RadioactivityNuclear Chemistry

RadiationRadiation: 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!

Background Radiation

Radon gas

Food

Cosmic rays

Gamma rays

Medical

Nuclear power

13% are man-made

• Nucleons – particles found in the nucleus of an atom ex. Neutrons and Protons

• Nuclear Forces – strong nuclear force holds neutrons and protons together to form a nucleus

• Isotopes – atoms with identical atomic numbers but different mass numbers

Review Atomic Terms

XA

Z

Mass number

Atomic number

Element symbol

= number of protons + number of neutrons

= number of protons

Number of neutrons = Mass Number – Atomic Number

Writing Isotopes

Writing IsotopesAn isotope is an atom with a different number of neutrons:

Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more.

Notice that the mass number is different. How many neutrons does each isotope have?

• Most of the isotopes which occur naturally are stable.

• A few naturally occurring isotopes and all of the man-made isotopes are unstable.

• Radioactive Decay– the spontaneous decomposition of a nucleus – Unstable isotopes can become stable by releasing

different types of particles.

• Radioactive - a substance that is capable of ALWAYS emitting radiation under any conditions

• Radioisotope - simply an isotope that is radioactive or that undergoes radioactive decay.

RadioactivityThree types of radiation (or radioactivity):•Alpha particles ()•Beta particles ()•Gamma-rays ()

Three types of radiation (or radioactivity):•Alpha particles ()•Beta particles ()•Gamma-rays ()

Alpha Decay ()

Radium

226Ra

88 protons138 neutrons

Radon

Rn222

Mass #

86 protons136 neutrons

+ nnp

p

He)

2 protons2 neutrons

The alpha-particle is a Helium nucleus.

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

Unstable nucleus

New nucleus Alpha particle

2

• These are examples of Radioactive Equations

• Result: 2 less protons and 2 less neutrons– loss of 4 in mass number and loss of 2 in atomic number.

Alpha Decay

Example 1

Example 2

Rn222

86He

4

2+Po

218

84He

4

2

Rn222

86+Y

A

ZHe

4

2

Alpha Decay, Practice #1

He4

2U

234

92+Th

230

90He

4

2

X A

Z+Th

230

90He

4

2

Alpha Decay, Practice #2

Th 230

90+Y

A

ZHe

4

2

Alpha Decay, Practice #3

He4

2+Ra

226

88He

4

2Th

230

90

X A

Z+Pb

214

82He

4

2

Alpha Decay, Practice #4

He4

2+Pb

214

82He

4

2Po

218

84

Beta Decay ()

CarbonC14

6 protons8 neutrons

NitrogenN14

7 protons7 neutrons

+ e-

electron(beta-particle)

Unstable nucleus

New nucleus

Beta particle

Beta DecayA beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay.

Beta decay occurs when a neutron changes into a proton and an electron.

Result: the nucleus has one less neutron, but one extra proton.

Th234

90Y

A

Z+

0

-1

Beta Decay, Practice #1

Th234

90Pa

234

91+

0

-1

X A

ZPb

210

82+

0

-1

Beta Decay, Practice #2

Tl210

81Pb

210

82+

0

-1

Bi210

83Y

A

Z+

0

-1

Beta Decay, Practice #3

Bi210

83Po

210

84+

0

-1

X A

ZBi

214

83+

0

-1

Beta Decay, Practice #4

Pb214

82Bi

214

83+

0

-1

Gamma particles ()

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.

A gamma is a high energy light particle.

Unstable nucleus

New nucleus

Gamma radiation

After or decay, surplus energy is sometimes emitted. This is called gamma radiation and has a very high frequency with short wavelength. The atom is not changed.

Gamma Decay• Gamma rays are not charged particles like and

particles.• Gamma rays are electromagnetic radiation with high

frequency.• When atoms decay by emitting or particles to

form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable.

• This excess energy is emitted as gamma rays (gamma ray photons have energies of ~ 1 x 10-12 J).