Physics: Radioactivity and Particles - Unit 7

name the particles that made up atoms and state their electrical charges.

proton: positively charged

neutron: neutral, no charge

electron: negatively charged

describe the structure of the atom

• it has a positively charged nucleus which is made up of protons and neutrons

• the nucleus is surrounded by negatively charged electrons, which all orbit the nucleus at different distances

an ‘isotope’ of an element

isotopes are atoms of the same element with same atomic (proton) number and different mass (neutron) number

• atomic number = number of protons

• mass number = number of protons + neutrons

relative masses of proton, neutron and electron

• proton = 1 unit

• neutron = 1 unit

• electron = 1/1850 unit

relative charge for proton and electron

proton = +1

electron = -1

reason why an atom is neutral

• atom contains the same number of protons as electrons

• the charges of protons and electrons balance out, so the atom has no overall charge

how does an atom become a positive ion

• by losing its outer electrons

• which means there is more protons than electrons, and so has an overall positive charge

types of radiation emitted from an unstable nuclei

• alpha particles

• beta minus particles

• gamma rays

• neutron radiation

types of ionizing radiation

• alpha

• beta

• gamma rays

background radiation

• radiation that is always around

• it is in very small amounts, so not harmful

sources of background radiation

• unstable nuclei in rocks (also give out radon gas)

• radiation used in medicine

• food and water (some)

• living things (plants absorb radioactive material as they grow which can be passed on to animals)

• cosmic rays from the sun

two pieces of equipment which can be used to detect radiation

• Geiger-muller (GM) Detector

• Photographic Film

how do you measure and detect background radiation using GM Detector

• when the GM tube absorbs radiation it produces a pulse, which a machine uses to count the amount of radiation

• frequency of the pulse depends on how much radiation is present

• high frequency would mean the tube is absorbing a large amount of radiation

how do you measure and detect background radiation using photographic film

• a photographic film turns dark when it absorbs radiation

• useful for people who work on radiation as the more radiation they are exposed to, the darker film becomes

• so workers know if they are exposed to too much radiation

order of radiations to least ionizing

• gamma (least ionizing)

• beta

• alpha (most ionizing)

order of radiations to least penetrating

• alpha (least penetrating)

• beta

• gamma (most penetrating)

alpha particle

• helium nucleus

• 2 neutrons and 2 protons

beta particle

an electron which is emitted from the nucleus

gamma ray

high energy carrying electromagnetic wave from the electromagnetic spectrum

beta decay

the process in which a neutron splits into a proton and an electron, and electron is emitted from the nucleus

alpha decay

when an alpha decay occurs the atomic number decreases by 2 and the mass number decreases by 4 (a new element is made)

gamma radiation effect

it has no affect on the mass number and atomic number of an atom

effect of a beta minus decay

• the mass number stays the same as the combined number of protons and neutrons hasn’t changed

• atomic number increases since there is one more proton

what causes gamma rays to be released

• in the atom, when the nucleus decays some of the nuclei rearranges itself so there is excess energy

• this may lead to it releasing this energy in form of gamma rays

the activity of a radioactive source

• it decreases exponentially

• it decreases by a constant ratio over constant time periods

half-life

this is the time taken for a source for half of its initial mass to decay

• time taken for activity to drop to half of the initial activity

unit for activity

Becquerel (Bq)

uses of radioactivity

• household fire alarms (smoke)

• irradiating food

• sterilization of equipment

• tracing and gauging thickness of materials

• diagnosis and treatment of cancer

smoke alarms

• radioactive substance is in the alarm which emits alpha radiation

• emitted alpha particle ionize the air in the detector and cause a current to flow between the plates

• smoke interferes with the radiation, air is no longer ionized and so no current can flow

