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nuclear decay Flashcards

1
Q

what was the big bang theory

A

all matter in the universe was contained in a single point. all this matter underwent an explosion expansion

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2
Q

what happened 3 minutes after the big bang

A

nuclei of hydrogen and helium formed from hot collections of tiny particles such as protons and neutrons

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3
Q

what happened 10,000 years after the big bang

A

the universe cooled sufficiently so electrons moved slowly enough to be captured by oppositely charged protons in nuclei to form atoms.

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4
Q

what was the universe mainly made up of

A

hydrogen and helium

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5
Q

what happened as the universe cooled

A

dust and gas was pulled together by gravity forming gas clouds

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6
Q

how were particles held together

A

they had low kinetic energy and moved around relatively slowly so gravitational forces were able to keep them together

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7
Q

what happened to the gas clouds

A

parts of the cloud contracted in on themselves compressing the gases and forming clumps of denser gas.

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8
Q

where was the densest part of the clumps of gas

A

at the centre, where temperatures were hot enough so atoms could not retain their electrons

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9
Q

what happens to atoms at high temperatures

A

they lose electrons to become a plasma of ionised atoms and unbound electrons

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10
Q

more gravity = …

A

… = more matter

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11
Q

how does the dense gas cloud become a star

A

nuclear reactions such as nuclear fusion occur releasing vast amounts of energy and causing the cloud to grow and become a star

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12
Q

what do nuclear reactions generate

A

a hot wind that drives away some of the dust and gas leaving the stars behind. planets condense out of the remaining dust clouds around these stars

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13
Q

what do nuclear reactions involve

A

the change in the nucleus of an atom. one element can change into another

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14
Q

what are the two types of nuclear reaction

A

fission and fusion

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15
Q

where is nuclear fusion common

A

at the centre of stars

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16
Q

what happens in nuclear fusion

A

lighter nuclei are fused together to form heavier nuclei such as hydrogen atoms joining together to form helium

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17
Q

what is also produced by fusion

A

other heavier elements produced in stars

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18
Q

how does nuclear fusion occur

A

nuclei approach each other at high speed with a large amount of kinetic energy to overcome repulsion by positive charges on the two nuclei

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19
Q

what does nuclear fusion require

A

high temperature and pressure

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20
Q

what is the most common element in the universe

A

hydrogen

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21
Q

what do all stars turn hydrogen into

A

helium

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22
Q

how are heavyweight stars formed

A

temperatures and pressures at the centre of heavyweight stars mean that along with hydrogen fusion, other fusion reactions can take place producing heavier elements than helium. layers of elements form within the stars with heaviest elements near the centre

