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Physics Paper 1 > Atomic Structure and Radioactivity > Flashcards

Atomic Structure and Radioactivity Flashcards

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1
Q

Describe the First Atomic Model

A

-Discovered by John Dalton in 1800.

-Atoms were tiny spheres that could not be divided.

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2
Q

Describe the Plum Pudding Model of the Atom

A

-Discovered by JJ Thompson in 1897.

-Atoms were balls of positive charge with negative electrons embedded inside of it.

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3
Q

Describe the Nuclear Model of the Atom

A

-Discovered by Ernest Rutherford in 1909/ 1910.

-Atoms contained negative electrons circling a positive nucleus.

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4
Q

Describe the Adapted Nuclear Model of the Atom.

A

-Discovered by Niels Bohr in 1913.

-Electrons orbit the nucleus at specific distances. They are in shells.

-In 1932, James Chadwick discovered neutrons in the nucleus along with protons.

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5
Q

Compare the Plum Pudding and Nuclear Models of the Atom.

A

Plum Pudding:
-solid ball
-positive charge spread throughout atom

Nuclear:
-mostly empty space
-positive charge in centre
-almost all mass concentrated in nucleus

Both:
-electrons
-neither have neutrons
-both have positive charge

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6
Q

Describe what the Scientists Did in the Alpha-Scattering Experiment

A

-The scientists took a piece of gold foil (sometimes called gold leaf).

-They bombarded this with a stream of alpha particles.

-The scientists then placed detectors around the gold foil to see where the alpha particles went.

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7
Q

Explain why Gold Foil was used in the Alpha-Scattering Experiment

A

-The scientists wanted to use a piece of metal that was only a few atoms thick.

-Gold is extremely malleable and can be hammered very thinly. Gold foil can be made which is only around a hundred atoms thick.

-Gold was also the most stable element available.

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8
Q

Describe the Observations and Conclusions from the Alpha- Scattering Experiment.

A

-Most of the alpha particles passed straight through the gold foil. This shows there must be very few collisions with the atom, suggesting that the atom is mostly empty space.

-Some of the alpha particles were deflected. Only positive charges can repel other positive charges.

-This shows that the nucleus of an atom must be positively charged if it repels the positive alpha particle.

-Very few of the alpha particles deflected straight back towards the source. Only particles which hit the nucleus exactly would do this.

-This shows all of the charge of the atom, and therefore all of the mass of the atom must be concentrated into a small area.

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9
Q

State the Radius of the Atom and the Nucleus of the Atom

A

Atom= 0.1nm (1x10 to the power of -10)

Nucleus= 10 to the power of -14m (1/1000 size of atom)

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10
Q

Describe what is Meant by Relative Atomic Mass

A

The relative atomic mass is an average of the masses of each isotope, taking into account the abundance of each isotope (how common the isotope is).

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11
Q

Sate the Relative Charge of Protons, Neutrons and Electrons

A

Proton- +1
Neutron- 0
Electron- -1

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12
Q

State the relative mass of Protons, Neutrons and Electrons

A

Proton- 1
Neutron- 1
Electron- almost zero (1/ 2000)

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13
Q

State the Location of Protons, Neutrons and Electrons in the Atom

A

Proton- nucleus
Neutron- nucleus
Electron- on the electron shell

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14
Q

Explain why the Nucleus has an Overall Positive Charge

A

The nucleus has an overall positive charge because it contains protons, which are positive.

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15
Q

Explain why the Charge on the Nucleus Does Not Depend on the Number of Neutrons

A

The charge on the nucleus does not depend on the number of neutrons because neutrons are neutral (they have no charge).

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16
Q

Explain why Atoms Have No Overall Charge.

A

-There are an equal number of electrons and protons in an atom so their charges cancel each other out.

-There are also neutrons in an atom but theses have no charge so the atoms’ overall charge remains at zero.

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17
Q

State how you Would Calculate the Number of Neutrons in an Atom

A

Number of neutron= Mass number- Atomic number

(Big number - Little number)

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18
Q

Describe what is Meant by an Isotope

A

-Isotopes are atoms of an element with the same number of protons but a different number of neutrons

-Isotopes have the same chemical properties but may have slightly different physical properties because of the different mass to the stable atom

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19
Q

Describe what is Meant by Radiation

A

-Radiation is the emission of matter or energy from an unstable nucleus (usually an isotope).

-In a radioactive isotope, the nucleus is unstable. The nucleus becomes stable by giving out radiation. This is called radioactive decay.

