Nuclear Radiation And Types

The Nucleus

The Nucleus • • • • • •

Nuclear stability and radioactive decay Kinetics of radioactive decay Nuclear transformations Detection and uses of radioactivity Nuclear fission and fusion Effects of radiation

Nuclear chemistry is the study of the nucleus Electron cloud Nucleus Electrons are very small and have a negative charge. They are light and far apart

The nucleus contains protons(+) and neutrons (0). They are very heavy and close together.

How do nuclei stick together?

Protons are all positive and repel each other. This is the electronic force.

All nucleons (p, n) have a new force, the strong nuclear force that holds them together anyway.

Nuclear Notation To keep track of what nucleons an atom has chemists write their symbols with two numbers atomic mass = protons + neutrons atomic number = protons

12 6

C

In any reaction (nuclear or chemical) these numbers must also balance.

Nuclear notation: Generic Symbols

Required, distinguishes one Isotope from another

Optional, redundant info With the element symbol

A

X Z

Element symbol

A nuclide can also be written: element-A carbon – 14, is 14 C uranium – 238 is 238 U

Find your Beaker! And respond to the following.

Write the following atoms in nuclear notation Pro/Neu 4/3 12/14 20/22 20/24 43/50

Symbol 7 Be 4 26Mg 12 42 Ca 20 44 Ca 20 93 Tc 43

Atom Be Mg Ca Ca Tc

Types of Radioactive Decay To balance nuclear reactions we need to include particles with special names

α particle = helium nucleus β particle = electron positron  e+ Neutron  n 1 Proton = hydrogen 0nucleus Gamma Ray  γ 0 0

 

He42 e- 0



H1

-1 0 +1

+1

Nuclear Stability

• Approx 1,500 different nuclei are known; about 264 are stable • Elements with N/P ratio = 1:1 are stable • Above atomic number 20, stable nuclei have a higher N/P ratio up to about 1.53:1 • Stable nuclei fall within a region called "band of stability"; if they fall outside area, they undergo spontaneous radioactive decay

Band of Stability • All nuclei with 84 or more protons are unstable • Heavy nuclei with too many neutrons or too many protons are unstable

Alpha Decay

Positron emission and/or electron capture

Nuclear Stability Nuclei below the zone of stability are likely to undergo: Positron production, β+ (too many protons and not enough neutrons so a proton is converted to a neutron and a positron is emitted) Electron capture, β- (too many protons and not enough neutrons so a proton is changed into a neutron and an electron is captured in the process.)

Nuclear Stability – Alpha particle production (an alpha particle is released dropping the atomic number by 2 and the atomic mass by 4) Nuclei above the zone of stability are likely to undergo: – Beta particle production, β- (too many neutrons and not enough protons so an electron is released as a neutron is converted to a proton)

Alpha Particle Production

Nuclear Stability – Gamma rays or γ rays are produced usually during a decay process that has emitted an alpha or beta particle. The gamma ray is a high energy photon. They almost always accompany electron capture processes to release excess energy.

Decay of Uranium - 238

Writing Nuclear Equations

Write the nuclear equation representing the decay of Potassium – 40 as it emits a positron.

Writing Nuclear Equations Answer

Find your Radioactiveman and try these HOT Problems!! a positron • 11 C produces • 214 Bi produces a β- particle • 237 Np produces an α particle • Potassium - 40 captures an electron Potassium 40 emits a β particle •

More Practice!

Balance the following nuclear reactions:

Gallium –73 transmutes to germanium73 Platinum -192 transmutes to osmium-188 Bombarding alpha particles to an unknown element produces berkelium243 and a neutron Fusion of uranium-238 and carbon-12 produces 6 neutrons and what other element?

Alpha Beta Gamma!

Geiger-Muller Counter

Relative Energies α particles are heavy, slow, and low energy. They can’t penetrate paper. β particles are small, fast, and medium energy. They can’t penetrate foil γ rays are photons, have no mass, are fast, and high energy. Some may be stopped by lead.

Nuclear Fission

Nuclear Power Plant

Nuclear Fusion

Stellar Formation of Carbon 12

Effects of a nuclear bomb 1) Explosive Blast - a lot of pressure makes houses fall down 2) Direct Radiation - radioactive nuclei ejected from the bomb 3) Thermal Radiation - heat and light that will burn you 4) Radioactive Fallout - dust and debris are made radioactive, enter the atmosphere and spread long distances http://www.pbs.org/wgbh/amex/bomb/sfeature/effects.html

Plasma Ball of Early Atomic Bomb Test

Plasma Ball of Early Atomic Bomb Test

How long does radioactivity stay around? Every radioactive nucleus has a half life. This is the amount of time before half of it is gone.

Half Life • The amount of time it takes for half of the nuclide to decay. Time N 0

100

1

50

2

25

3

12.5

4

6.25

5

3.125