P6 - radioactivity Flashcards
what is the absorption spectrum?
a continuous spectrum with dark lines where particular wavelengths/frequencies of EM waves have been absorbed
what is the atomic number?
number of protons in a nucleus
what is background radiation?
radiation from all around us including the air, rocks, the sun, space and artificial sources
what is a chain reaction?
a reaction where the product of the first reaction causes further reactions to take place
what is contamination?
having a radioactive source (material) inside the body or on the skin
what is decay?
a random process by which an unstable nucleus loses energy by emission of radiation or a particle
what is the emission spectrum?
a set of wavelengths/frequencies of EM waves emitted by an atom when excited electrons move to lower energy levels
what is nuclear fission?
the process of splitting a heavy nucleus to form two or more small nuclei, releasing large quantities of energy
what is nuclear fusion?
what is half-life?
the half-life of a radioactive element is the time that it takes half the nuclei in a sample to decay
what is ionisation?
the gain or loss of electrons from an atom, leaving it charged
what is irradiation?
being exposed to radiation from a source (usually external)
what is an isotope?
atoms with the same number of protons and electrons but different numbers of neutrons
what is the mass number?
number of protons + number of neutrons
what is a nucleon?
a proton or neutron
what are the four types of radiation which a nucleus will spit out when it decays?
- alpha
- beta
- gamma
- neutron
what is an alpha particle?
- 2 neutrons and 2 protons (same as a helium nucleus)
- relative mass of 4 and charge of 2
- relatively big and heavy and slow moving
what is a beta particle?
- an electron
- virtually no mass and charge of -1
- move quite fast and quite small
- for every beta particle emitted, a neutron turns to a proton in the nucleus
what is a gamma particle?
- a type of electromagnetic wave
- no mass and no charge
- just energy
- don’t change element of nucleus that emits them
why might a nucleus emit a neutron?
if a nucleus contains a lot of neutrons, it may just throw out a neutron
what happens when radiation travels through a material?
it can collide with the material’s atoms, which slows down or stops the radiation; this means that the radiation can only penetrate so far into a material before it’s absorbed
what does the range of radiation depend on?
the type of radiation and material it’s travelling through
rank the different types of radiation on their penetration properties? (most to least)
- gamma
- beta
- alpha
what is the count rate?
the number of radioactive particles that reach a detector in a given time
why does the count rate decrease the further from the detector is from a radioactive source?
the further the radiation has to travel, the higher the chance it will be absorbed by the material it is travelling through
what are alpha particles blocked by?
paper
what are beta particles blocked by?
thin aluminium
what are gamma particles blocked by?
thick lead
what happens to a nucleus when it emits an alpha particle?
- the mass number decreases by 4
- the atomic number decreases by 2
what happens to a nucleus when it emits a beta particle?
- the mass number doesn’t change
- the atomic number increases by 1
what happens to a nucleus when it emits a gamma ray?
- the mass number and the atomic number don’t change
why will a new element be formed in both alpha and beta emissions?
the number of protons changes
what do electrons in an atom sit in?
different energy levels or shells
how far from the nucleus are the energy shells?
each energy shell is a different distance from the nucleus
how can an inner electron move up one or more energy levels in one go?
if it absorbs electromagnetic radiation with the right amount of energy; when it does move up, it moves to a partially filled (or empty) shell
what is an electron said to be when it moves to a higher energy level?
excited
what happens when an electron the falls back to it’s original energy level?
it will lose the same amount of energy it absorbed; the energy is carried away by EM radiation
what does the part of the EM spectrum that the radiation is from depend on?
its energy (which depends on the energy levels the electron moves between)
what does a higher energy mean for the frequency of EM radiation?
higher energy means higher frequency of EM radiation
when is an atom ionised?
an atom is ionised if it loses an electron
what happens when an atom is ionised?
- if an outer electron absorbs radiation with enough energy, it can move so far that it leaves the atom
- it is now free and tom is said to have been ionised
- atom is now positive ion
- it’s positive because there are more protons than electrons
- atom can lose more than one electron
- the more electrons it loses, the greater its positive charge
what can ionise atoms?
nuclear radiation
what is ionisation power?
a measure of how likely it is that radiation will ionise an atom
which radiation has the highest ionisation power?
alpha particles
what does it mean that alpha particles have the highest ionisation power?
it means that they can’t travel very far through a substance without hitting an atom and ionising it
what do fluorescent tubes contain?
mercury vapour
how do fluorescent tubes use excited electrons to produce light?