-Radiation is spontaneous and random. This is because scientists cannot predict when any individual nucleus will decay.

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20
Q

Explain why the Count Rate of a Radioactive Substance Will Not be the Same as its Activity

A

-The activity of the sample is the number of decays every second. A Geiger-Muller (GM) tube detects radiation produced by radioactive decay.

-However, if we pointed a GM tube at the sample, the GM tube would detect decays from the sample plus decays occurring due to natural background radiation.

-Therefore the count rate of the GM tube would not be the same as the activity of the sample.

-A radioactive sample emits radiation in all directions. A
GM tube only detects radiation which passes into the tube.

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21
Q

Describe what Happens During Radioactive Decay

A

-When they decay, radioactive substances spit out one or more types of ionising radiation from their nucleus - alpha, beta and gamma.

-They can also release neutrons when they decay, as they rebalance their atomic and mass numbers.

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22
Q

Describe the Radioactive Decay of Alpha Radiation

A

-Alpha particles are made up of 2 protons and 2 neutrons. This is the same as helium nucleus. It has a relative charge of +2 and a relative mass of 4.

-When alpha decay occurs, the atom undergoing the decay would lose 2 neutrons and 2 protons from the nucleus. This means the atomic number would decrease by 2 and the mass number decrease by 4.

-This would cause the atom to change into another element.

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23
Q

Describe the Penetration Power of Alpha Particles

A

-Alpha particles don’t penetrate very far into materials and are stopped quickly.

-They are absorbed by a sheet of paper and can only travel around 5cm in air.

-Because of their size, they are strongly ionising.

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24
Q

Explain why Alpha particles Stop After Travelling a Short Distance in Air

A

-Alpha particles are extremely large and are travelling relatively slowly (compared to beta and gamma).

-They collide with a large number of air particles, losing energy each time until they stop.

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25
Q

Describe the Radioactive Decay of Beta Radiation

A

-Beta particles are made up of fast moving electrons. It has a relative charge of -1 and a relative mass of effectively 0.

-Beta is a nuclear radiation so the electron comes from the nucleus not from the electron shells. A neutron becomes a proton and an electron. The electron is released at a very high speed.

-When beat decay occurs, the atom undergoing the decay would lose 1 neutron and would gain a proton in the nucleus. This would increase the atomic number by 1 but would not change the mass number.

-This would cause the atom to change into another element.

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26
Q

Describe the Penetration Power of Beta Particles

A

-Beta particles penetrate moderately far into materials.

-They are absorbed by a sheet of aluminium can travel 15cm to 1m in air depending on the energy of the particle.

-Beta particles are moderately ionising.

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27
Q

Explain why Beta Particles Travel Further in Air Than Alpha Particles

A

-Beta particles are smaller than alpha particles. This helps to explain why beta particles travel further in air than alpha particles.

-Beta particles are also moving many times faster than alpha particles which also explains why they can pass through a greater distance in air before stopping

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28
Q

Describe the Radioactive Decay of Gamma

A

-Gamma waves are electromagnetic waves. It has a relative charge of 0 and a relative mass of 0.

-When gamma decay occurs the atom undergoing the decay would lose 0 neutrons and 0 protons from the nucleus. This would not change either the atomic or mass numbers.

-This would not cause the atom to change into another element.

29
Q

Describe the Penetration Power of Gamma

A

-Gamma waves penetrate far into materials without being and will travel a long distance through air.

-This means they are weakly ionising because they tend to pass through rather than collide with atoms. Eventually they hit something and do damage.

-Gamma waves are slowed by thick sheets of lead or metres of concrete but cannot be stopped.

30
Q

Explain how Radiation can Cause the Formation of Ions

A

-When radiation collides with atoms, the radiation has enough energy to knock outer electrons off the atom. This is ionisation.

-Alpha particles have an extremely large mass and carry a lot of energy. For this reason alpha particles are strongly ionising.

-Beta particles have a much smaller mass and carry less energy. This means that beta particles are less ionising than alpha particles.

-Gamma radiation is an electromagnetic wave (not a particle). As gamma radiation has a relatively low energy, it is the least ionising radiation.

-The ionising power of a radiation source is how easily it can do this.

31
Q

Describe how Alpha Radiation is Used in Smoke Detectors

A

-Smoke detectors contain a source of alpha radiation. In normal use, the alpha particles produce ions in the air. The ions are attracted to the negatively charge metal plate. This generates an electrical current.

