7.2 Nuclear Stability And Radioactivity Flashcards Preview

Physics Chapter 7 - Atomic, Nuclear And Particle Physics > 7.2 Nuclear Stability And Radioactivity > Flashcards

Flashcards in 7.2 Nuclear Stability And Radioactivity Deck (20):
1

What is the nucleon number?

Number of protons and neutrons in nucleus.

2

What is the atomic number?

Number of protons in nucleus.

3

What is a nuclide?

Nucleus with specific number of protons and neutrons.

4

What is an isotope?

Nuclei with same proton number but different nucleon number.
Have same chemical properties - same number of electrons - different physical properties.

5

What is the atomic mass unit?

1/12 of the mass of carbon 12.

6

What is the nuclear notation?

A
X
Z
A is nucleon number
Z is proton number
X is chemical symbol of element.
Approximate mass of nucleus is A x atomic mass units.

7

What is activity?

Rate of radioactive decay in Bq.

8

Why may a nucleus be unstable?

If nucleus contains too many protons it is unstable because electrical repulsion force overwhelms strong nuclear force. Also unstable if contains too many neutrons compared to protons.

9

How can a nucleus reduce its energy and become more stable?

Emission of particles and energy - radioactive decay.

10

What is important about radioactive decay?

Random process - cannot be predicted which nucleus will decay and when it will happen.
Spontaneous process - cannot be induced to happen or prevented from happening.

11

What are the three types of decay?

Alpha - emission of helium nucleus
Beta - emission of fast electrons
Gamma - emission of energetic photons

12

What is important about the energies of alpha, beta and gamma particles?

Energies of alpha and gamma decay are discrete.
Energies in beta decay are continuous.

13

What are the emissions ionising?

Knock electrons off atoms they collide with creating ions and radicals.

14

How ionising are alpha, beta and gamma?

Alpha is most ionising and least penetrating.
Gamma is most penetrating least ionising.
Beta in the middle.

15

What is the radioactive law decay?

Rate of decay is proportional to number of nuclei present: dN/dt is proportional to N. Implies exponential decrease in activity over time.

16

What is half life T1/2?

Time interval which activity of sample is reduced by half.

17

What is the mass defect?

Difference between mass of nucleus and sum of masses of its individual nucleons. Mass of nucleus will be smaller than the sum of masses of nucleons.

18

What is the energy corresponding to the mass defect?

Binding energy of nucleus - minimum energy needed to completely separate its nucleons.

19

What is important about binding energy?

Larger the binding energy of nucleus, more stable it is.

20

Why do most nucleus have the same binding energy per nucleon of 8.5MeV?

Consequence of short range of strong nuclear force - in larger nucleus any nucleon is surrounded by same number of nucleons as any other so requires the same amount of energy to remove it.