- electrons are accelerated through the mercury vapour, which ionises some of the mercury atoms, producing free electrons
- when this flow of free electrons collides with electrons in other mercury atoms, the electrons in the mercury atoms are excited to higher levels
- when these excited electrons return to their original energy levels, they emit radiation in the ultraviolet range of the electromagnetic spectrum
- a compound called phosphor coats the inside of the tube and absorbs the radiation, exciting its electrons to higher energy levels; these electrons then cascade down the energy levels, emitting many different frequencies of radiation, all in the visible part of the electromagnetic spectrum
what happens to the radioactivity of a sample over time?
it decreases
why can’t you predict when a particular nucleus is going to decay?
radioactive decay is a random process
information about decaying radioactive isotopes?
radioactive isotopes decay at different rates
what is activity and what is it measured in?
the number of unstable nuclei that decay in a given time is called the activity and is measured in becquerels (Bq) - the number of nuclei that decay each second
what is used to detect the radiation emitted from a decaying nucleus?
a Geiger Muller tube
what does the Geiger Muller tube measure?
the count rate in counts per minute (or per second)
why does a short half-life mean the activity falls quickly?
because lots of the nuclei decay in a short time
why does a long half-life mean the activity falls more slowly?
because most of the nuclei don’t decay for a long time - they just sit there, basically unstable, kind of biding their time
what are two things that can be used to calculate half-life?
- numbers
- a graph
what can ionising radiation harm?
living cells
what happens when some materials absorb ionising radiation?
it can enter living cells and interact with molecules
what is caused by the interactions with molecules that occur when ionising radiation enters living cells?
ionisation (they produce ions)
what results from lower doses of ionising radiation?
lower doses damage living cells by causing mutations in the DNA which can cause the cell to divide uncontrollably (which is cancer)
what can occur from higher doses of ionising radiation?
higher doses tend to kill cells completely, which causes radiation sickness if a lot of cells all get blasted at once
which radiation is the most dangerous OUTSIDE the body?
beta and gamma sources because they can still get inside to the delicate organs (they can pass through skin)
why is alpha less dangerous than beta or gamma outside the body?
it can’t penetrate the skin
which radiation is the most dangerous INSIDE the body?
an alpha source is the most dangerous because they’re the most ionising and they do all their damage in a very localised area
why are beta and gamma less dangerous than alpha inside the body?
they are less ionising and gamma will mostly pass straight out without doing much damage
what risks do all radioactive sources have?
irradiation and contamination risks
what do the hazards associated with a radioactive source depend on?
it’s half-life
what are some uses of radioactivity?
- smoke detectors
- thickness detecting
- treating cancer (radiotherapy)
- sterilisation
- leak locating
- medical tracers
how do smoke detectors use radioactivity?
- alpha particles are used in smoke detectors
- alpha radiation should ionise air inside the detector and create a current
- the alpha emitter is blocked when smoke enters, causing the alarm to be triggered by a microchip when the sensor doesn’t detect alpha
how does thickness detecting use radioactivity?
- if the paper is too thick, less beta radiation is detected because more is absorbed
- the rollers are then automatically told to move closer together (opposite is also true)
- use beta (all alpha would get blocked and all gamma would get through regardless of thickness)
- vey long half-life; otherwise count would decrease and make the computer think the paper had become too thick
how does radiotherapy/treating cancer use radioactivity?
- an x-ray or gamma source is rotated around a person’s body, continuously aiming the x-rays/gamma at the tumour
- this ensures the tumour gets a large amount of radiation (and hopefully the cells die) whilst surrounding healthy cells receive the lowest amount possible (so that they don’t get damaged or killed)
how does sterilisation use radioactivity?
- gamma radiation can be used to kill bacteria on medical equipment and fresh food
- this prolongs the life of food by slowing biological decay
- this does not make food radioactive at all
- makes old food look fresh but nutritional content decreases over time
how does leak locating use radioactivity?
- a radioactive tracer is put into an underground water pipe to locate a leak
what radiations are emitted from the medical tracers we use/why?
beta or gamma; isotopes of iodine only have beta
why is alpha never used for medical tracers?
alpha is highly ionising and not very penetrative (couldn’t be detected)
how do we get medical tracers into the patient?
inject, ingest, inhale
why is it good that radioactive iodine behaves the same as non-radioactive iodine?
the body will function normally (wouldn’t reject it etc)
do we want a long or short half-life for medical tracers/why?
short half-life (abt 4-6 hours)
- so it can be transported and still be radioactive
- also don’t want it continuously emitting radiation within the body