-If smoke is present, the smoke particles attach to the ions and prevent them from moving. The electrical current now falls. This is detected by the alarm circuit, which activates the alarm.

32
Q

Explain why Alpha Radiation is Used in Smoke Detectors Rather than Beta or Gamma

A

-Alpha radiation is easily stopped by plastic.

-This means that none of the alpha radiation from the radioactive source can penetrate the plastic case and present a hazard to anyone nearby.

-Both beta radiation and gamma radiation could penetrate through the plastic. This would mean that anyone near the smoke detector could be irradiated by the beta or gamma source.

-For this reason, beta and gamma sources are never used in smoke detectors.

33
Q

Explain why Beta and Gamma Radiation Would Not be Effective in a Smoke Machine

A

-Alpha radiation is the most ionising radiation and generates a large amount of ions in air.

-However, beta and gamma radiation are both less ionising than alpha radiation.

-This means that beta and gamma radiation would be less effective in the smoke detector (making the smoke detector less sensitive to smoke).

34
Q

Describe what is Meant by Half Life

A

-Radioactive decay is a random process. Scientists cannot predict when any nucleus will decay. Instead, scientists measure the half-life.

-This is the time it takes for the number of undecayed nuclei in a sample to halve.

-The half-life is also the time taken for the count rate to fall to half its original level.

35
Q

Explain how to Calculate Half Life on a Graph

A

-Choose any value on the y-axis. Draw a line from this to the curve. At this point, draw a line down to the x- axis. This is the corresponding value.

-Find half of the first value on the y-axis and then find its corresponding value.

-The difference between the values on the x-axis is the half life.

36
Q

Explain how to Calculate Half Life From a Question

A

-Draw a table with Activity on one side and Number of Half-Lives on the other.

-Write the initial activity of the given element into the table and next to it write 0. Then half this original value and write one next.

-Continue halving the activity and increasing the number of half-lives by 1 until you reach the second given activity in the question.

-Divide the number of years in the question by the number of half-lives in the table. This value is the half-life of the element.

37
Q

Describe What is Meant by Irradiation

A

-Objects near a radioactive source are irradiated by it. This means they’re exposed to it.

-Irradiating something does not make it radioactive.

-Keeping sources in lead-lined boxes, standing behind barriers or being in a different room and using remote controlled arms to hold sources are ways of reducing the effects of irradiation.

38
Q

Describe What is Meant by Contamination

A

-If unwanted radioactive atoms get onto or into an object, the object is said to be contaminated.

-These contaminating atoms might then decay, releasing radiation which could cause you harm.

-Contamination is especially dangerous because radioactive particles could get inside your body.

-Gloves and tongs should be used when handling sources, to avoid particles getting stuck to your skin or under your nails. Some industrial workers wear protective suits to stop them breathing in particles.

39
Q

Explain why a Syringe is Wrapped in a Plastic Wrapper When Being Sterilised by Irradiation With Gamma Rays

A

-When the syringe is irradiated with gamma rays, the gamma rays will destroy any microbes on the syringe. This is because intense gamma radiation is ionising.

-However, once we remove the syringe from the box, it can now be re-infected with microbes. To prevent this, the syringe is sealed inside a plastic wrapper.

Gamma rays can easily penetrate the plastic and destroy any microbes. However, once the syringe is removed from the box, no microbes can now get through the plastic wrapper and reinfect the syringe.

40
Q

Give an Advantage of Using Irradiation to Sterilise Equipment Compared to Sterilisation by Heating

A

An advantage of using irradiation to sterilise equipment is that some equipment is damaged by heating.

41
Q

Explain why a Syringe Does Not Become Radioactive After it has Been Irradiated

A

-While the syringe is inside the lead box, it is exposed to gamma radiation. This means that it is being irradiated.

-However, none of the gamma source will ever touch the syringe (or the plastic wrapper). This means that the syringe and the plastic wrapper cannot become radioactive.

42
Q

Why is it Important that People are Not Exposed to Gamma Radiation

A

-Gamma radiation is ionising and penetrating.

-If a worker is exposed to gamma radiation, it can pass through their skin and ionise molecules in the worker’s cells.

-This will increase the risk of the worker developing cancer.

43
Q

Explain why Lead Aprons are Not Required When Working With Alpha Radiation

A

-Beta and gamma radiation are both much more penetrating than alpha radiation. Alpha radiation is easily stopped by the skin (and by simple wearing a pair of plastic gloves).

-However, both beta and gamma radiation would easily penetrate plastic gloves and irradiate the person’s body (increasing the risk of cancer).

-Therefore, when regularly working with beta or gamma radiation, we should wear a lead apron to prevent the radiation from penetrating into the body.

44
Q

Explain the Purpose of Radiation Monitors

A

-Radiation monitors allow a person to check how much radiation their body has been exposed to.

-Although any radiation is potentially harmful, scientists have determined the levels that are considered safe.

-If a radiation monitor shows that a person has been exposed to the safe limit for radiation, then that person can stop working in the radioactive area.

45
Q

Explain the Seriousness of Radiation Outside of the Body

A

-Outside the body, beta and gamma are most dangerous. This is because beta and gamma can penetrate the body and get to the delicate organs.

-Alpha is less dangerous because it can’t penetrate the skin and is easily blocked by a small distance of air.

-High levels of irradiation from all sources are dangerous but especially from ones that emit beta or gamma.

46
Q

Explain the Seriousness of Radiation Inside the Body

A

-Inside the body, alpha sources are the most dangerous because they do all their damage in a very localised area. So contamination rather than irradiation is the major concern when working with alpha sources.

-Moreover, alpha can only travel short distances in air so cannot exit the body.

-Beta sources are less damaging inside the body as radiation is absorbed over a wider area and some passes out of the body.

-Gamma sources are least dangerous inside the body because they mostly pass straight out- they have low ionising power.

47
Q

Describe what is Meant by Background Radiation

A

Background radiation is radiation from the environment. Background radiation is present all the time.

48
Q

State Different Sources of Background Radiation

A

Some sources of background radiation are natural whereas other are artificial:

Air (Radon Gas) - 50%
Medical - 14%
Ground (Rocks) -14%
Food and Drink - 11.5%
Cosmic - 10%

Other - 0.5% :
Nuclear Weapons -0.2%
Air Travel - 0.2%
Nuclear Reactors - 0.1%

49
Q

Explain why the Dose of Background Radiation is Higher in Cornwall than Other Parts of the UK

A

The rocks under Cornwall contain granite. Granite contains natural radioactive isotopes, which increase the level of background radiation.

50
Q

Explain why a Person Receives a Greater Dose of background radiation on a Flight than on the Ground

A

-The background radiation on a transatlantic flight is mainly due to cosmic radiation entering the atmosphere from space.

-Most cosmic radiation is absorbed by the atmosphere, so only a small amount reaches the surface of the Earth.

-However, as airplanes flight at high altitudes, they are more exposed to cosmic radiation.

51
Q

Explain the Risks of Using Radiation

A

-Radiation can enter living cells and ionise atoms and molecules within them. This can lead to tissue damage.

-Lower doses tend to cause minor damage without killing the cells. This can give rise to mutant cells which divide uncontrollably. This is cancer.

-Higher doses tend to kill cells, causing radiation sickness (leading to vomiting, tiredness and hair loss) if a lot of cells all get hit at once.

52
Q

Give the Uses of Radioactive Tracers in Medicine

A

-Radioactive tracers allow doctors to see if a cancer has developed.

-Radioactive tracers can be used to see if organs are functioning normally.

-Tracers can diagnose life threatening conditions while the risk of cancer from one use of a tracer is very small.

53
Q

Explain why Alpha Emitters are Never Used as Tracers in the Body

A

-A radioactive tracer has to emit radiation that can be detected from outside the body (eg using a scanner).

-Any alpha radiation emitted from a tracer inside the body would not be able to penetrate the body and be detected.

-Also, alpha radiation is strongly ionising and would cause a great deal of damage to body cells.

54
Q

Explain why Gamma Emitters Make Better Tracers than Beta Emitters

A

-Gamma radiation is very penetrating so virtually all of the gamma radiation emitted by a tracer will pass out of the body and can be detected.

-Also gamma radiation is the least ionising radiation so is unlikely to damage the patient’s cells.

-Beta radiation is much less penetrating than gamma. This means that a large amount of beta radiation would be stopped by the structures in the body (eg bones). This would make beta radiation hard to detect from outside the body.

-Also, beta radiation is quite ionising so this
would cause a large amount of damage to body cells.

55
Q

Explain why Radioactive Tracers Should have Short Half-Lives

A

-Radioactive tracers must have short half lives so that they do not decay into radioactive isotopes.

-This is because they will continue to decay, producing ionising radiation and damaging the patient’s healthy cells.

56
Q

Describe how Radiation is Used to Kill Cancer in Radiotherapy

A

-Since high doses of ionising radiation will kill all living cells, it can be used to treat cancers.

