Physics - Radioactivity

Question 1

radius of a nucleus compared to radius of atom

Answer 1

nucleus radius = 100,000 times smaller than atom radius

Question 2

reasons for unstable nuclei

Answer 2

• nucleus is too large
• number of protons is very different to number of neutrons
• nucleus has a lot of energy

Question 3

what happens when nuclei is stabilised

Answer 3

radiation emitted

Question 4

types of ionising radiation

Answer 4

• alpha decay
• beta decay
• gamma decay

Question 5

what is alpha decay

Answer 5

• when alpha particle emitted from nucleus
• alpha particle is made up of 2 protons and 2 neutrons (helium nucleus)
• highly ionising, slow moving and low penetrance due to large size
• stopped by a few cm of air
• due to the loss of 2 protons and 2 neutrons, element emitting alpha particle is a new particle

Question 6

what is beta decay

Answer 6

• when beta particle is emitted from nucleus
• when neutron is converted to a proton and an electron
• element gains a proton in beta emission, hence a new element
• beta negative decay - electron emitted
• possible for positron to be emitted instead of an electron
• beta particles are smaller than alpha and are moderately ionising, fast moving, moderate penetrance (stopped by foil)

Question 7

what is a positron

Answer 7

• positively charged antiparticle of electron
• when positron is emitted, proton changes into a neutron thereby creating a new element

Question 8

what is gamma decay

Answer 8

• occurs when a gamma ray is emitted
• gamma ray is a high energy photon
• mass and atomic number of element remain unchanged
• weakly ionising, highly penetrating (stopped by thick lead)

Question 9

uses of alpha particles

Answer 9

smoke alarms
- alpha emitter in smoke alarms produces alpha particles which ionise air molecules.
- ionised molecules carry current and complete a circuit in the smoke alarm
- smoke particles prevent ionisation of air molecules, hence breaking the circuit

Question 10

dangers of
alpha particles

Answer 10

due to them being highly ionising - can damage dna of cells and tissues
low penetrance so have to be inhaled or digested

Question 11

uses of beta particles

Answer 11

tracers/material quality control
used to measure thickness of paper/aluminium - if material is too thick, fewer beta particles will penetrate

medial uses - imaged certain body parts - POSITRON EMISSION TOMOGRAPHY

Question 12

danger of beta particles

Answer 12

moderately penetrating so present a hazard if inhaled, ingested or direct exposure without barrier

Question 13

uses of gamma particles

Answer 13

sterilising medical equipment/food/radiotherapy

radiotherapy - multiple angles are used to maximise tumour exposure to gamma rays whilst simultaneously minimising damage to non-cancerous tissue

Question 14

dangers of gamma particles

Answer 14

weakly ionising so gamma rays aren’t particularly dangerous provided the dose is low enough
highly penetrating so only thick lead/concrete will prevent exposure

Question 15

half life

Answer 15

time taken for 50% of sample to decay

Question 16

what does half life depend on

Answer 16

decay constant

Question 17

what is half life measured in

Answer 17

becquerels using a geiger counter

Question 18

one becquerel =

Answer 18

one decay per second

Question 19

nuclear fission

Answer 19

nuclear reaction which heavy nucleus splits spontaneously into smaller nuclei with the release of energy

Question 20

how do power plants use nuclear fission

Answer 20

• uranium-235
• in a fission reactor
• uranium-235 absorbs a neutron producing the unstable isotope uranium-236
• uranium-236 splits into two random smaller nuclei releasing neutrons and energy in the process
• three neutrons can then be absorbed by other uranium-235 atoms in chain reaction that needs to be controlled in a nuclear reactor through the use of neutron absorbing control rods to prevent nuclear explosion

Question 21

nuclear fusion

Answer 21

• nuclear reaction which atomic nuclei of low atomic number fuse to form a heavier nuclei with release of energy
• fusion requires an incredible amount of energy to occur as mutual repulsion of nuclei needs to be overcome

Question 22

nuclear fusion in the sun

Answer 22

fusion mainly occurs between hydrogen and deuterium to produce helium