P4: Atomic Structure Flashcards
Explain how the properties of alpha, beta, gamma radiation affects the level of the hazard at different distances (4)
- At short distances, the most hazardous radiation would be alpha radiation
- as it has the highest ionizing power
- at long distances gamma radiation would be the most hazardous
- as it has the highest penetrating power
- medium distance: beta is more hazardous than gamma as it has a higher ionizing power but less hazardous than alpha
Give 4 sources of background radiation (natural + man-made
natural:
- rocks
- cosmic rays from space
man-made:
- nuclear power / weapons
- medical imaging
Define background radiation
- low-level radiation that is around us all the time
What is the unit used to measure radiation dosage?
- sieverts (Sv)
What factor determines how dangerous a particular radioactive isotope is?
- the half life of the isotype
What factor determines how dangerous a particular radioactive isotope is?
- the half-life of the isotype
Why are isotypes with long half-lives particularly harmful?
- they remain radioactive for much longer particularly periods of time
State two uses of nuclear radiation in the field of medicine
- Examining of internal organs
- Controlling and destroying unwanted tissue
State a use for each type of radiation
alpha: smoke detectors
beta: used in medical tracers to explore internal organs
gamma: treat cancer cells or sterilisation
Explain the process of radiotherapy using gamma radiation
- gamma emitters direct gamma rays at the cancerous cells
- the cancerous cells absorb the radiation and are killed
Describe how radioactive tracers’ work (4)
- patients drink a small amount of radioactive isotype that emits ionizing radiation (beta or gamma)
- the tracer passes through the organ
- if the organ is healthy, the tracer will flow through it in the blood
- if the organ is blocked, the tracer will be stopped, and radiation will be detected for longer
give 4 properties a medical tracer must have to be chosen
- must emit radiation that can be detected (high penetrating power) from outside the body
- must not be strongly ionizing to minimize damage to the body tissue
- must have a short half life
- must not decay into another radioactive isotype
Describe how nuclear radiation is used to destroy a tumor using a radioactive implant. Include details about half life (4)
- small implant of radioactive isotype placed in tumor
- radiation from isotype destroys cancer cells
- use isotype with short half-lives to ensure healthy cells are not damaged
- do not make half times too short otherwise the radiation would not have time to kill cancer cells
Explain why the source chosen for a tracer should have a short half life (2)
- as short half-life means the level or radiation
- decreases rapidly
How can workers reduce their exposure to radiation (2)
- protective clothing such as lead lines coats
- reduce exposure times
Describe the process of nuclear fusion (4)
- an unstable nucleus
- must absorb a neutron
- the nucleus splits into two smaller nuclei
- and releases 2 or 3 neutrons and energy
What is a chain reaction in terms of nuclear fission?
- when the neutrons released in a fission reaction cause further fission reations
Describe a chain reaction in terms of nuclear fission
- each released neutron from nuclear fission, if travelling at the right slow speed, can be absorbed by another nucleus causing further fission reactions
What is the consequence of an uncontrolled chain reaction
- the rate of fission events becomes to high and results in the production of too much energy
- this can led to a nuclear explosion
What are the three main components of the core a nuclear reactor?
- fuel rods
- control rods
- moderator
What is the role of the moderator in a nuclear reactor?
- to slow down the neutrons so they are travelling at speeds which allow them to be absorbed by fissile nuclei and cause fission
Why is the reactor in a thick steel vessel, surrounded by concrete ( 2 )
- to withstand the high temperature and pressure in the nuclear reactor core
- steel absorbs any ionising radiation that escapes
Explain what happens in the process of nuclear fusion (3)
- light nuclei
- join to form a heavier nucleus
- mass of the nuclei is converted to energy
give the approximation for the radius of an atom
1 x 10 “ -10 metres
What are the three subatomic constituents of an atom
- proton
- neutron
- electron
where is the mass of an atom mostly concentrated
in the nucleus
Approximately what proportion of the total radius of an atom is the radius of the nucleus
1/ 10,000 metres
Describe the arrangement of protons , neutrons and electrons in an atom
- the protons and neutrons are found in the atom’s nucleus
- the electrons are found in discrete energy levels around the nucleus
what type of charge does the nucleus of an atom have? Why?
- positive charge
- the nucleus contains protons and neutrons
- protons have a positive charge
- neutrons have no charge
Give two ways that an atom’s electron arrangement can be changed
- Absorbing electromagnetic radiation
- Emitting electromagnetic radiation
Explain how an atom’s electron arrangement changes when it absorbs EM radiation.
- electrons move further from the nucleus
- to a higher energy level.
Explain how an atom’s electron arrangement changes when it emits EM radiation.
- electrons move closer to the nucleus
- to a lower energy level.
How does the ratio of electrons to protons in an atom result in the atom having no overall charge?
- the number of protons is equal to the number of electrons
- protons and electrons have equal and opposite charges, so charge cancels out
What do all forms of the same element have in common?
- they all have the same number of protons
what is the atomic number
the number of protons in an atom
what is the mass number ?
