Particle physics paper 2

Question 1

thompson plum pudding model

Answer 1

neutral atom is made up of a uniform sphere of positive charge with tiny electrons embedded

Question 2

Rutherfords alpha scattering experiment

Answer 2

disproved plum pudding model. alpha particles fired at thin sheet of gold foil under a vacuum. deflected particles were detected on all sides by a ring of scintillators.

Question 3

scintillators

Answer 3

materials that release photons when a particle hits them

Question 4

rutherford prediction

Answer 4

expected most alpha particles to travel through with deflection and rebound off charged wall.Majority of particles passed straight through with only a slight deflection of on average only a degree. Therefore atom is mostly empty, mass is concentrated in centre

Question 5

Rutherfords development of the nucleus

Answer 5

small portion of alpha particles were deflected by more than 90, this is only possible if the charge on the nucleus was the same as the alpha particle (positive). Hence the concentrated mass was positively charged with electrons orbiting

Question 6

isotopes

Answer 6

atoms of the same element with differing numbers of neutrons so they can undergo the same chemical reactions but will undergo different nuclear reactions

Question 7

nucleon

Answer 7

subatomic particle that resides in the nucleus so either a proton or neutron

Question 8

atomic or proton number

Answer 8

z

Question 9

mass number

Answer 9

a

Question 10

weak nuclear force

Answer 10

force responsible for beta decay acts to change quark types over very small distances

Question 11

strong nuclear force

Answer 11

acts between all nucleons and all quarks, counteracts the repulsive electrostatic forces, attractive at small distances >3fm and repulsive at small 0.5>fm

Question 12

concept of mass as a form of energy

Answer 12

demonstrated by annihilation of matter and antimatter where the combined mass of the two particles is related by the mass energy equivalence

Question 13

binding energy

Answer 13

minimum energy required to break a nucleus into its constituent parts
this would include the thermal energy and electrostatic potential energy that arise from strong nuclear forces

Question 14

mass defect of a reaction

Answer 14

difference in the mass of the constituent nucleons against the mass of the nucleus due to the potential of the electrostatic and strong forces

radiation is emitted in the form of high energy particles or photons. this energy must come from a change in mass. when a parent nucleus emits a daughter nucleus and a high energy particle there is a mass difference. this is known as the mass defect.

Question 15

binding energy per nucleon

Answer 15

most stable isotope is iron 56, max binding energy per nucleon. for low nucleon numbers A<56 Binding energy per nucleon increases otherwise decreases

Question 16

anti particles

Answer 16

every particle has a corresponding antiparticle which have equal mass but opposite charge, they annihilate to produce energy in the form of photons in space

Question 17

pair production

Answer 17

occurs when a high energy photon spontaneously creates a matter-anti matter pair. the photon must have an energy greater than combined rest masses of the two particles. ev=mc^2

Question 18

fundamental particles

Answer 18

consist of two main classes, hadrons and leptons

Question 19

hadrons

Answer 19

made up of fundamental particles called quarks and are acted on by Bothe strong and weak nuclear force, can only exist in quark-antiquark pairs which make a class of hadrons called the mesons. protons and neutrons are baryons whereas particles such as pions are mesons.all baryons have number of 1 anti baryons -1

Question 20

how do we know quarks exist

Answer 20

from particle collisions, some of the kinetic energy and mass energy of the particles can be transferred into other forms and particles created or destroyed by the mass energy equivalence.

Question 21

strong interactions conserves

Answer 21

the strangeness (as
well as top-ness, charm etc.). If a hadron contains a strange quark it will have a
strangeness of -1 and if it has an anti-strange quark it has a strangeness of 1

Question 22

Leptons

Answer 22

Leptons are also fundamental particles but unlike quarks they are not affected by the
strong force. They are subject to the weak nuclear force however and so are created in
nuclear decays such as beta decay to conserve the charge and mass-energy of the
interaction. Leptons have a lepton number of 1 whereas their antiparticles have a lepton
number of -1.e electrons, positrons (antielectrons),
neutrinos and muons

Question 23

Radioactive decay

Answer 23

spontaneous breakdown of an atomic nucleus resulting in the
release of energy and matter from the nucleus

Question 24

random process

Answer 24

that it is
impossible to predict which of a number of identical nuclei will decay next. decay follows a defined pattern and given a large enough number of nuclei this yields
predictable results

Question 25

types of radiation can be easily distinguished

Answer 25

different
penetrating powers so simply screening the source with different materials and
measuring the drop in activity should allow for the type of source to be determined. In
addition to this, all three have different responses to magnetic fields and electric fields
due to their differing charges making specific radiation detectors easy to design.

Question 26

bubble chambers

Answer 26

use tanks of water that from tracks of bubbes when ionising particles pass
through them and Geiger-Muller tubes (Geiger counters) which form cascades of
electrons when an ionising particle hits the detector.

