1. Nuclear Chemistry Introduction Isotopes
atomic number (Z) =
the number of protons
the number of protons
mass number (A) = +
the number of neutrons
mass number (A) 12 C
atomic number (Z) 6
number of protons 6
number of neutrons
12 – 6 = 6

2. Nuclear Chemistry Introduction Isotopes
Isotopes are atoms of the same element having a
different number of neutrons.

3. Nuclear Chemistry Introduction Isotopes
A radioactive isotope, called a radioisotope, is
unstable and spontaneously emits energy to form
a more stable nucleus.
Radioactivity is the nuclear radiation emitted by a
radioactive isotope.
Of the known isotopes of all elements, 264 are stable and 300 are naturally occurring but unstable.
An even larger number of radioactive isotopes, called artificial isotopes, have been produced in the laboratory.

4. NUCLEAR RADIATION
Used to :
treat medical conditions
detect and treat tumors
detect the function of an organ
produce scans/images of organs
ORIGIN
Most element have at least one unstable isotopes.
Unstable isotopes arise when the attraction/repulsion between protons and neutrons in the nucleus is unbalanced.
An unstable nucleus has too few or too many neutrons as compared to protons.
e.g. 2412Mg 2312Mg (Mg-23) 2712Mg (Mg-27)

5. RADIOACTIVITY
* This is emission of small particles of energy or rays (radiation) by unstable elements (to be stable).
* Elements that emit radiation spontaneously (e.g. Thorium, Th and Uranium, U) are said to be radioactive and called radioisotope.
* The radiation is emitted from the nucleus of the atom
TYPES OF RADIATION
* Particles and Rays
Alpha and Beta Particles and Gamma Rays

6. 1. ALPHA PARTICLES (α particles)
* Attracted towards negative field (positively charged).
* Made up of (two protons and two neutrons), helium nuclei, therefore have charge of +2.
* Have low penetrating power and are harmless when they strike the body.
* Harmful when inhaled or get into body through open wound and can cause damage to internal organs.

7. 2. BETA PARTICLES ( β particles)
* Attracted towards positive field (negatively charged)
* Made up of electrons, therefore have a charge of -1
* Produced in the nucleus by transformation of neutron into a proton and an electron.
* Slightly more power than the alpha particles but can be stopped by heavy clothing.
* Harmful when inhaled or get into body through open wound and can cause damage to internal organs.

8. * Not affected by electrostatic field, therefore have no charge
3. GAMMA RAYS (γ rays)
* Not affected by electrostatic field, therefore have no charge
* Very penetrating, pass through body and can cause damage to internal organs and cells as they pass through the body.
* Used to treat inaccessible brain tumors.
PROTECTION
1. DISTANCE
* Increasing the distance between the source of radiation and the body reduces the effect of the radiation.

9. 3. Limiting Exposure (time)
Radiation = 1
(distance)2
2. SHIELDING
* Protective gloves, clothing and tongs must be used at all times when handling radioactive material.
3. Limiting Exposure (time)
* Limit the time that one spends next to radioactive material. The shorter the time, the lesser the dose of radiation.

10. NUCLEAR REACTIONS
* Process by which an unstable radioactive nucleus emits radiation, forming a new nucleus of different composition
* This result in change of either atomic number, mass number or both on the new nucleus.
* The following can be emitted during nuclear reactions;
Alpha particles, α, (42He)
Beta particles, β, (o-1e)
Gamma ray (γ)
Neutron (10n)
Proton (11p) or (11H)
Positron (o1e)

11. e.g. 1. A thorium atom (23490Th) decays by alpha emission.
23490Th → α + X
23490Th)→ 42He X
23490Th→ 42He Ra
2. A thorium atom (23490Th) decays by beta and gamma emission
23490Th → β + γ + X
23490Th → o-1e + γ + X
23490Th→ o-1e + γ X
23490Th → o-1e + γ Pa

12. Units Of Radiation
Radiation measured using the Geiger Counter.
Curie. This indicates the number of nuclear disintegrations occurring per second from 1g of a radioactive substance (radium)
1 curie = 3.7 x disintegrations per second
Becqurel (Bq) = 1 disintegration per second (SI unit)
Rad (radiation absorbed dose) = amount of radiation dosage absorbed by one gram of substance (human tissue)
Unit gray (Gy)
Rem (radiation equivalent in man) measures biological damage or damage to body tissues or organs.
LD50 (lethal dose that can cause death to 50 % of the population).
LD50 (dogs) = 300 rem
LD50 (humans) = 500 rem
LD50 (rats) = 800 rem

13. Remianing Mass = Mi (1/2)n
HALF-LIFE (t1/2)
The amount of time required for half the amount of a radioactive substance to decay.
Remianing Mass = Mi (1/2)n
e.g. A 400 mg sample of iodine-131 is left in a laboratory cupboard. How much of the sample will be left after 80 days if the half-life of iodine is 8 days.
NB: For medicinal purposes only radioisotopes with short half-lives are used to treat patients.
e.g. Technetium (6 hours), I-131 (8 days), Gold (2.7 days)
C-14 (5730 yrs) Used for carbon dating. o

14. NUCLEAR ENERGY
Energy generated from the nucleus of radioactive substances.
NUCLEAR FISSION
Splitting of heavy elements into smaller pieces, accompanied by large amounts of energy.
 23690U n → 9136Kr Ba n + energy (E = mc2)
Chain reaction (The three neutron produced can bombard other nuclei to produce more energy)
e.g. Atomic bomb

15. NUCLEAR FUSION
Small nuclei combine to form larger nuclei.
21H H → 42He n, + energy (E = mc2)
e.g. Sun

16. Write a balanced equation for the following nuclear reactions;
When two oxygen-16 atoms collide, one of the products is an alpha particle.
When californium-249 is bombarded by oxygen- 18, a new isotope and four neutrons are produced.
Silicon-26 decays by positron emission.
d. Rb-77 decays by beta and alpha emission.

17. Cesium-137 has a half-life of 30 years
Write a nuclear equation for beta decay of cesium-137
How many grams of a 16 g sample would remain after 90 years.
How many years would be needed for 28 g of cesium-137 to decay to 3.5g?