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23
Q

what will be the element in the centre of heavyweight stars

A

iron

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24
Q

what will the core contain after millions of years

A

helium, carbon, neon, silicon and iron

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25
what happens when iron nuclei fuse together
they do not release energy they absorb it.
26
what happens when the core of a heavy star mostly contains iron
it becomes unstable and explodes to form a supernova
27
what does a supernova do
causes elements in the star to be dispersed into the universe as clouds of dust and gas
28
what is different about lightweight stars
they arent as hot as most other stars and will last longer than heavyweight stars. they will keep shining until all hydrogen has been used up and the core stops producing energy. there is no supernova
29
how are lightweight stars formed
once hydrogen is used up, the sun will expand into a red giant swallowing up Mercury and Venus. oceans in Earth will start to boil and will eventually be engulfed by the sun
30
what happens as red giants get bigger
they become unstable and outer gases drift off into space leaving behind a white dwarf 1/100th the size of original star
31
what happens to unstable isotopes
their nuclei spontaneously break down and they become radioactive
32
what is the name given to radioactive isotopes
radioisotopes
33
what happens as nuclei break down
they emit rays and particles called emissions. this break down occurs of its own accord
34
what is the breaking down to form new elements called
radioactive decay
35
what are the three ionising radiations/emissions called
alpha, beta, gamma
36
what are all three emissions capable of doing
knocking of electrons out of the atoms they collide with - ionise the atoms
37
what is the relative charge, mass, nature, range in air, deflection by electric field of alpha and what can it be stopped by
+2 4 helium nucleus few cm stopped by paper low deflection
38
what is the relative charge, mass, nature, range in air, deflection by electric field of beta and what can it be stopped by
-1 0.00055 electron few m stopped by aluminium foil high deflection
39
what is the relative charge, mass, nature, range in air, deflection by electric field of gamma and what can it be stopped by
0 0 very high frequency EM radiation very long range in air stopped by lead sheet nil deflection
40
what do nuclear equations do
summarise processes which produce alpha and beta emissions
41
what do nuclear equations include
the mass number, nuclear charge/atomic number and chemical symbol of each particle involved
42
what is important about nuclear equations
both mass and charge should balance
43
what does alpha decay involve
emission of alpha particles (helium nuclei)
44
where is alpha decay common
among heavier elements with atomic numbers greater than 83. alpha decay reduced the mass of these heavier nuclei
45
what happens to the mass number and atomic number in alpha decay
mass number decreases by 4 atomic number decreases by 2
46
what does beta decay involve
emission of electrons
47
where is beta decay common
among lighter elements in which isotopes contain a relatively large number of neutrons
48
what happens to the mass number and atomic number in beta decay
mass number stays the same atomic number increases by 1
49
what happens in beta decay
a neutron is converted into a proton and an electron. the electron is ejected from the nucleus
50
what happens in both alpha and beta decay
new elements are formed
51
what happens in gamma decay
emission of energy from a nucleus which is changing from a high energy level to a lower one. accompanies emission of alpha and beta decay
52
do new elements form in gamma decay
no
53
what does nuclear fusion release
high quantities of energy
54
why can't nuclear fusion occur at normal temperatures
the positive nuclei repel each other. for two nuclei to fuse they must come together which can only happen once the repulsion between them is overcome.
55
why is a higher temperature required for nuclear fusion
nuclei move much more quickly and collide with so much more energy that they can overcome the repulsion
56
what happens once nuclei are close to one another
the strong nuclear forces holding protons and neutrons together in the nucleus take over and the nuclei fuse
57
where does nuclear fusion take place
in gas clouds of stars and reuslts in the formation of new elements
58
give examples of nuclear reactions that take place in the sun
1 2 3 H + H ------> He 1 1 2 2 3 4 1 H + H ------> He + n 1 1 2 0
59
what can happen in the high temperatures of gas clouds of stars
the electrons have enough energy to escape from the nuclei.
60
how do gases exist in gas clouds
the gases exist in an ionised form in which positive atomic nuclei exist in a sea of delocalised electrons
61
what is the future for nuclear reactions
to be able to harness them under controlled conditions to produce electricity
62
what is needed to be able to produce electricity using nuclear energy
- needs to safely generate plasma at high temperature - needs to be sustainable and economic
63
as more of the nuclei in the sample decay....
.... the sample becomes less radioactive
64
what is half life
the time taken for half the nuclei to decay. this is fixed for a given isotope
65
what happens in the course of one half life
half of the radioactivity of the sample always disappears but the sample never completely disappears
66
suppose a sample of a radioisotope has a count rate of 52 counts min-1 and 4 hours later the count rate is 13 mins-1 what is the half life of the radioisotope
start count rate = 52 after 1 half life = 26, 2 half lives = 13 count rate = 13 counts min-1 after 2 half lives 2 half lives = 4 hours 1 half life = 2 hours
67
what can we use half life for
calculating the time needed for activity or mass of the isotope to fall to a certain value. calculating the mass of isotope of activity after it has been decayed for a certain time
68
what are radioactive tracers used for
locating problems including cancerous tumours. Iodine-131 for thyroid problems and Technetium-99 for tumours
69
what should the radioactive tracers be
gamma emitters enabling detection and minimising ionisation of cells
70
what else can be used as tracers instead of gamma
alpha
71
what is Radium-266 used for
to treat cancer by injecting tiny amoiunts of radium into a tumorous mass
72
why should radioactive tracers have a short half life
to allow detection but minimise harm to the patient

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