Nuclear Chemistry

Nuclear Radiation

What is radiation?Transfer of energy by electromagnetic waves.

What is radioactivity?Spontaneous emission of radiation when

the nucleus of an atom breaks down to form a different element.

Radiation is organized on the Electromagnetic Spectrum

LOW ENERGY

HIGH ENERGY

V I B G Y O R

Electromagnetic radiation is classified into two types:

Non-ionizing Radiation: Transfers energy causing vibrations, electron

excitation, and heat Parts of the spectrum: radio, microwaves, infrared,

and visible Ionizing Radiation:

High energy that ejects electrons and transforms molecules into reactive unstable fragments

Parts of the spectrum: UV, X-ray, Gamma Ray

Electromagnetic Spectrum

Radio WavesWhere have you encountered radio waves?

Radio waves have the longest wavelength, smallest frequency, and ___lowest___ energy.

MicrowavesWhere have you encountered microwaves?

Microwave radiation is used to cause particles in your food to vibrate. If particles are moving faster, what does that mean for their temperature? It increases!

Microwaves have long wavelengths, low frequency, and _____low_______ energy.

InfraredWhere have you encountered infrared radiation?

Some infrared radiation is given off from the ____sun_____, which feels warm on the skin.

Infrared radiation has a long-medium wavelength, medium-low frequency, and __medium-low____ energy.

Visible LightWhere have you encountered visible radiation?

This light given off by the sun is the energy provided for ___photosynthesis____.

Visible light has a medium wavelength, medium frequency, and __medium____ energy.

Ultraviolet Where have you encountered UV radiation?

UV radiation is beneficial for the body to get Vitamin D, however overexposure kills healthy cells and leads to skin cancer. The ___ozone____ layer filters this radiation from the sun.

UV radiation has medium-short wavelength, medium-high frequency, and

_____medium-high_____ energy.

X-RayWhere have you encountered X-ray radiation?

X-rays can pass through skin/muscle but are absorbed by the bone. Why should you limit the number of x-rays you get in a year?

X-rays have a short wavelength, high frequency, and __high____ energy.

Gamma Ray

Where have you encountered gamma rays?

Gamma rays can be emitted when an atomic bomb goes off. These rays are destructive to human cells and forms of them are used in cancer treatment.

Gamma rays are emitted when ______radioactive________ elements decay.

Gamma rays have the shortest wavelength, highest frequency, and the ___highest___ energy.

Circle the radiation with the highest energy in each grouping:

gamma ray microwave visible ultraviolet radio x-ray infrared ultraviolet visible blue color red color yellow color

Background RadiationThe constant level of radioactivity always

present around usCaused by:

Cosmic rays Naturally occurring uranium Radon in the air Radioactive isotopes in food and environment

What is your radiation exposure?National Average: 500 mremBackground Average: 360 mrem

Types of Decay

How do nuclear and chemcial reactions differ?

Nuclear reactions involve the nucleus (protons and neutrons)

BUTchemical reactions involve the

transfer and sharing of electrons

Band of Stability

After element 83 (Bismuth)the elements are naturally unstable

and may emit decay particles

The bigger the atom gets and the further from a 1:1 ratio of

protons and neutrons, the less stable the

atom is

Types of Radioactive Decay

Decay Type Symbol Charge Reaction

Particle StrengthCan be

stopped by…

AlphaBeta

Gamma

Radioactive Decay

Nuclear Symbols Review

• The superscript indicates the mass number and the subscript indicates the atomic number.

C12

6

XAZ

Mass Number

Atomic NumberElement Symbol

Steps to writing decay reactions:

1. Write the nuclear symbol for the element that is given.

2. Draw an arrow.3. Identify the type of particle that has decayed

and write it after the arrow.4. Balance the mass number (top) and the

atomic number (bottom). 5. Identify the new element.

Alpha Decay Loss of an alpha particle 4

2He42α

239Pu 94

235U 92

Beta Decay Loss of a beta particle

0-1 e0

-1 β

42K 19

Gamma Decay Loss of a gamma particle

Does it effect the outcome of the reaction?

Alpha and gamma decay of:

00γ

239Pu 94

Half Life

Half-LifeTime required for half a sample to decay

The stability of the isotope is what determines the rate of decay.

Less Stable = faster decay

Half-Life After each half-life, half of

the sample decays. Start = 100%

40 blue particles are present 1 half-life = 50%

20 blue remain 2 half-lives = 25%

10 blue remain 3 half-lives = 12.5%

5 blue remain 4 half-lives = 6.25%

2.5 blue remain

Amount never becomes zero!!

Half-Life After 10 half-lives sample considered

nonradioactive because it approaches the level of background radiation.

Because the amount never reaches zero, radioactive waste disposal and storage causes problems. Would you want radioactive waste stored in your community?

How can we get rid of nuclear radioactive waste?

Half Life PracticeExample 1:

The half-life of mercury-195 is 31 hours. If you start with a sample of 5.00 g of the sample, how much of it will still be left after 93 hours?

Half Life Practice ContExample 2:

How many half lives have passed if there is only 1.875 g left of a 30 g sample?

If the half life for this sample is 1 hour, how many total hours have gone by?

Applications

Where do we use nuclear chemistry?

Sun is powered by nuclear reactionsElectricity from nuclear power plantsMedical:

x-rays, cancer treatment, radioactive tracers Industrial:

Sterilize equipment, sterilize (irradiate) food, x-rays of metal equipment (scan for cracks in airplanes)

Military

Radiation ExposureExposure to radiation can cause cell mutations

and illness.Four factors that affect exposure:

Dose (strength of radiation) Exposure time Area exposed Tissue exposed

HOW DO WE BENEFIT FROM NUCLEAR

REACTIONS?

FusionTwo light atoms combine to form a heavier

atom of higher energy

This reaction powers the sun!

FissionOne heavy atom breaks down into two or more

smaller atoms and produces energyThis becomes a chain reaction

(as one atom splits and hits more, and those split and hit more)

Supercritical:creates a great release of energy - atomic bomb

Will a chain reaction always occur?Particles reacting must have critical mass:

The minimum amount of mass needed for the neutron to hit and react with

No critical mass = no reaction

Fission reactions can also be controlled to contain the energy.

Controlled FissionControlled Fission: used for nuclear power

Controlled Diagram: