P1 7 Atomic Structure/Radioactivity Flashcards
describe alpha radiation
- 2 protons and 2 neutrons - helium nucleus
- mass of 4
- charge of +2
- range in air around 5cm
- stopped by paper/skin (as well as metal/concrete)
- low penetrating power
- high ionising power
- represented as (He) (α)
describe beta radiation
- fast moving electron
- mass of 0 (very small)
- charge of -1
- range in air around 1m
- stopped by thin metal (aluminium)/plastic (as well as concrete)
- medium penetrating power
- medium ionising power
- represented as (e) (β)
describe gamma radiation
- high frequency electromagnetic wave
- mass of 0
- charge of 0
- range in air infinite (in theory)
- stopped by thick lead/concrete
- high penetrating power
- low ionising power
- represented as (γ)
describe neutron radiation
- when the nucleus emits a neutron
- mass of 1
- charge of 0
- represented as (n)
describe rutherford’s observations and conclusions in the alpha particle scattering experiment
(fired a beam of alpha particles at thin gold foil and measured where they scattered to)
* most went straight through - atom is mostly empty space
* very few were reflected straight back - nucleus of atom is very small but contains most of the mass
* some were deflected/scattered - positive nucleus
describe alpha decay
- an unstable nucleus emits an alpha particle (2 protons and 2 neutrons)
- mass number decreases by 4 and atomic number decreases by 2
- more risk of harm to human bodies from contamination than irradiation
describe beta decay
- a neutron from the nucleus turns into a proton and an electron, then an electron is released
describe radioactive contamination
- when an object has a radioactive source in or on it
- if the type of radiation emitted by the decay of the source’s nuclei is highly ionising, it will be a greater hazard
- the hazard lasts as long as the radioactive material is on the object but reduces over time
- difficult to remove all radioactive atoms off contaminated object so it continues to be exposed
describe irradiation
- when an object is exposed to radiation from an external source
- the object doesn’t become radioactive - objects are safe after irradiation has stopped so is used for sterilising
describe the precautions for irradiation (6)
- wear protective clothing e.g. lead apron
- wear a film badge - monitors dose levels
- carry out procedures remotely (e.g. robots)
- keep your distance/ maximise distance away from source
- limit exposure time
- source held with tongs
- source kept in lead-lined container
describe peer review
- where independent scientists check a scientific report before it is published - to see if the method is valid and calculations correct
describe the number of half-lives elapsed in correlation to the fraction of unstable nuclei remaining
half-lives elapsed –> fraction of unstable nuclei
0 –> 1/1
1 –> 1/2
2 –> 1/4
3 –> 1/8
4 –> 1/16
5 –> 1/32
formula: 1 / 2 to the power of (no. half-lives)
(uses of nuclear radiation) describe industrial tracers and radiation used
- radioactive source is added to e.g. water supply and GM counter is above the ground detecting radiation - to locate blocked/leaking pipe
- use gamma with short half-life - most penetrating to get through ground above, don’t want the source to be radioactive for too long
(uses of nuclear radiation) describe medical tracers and radiation used
- patient swallows/injects radioactive isotope and is detected outside body to trace its path - identify blockages
- use gamma with short half-life - most penetrating to get through body, limit patient’s exposure time
(uses of nuclear radiation) describe radiotherapy and radiation used
- source is moved around patient directed at the tumour - to kill cancerous cells
- use gamma with long half-life - most penetrating to get through body, don’t want to have to replace the source often
(uses of nuclear radiation) describe sterlising and radiation used
- kills bacteria on food/medical equipment
- use gamma with long half-life - most penetrating to kill all bacteria and least ionising when swallowed, don’t want to have to replace the source often
(uses of nuclear radiation) describe smoke alarms and radiation used
- use alpha with long half-life - low penetrating power so it cannot pass through smoke, don’t want to have to replace the source
(uses of nuclear radiation) describe thickness control and radiation used
- use beta with long half-life - medium penetrating power so is stopped by thick paper but can pass through thin paper, don’t want to have to replace the source
define an isotope
different atoms of an element with different numbers of neutrons (but same number of protons)
describe the Geiger Muller tube (G-M) and count rate
- detects nuclear radiation particles
- count-rate - number of decays recorded each second
describe radioactive decay
- it is random and impossible to predict (can be estimated)
- activity - the rate at which a nuclei in a source decay, measured in Becquerels (Bq)
describe how nuclear radiation/ radioactive materials are hazardous
- nuclei of atoms release radiation when they decay
- ionising radiation from radioactive source passes into living cells+ ionises atoms in them
- cells are damaged or killed
- ionisation of atoms in a cell’s DNA can lead to a copying error (mutation) and cancer
define half-life
- average time for the number of nuclei to halve
- time for count rate to halve
