Nuclear Physics

Question 1

Nuclide

Answer 1

A particular species of nucleus that is specified by its proton and neutron number

Question 2

Isotopes

Answer 2

Isotopes are VARIANTS of the same element with the same number of protons but a different number of neutrons in the nucleus.

Question 3

Mass defect

Answer 3

The DIFFERENCE in mass between the MASS OF A NUCLEUS and the total mass of its CONSTITUENT NUCLEONS.

Question 4

Nuclear binding energy

Answer 4

The energy required to completely SEPARATE the nucleons in a nucleus to infinity.

Question 5

Binding energy per nucleon (BE CLEAR if it is per nucleon or not)

Answer 5

The energy per nucleon required to completely separate the nucleons to infinity

Question 6

Conservation of mass-energy

Answer 6

For an isolated system, the total mass-energy of the system remains constant.

Question 7

Nuclear fission

Answer 7

Nuclear fission is the splitting of a nucleus of high nucleon number and low binding energy per nucleon into 2 smaller nuclei of approximately the same mass with higher binding energy per nucleon with the release of energy and neutrons.

Question 8

Nuclear fusion

Answer 8

Nuclear fusion is the combining of two nuclei of low nucleon number to produce a larger nucleus with a greater binding energy per nucleon with the release of energy.

Question 9

Radioactivity

Answer 9

Radioactivity is the spontaneous and random disintegration of the unstable nucleus, emitting some or all of the following nuclear radiations: alpha particles, beta particles and gamma radiations.

Question 10

Spontaneous decay

Answer 10

Decay that is not affected by external or environmental factors.

Question 11

Random decay

Answer 11

The nucleus has a constant probability for decay per unit time, where the time of decay of a nucleus cannot be predicted.

Question 12

Activity of the radioactive nuclide

Answer 12

Activity of the radioactive nuclide is the number of nuclear disintegrations per unit time of the nuclei.

Question 13

Decay constant

Answer 13

The constant probability of decay per unit time of a nucleus.

Question 14

Half-life*

Answer 14

The average time taken from the initial number of that particular radioactive nuclide to reduce to half of its initial value.

Question 15

Background radiation

Answer 15

The radiation detected by a radiation counter when there is no radioactive source nearby.

It is an unavoidable radiation arising from natural resources.

Question 16

Count rate

Answer 16

Rate at which emissions from a radioactive source are detected.

Question 17

Observations of Rutherford’s experiment

Answer 17

1) Most of the alpha particles were deviated through small angles or undeflected
2) A small but significant percentage of the alpha particles deviated through large angles greater than 90 and up to 180

Question 18

Inference of most of the alpha particles were deviated through small angles or undeflected

Answer 18

For the structure of the atom, the nucleus exists and the size of the nucleus is small compared to the atom

Question 19

Inference of a small but significant percentage of the alpha particles deviated through large angles greater than 90 up to 180

Answer 19

For the structure of the atom, the nucleus is charged and the mass is concentrated in the nucleus.

Question 20

What is the maximum binding energy per nucleon for all nuclei?

Answer 20

8.8MeV (Fe-56)

Question 21

Radioactive decay of an unstable nucleus

Answer 21

The emission of alpha, beta, and/or gamma ray photons with the release of energy and the formation of a more stable nucleus.

Question 22

Penetrating ability of alpha particles + Range in air + Ionising strength + Typical energy

Answer 22

Stopped by a piece of paper
~1 to 3cm
Strong
Characteristic emissions

Question 23

Penetrating ability of beta particles + Range in air + Ionising strength + Typical energy

Answer 23

Stopped by a few mm of aluminium
~1m
Weak
Continuous spectrum

Question 24

Penetrating ability of gamma particles + Range in air + Ionising strength + Typical energy

Answer 24

Stopped by about 10cm of lead
~1km
Very weak
Characteristic emissions

Question 25

The general equation for radioactive decay

Answer 25

x = x0e^(-lambda)(t)

Remember to minus background radiation!

Question 26

What are the direct and indirect effects of ionising radiation on living tissues and cells?

Answer 26

1. Direct damage to DNA through breaks and mutations
2. Indirect generation of free radicals which initiate harmful chemical reactions within cells and cause similar effects as direct action.

At low levels of exposure, cells have mechanisms that can repair the damage, but with prolonged exposure, severe damage can lead to creation of tumour cells or cell death.