• reduction in the current flow triggers the alarm

uses of radiation in medicine

• sterilize equipment: gamma radiation can kill bacteria cells

• help treat cancer, as it can be used to kill cancer cells

beta radiation in tracers

• tracer is inserted in your body, which targets a specific part of the body

• radioactivate substances in the tracer releases beta radiation which can be detected by external machines

how beta radiation is used to determine thickness

• a beta source is placed above the material and a detector is placed below it

• if a lot of radiation is detected by the detector, too much radiation is passing through the material, meaning it is too thin

• if only little radiation is detected, then the material blocks too much radiation, so it is too thick

why is ionizing radiation dangerous

• it can damage tissue and kill cells

• it can cell mutations which leads to cancer

precautions people should take when using ionizing radiation

• avoid handling the source directly (use tongs)

• wear radiation protective clothing

• keep the radiation in lead containers to reduce the amount of radiation that can escape

• avoid being exposed to the radiation for long periods of time

what is more dangerous, a long half life or a short half life?

if it has a long half life then it would remain highly radioactive for longer, so it is more dangerous

precautions taken to reduce harm for doctors and patients using ionizing radiation

• only a small dose is given to the patient so they are not exposed to too much

• the radiation used has a very short half life so it won’t remain radioactive for too long

• medical staff must wear protective clothing

contamination

this is when radioactive substances are transferred to objects though processes such as touching the or breathing it in

irradiation

this is when the object comes in contact with the radioactive source, the source doesn’t actually enter your body and the radiation will only stop if you move away from the area

treating tumors: internally and externally

• both try to only target specific cancer cells, but some healthy tissue surrounding it is also damaged

• both methods are designed to keep to a minimum

• internal uses a tracer and can use alpha radiation, which is poorly penetrating and can’t reach the healthy cells, short half-life is required so it doesn’t stay in the body for too long

• external concentrates the beam on specific parts of the body, and a long half-life is required

uses of radioactive tracer in medicine

• tracer is placed inside the body (drunk, eaten or injected)

• tracer releases gamma radiation which is detected by a detector which moves around the body

• this can be used to produce a picture of the patient’s body

advantages of nuclear power for generating electricity

• nuclear power don’t produce CO2

• fuel is readily available, it would reduce pressure of the fossil fuel supplies

• less nuclear fuel has to be used to produce the same amount of energy as a fossil fuel

• does not contribute to the global warming

disadvantages of using nuclear power to generate electricity

• public perceive nuclear power as very dangerous, therefore they are against power stations

• there are security risks as the radioactive substances can be useful for terrorists

• a lot of money and time is required to commission and decommission the stations, which is bad for the country’s economy

• the radioactive waste can be difficult to dispose of and will remain radioactive for many years, which is dangerous for humans and the environment

• can cause widespread disasters, chernobyl

process of fission of uranium-235

• the uranium-235 absorbs a neutron which makes it unstable

• this causes it to split into two daughter nuclei

• which releases two or more neutrons, as well as energy

controlled chain reaction

• the neutrons released are absorbed by another nuclei, causing this nuclei to also undergo fission, releasing further neutrons

moderator

it slows down the neutrons until they are travelling at a speed slow enough for them to be absorbed

control rods

• they are raised or lowered so that they absorb fewer or greater neutrons

• the number of neutrons that they absorb will determine how many reactions that can take place

how electricity is produced in a nuclear power station

• the reactions release thermal energy

• this energy is used to boil water and then produce steam

• this steam is then used to turn a turbine which starts the generator

nuclear fusion

this is when two small nuclei fuse together to form a larger nuclear, which also releases energy

examples of day-to-day fusion

fusion occurs in the sun: stars use fusion as their energy source

why can’t nuclear fusion be used as an energy source

• because we can’t get high temperature and pressures for nuclear fusion to happen, while still being cost effective

• this is because both nuclei are positive, so a lot of energy is required to overcome the electrostatic repulsion between the two nuclei

why is fission used instead of fusion

• fission can be used for nuclear power and is easily controlled, whereas, fusion is harder to control

• fusion require very harsh condition (high temperatures/ pressure), while fission doesn’t