CHAPTER 24

Nuclear Energy

CHAPTER 24

Nuclear Energy

I. RadioactivityI. Radioactivity(p.674-683)

I. RadioactivityI. Radioactivity(p.674-683)

A. DefinitionsA. DefinitionsA. DefinitionsA. Definitions

Radioactivity emission of high-energy radiation from

the nucleus of an atom

Nuclide nucleus of an isotope

Transmutation process of changing one element into

another via nuclear decay

He42

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

Alpha () helium nucleus paper2+

Beta-minus (-) electron e0

-11- lead

Gamma () high-energy photon 0 concrete

C. Nuclear DecayC. Nuclear DecayC. Nuclear DecayC. Nuclear DecayWhy nuclides 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

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

Half-life (t½)

time it takes for half of the nuclides 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

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.