radioactive nuclide nuclide which is unstable. it emits radiation & changes into another kind of...

Radioactive Nuclide

Nuclide which is unstable. It emits radiation &

changes into another kind of atom.

Nuclide

An atom with a specific number of protons and a

specific number of neutrons.

14C 12C 14N are all nuclides6 6 7

Isotopes

Two atoms with the same atomic number but

different mass numbers.

Transmutation Reaction

A change in the identity of a nucleus as a result of a change in the number of

its protons.

Relationship between stability and energy

As stability , energy .

Nuclear Strong Force

Attractive force between all nucleons. Holds the nucleus together.But it is a very short-range force.

Electrostatic repulsive forces

Occur between like charges.Occur between protons in the nucleus.Longer-range force.

Stability of nuclide

- Can be assessed by neutron to proton ratio.- A certain number of neutrons are needed to increase the strong nuclear force (the attractive force) enough to hold the nucleus together.-Small atoms, a stable N/P ratio is 1:1-Large atoms: 1.5:1

Which elements are unstable?

All the elements with atomic number > 83 (or

beyond Bismuth) That’s all nuclides 84!

Types of Radiation

Alpha, Beta, GammaSeparated by electric or

magnetic fields.

Opposites attract.

Rays are pure energy. No charge so they are not deflected by an electric field.

Least penetration power

Alpha radiation. Shielding can be paper or cloth.

Most penetration power

Gamma radiation. Requires lead/concrete

shielding.

2He or 2

Symbol for alpha radiationSame as the nucleus of a helium

atomMass = 4 amuCharge = +2

4 4

-1e or -1 or - or

Symbol for beta particleFast moving electron

originating from nucleusMass = “zero”Charge = -1

0 0

+1e or +1 or +

Symbol for positron.Mass = “zero.”Charge = +1.

Positive electron

0 0

0 or

Symbol for gamma radiation.Pure Energy

0 mass0 charge

0

0n or n

Symbol for neutron

1

1H or 1p

Symbol for proton

1 1

Have mass numbers & atomic numbers

Describes changes in the nucleus of an atom

Nuclear Equations

Alpha Decay

Unstable nucleus emits an alpha particle.

Atomic # by 2. Mass # by 4.

220Fr 4 + 216At

Alpha Decay

Atomic # by 2. Mass # by 4.

87 2 85

220Fr 4 + 216At

Equation represents natural transmutation. 1 term on reactant side.

87 2 85

220Fr 4 + 216At

Balance nuclear equations using conservation of

atomic number & conservation of mass

number.

87 2 85

4 + 216=220

87 = 2 + 85

Predicting Decay Modes

Use a nuclide chart!

For elements 1-20:

If the n/p ratio is too high, beta emission happens.

If the n/p ratio is too low, positron emission happens.

42K 0e + 42Ca

Beta Decay

Atomic # by 1.Mass # stays the same.

19 -1 20

19Ne 0e + 19F

Positron Emission

Atomic # by 1.Mass # stays the same.

10 +1 9

# of Half-Lives =

Elapsed timeLength of H.L.

Half-Life Map

Fraction Remainin

g

Amount (mass)

Elapsed Time

# of Half Lives

1 Initial Mass 0 0

½ 1 X H.L. 1

¼ 2 X H.L. 2

1/8 3 X H.L. 3

1/16 4 X H.L. 4

Fraction = 1/2n where n = # of half-lives

Decay Mode

Same as type of particle emitted

Average Atomic Mass

Weighted average of the masses of the naturally

occurring isotopes.

Cl has 2 isotopes: 25% Cl-37 & 75% Cl-35

How to calculate the Average Atomic Mass of Cl

1) Convert percent abundances to decimal format

2) Multiply each abundance factor by the appropriate isotopic mass

3) Sum4) Do a reality check.0.25(37) + (0.75)(35) = 9.25 + 26.25 = 35.5

35.5 is in between the high & the low, and it is closer to the more abundant isotopic mass.

