P7 Radioactivity

Question 1

Describe the basic structure of an atom.

Answer 1

nucleus containing protons and neutrons, around which electrons orbit in fixed energy levels/shells

Question 2

Describe the plum pudding model of the atom.

Answer 2

sphere of positive charge with negative electrons embedded in it

Question 3

What charges do protons, neutrons, and electrons carry?

Answer 3

protons = positive, neutrons = no charge, electrons = negative

Question 4

Why do atoms have no overall charge?

Answer 4

equal numbers of positive protons and negative electrons

Question 5

What is the radius of an atom?

Answer 5

around 1x10 to the power of -10 m

Question 6

What is ionisation?

Answer 6

process which adds or removes electrons from an atom

Question 7

What is the mass number of an element?

Answer 7

number of protons + number of neutrons

Question 8

Which particle do atoms of the same element always have the same number of?

Answer 8

protons

Question 9

What are isotopes?

Answer 9

atoms of the same element (same number of protons) with different numbers of neutrons

Question 10

What were the two main conclusions from the alpha particle scattering experiment?

Answer 10

• most of the mass of an atom is concentrated in the nucleus
• nucleus is positively charged

Question 11

What are the three types of nuclear radiation?

Answer 11

alpha, beta, and gamma

Question 12

Which type of nuclear radiation is the most ionising?

Answer 12

alpha

Question 13

What is the range in air of alpha, beta, and gamma radiation?

Answer 13

a few cm, 1 m, and unlimited, respectively

Question 14

What are the equation symbols for alpha and beta particles?

Answer 14

alpha particles (α) beta particles (β) gamma rays (γ)

Question 15

What is meant by the half-life of a radioactive source?

Answer 15

time taken for half the unstable nuclei to decay or the time taken for the count rate to halve

Question 16

What is radioactive contamination?

Answer 16

unwanted presence of substances containing radioactive atoms on or in other materials

Question 17

Where does background radiation come from?

Answer 17

rocks, cosmic rays, fallout from nuclear weapons testing, nuclear accidents

Question 18

Why are gamma-emitting sources used for medical tracers and imaging?

Answer 18

gamma rays pass through the body without causing much damage to cells

Question 19

What is nuclear fusion?

Answer 19

when two light nuclei join to make a heavier one

Question 20

How does nuclear fussion occur?

Answer 20

an unstable nucleus absorbs a neutron, it splits into two smaller nuclei, and emits two or three neutrons plus gamma rays