6.4 Nuclear and Particle Physics

What was the plum pudding model?

Thompson’s idea that the atom is made up of a uniform sphere of positive charge with electrons embedded like fruit in a plum pudding

What was the alpha scattering experiment?

alpha particles were fired at a thin sheet gold foil under a vacuum, deflected alpha particles were detected by a ring of scintillators - materials that release photons when a particle hits them

What were the results of the alpha scattering experiment?

majority of alpha particles passed straight through, some with only a slight deflection, very few were deflected by more than 90 degrees

What did the results of the alpha scattering experiment show?

it proved the plum pudding model wrong as instead of most particles being deflected they mostly passed through, proving that atoms are mostly empty space and mass must be concentrated at some point (the nucleus); as some were deflected by more than 90 degrees it shows the nucleus has the same charge as the alpha particles, a positive charge

What is nuclear size?

R=r₀A^1/3

What is r₀?

1.2 fm

How do you find density of a nucleus?

use density=m/V, volume is given by 4piR³/3, R is given by other equation, mass is proportional to A

How is density independent of nucleon number?

mass is proportional to A, volume is proportional to A, it cancels out

What is an isotope?

atoms of the same element with differing numbers of neutrons and so they can undergo the same chemical reactions but will undergo different nuclear reactions - their electronic configurations being identical however the stability of their nuclei may differ greatly

What is a nucleon?

a subatomic particle that resides in the nucleus of the atom and so is either a proton or a neutron

What is the mass number?

also known as the nucleon number, it is a sum of the number of protons and neutrons in the nucleus

What letter is the mass number represented with?

A

What is the proton number?

also known as the atomic number, it is the number protons in the nucleus

What letter is the proton number represented with?

Z

What is the gravitational force?

comprising all weight and forces between bodies with mass such as stars, galaxies and planets, it acts on particles with mass, it is always attractive, has an infinite range but is very weak.

What is the electromagnetic force?

comprising of all electrostatic and magnetic forces as well as radiation pressure, it has an infinite range and acts on particles with charge

What is the weak nuclear force?

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

What is the strong nuclear force?

it acts between all nucleons and all quarks (i.e. the hadrons), it counteracts the repulsive electrostatic forces between protons in the nucleus, it is attractive at small distances (up to ~3 fm) and repulsive at incredibly small distances (below ~0.5 fm) and has a limited range

What is antimatter?

every particle has a corresponding antiparticle with equal mass but opposite charge

What happens when a particle and antiparticle meet?

they annihilate to produce energy in the form of photons

What are the two main classes of fundamental particles?

hadrons and leptons

What is a lepton?

a fundamental particle that is affected by the weak nuclear force but not the strong nuclear force

What is a hadron?

made up of fundamental particles called quarks, it is affected by the weak nuclear force and the strong nuclear force

What are two examples of hadrons?

mesons and baryons

What is a meson?

a quark antiquark pair

What is a baryon?

a group of three quarks

What are two examples of baryons?

protons and neutrons

What is a quark?

a fundamental particle that cannot be isolated and have fractions of charge

What is the quark model of a proton?

uud

What is the quark model of a neutron?

udd

What is the charge of an up quark?

+2/3 e

What is the charge of a down quark?

-1/3 e

What is the charge of an up antiquark?

-2/3 e

What is the charge of a down antiquark?

+1/3 e

What is the charge of a strange quark?

-1/3 e

What is the charge of a strange antiquark?

+1/3 e

When does beta minus decay happen?

when there are too many neutrons in the nucleus compared to protons

When does beta plus decay happen?

when there are too many protons in the nucleus compared to neutrons

What causes beta decay?

thye weak nuclear force causes quarks to mutate, e.g. an up turns into a down

What is the equation for beta-minus decay?

What is the equation in terms of quarks for beta-minus decay?

What is the equation for beta-plus decay?

What is the equation in terms of quarks for beta-plus decay?

What happens during beta-minus decay?

the weak force mutates a down quark into an up quark within a neutron, transforming it into a proton - this releases energy in the form of a beta-minus particle (high speed electron) and an antineutrino is created to conserve lepton number

What happens during beta-plus decay?

the weak force mutates an up quark into a down quark in a proton, changing it to a neutron - this releases energy in the form of a beta-plus particle (high speed positron) and a neutrino is created to conserve lepton number

What is the nature of radioactive decay?

random and spontaneous

Describe the nature, penetration and range of alpha particles

they are heavy and slow, have a charge of positive 2, and have high ionising ability, but low penetrating power, stopped by paper

Describe the nature, penetration and range of beta particles

they have a charge of positive or negative 1, they are not heavy and fast, they have medium ionising ability and medium penetrating power, stopped by 5mm aluminium

Describe the nature, penetration and range of gamma rays

they have no mass or charge, they are as fast as the speed of light, they have no ionising ability and high penetrating power, stopped (mostly) by 5cm lead

Describe an experiment to investigate the absorption of alpha, beta and gamma particles

What is activity?

rate of decay of a radioactive source, number of decays per unit time

What is the activity equation?

product of decay constant and number of particles

What is the decay constant?

the probability of decay of a single nucleus per second

How does activity or number of atoms decrease?

exponentially

What is the derivation half life of an isotope?

Describe an experiment to determine the half lfie of an isotope

How can you use carbon dating to tell the age of a dead organism?

the ratio of C12, C13 and C14 in the atmosphere is a known constant, organism will absorb C14 during their lifetimes, maximum at death, C14 has a half life of 5700 years, so by measuring the ratio of C12 to C14 and comparing this to the atmospheric ratio, estimation for the time since death can be calculated

What is the frequency of one photon released by annihilation of an electron positron pair?

hfx2=mc², 2×9.11×10^-31xc² =hfx2

9.11×10^-31xc² =hf

find frequency

What is binding energy?

energy required to completely separate a nucleus into its constituents

What is mass defect?

the difference between the mass of a completely seperated nucleus and the nucleus itself

What is binding energy per nucleon?

minimum energy required to remove a nucleon from the nucleus

What is nuclear fusion?

two lighter nuclei combine to produce a heavy nucleus

What is nuclear fission?

a heavy nucleus splits into two lighter nuclei

What is required for nuclear fusion?

extremely high temperature and pressure to overcome electrostatic repulsion between nuclei

What does a binding energy per nucleon against nucleon number graph look like?

How can Einstein’s mass-energy equation be applied?

energy/mass is released or absorbed in simple nuclear reactions

What is a chain reaction?

in nuclear fission, more reactions are caused by products (neutrons) from previous reactions

How can you cause nuclear fission?

fire a neutron at an unstable nucleus

What are the components of a nuclear fission reactor?

fuel rods contain the uranium fuel, controls rods absorb some neutrons to control the rate of nuclear reaction so only one neutron is a product so only one reaction is caused per reaction so power output is constant, moderator slows down the fast moving neutrons to create thermal neutrons e.g. water

What is the environmental impact of nuclear waste?

products of fission are usually radioactive, known as toxic waste and may have high half lives so remains hazardous for millenia - it may have to be buried deep underground and these sites must be safe from attack and protected against earthquakes