atomic physics

Question 1

What does Rutherford’s nuclear model of an atom state

Answer 1

• an atom consists of a positively charged centrally located nucleus which makes up almost the entire mass of the atom
• it is surrounded by orbits filled with negatively charged electrons that remain in a circular path around the nucleus due to the strong electrostatic force of attraction between the positive nucleus and the negatively charged electrons

Question 2

What are the observations and conclusions of the greiger-marsden alpha-particle scattering experiment

Answer 2

(through a thin gold foil)

• the majority of particles go straight through without deflection (conclusion: this happens because majority of the space inside the atom is empty)
• some are deflected at angles less than 90deg (conclusion: this is because there is a positive charge in the atom)
• very few are deflected at angles greater than 90/backscattered
  (conclusion: the nucleus with positive charge takes up a very small space inside the atom)

Question 3

what is nuclear fission

Answer 3

when large unstable nuclei break up into smaller nuclei and the process releases energy. This occurs in power stations

Question 4

what is nuclear fusion

Answer 4

nuclear fusion takes place in stars like the sun and is the process in which smaller nuclei collide with each other at high speeds to form larger nuclei and release energy in the process.

Question 5

what is a nuclear reaction

Answer 5

the nucleus reacts and we balance mass numbers and atomic numbers

Question 6

what is background radiation

Answer 6

background radiation is always present in the environment around us

Question 7

natural sources of background radiation

Answer 7

radioactive argon gas present in the atmosphere, radioactive rocks and minerals beneath the earth’s surface and background cosmic radiation from outer space

Question 8

artificial sources of background radiation

Answer 8

uses of radioactive isotopes in medicine, radioactive waste from nuclear power stations and nuclear weapons

Question 9

ways to detect radiation

Answer 9

• photographic film
• geiger-muller tube/counter (GM tube)
• gold-lead electroscope
• scintillation counters
• spark counters

Question 10

properties of radioactive emission

Answer 10

• spontaneous: can occur without excitation or external factors
• random: we do not know which radioactive atom is going to decay at a certain point of time but we know that a fixed proportion of atoms will decay in a period of time

Question 11

what are alpha particles

Answer 11

• consists of 2 protons and 2 neutrons

- essentially a helium nucleus

Question 12

charge of alpha particles

Answer 12

2+

Question 13

range of alpha particles in air

Answer 13

2cm

Question 14

penetration of alpha particles

Answer 14

stopped by paper

Question 15

ionization of alpha particles

Answer 15

high

Question 16

what is a beta particle

Answer 16

a high speed electron

Question 17

charge of beta particles

Answer 17

-1

Question 18

range of beta particles in air

Answer 18

few 10s of cm

Question 19

penetration of beta particles

Answer 19

stopped by few mm of aluminium

Question 20

ionization of beta particles

Answer 20

medium

Question 21

what are gamma rays

Answer 21

electromagnetic waves

Question 22

charge of gamma rays

Answer 22

0

Question 23

range of gamma rays in air

Answer 23

infinite

Question 24

penetration of gamma rays

Answer 24

reduced by few mm lead

Question 25

ionization of gamma rays

Answer 25

low

Question 26

deflection of gamma rays in electrical field

Answer 26

passes straight through

Question 27

deflection of alpha radiation in electric field

Answer 27

deflected towards negatively charged plate

Question 28

deflection of beta radiation in electric field

Answer 28

deflected towards positively charged plate

Question 29

deflection of gamma radiation in magnetic fields

Answer 29

gamma radiation passes straight through without any deviation

Question 30

deflection of alpha and beta radiation in magnetic fields

Answer 30

- both deflected in opposite directions (which can be found using Flemings left hand rule) - beta particles deflect more than alpha particles as they are much lighter

Question 31

what is ionisation

Answer 31

the process by which electrons are removed or added to a substance by applying energy

Question 32

why does alpha ionise the most

Answer 32

-greater mass and charge

Question 33

why do alpha particles have the shortest range

Answer 33

- they ionise virtually every atom they pass | - so they lose energy quickly and have a short range

Question 34

why do beta particles have a moderate range

Answer 34

- the particles create a less dense trail of ions than alpha, and consequently have a longer range - they tend to be more dangerous than alpha because they are able to travel further and penetrate skin yet are still ionizing enough to cause damage

Question 35

why do gamma rays have unlimited range

Answer 35

they are the least ionizing form of radiation

Question 36

common uses of radiation

Answer 36

- controlling thickness of material - medical tracers to detect blood clots - industrial tracers to detect leaks in pipes - cancer treatment - sterilization - smoke detectors

Question 37

what is radioactive decay

Answer 37

-occurs due to the presence of unstable nuclei in some isotopes, as a result they emit radiation to become stable

Question 38

alpha/beta radiation in radioactive decay

Answer 38

affects the composition of the nucleus and changes to that of a different element

Question 39

gamma radiation in radioactive decay

Answer 39

does not affect the composition of the nucleus and is released only after alpha or beta emission to get rid of excess energy in the nucleus

Question 40

what is the half life of an isotope

Answer 40

the time taken for the number of original nuclei to drop to half of its initial value/the time taken for half a radioactive substance to decay (can be found from a nuclide graph)

Question 41

what can radioactive radiation cause to living cells

Answer 41

- mutations - breed cancerous cells - may kill living cells

Question 42

safety precautions for radioactive radiation

Answer 42

- store the sources in lead-lined boxes - minimise the amount of time you handle sources for and return them to their boxes as soon as you have finished using them - stay at a safe distance from the radioactive source - when handling sources do so at an arm's length, using a pair of tongs or forceps and other source-handing tools - wear protective clothing