Unit E (1-5)

Question 1

What did the Gieger-Marsden-Rutherford experiment reveal?

Answer 1

In these experiments, particles called alpha particles were fired at a thin sheet of gold foil. Rutherford expected that the positively charged alpha particles would interact with the positive and negative charges in the ‘plum pudding’ atoms in the gold foil. This model states that most of the atom is empty space. Almost all of the positively charged matter in the atom is concentrated in a very small region at its centre, called the nucleus. Electrons are in orbit around the nucleus.

Question 2

What do we call the places where electrons reside? Note there are a few names here -
list as many as you can

Answer 2

Atomic energy levels, electron shells, orbital rings

Question 3

What can we see an emission spectrum? Absorption spectrum? And what do they
reveal?

Answer 3

They show either the emitted or absorbed photos that occur during an atomic transition. These spectrum show proof of the discrete atomic energy levels in the atom

Question 4

When are photons absorbed or emitted?

Answer 4

Atomic transition between energy levels: When an atom gains energy, an electron may transition to a higher energy level.
When an electron loses energy, it transitions to a lower energy level.

Question 5

What is an isotope? Nucleon? Neutrino?

Answer 5

Isotope: different versions of the same atom containing different numbers of neutrons
Nucleon: any of the molecules/particles inside of the nucleus of the atom, they are attracted by a force
Neutrino (v): a type of particle released when an atom goes through beta+ decay
Antineutrino: beta- decay

Question 6

Why do we need more n’s as the number of p’s in a nucleus increases?

Answer 6

To keep the atom stable

Question 7

What are the alpha, beta-, beta+ and gamma particles?

Answer 7

Alpha: has a positive charge and is helium nucleus (2 p, 2n)
Beta- an electron, zero nucleons, same mass as electron
Beta+ an electron but with positive charge, same mass as electron
gamma: a photon that is produced in gamma radiation, short wavelength, passes through most substances

Question 8

What are the types of decay that can happen?

Answer 8

Alpha decay: a nucleus emits an alpha particle consisting of two protons and two neutrons, is the most ionising and the least penetrating
Beta- decay: a nucleus emits a beta-minus particle (electron) and an anti-nuetrino, there is a proton increase by 1
Beta+ decay: a nucleus emits a beta-plus particle (positron) and a neutrino, proton decrease by 1
gamma decay: a gamma photon is emitted, no change from one element to another, *means excited state, is the least ionising and the most penetrating

Question 9

Define half-life

Answer 9

The amount of time it takes for half the nuclei in a sample to decay. The graph shows an exponential decay showing the relationship between activity and time, but can also show the relationship between count rate and time. The half-life remains constant.

Question 10

Define radioactive activity

Answer 10

the release of energy from the decay of the nuclei of certain kinds of atoms and isotopes, also known as the number fo decays per unit time

Question 11

How do we measure radioactivity? With what tool?

Answer 11

A detector: Geiger counters are commonly used to measure the amount of radioactivity

Question 12

What is background radiation?

Answer 12

The natural radiation that is always present in the environment. It includes cosmic radiation which comes from the sun and stars, terrestrial radiation which comes from the Earth, and internal radiation which exists in all living things.

Question 13

What is radioactive dating?

Answer 13

A technique called radioactive dating can be used to measure the ages of certain types of object by measuring their activities. This makes use of the fact that the activity of an isotope sample decreases over time.

Question 14

How is radioactivity used in medicine?

Answer 14

For therapy, radioactive materials are used to kill cancerous tissue, shrink a tumor or reduce pain. Teletherapy targets cancerous tissue with an intense beam of radiation.

Question 15

Define atomic mass unit, mass defect and binding energy

Answer 15

Atomic mass unit: formula booklet, the unit of some mass-energy in kg
Mass Defect: the mass of a nucleus is less than the sum of the masses of the separate nucleons it is made from. The difference between the mass of the nucleus and the sum of the masses of its separated nucleons is called the mass defect.
Binding Energy: indicates how tightly bound the nucleus is, the work required to break apart a nucleus into its separate nucleons, the binding energy increases as the number of nucleons increases because it requires more energy to separate more nucleons

Question 16

What is the typical value of binding energy per nucleon for a metal?

