CHAPTER 9

Nuclear Energy

CHAPTER 9

Nuclear Energy

I. RadioactivityI. Radioactivity(pg.284-292)

I. RadioactivityI. Radioactivity(pg.284-292)

Radioactive ElementsRadioactive ElementsRadioactive ElementsRadioactive Elements

A. DefinitionsA. DefinitionsA. DefinitionsA. Definitions

Radioactivity Process of unstable nuclei of

elements becoming stable through emitting particles or releasing energy away from the atom

Also called nuclear decay

DefinitionsDefinitionsDefinitionsDefinitions

During nuclear decay, the element can transform into a different isotope of the same element or to a different element completely.

Transmutation process of changing one element into

another element by nuclear decay

DefinitionsDefinitionsDefinitionsDefinitions

Nuclear radiation is the released energy and matter during nuclear decay.

This can have both positive and negative effects for life on earth.

DefinitionsDefinitionsDefinitionsDefinitions

Isotopes – elements that have the same number of protons but different number of neutrons in their nuclei.

IsotopesIsotopesIsotopesIsotopes

Carbon-12, Carbon-13, Carbon-14

Where does this take Where does this take place?place?

Where does this take Where does this take place?place?

Radioactivity (nuclear decay) happens in the nucleus of the atom.

He42

B. Types of RadiationB. Types of RadiationB. Types of RadiationB. Types of Radiation

Alpha () helium nucleus paper2+

Beta-minus (-) electron e0

-11- plastic

Gamma () high-energy photon 0 lead

Types of RadiationTypes of RadiationTypes of RadiationTypes of Radiation

Neutron emission (n) 1

0 n 0 charge

C. Nuclear DecayC. Nuclear DecayC. Nuclear DecayC. Nuclear Decay

Why some nuclei decay… to obtain a stable ratio of neutrons to protons

K

K4019

3919

Stable

Unstable(radioactive)

C. Nuclear DecayC. Nuclear DecayC. Nuclear DecayC. Nuclear Decay

Alpha Emission

He Th U 42

23490

23892

Beta Emission

e Xe I 0-1

13154

13153

TRANSMUTATIONTRANSMUTATIONTRANSMUTATIONTRANSMUTATION

ExampleExampleExampleExample

Actinium-217 decays by releasing an alpha particle. Write the equation for this decay process and determine what element is formed.

Step 1: Write the equation with the original element on the reactant side and products on the right side.

ExampleExampleExampleExample

217 A 4

89 Ac Z X + 2 He Step 2: Write math equations for the atomic

and mass numbers.217 = A + 489 = Z + 2

ExampleExampleExampleExample

Step 3: Rearrange the equations.

A = 217 – 4 Z = 89 - 2

Step 4:Solve for the unknown value, and rewrite the equation with all nuclei.

A = 213 Z = 87

ExampleExampleExampleExample

217 213 4

89 Ac 87 Fr + 2 He

This is an example of alpha decay.

D. Half-lifeD. Half-lifeD. Half-lifeD. Half-life

Half-life (t½)

time it takes for half of the radioactive nuclei in a sample to decay

Nuclear Decay

0

2

4

6

8

10

12

14

16

18

20

0 2 4 6 8 10

# of Half-Lives

Ma

ss

of

Iso

top

es

(g

)

Example Half-lives

polonium-194 0.7 seconds

lead-212 10.6 hours

iodine-131 8.04 days

carbon-14 5,370 years

uranium-238 4.5 billion years

Half-lifeHalf-lifeHalf-lifeHalf-life

If we start out with 1 gram of the parent isotope, after the passage of 1 half-life, there will be 0.5 gram of the parent isotope left.  

If we start out with 1 gram of the parent isotope, after the passage of 1 half-life, there will be 0.5 gram of the parent isotope left.  

D. Half-lifeD. Half-lifeD. Half-lifeD. Half-life How much of a 20-g sample of sodium-24 would

remain after decaying for 30 hours? Sodium-24 has a half-life of 15 hours.

GIVEN:

total time = 30 hours

t1/2 = 15 hours

original mass = 20 g

WORK:

number of half-lives = 2

20 g ÷ 2 = 10 g (1 half-life)

10 g ÷ 2 = 5 g (2 half-lives)

5 g of 24Na would remain.

Nuclear ForcesNuclear ForcesNuclear ForcesNuclear Forces

There are two types of forces in the nucleus.

•Strong nuclear force – helps attract the protons and neutrons in the nucleus and keep them together.

•Repulsive force- protons repel each other because they are the same charge

Nuclear ForcesNuclear ForcesNuclear ForcesNuclear Forces

In stable atoms, the attractive forces are stronger than the repulsive forces.

A. FA. F issionissionA. FA. F issionission

splitting a nucleus into two or more smaller nuclei

some mass is converted to large amounts of energy

n3 Kr Ba U n 10

9236

14156

23592

10

A. FA. F issionissionA. FA. F issionission

chain reaction - self-feeding reaction

FissionFissionFissionFission

Chain reactions can be controlled and used to create electricity in nuclear power plants.

The minimum amount of a substance that can undergo a fission reaction and sustain a chain reaction is called critical mass.

B. FusionB. FusionB. FusionB. Fusion

combining of two nuclei to form one nucleus of larger massproduces even more

energy than fissionoccurs naturally in

stars

FusionFusionFusionFusion

Nuclear Radiation in LifeNuclear Radiation in LifeNuclear Radiation in LifeNuclear Radiation in Life

Background radiation is nuclear radiation that is around you from natural sources like the sun, soil, rocks, and space.

A rem or millirem (1 rem = 1000millirems) is the unit for radiation.

Nuclear Radiation in Life Nuclear Radiation in Life Nuclear Radiation in Life Nuclear Radiation in Life

A safe limit is set at 5000 millirems/year.

Occupation – X-ray tech, flight attendant

Where you live- high elevation, near rocks

Activities - smoking

A. Nuclear PowerA. Nuclear PowerA. Nuclear PowerA. Nuclear Power

Fission Reactors

A. Nuclear PowerA. Nuclear PowerA. Nuclear PowerA. Nuclear Power

Fusion Reactors (not yet sustainable)

Tokamak Fusion Test Reactor

Princeton University

National Spherical Torus Experiment

A. Nuclear PowerA. Nuclear PowerA. Nuclear PowerA. Nuclear Power

235U is limited danger of meltdown toxic waste thermal pollution

Hydrogen is abundant no danger of meltdown no toxic waste not yet sustainable

FISSION

FUSION

vs.

Other benefits to Other benefits to radiationradiation

Other benefits to Other benefits to radiationradiation

Smoke detectorsDisease detectionUltra soundCT scanMRICancer treatment