P5 - nuclear physics

Question 1

State the 3 particles in atom + properties

Answer 1

1. Proton - relative mass: 1, relative charge: +1e, location: nucleus
2. Neutron - relative mass: 1, relative charge: 0, location: nucleus
3. Electron - relative mass: 1/2000, relative charge: -1e, location: electron shells surrounding the nucleus

Question 2

Nuclide notation

Answer 2

A notation using symbols for elements along with atomic number and nucleon number to desribe the composition of an element’s nucleus.
X - symbol for element
Z - proton/atomic number (number of protons in nucleus)
A - nucleun/mass number (total number of protons and neutrons are found in the nucleus)
n (number of neutrons) = A - Z

Question 3

Isotopes + 2 variations

Answer 3

Variations of atoms of the same element (same number of protons and electrons) but with a different number of neutrons.
Can be stable (last forever) or radioactive (will change & give out radiation)

Question 4

Nuclear fusion + 2 requirements

Answer 4

The joining of nuclei. The process by which lighter nuclei collide with high energy and join to form a larger nucleus. This leads to an energy release.
Requires extremely high pressure and high temperature to increase kinetic energy of nuclei in order to overcome electric repulsion forces.

Question 5

Nuclear fission + example reaction with Uranium + use

Answer 5

The splitting of nuclei. Heavy nuclei with very large nucleon numbers are often unstable. Due to this instability, they often break apart. This can happen independently or if a slow neutron is fired at the large nucleus, triggering it to break apart into 2 smaller daughter nuclei and fast moving neutrons. This also releases energy, and this process is used in nuclear power stations to generate electricity (by slowing down the released fast moving neutrons in a moderator such as water, which releases heat due to friction and causes the water to evaporate into steam)
Uranium-235 becomes uranium-236 when neutron is fired at it. The heavier isotope is unstable and it splits into krypton, barium & 3 neutrons. (235,92) U + (1,0) n -> (236,92) U -> (92,36) K + (141,56) Ba + 3 (1,0) n

Question 6

What is ionising (nuclear) radiation + 2 dangers?

Answer 6

Radiation with enough energy to remove electrons from atoms (producing an ion). All 3 (alpha, beta & gamma) types of radiation are ionising. This can be very harmful to living beings and damage electronics.

Question 7

Background radiation + 6 sources

Answer 7

Low, not harmful levels of radiation always present in the environment. Mainly comes from radon gas, radioactive rocks & buildings (produce radon gas), food & drink (contain/absorb mildly radioactive nutrients/minerals), and cosmic rays. Artificial sources also include medical procedures and nuclear accidents/testing on nuclear weapons.

Question 8

Radiation detector + how it works + what it detects & measures

Answer 8

A Geiger–Müller (GM) tube detects alpha, beta and gamma radiation. A ‘click’ can be heard as the radiation is detected and a digital count is recorded. Can be used to measure rate of radioactive decay by count rate (number of emissions of radiation in certain time). Usually count/s but can be count/min

Question 9

Radioactivity/radioactive decay

Answer 9

Process by which an unstable nucleus becomes more stable by emitting energy and alpha, beta or gamma radiation. Radioactive decay is spontaneous and random, meaning that we cannot predict when an individual nuclei will decay.

Question 10

3 types of radiation + 5 properties

Answer 10

1. Alpha (α) particles - particles made up of 2 protons & 2 neutrons (like a Helium nucleus). Total relative mass = 4, relative charge = +2e. Highly ionising due to its large mass and charge. Least penetrating (can travel 5cm through air, stopped by materials like paper or skin). Relatively slow speed (<10% speed of light)
2. Beta (β) particles - high-energy, fast-moving electrons. Relative mass = 1/2000, relative charge = -1e. Only mildly ionising. Can travel through skin but are stopped by a few millimetres of aluminium foil. Relatively fast speed.
3. Gamma (γ) emissions - electromagnetic waves with high frequency and very high energy. No mass & no charge, so very weakly ionising. Most penetrative type of radiation, cannot be fully stopped but can be significantly reduced by thick lead/concrete. Travel at speed of light.

Question 11

State which types of radiation bend in magnetic/electric field and why

Answer 11

Alpha & beta particles bend because they have a charge.
Gamma emissions have no charge so don’t bend.