-Gamma rays are directed carefully and at just the right dosage to kill the cancer cells without damaging too many normal cells.

-Radiation implants (usually beta emitters) can also be put next to or inside tumours.

-However, a fair bit of damage is inevitably done to normal cells, which makes the patient feel very ill. But if the cancer is killed off in the end, the treatment is worth it.

57
Q

Explain the Benefit of Using Radiation Implants in Radiotherapy

A

When a radioactive source is placed inside the body, the radiation is targeted more precisely at the cancerous cells. This means that there is less damage to healthy cells.

58
Q

Give an Advantage and Disadvantage of Using Gamma Rays for Radiotherapy

A

Advantage:
-Gamma radiation is very penetrating. This means that gamma radiation from a gamma source outside the body can pass into the body and destroy cancer cells.

Disadvantage:
-As the gamma radiation passes through the body, it can damage healthy cells.

59
Q

Describe the Procedures that People Working with Radiation Should Take

A

-Use tools to handle radiation.

-Reduce time exposed to radiation.

-Shield themselves (such as with barriers of lead or concrete).

-Monitor exposure with a film badge.

60
Q

Describe what is Meant by Nuclear Fission

A

-Nuclear fission is the splitting of large radioactive nuclei to release energy. It can be spontaneous or induced.

-Spontaneous fission involves a nucleus splitting naturally.

-Induced fission involves firing a neutron at a fissionable substance ( e.g. Uranium-235 and Plutonium-239).

61
Q

Describe the Process of Induced Nuclear Fission

A

-A single neutron is fired at the nucleus of a fissionable substance. This makes it unstable.

-The unstable nucleus will split into two smaller nuclei (daughter nuclei). This releases 2 or 3 neutrons.

-The fission process also releases lots of energy in the form of gamma radiation.

-The neutrons released in nuclear fission can now go on to hit another fissionable nuclei. This is called a chain reaction.

62
Q

Explain how the Energy Produced by Nuclear Fission is Used

A

-Energy not transferred to the kinetic energy stores of the products in fission is carried away by gamma rays.

-The energy carried away by the gamma rays and in the kinetic energy stores of the remaining free neutrons and the other decay products can be used to heat water, making steam to turn turbines and generators.

63
Q

Explain how Nuclear Fission is Controlled

A

-The amount of energy produced by nuclear fission in a nuclear reactor is controlled by changing how quickly the chain reaction can occur.

-This is done by using control rods which are lowered and raised inside a nuclear reactor to absorb neutrons, slow down the chain reaction and control the amount of energy released.

-Uncontrolled chain reactions quickly lead to lots of energy being released as an explosion - this is how nuclear bombs work.

64
Q

Explain why the Walls of a Nuclear Reactor are Very Thick

A

-Nuclear fission releases a great deal of radiation (mainly gamma radiation). Gamma radiation is extremely penetrating and can easily pass through most materials.

-The walls of the reactor are made of thick concrete to prevent gamma radiation from penetrating and irradiating any workers near the reactor.

-The concrete walls also prevent the workers from being irradiated by neutrons. Neutrons are also extremely penetrating.

65
Q

Explain why the Rate of Nuclear Fission is Slowed when Control Rods are Lowered into the Reactor

A

-The control rods absorb neutrons. This means that when a nucleus undergoes fission and releases 2 or 3 neutrons, some of these neutrons are now absorbed by the control rods.

-This means that not all of these 2 or 3 neutrons can then go on to trigger nuclear fission. This slows
down the rate of nuclear fission.

66
Q

Describe what is Meant by Nuclear Fusion

A

-Nuclear fusion is the fusing of smaller nuclei to release energy.

-Some of the mass of the smaller nuclei is converted into energy.

67
Q

Describe the Process of Nuclear Fusion

A

-Two hydrogen nuclei (protons) collide to form a deuterium nucleus (heavy hydrogen) and releases energy.

-A deuterium nucleus collides with another hydrogen nucleus. This forms a nucleus of helium-3 (helium isotope) and releases energy.

-Two helium-3 nuclei collide to form a helium nucleus and two hydrogen nuclei (protons). Energy is again released.

68
Q

Explain why Nuclear Fusion is Not Used to Source Energy on Earth

A

-Currently, scientists have not found a way of using fusion to generate energy for us to use.

-The temperature and pressures needed for fusion are so high that fusion reactors are really hard and expensive to build.

Physics Paper 1 (4 decks)

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