P7.1/P7.2/P7.3/P7.4/P7.5 - Radioactivity.

Question 1

A key discovery

Answer 1

-Becquerel discovered image of key under pack of uranium
-uranium slats emitted radiation that passed through film but not key

Question 2

radioactivity

Answer 2

-random process of radiation emission

Question 3

Alpha particle

Answer 3

• aka helium nucleus
  -2 protons and 2 neutrons
  -more mass = heavier = slower

Question 4

Beta particle

Answer 4

-negative charge
-electron emitted from nucleus

Question 5

Beta particle formation

Answer 5

neutron in an unstable nucleus splits
-forms 1 proton and 1 electron (beta)

Question 6

Gamma rays

Answer 6

-electromagnetic radiation
-emitted from nucleus
-no mass or charge
-cannot interfere with other atoms

Question 7

Properties of alpha

Answer 7

-slowest
-6-8cm distance movement
-High ionisation
-stopped by paper

Question 8

Properties of beta

Answer 8

-medium ionisation
-moves 1-2m
-penetrates paper
-stopped by aluminum

Question 9

Properties of gamma

Answer 9

-fastest
-moves 300-500m
-low ionisation
-stopped by lead/concrete

Question 10

Nuclear Equations: alpha

Answer 10

-nucleus loses 2 neutrons + 2 protons
-atomic mass decreases by 4
-atomic number decreases by 2

Question 11

Nuclear Equations: Beta

Answer 11

-nucleus loses 1 electron
-atomic mass = no change
-atomic number = increases by 1

Question 12

Neutron emission

Answer 12

-alpha particles collide with unstable nucleus
= emits neutrons
-neutron is uncharged so passes through matter easier

Question 13

radioactive substance

Answer 13

-unstable nucleus
-becomes stale by emitting radiation
-

Question 14

decaying nucleus

Answer 14

unstable nucleus emitting radiation
-random process = no cause
-cannot be predicted

Question 15

Calculate penetrating power

Answer 15

-measure count rate per sec without isotope = background count rate
-measure count rate with source
-subtract values = count rate of isotope without background radiation

Question 16

Ionisation

Answer 16

-radiation knocks out electrons from atoms
-becomes charged ions or kills living cell
-may cause cancer = change in DNA

Question 17

irradiated

Answer 17

object is exposed to radiation
-isn’t radioactive

Question 18

Radioactive contamination

Answer 18

–unwanted presence of materials containing radioactive atoms
-direct contact with radioactive source
-ingested or inhaled

Question 19

Safety precautions

Answer 19

-minimise time with source
-shield self with concrete or lead aprons
-long handle equipment
-distance from source

Question 20

Radiation - smoke alarms

Answer 20

-contains isotope that emits alpha particles into gap in circuit
-alpha ionises air = current flows
-smoke absorbs alpha particles so current is stopped
-alarm sounds

Question 21

Why would beta or gamma radiation not be used in smoke alarms

Answer 21

-lower ionisation so current will not flow to begin with

Question 22

activity

Answer 22

number of unstable atoms that decay per second in a radioactive isotope

Question 23

Becquerel

Answer 23

1 decay per second

Question 24

As each parent atom decays…

Answer 24

the number decreases so activity decreases

Question 25

Geiger counter

Answer 25

-measures count rate per sec
-proportional to activity of source as distance is constant

Question 26

half-life

Answer 26

-time taken for count rate to halve
-number of parent atoms (nuclei) to halve

Question 27

Every half-life

Answer 27

-count rate halves
-number of atoms in substance halves

Question 28

count rate after n half-lives

Answer 28

initial count rate /2n