Artificial Transmutation

Particle “bullet” hits target nucleus & new isotope is produced.

2 terms on reactant side.

Artificial Transmutation

32S + 1n 32P + 1H16 0 15 1

bullettarget

Artificial Transmutation

Particle “bullet” may be proton or alpha particle. To react with a nucleus, must overcome + + repulsive forces by accelerating bullet to high speeds.Particle “bullet” may be a neutron. Neutrons have no charge, so no repulsive forces to overcome. No acceleration necessary.Target can be anything from PT.

Fission

Fission is division.

Large nucleus (U-235 or Pu-239) is split into 2 medium sized nuclei by a neutron bullet. Excess neutrons & a great deal of energy are also produced.

239Pu + 1n 90Sr + 147Ba + 3 1n

Fission

94 0 038 56

Fusion

Fusion: U for unite and U for sun.

Very small nuclei (H & He) are jammed together. Huge amounts of energy are released.

1H + 2H 3He

Fusion

1 1 2

Identify each of the rxns

a) 1n + 235U 142Ba + 91Kr + 3 1n + energy

b) 59Co + 1n 60Co

c) 3He + 1H 4He + 0e

d) 14C 14N + 0e

0 92 56 36 0

27 0 27

2 1 2 +1

6 7 -1

fission

Artificial transmutation

fusion

Natural transmutation

Mass Defect, m

The difference between the mass of a specific atom and the sum of the masses of its protons, neutrons, & electrons.Can be expressed in amu or kg.

In nuclear reactions, a small amount of mass is converted to a huge amount of energy.

Nuclear Binding Energy

The energy released when a nucleus is formed from its nucleons.

Often expressed per nucleon.

Potential Well Diagram

Po

ten

tial E

ner

gy o

f Sys

tem

Separate Nucleons

Stable Nucleus

Reference level

r, distance between nucleons

4He + energy 2 protons + 2 neutrons2

Represents potential energy changes during a process

Yellow arrow shows the binding energy!

E = mc2 or E = mc2

Einstein’s Equation relating energy and mass!

Recall that to use this equation, the mass needs to be in kilograms, not amu’s.

STEPS TO CALCULATE BINDING ENERGY

1. Count up protons, neutrons, & electrons.2. Multiply the number of particles X the mass of

the particles.3. Sum the terms.4. Subtract the isotopic mass. This is m in

amu’s.5. Convert to kg.6. Plug into Einstein’s famous equation, E = mc2

or E = mc2.7. Divide by the number of nucleons to get BE

per nucleon.8. Multiply by Avogadro’s number to get binding

energy per nucleon for 1 mole of substance.

Curve of Binding Energy

Binding Energy & Stability

Fe and Ni have the highest binding energies. The higher the binding

energy, the more energy is released when the nucleus is formed. So the nucleus is in a deeper potential well,

and it is MORE stable.

Nucleon

Protons and Neutrons

Mass # = # of nucleons

Parts of a nuclear reactor

FuelControl rodsContainment or shieldingCoolantModerator

Moderator

Substance that slows down fast neutrons. Increases the efficiency of the fission process.

Sometimes the moderator is also the coolant. Sometimes it is in the fuel rods.1n + 235U 142Ba + 91Kr + 3 1n + energy

0 92 03656

Slow neutrons work better!

But fast neutrons come off here!

Control Rods

Contain a substance that absorbs neutrons, removing them from the reaction. On days with high electrical demand, the control

rods would be removed from the core.

Chain Reaction

One of the products is also one of the reactants

Neutron reactant

Neutron products

Critical Mass

The minimum amount of U-235 or Pu-239 that will undergo a self-sustaining chain reaction.

Uses of radioisotopes

Radioactive Dating: C-14 to C-12 for organic material.

U-238 to Pb-206 for rocks.Killing bacteria/spores in food and mail.

Chemical tracers: follow the path of material in a system. Used to study

organic reaction mechanisms.Medical uses: I-131, Tc-99