CHAPTER 3.4 & 24.1

Nuclear Chemistry

Radioactivity

Radiation

Radiation: The process of emitting energy in the form of waves or particles.

Where does radiation come from?Radiation is generally produced when particles interact or decay.

A large contribution of the radiationon earth is from the sun (solar) or from radioactive isotopes of the elements (terrestrial).

Radiation is going through you atthis very moment!

http://www.atral.com/U238.html

Man-made radiation sources that people can be exposed to include tobacco, television, medical x-rays, smoke detectors, lantern mantles, nuclear medicine,

and building materials.

Adding it all up, the average American is exposed to a total of about 360 millirems a year from natural and man-made radiation.

IsotopesWhat’s an isotope?

Two or more varieties of an element having the same number of protons but different number of neutrons. Certain isotopes are “unstable” and decay to lighter isotopes or elements.

Deuterium and tritium are isotopes of hydrogen. In addition to the 1 proton, they have 1 and 2 additional neutrons in the nucleus respectively*.

Another prime example is Uranium 238, or just 238U.

Definitions

• Radioactivity– emission of high-energy radiation from the nucleus of an

atom

• Nuclide– nucleus of an isotope

Nuclear Decay• Why nuclides decay…

– to obtain a stable ratio of neutrons to protons

K

K4019

3919

Stable

Unstable(radioactive)

He42

Types of Radiation

• Alpha ()– helium nucleus paper2+

Beta-minus () electron e0

-11- lead

Gamma () high-energy photon 0 concrete

Where do these particles come from ?

These particles generally come from the nuclei of atomic isotopes which are not stable.

The decay chain of Uranium produces all three of these formsof radiation.

Let’s look at them in more detail…

Alpha Particles (a)

Radium

R226

88 protons138 neutrons

Radon

Rn222

Note: This is theatomic weight, whichis the number ofprotons plus neutrons

86 protons136 neutrons

+ nnp

p

a (4He)

2 protons2 neutrons

The alpha-particle ( )a is a Helium nucleus.

It’s the same as the element Helium, with the electrons stripped off !

Beta Particles (b)

CarbonC14

6 protons8 neutrons

NitrogenN14

7 protons7 neutrons

+ e-

electron(beta-particle)

We see that one of the neutrons from the C14 nucleus “converted” into a proton, and an electron was ejected. The remaining nucleus contains 7p and 7n, which is a nitrogen nucleus. In symbolic notation, the following process occurred:

n p + e ( + )n And a neutrino is produced too.

Gamma particles (g)In much the same way that electrons in atoms can be in an excited state, so can a nucleus.

NeonNe20

10 protons10 neutrons

(in excited state)

10 protons10 neutrons

(lowest energy state)

+

gamma

NeonNe20

A gamma is a high energy light particle.

It is NOT visible by your naked eye because it is not in the visible part of the EM spectrum.

Gamma Rays

NeonNe20 +

The gamma from nuclear decayis in the X-ray/ Gamma ray

part of the EM spectrum(very energetic!)

NeonNe20

Nuclear Decay…the ones we care about

• Alpha Emission

He Th U 42

23490

23892

Beta Emission

e Xe I 0-1

13154

13153

TRANSMUTATION

Half-life

• Half-life (t½)– time it takes for half of the nuclides in a sample to

decayNuclear 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-life Problem 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.

F ission

• 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

F ission

• chain reaction - self-feeding reaction

Nuclear Weapons

Nuclear Power

• Fission Reactors Cooling Tower

Nuclear Power

• Fission Reactors

Nuclear Power

• Chernobyl

Nuclear power

• Three mile Island

Fusion

• combining of two nuclei to form one nucleus of larger mass• produces even more

energy than fission• occurs naturally in

stars

Nuclear Power

• Fusion Reactors (not yet sustainable)

Nuclear Power

• Fusion Reactors (not yet sustainable)

Tokamak Fusion Test Reactor

Princeton University

National Spherical Torus Experiment

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.

Cold Fusion?

OthersIrradiated FoodRadioactive DatingNuclear MedicineNuclear Weapons