RADIOACTIVITY AND PARTICLES

Question 1

what is the nucleus?

Answer 1

• an atom made up of protons and neutrons
• the number of protons determines what element the nucleus is

Question 2

what are isotopes?

Answer 2

• contain the same number of protons, but a different number of neutrons
• same atomic number, different mass number

Question 3

what is the number of protons in the nucleus known as?

Answer 3

• atomic number or proton number

Question 4

what is the number of protons plus neutrons known as?

Answer 4

• mass or nucleon number

Question 5

what is the mass of the nucleus?

Answer 5

relative atomic mass

Question 6

what are unstable nuclei?

Answer 6

• emit particles, or energy, in order to become stable again
• these unstable nuclei are called radioactive nuclei

Question 7

what is the unit for radioactive activity?

Answer 7

becquerel (Bq)
one becquerel is one decay per second

Question 8

three types of radioactive decay:

Answer 8

• alpha
• beta
• gamma

Question 9

what are alpha particles?

Answer 9

made of two protons and two neutrons bound together

Question 10

what speed are alpha particles emitted at?

Answer 10

10% the speed of light

Question 11

what charge do alpha particles have?

Answer 11

+2

Question 12

are alpha particles highly or lowly ionising?

Answer 12

highly ionising

Question 13

what are alpha particles stopped by?

Answer 13

a few centimetres of air or a sheet of paper

Question 14

what are beta particles?

Answer 14

an electron emitted when a neutron in the nucleus is turned into a proton

Question 15

what speed are beta particles emitted at?

Answer 15

50% the speed of light

Question 16

what charge do beta particles have?

Answer 16

-1

Question 17

are beta particles weakly or highly ionising?

Answer 17

weakly ionising

Question 18

what are beta particles stopped by?

Answer 18

a few millimetres of aluminium

Question 19

what is a gamma ray?

Answer 19

high energy electromagnetic wave

Question 20

what speed to gamma rays travel at?

Answer 20

the speed of light

Question 21

are gamma rays highly or weakly ionising?

Answer 21

weakly ionising

Question 22

what are gamma rays stopped by?

Answer 22

a few centimetres of lead

Question 23

background sources of radioactivity:

Answer 23

• radon gas
• medical exposure
• rock
• cosmic rays

Question 24

what happens to the atomic and mass number when you emit an Alpha particle?

Answer 24

atomic number lowers by two
mass number lowers by four

Question 25

what happens in beta decay?

Answer 25

a neutron turns into a proton and emits an electron

Question 26

what happens to the atomic and mass number when beta decay occurs?

Answer 26

atomic number increases by one
mass number does not change

Question 27

what happens to the atomic and mass number when you emit a gamma ray?

Answer 27

has no mass
no effect

Question 28

what is radioactive decay?

Answer 28

a random process

Question 29

what is the half-life?

Answer 29

the time taken for one half of the nuclei to decay

Question 30

what is ionisation?

Answer 30

the formation of an ion

Question 31

how to find half-life:

Answer 31

• measure at least three half from your graph and calculate the average

Question 32

dangers of alpha, beta and gamma:

Answer 32

• alpha sources are only dangerous if they get into the body
• gamma and beta sources can cause harm from outside the body

Question 33

what happens when ionisation occurs in the DNA?

Answer 33

• strand can become damaged
• damage to DNA causes mutations when cells divide and reproduce
• mutations in DNA can lead to cancer

Question 34

how to store nuclear waste:

Answer 34

burying it

Question 35

what is nuclear fission?

Answer 35

• released fission neutrons trigger further fissions
• energy from fission-energy is released primarily as the kinetic energy of fission fragments

Question 36

what are control rods?

Answer 36

in order to maintain a constant rate of reaction, control rods are used to absorb excess neutrons

Question 37

control rod material?

Answer 37

boron and cobalt

Question 38

what are moderators?

Answer 38

when the fast neutrons emitted by the neutron process are travelling too fast to cause further fissions, they must be slowed to ‘thermal’ speeds by a moderator

Question 39

moderator materials:

Answer 39

graphite
light water
heavy water

Question 40

what is shielding?

Answer 40

reactors are surrounded by thick sheilding (usually concrete or steel) which prevents workers from being exposed to radiation

Question 41

what can be detectors of ionising radiation?

Answer 41

photographic film or a Geiger-Muller detector

Question 42

what does the fission of U-235 produce?

Answer 42

• two radioactive daughter nuclei and a small number of neutrons

Question 43

similarities between fission and fusion?

Answer 43

mass of the products is less than the mass of the reactants
this missing mass is converted into energy- E= mc^2

Question 44

differences between fission and fusion:

Answer 44

• in fission, a heavier nucleus is split into two lighter, radioactive parts called fission fragments
• in fusion, two lighter nuclei are joined together to create a heavier nucleus

Question 45

what is nuclear fusion?

Answer 45

when two lighter nuclei are fused together, the heavier nucleus that us created has lower mass than the two initial nuclei combined

Question 46

what does fusion require?

Answer 46

very high temperatures and pressures, because the positively charged nuclei repel each other

Question 47

what is the energy source for stars?

Answer 47

fusion

Question 48

uses of radioactivity in medical contexts:

Answer 48

• lead lined syringes
• finding tumours
• gamma knife