radioactivity Flashcards
Atomic mass:
how many protons and neutrons there are in an atom’s nucleus (top)
Atomic number:
how many protons OR electrons there are in an atom (bottom)
Isotope:
A version of an elements with a varying amount of neutrons in its nucleus whilst having the usual amount of protons and electrons, resulting in variations in an atom’s atomic mass.
Ionisation:
When radiation knocks out an outer electron from an atom, causing it to gain a positive charge.
Excitation:
When radiation isn’t strong enough to fully knock out an atom’s outer electron and instead displaces it to a higher energy level, making the atom be in an unstable ‘excited state’. the electron eventually drops back dow to its original energy level whilst emitting the radiation out as electromagnetic energy (light)
Radiation/radioactivity:
The excess mass or energy an excited atom emits out to become stable again.
Radioactive decay:
the process where a radioisotope becomes stable by emitting radiation.
Give and explain two characteristics of radioactive decay:
Random- we cannot predict which nuclei will decay next or when.
Spontaneous- no external changes applied to it will effect its radioactivity
How do you calculate the radioactivity of a material?
measured in Bq
divide number of nuclei that decay by the time it takes
What are the 4 types of radiation?
Gamma (energy)
Alpha (mass)
Beta (mass)
Neutron (mass)
Describe gamma radiation: (relative mass, charge, physical description, how it’s produced, how it changes the atom)
Gamma radiation (y) may occur after alpha or beta radiation when there is excess energy to be emitted. it is emitted via short wavelength and high frequency waves, this doesn’t change the atom. it has a relative mass of 0 and has a relative charge of 0.
Describe alpha radiation: (relative mass, charge, physical description, how it’s produced)
Alpha radiation (a) is a particle consisting of 2 protons and 2 neutrons that are emitted from a radioactive atom to become stable, resulting in it becoming a new element and isotope. it has a relative mass of 4 and a relative charge of +2.
Describe beta radiation: (relative mass, charge, physical description, how it’s produced)
Beta radiation (b) is when a neutron turns into a proton (which stays in the nucleus, changing the atom’s atomic number thus changing its element) and an electron which is released giving the nucleus a positive charge. the atom’s relative mass remains unchanged. the relative mass of the beta particle is 0 but it has a charge of -1.
Describe neutron radiation: (relative mass, charge, physical description, how it’s produced)
Neutron radiation (n) is when a radioactive atom become even more unstable and emits a high speed neutron. it therefore makes another isotope, and have no charge but a relative mass of 1.
Describe the difference between alpha, beta and gamma radiation ionising power and penetrating power:
Alpha particles have a low penetrating power but high ionising power.
Beta particles have a higher penetrating power and a lower ionising power.
Gamma rays have a high penetrating power but a low ionising power.
Explain a practical to investigate the penetrating power of a radioactive substance:
- place a geiger counter on a surface
- measure the count rate (radiation) detected without the presence of the source to get the base background radiation in the environment.
- place the source of radiation a set distance away from a Geiger counter.
- with nothing in between, measure the counts emitted from the source.
- at a set distance between the source and the counter, place an absorber (paper, aluminium or lead)
- measure the count rate and minus the background radiation from it.
- repeat for the different absorbers.
Irradiation
when something is exposed to radiation but doesn’t become radioactive
Contamination
when something comes into contact with a radioactive source and becomes radioactive.
How can the level of irradiation be affected?
- how long the object is exposed to the source
- the activity of the source (how much radiation is emitted in a given time)
- how penetrating the type of radiation is.
How can the level of contamination be affected?
- the penetrating power of the source
- the ionising power of the source.
How can we reduce the risk of ionising radiation to humans?
- no contact (wear glove and use tongs)
- limit exposure times
- use shields and barriers to absorb the radiation before we do
- stay a good distance away.
What are non-medical uses of radiation?
smoke detectors- alpha particles are used to ionise the air in the detector, this helps generate a current in the circuit, completing it. in a fire, smoke absorbs the alpha radiation and stops the circuit, which causes it to alarm.
automatic thickness monitoring in metal foil production- when foil passes between a beta radioactive source and a geiger counter. if the foil is too thick, the counts decrease as less radiation passes through the sheet, which signals for the rollers to thin it out more.
What makes some radiation viable for medical uses? (3)
penetration power: the radiation must be able to pass through the patient’s skin to the detector
activity:
the radiation must’t be so active that it poses as an ionising risk.
half-life:
if the radiation has too short of a half life it won’t be able to do anything significant and if the radiation has a long half life it will have little effect
activity:
how many radioisotopes decay in a same per second
two definitions for radioactive half-life:
- the average time it takes for the number of parent nuclei to half
- the average time it takes for the activity to half
