Unit 3 - Topic 5 - Nuclear Chemistry

Question 1

What is nuclear chemistry?

Answer 1

• Nuclear chemistry is the study of the break up of unstable nuclei, which results in the emission of radiation and the release of energy. This changes the unstable nuclei into more
stable nuclei.

• The stability of a nucleus depends on the proton to neutron ratio or balance. Radioactive emissions change the neutron to proton ratio and at the same time releases energy.

Question 2

Describe unstable nuclei

Answer 2

Unstable nuclei emit radiation to become stable.

There are three types of radiation an unstable nucleus can emit:

1. Alpha (α)
2. Beta (β)
3. Gamma (γ)

Question 3

Describe the properties of radiation

Answer 3

The properties of radiation can be studied using an electric field.

Question 4

Describe Alpha (α)

Answer 4

Slow moving positively charged particle, attracted to the negative plate

Question 5

Describe Beta (β)

Answer 5

Fast moving negatively charged particle, attracted to the positive plate.

Question 6

Describe Gamma (γ)

Answer 6

Electromagnetic radiation (travels at the speed of light). No deflection. Neutrally charged.

Question 7

Describe the radioactive penetration of each type of radiation

Answer 7

Alpha particles are absorbed by something as thin as paper.

Beta particles are absorbed by thin aluminium sheets.

Gamma rays are absorbed by thick lead.

Question 8

Which radiation is most dangerous?

Answer 8

Gamma, because it takes a thick layer of something quite robust in order to be absorbed.

Question 9

Describe Alpha (α) radiation

Answer 9

Alpha particles come from the nucleus of a radioactive atom. They consist of 2 protons and 2 neutrons; hence have a 2+ charge. A few centimetres of air will stop them.

• Alpha radiation consists of helium nuclei ^4_2He^2+
• When a nucleus emits alpha radiation is emits a positively charged helium particle.

Question 10

Describe Beta (β) radiation

Answer 10

A beta particle is an electron, _−1^0e^−

Since the nucleus does not contain electrons, it is thought that a beta particle is formed when a neutron splits up into a proton and an electron.

While it will pass through air, it cannot penetrate thin metal foil.

Question 11

Describe Gamma (γ) radiation

Answer 11

Gamma waves come from the nucleus of a radioactive atom. They are electronegative waves.

They do not change the nature of an atom.

Thick lead or concrete will absorb gamma rays.

Question 12

Describe alpha decay

Answer 12

When a nucleus emits alpha radiation, the mass number decreases by 4 and the atomic number decreases by 2.

Question 13

Describe beta decay

Answer 13

When a nucleus emits beta radiation, the mass number stays the same and the atomic number increases by 1.

Question 14

Describe gamma decay

Answer 14

When a nucleus emits gamma radiation, the mass number and atomic number stay the same.

Question 15

Describe half-life

Answer 15

The time taken for the activity of a radioactive source to decrease by half is always the same. This length of time is called the HALF-LIFE.

Question 16

Describe radioactive decay

Answer 16

Radioactive decay is a nuclear change, the rate of decay is unaffected by anything outside the nucleus. It is not affected by factors, which affect the rate of a chemical change, such as temperature, pressure, concentration, or a catalyst.

Half-life is not affected if the radioisotope is present as a solid, liquid or gas, or whether it is present as atoms or ions, in an element or compound.

Question 17

Describe the uses of radioisotopes

Answer 17

Radioisotopes have a range of uses in medicine and industry.

Question 18

Describe carbon dating

Answer 18

Radioisotopes can be used to determine the age of materials.

Question 19

Describe smoke detectors

Answer 19

Alpha particles are easily absorbed. A household smoke alarm measures the movement of alpha particles across a small gap. If smoke enters the detector, it will absorb the alphas and the detector
will measure a drop in the number getting across the gap. This drop in measurement will trigger the alarm to sound.

Americium-241 is the most common material used as the alpha emitter in a domestic smoke alarm.