The nucleus and nuclear reactions

Question 1

The nucleus

Answer 1

1. The nucleus is a very dense particle at the center of each atom that is made up of all the protons and neutrons in that atom.
2. The nucleus makes up most of the atoms mass
3. The nucleus is very small compared with the diameter of the atom.

Question 2

Atomic number

Answer 2

The atomic number is equal to the number of protons in the nucleus.

Question 3

Atomic mass

Answer 3

The atomic mass is the total number of protons and neutrons in the nucleus.

Question 4

How to find the number of neutrons

Answer 4

Subtract the number of protons from the atomic mass.

Question 5

Isotopes and elements

Answer 5

1. Two atoms with the same number of protons are the same element.
2. Two atoms with the same number of protons and neutrons are the same isotope.

Question 6

Nuclear reactions

Answer 6

1. Nuclear reactions involve changes to the composition of the nucleus.
2. When a nuclear reaction occurs the number of protons or neutrons changes and/or the arrangement of the protons and neutrons change

Question 7

Types of nuclear reactions

Answer 7

The two major types of nuclear reaction are fission and fusion.

Question 8

Nuclear fission

Answer 8

In nuclear fission, the nucleus splits apart.

Question 9

Nuclear fusion

Answer 9

In nuclear fusion, two nuclei join together.

Question 10

Steps in nuclear fission

Answer 10

1. A fast neutron is shot into a large nucleus
2. The neutron joins with the nucleus, creating a new isotope.
3. To reach a more stable state, the unstable nucleus splits apart into two nuclei and some extra neutrons.
4. The extra neutrons that are given off fly off with great speed and hit other nuclei, starting nuclear chain reactions.

Question 11

Energy released by nuclear fission

Answer 11

When fission occurs, the nuclear potential energy drops, so kinetic energy is released.

Question 12

Composition changes in nuclear fission

Answer 12

In fission, the protons and neutrons rearrange from one nucleus to two nuclei, but the total number of each doesn’t change.

Question 13

Steps in nuclear fusion

Answer 13

1. Two nuclei hit each other at a high speed (original substances must have a very high temperature)
2. The two nuclei join together, forming a larger nucleus.
3. The energy released adds heat, speeding up other nuclei and continuing the reaction in a nuclear chain reaction.

Question 14

Energy released by nuclear fusion

Answer 14

If two nuclei have low atomic numbers, the new nucleus has lower nuclear energy than the original, and energy is released.

Question 15

Composition changes in nuclear fusion

Answer 15

In fusion, the protons and neutrons rearrange from two nuclei to one nucleus, but the total number of each does not change.

Question 16

Nuclear radiation

Answer 16

1. some isotopes have unstable nuclei
2. Unstable nuclei can reach a more stable state by emitting particles, called nuclear radiation
3. The particles have a lot of kinetic energy, so they are ionizing radiation.

Question 17

Radioactivity

Answer 17

1. A substance is considered radioactive if it emits nuclear radiation.
2. A radioactive decay occurs each time unstable nuclei become more stable by emitting a particle
3. In each radioactive decay, changes occur to the nucleus’ composition and energy.

Question 18

Types of nuclear radiation

Answer 18

1. Alpha
2. Beta
3. Gamma

Question 19

Alpha radiation

Answer 19

A nucleus emits an alpha particle with two protons and two neutrons.

• most energy
• most deadly
• easiest to stop (piece of paper)

Question 20

Beta radiation

Answer 20

One of the neutrons turns into a proton, and the nucleus emits an electron.

• less energy
• less deadly
• harder to stop (metal sheet)

Question 21

Gamma Radiation

Answer 21

The protons and neutrons rearrange in the nucleus to reach a more stable state and the nucleus emits a photon.

• least amount of energy
• least deadly
• hardest to stop (thick walls of concrete)