Question 27

Beta Decay and the Weak Nuclear Forc

Answer 27

weak nuclear force causes the transformation of quarks via emission of leptons. In
beta minus decay, the weak force mutates a down quark into an up quark within a
neutron transforming it into a proton. This process releases energy in the form of a high
speed electron or beta particle which is also needed to conserve charge. However, an
antineutrino is also created in order to conserve lepton number.

Question 28

beta minus decay formula

Answer 28

Question 29

Beta plus decay

Answer 29

also occurs when an up quark transforms into a down quark in a proton
changing it to a neutron. Again, energy is produced creating a positron and neutrino

Question 30

Beta plus decay formula

Answer 30

Question 31

Alpha decay

Answer 31

occurs in very unstable nuclei and sees the loss of an alpha particle or
helium nucleus

Question 32

Alpha emission

Answer 32

can be thought of as spontaneous fission of unstable
nuclei in which the strong nuclear force is not great enough to overcome the electrostatic
repulsion between protons in the nucleus. The high binding energy per nucleon of the
helium nucleus makes this daughter nucleus a favourable choice as total binding energy
will increase vastly as the parent nuclei moves closer to the middle of the binding
energy per nucleon graph.

Question 33

Alpha decay FORMULA

Answer 33

Question 34

decay chain

Answer 34

A common occurrence in nuclear decays is many will happen in succession until a stable
atom is reached,

Question 35

Nuclei with greater than 82 protons

Answer 35

likely to decay via alpha radiation

Question 36

Nuclei to the right of the belt of stability

Answer 36

have too many protons and therefore are
proton-rich meaning that they are more likely to decay via beta-plus decay

Question 37

Nuclei to the left of the belt of stability

Answer 37

have too many neutrons and therefore are
neutron-rich meaning that they are more likely to decay via beta-minus decay.

Question 38

Gamma decay

Answer 38

s caused when a nucleus has surplus energy following alpha or beta
emission. There is no change to nucleon composition, but energy is released in the form
of a gamma photon

Question 39

activity

Answer 39

the rate at which nuclei decay, or number of decays per
second, measured in Becquerel (s-1)

Question 40

decay constant,

Answer 40

probability that an individual nucleus
will decay per unit time.

Question 41

background radiation

Answer 41

must be recorded before the expirement then measure the sources radiation then subtract the difference to find the true activity

Question 42

Radiocarbon Dating

Answer 42

ratio of C-14 to C-12 in the organism will match the atmospheric ratio yet at the point of
death the number of C-14 atoms will be capped. C-14 is a radioactive isotope that decays
via beta emission with a half-life of ~5700 years. Hence, by measuring the ratio of C-14 to
C-12 in the dead tissue and comparing this to the atmospheric composition an estimation
for the time since the organism’s death can be calculated

Question 43

CNO cycle

Answer 43

in which carbon, nitrogen
and oxygen are synthesised.

Question 44

proton-proton chain

Answer 44

which lone protons in the star’s plasma fuse to form an unstable 𝐻𝐻𝑒𝑒2
2 nuclei. This
particle then undergoes beta decay forming deuterium nuclei ( 𝐻𝐻1
2 , an isotope of
hydrogen). The next reaction in the chain fuses deuterium with a further proton to form
𝐻𝐻𝑒𝑒2
3 and so the process continues forming nuclei up to 𝐻𝐻𝑒𝑒2
4

Question 45

Artificial fusion reactors

Answer 45

alternative power sources as
they have no radioactive by-products. However, the extremely high temperatures and
pressures needed to maintain fusion and can only be operated for short periods of time

Question 46

Nuclear Fission

Answer 46

Fission is the breaking apart of large nuclei into small nuclei causing a reduction in the
total binding energy, a mass defect and energy to be released

Question 47

Nuclear Fission process

Answer 47

Typically, uranium-235 is
used the fissile material as it easily undergoes fission and is relatively abundant. A low
speed, thermal neutron is fired at the U-235 nuclei which absorbs the extra nucleon to
become the unstable U-236 isotope. This isotope then either decays via fission (about
85% of the time), splitting into two smaller daughter nuclei and more fast neutrons or
decays via gamma emission.

Question 48

fissile materials sit inside a

Answer 48

reactor core which is surrouned by a thermal coolant which absorbs the thermal energy
from the fission and transforms this thermal energy into kinetic energy in the turbines
which then turn the generator transferring this energy into electrical energy i.e.
alternating current

Question 49

fuel rods

Answer 49

within the core contain
the fissile material and are surrounded by the moderator and control rods.

Question 50

moderator

Answer 50

The absorption of neutrons and consequent fission is more likely to occur with slower
neutrons, which means the neutrons released by the fission process are too high energy
to continue the reaction. They are slowed by a moderator

Question 51

rate of the reaction is
controlled by

Answer 51

control rods (e.g. boron, cadmium) which absorb thermal neutrons to
prevent these neutrons from causing further fission reactions.