Answer 16

It is typically around the value of 7 or 8 MeV

Question 17

What do we mean by fission?

Answer 17

the splitting of a larger nucleus into smaller nuclei

Question 18

Define the following words
Enrichment
Critical mass
Moderator
Control rod
heat exchanger
shielding

Answer 18

Enrichment - removes unwanted uranium-238, making the concentration of uranium-235 atoms higher
Critical mass - the minimum amount of fissionable material that will support a self-sustaining chain reaction. At this mass the neutrons released as a product of one fission reaction can cause neighboring atoms to fission.
Control rods - absorbs neutrons, controlling the rate of fission in reactor
Moderator - slows down neutrons, making them more likely to be absorbed by nuclei and cause fission
heat exchanger - the system used to transfer thermal energy from one fluid to another
shielding - to absorb radiation in order to protect people and the environment from its harmful effects

Question 19

Outline the main pros and cons of nuclear power generation from fission

Answer 19

Pros: low green footprint, produces large amounts of energy, reliable energy source
Cons: produces nuclear waste, malfunctions can be catastrophic, uranium has the possibility of running out

Question 20

What is the difference between neutron-induced and spontaneous fission

Answer 20

Neutron-induced - a nucleus absorbs a slow-moving neutron, becomes unstable and then the nucleus splits
Spontaneous - a heavy nucleus splits into two almost equal smaller nuclei without absorbing a neutron

Question 21

Define the following distance units
a) AU
b) Lightyear
c) parsec

Answer 21

AU - astronomical unit, average distance from the earth to the sun
Lightyear - distance that light travels in a vacuum in one year
Parsec - distance to an object with a parallax angle of 1 arcesecond

Question 22

What is parallax and how do we use it to find the distance to stars?

Answer 22

a method of calculating the distance to faraway stars using the relative motion of the star against a fixed background

Question 23

What do we mean by hydrostatic equilibrium

Answer 23

when a star is stable, the inwards gravitational force is in equilibrium with the outwards radiation force

Question 24

Whose law allows us to obtain the surface temperature of stars?

Answer 24

Wiens law: max wavelength*T=2.9x10^-3mK

Question 25

What is the proton-proton chain and what is the overall reaction that takes place?

Answer 25

Series of three reactions that concert H into He
* ^1_1H + ^1_1H -> ^2_1H + ^0_1e + ^0_0ν
* ^1_1H + ^2_1H -> ^3_2He + γ
* ^3_2He + ^3_2He -> ^4_2He + ^1_1H + ^1_1H
Overall 4H convert to 1He and 26.7MeV of energy is released

Question 26

What is the HR Diagram? How is radius outlined in the HR diagram?

Answer 26

a graph of luminosity against temperature for stars, with four main regions, it shows lines of constant radius, can show the evolution of a star

Question 27

Define
a) Main sequence star
b) Red giant
c) White dwarf
d) Neutron star
e) Black hole

Answer 27

Main - group of stars consisting of young to middle-aged stars with a wide range of temperatures and luminosities
Red giant - has increased dramatically in size to continue fusing elements in its core comes from a low mass main sequence star
Supergiant - has a very high mass and can fuse elements up to iron, comes from a high mass main sequence star or a high mass red giant
white dwarf - the core of a small dead star, consists of leftover material that was nor fused in the star (carbon or iron)
neutron star - after supernova of supergiant, it compresses to core of just atomic nuclei
Black hole - when the center of the star collaspes in on itself causing a supernova, in order for something to escape, it has to move faster than the speed of light

Question 28

Chain reaction

Answer 28

neutrons released by fission are absorbed by other nuclei which undergo fission which releases more neutrons