Topic 6

Question 1

describe an atom

Answer 1

positively charged nucleus, consisting
of protons and neutrons, surrounded by negatively charged
electrons

Question 2

Describe how and why the atomic model has changed over
time

Answer 2

plum pudding model [J.J. Thompson]

• overall charge is neutral so negative electrons cancels out with the positive pudding [protons]

Rutherford Gold foil

• most particles went straight through - so empty space
• some reflected back - nucleus is positive repelling alpha particles
• some particles deflected over 90 - nucleus contained most of the mass

Question 3

what are isotopes

Answer 3

• same proton different number of neutrons
• atoms of same element but different mass.

Question 4

Recall the relative masses and relative electric charges of
protons, neutrons, electrons and positrons

Answer 4

mass, charge
proton: 1,+1
neutron: 1, 0
electron: 0.0005, -1
positron: 0.0005, +1

Question 5

Explain that electrons change orbit when there is absorption or
emission of electromagnetic radiation

Answer 5

• when electrons more to a higher orbit (further away from nucleus) the atoms absorb EM radiation
• when electrons fall to a lower orbit (closer to nucleus ) the atoms emit EM radiation

Question 6

Explain how atoms may form positive ions by losing outer
electrons

Answer 6

when electron gain enough energy to leave the atom as an ions

Question 7

how are alpha, β– (beta minus), β+ (positron), gamma rays
and neutron radiation are emitted from

Answer 7

unstable nuclei in a random process

Question 8

Explain what is meant by background radiation

Answer 8

weak radiation detected from natural sources

Question 9

Describe the origins of background radiation from Earth and
space

Answer 9

• cosmic rays
• radiation from underground rocks

Question 10

Describe methods for measuring and detecting radioactivity
limited to photographic film

Answer 10

• film gets darker when absorbs radiation
• more darker the film for radiation

Question 11

Describe methods for measuring and detecting radioactivity
limited to a Geiger–Müller tube

Answer 11

• a tube that can detect radiation
• each time it absorbed radiation it sends and electrical pulse tot he machine produces a clicking sound
• more clicking sound more radiation

Question 12

Compare alpha, beta and gamma radiations in terms of their
abilities to penetrate and ionise

Answer 12

ALPHA
penetrating: weak
ionising: strong

BETA
penetrating: moderate
ionising: moderate

GAMMA
penetrating: strong
ionising: weak

Question 13

Describe the process of β– decay

Answer 13

a neutron becomes a proton plus an electron

Question 14

Describe the process of β+ decay

Answer 14

a proton becomes a neutron plus a positron

Question 15

Explain that the half-life of a radioactive isotope

Answer 15

is the time taken for half the undecoyed nuclei to decay or the activity of a source to decay by half

Question 16

Describe uses of radioactivity smoke alarms

Answer 16

• alpha particles ionise the air - allows current to flow across the gap and complete circuit
• when smoke gets in the way the current can not flow ions have slowed down
• alarm will sound

Question 17

Describe uses of radioactivity tracing and gauging thicknesses

Answer 17

• beta radiation
• source and receiver is placed either side of the paper
• if count rate is high/low the thickness changes

Question 17

Describe uses of radioactivity irradiating food

Answer 17

• gamma rays kill bacteria to store food for longer

Question 18

Describe uses of radioactivity sterilisation of equipment

Answer 18

• irradiate with gamma rays
• penetrate the equipment and kill bacteria

Question 19

Describe uses of radioactivity diagnosis and treatment of cancer

Answer 19

• a tracer moves around the body
• before a a radiographer positions a radioactive detector outside the body
• this produces picture showing where the tracer has accumilated

Question 20

Explain how the dangers of ionising radiation depend on half-life and relate this to the precautions needed

Answer 20

• long half life may affect cells and tissues by mutating them or damaging them

=> use a shorter half life [it can decay faster]

Question 20

Describe the dangers of ionising radiation in terms of tissue
damage and possible mutations

Answer 20

• radiation sickness
• cancer
• burns and blisters
• weak immune system
• diarrhoea
• vomiting

Question 21

describe how ionising radiation can damage cells and cause mutations

Answer 21

• removes electrons from atoms that make up cell
• break chemical bonds
• damage tissues
• change structure of DNA

Question 22

explain how people that work with radiation can ensure that they stay safe

Answer 22

=> increase distance from source
=> minimising time spent near source
=> wear a dosimeter to monitor he exposure
=> shielding

Question 23

Describe the differences between contamination and
irradiation effects and compare the hazards associated with
these two

Answer 23

• contamination lasts for a LONG period of time
  and a the source of radiation is transferred to an object
• irradiation last for a SHORT amount of time
  emits radiation tot he object

Question 24

define contaminated

Answer 24

when radioactive particle comes into contact with skin

Question 25

define irradiated

Answer 25

exposed to radiation

Question 26

Compare and contrast the treatment of tumours using
radiation applied internally or externally

Answer 26

internal - injection with radiation is injected directly at the tumour
external - a beam of gamma rays rotates around the body, mainly on tumour but momentary on the healthy cells

• external has some effect to healthy cells internal has nearly no affect to healthy cells

Question 27

Explain some of the uses of radioactive substances in
diagnosis of medical conditions, including PET scanners and
tracers

Answer 27

• radioactive tracer in the body attached to glucose
• the scanner recodes where the tracer emits radiation.
• produces image of body

Question 28

Explain why isotopes used in PET scanners have to be
produced nearby

Answer 28

• it has a short half life meaning it will decay very fast