- the total number of protons and neutrons in the atom
what is an isotope of an atom?
- an atom of an element that has the same number of protons but different numbers of neutrons
how do atoms turn into positive ions?
- they lose one or ore of their outer elcteons
- electrons are negatively chatged, so the resultant charge of the atom is postive
What may lead to a scientific model being changed or replaced?
- the discovery of new experimental evidence which doesn’t agree with the existing theory
How did the plum-pudding model describe the atom?
- a ball of positive charge, with negatively charged electrons distributed evenly throughout it
Prior to the discovery of the electron, what was believed about the atom?
- the atom was believed to be indivisible
what experiment led to the plum-pudding model being discarded?
Rutherford’s alpha scattering experiment
What is given to the currently accepted model of the atom
- The Bohr nuclear model
State the conclusions of the Alpha-Scattering experiment
- most of the mass of the atom is concentrated at the centre in the nucleus
- the nucleus is positively charged
What reinforces a scientific theory?
- when experimental results agree with the hypothesised theoretical calculations and theories
What did James Chadwick’s experiments on the atom prove?
- the existence of neutrons
How did Niels Bohr adapt this
model? ( The Alpha Scattering experiment)
He suggested that electrons orbit the nucleus at specific distances
Why do unstable nuclei give out radiation?
- unstable nuclei undergo decay to become more stable
- as they release radiation their stability increases
what is radioactive decay?
when unstable nuclei give out radiation to become more stable
Define the term ‘ activity ‘ of an unstable nucleus
activity is the rate of decay of a source of unstable nuclei
What is the unit for radioactive activity?
- Becquerel (Bq)
define ‘ count-rate’?
- the number of radioactive decays per second for a radioactive source
Give an example of a detector that may be used to measure count-rate
Geiger-Muller tube
State 4 types of nuclear radiation
- Alpha particles
- Beta particles
- Gamma rays
- Neutrons
what are alpha particles made up of and give the range of an alpha particle through air?
- two protons and two neutrons
- it is the same as the helium nucleus
- a few centimetres of air
what are beta particles and what will stop it from passing through a point
– a high speed electron
- ejected from the nucleus as a neutron turns into a proton
- a thin sheet of aluminium/ several metres of air
What does gamma radiation consist of and what will stop it from passing through a point?
- a gamma ray (γ) – electromagnetic radiation
from the nucleus - several cm of lead / a few metres of concrete
which type of nuclear radiation is
the most and least ionising?
Most ionising - alpha
slightly ionising - beta
least ionising - gamma
State any changes to mass or charge that occur due to the emission of a gamma ray
both mass and change remain unchanged
Describe the nature of radioactive decay
- random
- the nuclei which decays and when is determined only by chance
- it is impossible to predict which nuclei will decay and when
Define the half-life of a radioactive isotope
- the time it takes for the number of unstable nuclei in a substance to halve
- the time it takes for the count-rate from a sample to fall to half its initial level
what is radioactive contamination?
- the presence of unwanted radioactive nuclei on other materials
what is irradiation?
- the process of exposing a material to nuclear radiation
- the material does not become radioactive
why is it important for the results of studies on the effects of radiation to be published and shared with other scientists?
- to allow the findings to be independently checked
- this is known as peer review
. State a use of alpha particles:
They are used in smoke alarms, as smoke
particles will stop alpha particles from reaching a detector
State a use of beta particles:
- Thickness monitoring of paper or aluminium
sheets. - The beta must be able to pass through the sheet to be detected and different amounts will be detected if the sheet is too thin or too thick.
State a use for gamma rays:
They have several uses in medicine; the kill
cancer cells, to sterilise medical equipment and in radioactive tracers
why is ionising radiation dangerous ?
It can damage the DNA in cells which can cause them to replicate uncontrollably into tumours
Give 4 sources of background radiation
- Rocks
- Cosmic rays from space
- Nuclear weapon testing
- Nuclear accidents
How should background radiation be dealt with in calculations?
The background count should be subtracted from any readings before calculations ( half life etc.) are attempted
what is the unit used to measure radiation dosage?
Sieverts ( Sv)
Why might the radiation dosage that different people experience differ?
- some occupations involve working with radiation
- background radiation differs with location due to things such as the locality of nuclear power stations or radiation related testing
Which factor determines how dangerous a particular radioactive isotope is?
- the half-life of the isotope
Why are isotopes with long half-lives particularly harmful?
- they remain radioactive for much longer periods of time
- they must be stored in specific ways to avoid humans and the environment from being exposed to radiation for too long
rab
bles
How is radiation used in sterilisation?
- gamma emitters are used to kill bacteria/ parasites on equipment
i do not
consent
How are medical tracers chosen?
- they should have a short life and decay into a stable isotope which can be excreted
- they should only release gamma radiation since it is weakly ionising and can easily pass through body tissue without damaging it
How is an alpha particle represented in a nuclear equation
4 He
2
how is a beta particle represented in a nuclear equation?
0 e
-1
What changes to the nucleus does
emission of nuclear radiation cause?
Changes to the mass and/or charge of the
nucleus.
