction Nuclear Fission: Nuclear Fission: Pros and Cons Pros and Cons

Nuclear Meltdown Nuclear Meltdown

Cooper Nuclear Station near Brownville, NECooper Nuclear Station near Brownville, NE

Fort Calhoun Nuclear Generating System between Ft. Fort Calhoun Nuclear Generating System between Ft. Calhoun and BlairCalhoun and Blair

Nuclear FusionNuclear FusionNeed very high temperatures in order Need very high temperatures in order to overcome the repulsive forces. Sun's to overcome the repulsive forces. Sun's Fusion Fusion

Scientists cannot control fusion Scientists cannot control fusion reactions for the purpose of power.reactions for the purpose of power.

We can, however, use it to make We can, however, use it to make nuclear weapons. Large ones. nuclear weapons. Large ones. Hydorgen Bomb - Fusion Hydorgen Bomb - Fusion

Nuclear Decay vs. Nuclear Decay vs. Nuclear ReactionsNuclear Reactions

Decay happens spontaneouslyDecay happens spontaneously

Reactions are controlled and self-Reactions are controlled and self-sustaining and release much more sustaining and release much more energyenergy

Nuclear Reaction: Nuclear Reaction: Plutonium Plutonium

Pu-239 Used to make nuclear weapons Pu-239 Used to make nuclear weapons like the one dropped on Nagasaki in like the one dropped on Nagasaki in 19451945