Question 12

2 examples nuclear alpha decay equations (Po & U) + explanation

Answer 12

Alpha decay: (211,84) Po -> (4,2) He^2+ + (207,82) Pb.
Emission of alpha particles causes the nucleus to lose 2 protons, which reduces the atomic number by 2 (forming a new element)

Question 13

2 examples of nuclear beta decay equation + explanation

Answer 13

Beta (-) decay:
When a neutron in a nucleus becomes unstable, it decays into a proton, and an electron is released. Neutron -> proton + electron. This means there is one more proton in the nucleus than there was originally so a different element was formed. The mass number remains the same.
E.g. (3,1) H -> (3,2) He + (0,-1) e

Question 14

Explain the effect gamma emission on atom

Answer 14

Gamma radiation does not increase or decrease number of protons, therefore the element is unchaged. The nucleus is idential before and after gamma emission. It just reduces overall energ of the nucleus.

Question 15

2 things that are preserved in nuclear decay equations

Answer 15

1. Total mass
2. Proton number

Question 16

Half-life (2 definitions) + units

Answer 16

1. The time taken for half of the radioactive nuclei (in a sample of an unstable isotope) to decay
2. Time taken for activity (count rate) of a radioactive source to decrease by half.
   Can be measured in seconds, weeks, months or years.

Question 17

Example of decay curve + what does it show

Answer 17

The graph shows that the half-life is a costant period of time for a particular element.
The x-axis is always time, while the y-axis may be radioactive activity, mass or radioactive isotopes, number of radioactive nuclei, percentage of radioactive nuclei remaining, etc.

Question 18

State & explain 3 uses of alpha/beta radiation

Answer 18

1. Irradiating food using beta or gamma radiation to kill bacteria which increases shelf life of fresh food
2. Smoke detectors use alpha radiation, as alpha particles ionise the air and allow current to flow between positive & negative plates with a potential between then. When smoke is present, the alpha particles collide with and are absorbed by the smoke particles, so less current slows which causes alarm to sound
3. Testing & controling thickness of some materials is done using beta particles (mildly penetrating & ionising), as beta radiation can penetrate a sheet of metal but the quantity of beta detected on other side depends on material’s thickness

Question 19

State & explain 3 uses of gamma radiation

Answer 19

1. Medical tracers use gamma radiation (injected or inhaled as tracer). It is highly penetrating but weakly ionising so not dangerous in small doses
2. Cancer treatment is done by focusing gamma radiation in a single point within the body. When focused, its intensity can kill cancer cells
3. Sterilising equipment such as medical instruments can be achieved by passing gamma rays through the material, which kills viruses & bacteria.

Question 20

Explain effects of ionising radiation

Answer 20

Radioactive materials are dangerous because ionising radiation can damage cells and affect DNA.

Question 21

State main danger of radiation for pilots, radiologists, & nuclear physicists + how they’re protected

Answer 21

1. Pilots are only allowed a set number of flyong hours/year due to cosmic rays
2. Radiologists wear lead vests to protect themselves from X-rays
3. Nuclear physiscists at CERN/power stations use radiation badges that count the accumulated radiation exposure

Question 22

4 safety precautions when handling radioactive materials

Answer 22

1. Wear protective gear like mask, goggles, etc. to avoid injestion/breathing in radioactive particles
2. Use robotics time to avoid touching source of radiation, having as much distance away from it as possible
3. Reduce exposure time
4. Shielding by placing a barrier between person & radioactive object

Question 23

2 safety precautions when storing radioactive materials

Answer 23

1. Store in appropriate container (alpha: thin package; beta: lead/similarly dense metal container; gamma: thick lead/concrete, often stored underground
2. Keep it locked away and mark containers with radioactive material with a distinctive label to warm and keep the people away from it

Question 24

Most dangerous radiation for humans

Answer 24

Alpha - most harmful internal hazard (if it is ingested/inhaled) because it is highly ionising
Gamma - most harmful external hazard (can go deep) due to its high energy

Question 25

Explain dangers of gamma radiation to humans NOT FINISHED

Answer 25

Can cause burns, cancer

Question 26

Ruthford scattering experiment + 3 results

Answer 26

Alpha particles were shot at a very thin piece of gold foil. 1. Most alpha particles passed straight through (no change in direction) because most of the atom is empty space 2. Some alpha particles deflected, indicating that the nucleus is positive 3. Very few bounched back, indicating that nucleus is very small