P8 - Atomic Physics

Question 1

An atom

Answer 1

a small positive nucleus, surrounded by negative electrons

Question 2

Ion

Answer 2

An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons

Question 3

Stable atom

Answer 3

One that has the same number of protons and electrons and is normally electrically neutral

Question 4

Positive ion

Answer 4

Atoms which have lost electrons: more protons than electrons

Question 5

Negative ion

Answer 5

Atoms which have gained electrons: more electrons than protons

Question 6

Proton number, Z

Answer 6

The number of protons in an atom (also called the atomic number)
* dictate the order of the elements in the periodic table
* also equal to the number of electrons - in order to have no overall charge

Question 7

Nucleon number, A

Answer 7

Total number of particles in the nucleus (also called mass number)
* number of prtons + number of neutrons

Question 8

Nuclide notation (ZXA)

Answer 8

• Top number A - nucleon/mass number
• Bottom number Z - proton number

Question 9

Nuclide

Answer 9

A nuclide is a group of atoms containing the same number of protons and neutrons

Question 10

Isotope

Answer 10

Isotopes are atoms of the same element that have an equal number of protons but a different number of neutrons
* tend to be more unstable due to this imbalance and are more likely to decay

Question 11

Charge of proton, neutron and electron

Answer 11

• Proton: +1
• Neutron: 0
• Electron: -1

Question 12

Relative atomic mass of proton, neutron, electron

Answer 12

• Proton: 1
• Neutron: 1
• Electron: 1/2000

Question 13

Nuclear charge

Answer 13

The relative charge of the nucleus
* The term ‘relative’ refers to the charge of the particle divided by the charge of the proton
* So, proton number determines relative charge

Question 14

Nuclear fission

Answer 14

The splitting of a large, unstable nucleus into two smaller nuclei

Question 15

Nuclear fusion

Answer 15

When two light nuclei join to form a heavier nucleus

Question 16

Background radiation

Answer 16

The radiation that exists around us all the time

Question 17

Natural sources of background radiation (name and explain 3)

Answer 17

• Radon gas (in the air)
  
  • airborne radon comes from the ground from the natural decay of uranium in rocks and soil
  • tasteless, colourless and odorless but unhealthy
• Rocks and Buildings
  
  • decay of heavy radioactive elements such as uranium and thorium which occur naturally in rocks
• Cosmic rays from space
  
  • collision of protons from the sun with molecules in the Earth’s air lead to gamma radiation production
  • also can come from supernovae
• Carbon-14 biological material
  
  • all organic material contain it but constantly replace the supply of carbon in their system leaving its amount constant
• Radioactive material in food and drink
  
  • naturally occuring radioactive elements can get into food and water since they are in contact with rocks and soil

Question 18

Man made sources of background radiation (name and explain 3)

Answer 18

• Medical resources
  
  • Used in X-rays, CT scans, tracers and radiation therapy
• Nuclear waste
  
  • Does not contribute much to it, it can still be dangerous to the people handling it
• Nuclear fallout from nuclear weapons
  
  • The residue radioactive material that is thrown into the air after a nuclear explosion
  • Presently low in general but would increase significantly in areas where nuclear weapons are tested
• Nuclear accidents
  
  • Though are extremely rare, the can be catastrophic and contribute a large dose of radiation into teh atmosphere

Question 19

Dose

Answer 19

The amount of radiation received by a person is called the dose

Question 20

Count rate

Answer 20

Count rate is the number of decays per second recorded by a detector and recorded by the counter (measured in counts/s or counts/min)
* decreases the further the detector is from the source - radiation becomes more spread out

Question 21

Geiger-Müller cube

Answer 21

The Geiger-Müller tube is the most common device used to measure and detect radiation
* each time it absorbs radiation, it transmits an electrical pulse to a counting machine which makes a clicking sound or displays the count rate
* greater click frequency suggests higher radiation
* lower count, the further away from source

Question 22

Examples of radiation detectors (name 3)

Answer 22

• Geiger-Müller tube
• Photographic film
• Ionisation chambers
• Scintillation counters
• Spark counters

Question 23

Why are some atomic nuclei unstable?

Answer 23

• Because of an imbalance in the forces within the nucleus
• Some isotopes are unstable because of their large size or because they have too many or too few neutrons

Question 24

How can unstable nuclei become more stable?

Answer 24

Emit radiation
* can be in the form of a high energy particle or wave
* as the radiation moves away from the nucleus it takes some energy with it which reduces the overall energy of the nucleus

Question 25

Radioactive decay

Answer 25

The process of emitting radiation is called radioactive decay * it is a random, unpredictable process

Question 26

What does the randomness of radioactive decay mean? (name 3 qualities)

Answer 26

* There is an equal probability of any nucleus decaying * It cannot be known which particular nucleus will decay next * It cannot be known at what time a particular nucleus will decay * The rate of decay is unaffected by the surrounding conditions * It is only possible to estimate the probability of a nuclei decaying in a given time period

Question 27

Two properties of radiation

Answer 27

* spontaneous * random in direction

Question 28

Three types of radiation

Answer 28

* Alpha (α) particles * Beta (β-) particles * Gamma (γ) radiation

Question 29

Describe alpha particles

Answer 29

* Symbol: α * It is the same as a helium nucleus * because it consists of two neutrons and two protons * Have a charge of +2 and so can be affected by an electric field

Question 30

Describe beta particles

Answer 30

* Symbol: β- * Fast moving electrons * Produced in the nuclei when a neutron changes into a proton and a neutron * Have a charge of -1 so they can be affected by an electric field

Question 31

Describe gamma rays

Answer 31

* Symbol: γ * Are electromagnetic waves * Have the highest energy of the different types of electromagnetic waves * Have no charge

Question 32

Charge of three radioactive particles

Answer 32

* Alpha: +2 * Beta: -1 * Gamma: 0

Question 33

Range of three radioactive particles

Answer 33

* Alpha: few cm * Beta: few 10s of cm * Gamma: ifinite

Question 34

Penetration of three radioactive particles

Answer 34

* Alpha: stopped by paper * Beta: stopped by few mm of aluminium * Gamma: reduced by few mm of lead

Question 35

Ionisation of three radioactive particles

Answer 35

* Alpha: high * Beta: medium * Gamma: low

Question 36

Ionisation

Answer 36

Ionisation is the process of which an atom becomes negative or positive by gaining or losing electrons

Question 37

Ionisation of alpha particles

Answer 37

Alpha is by far the most ionising form of radiation * leave dense trail of ions behind them because of this they quickly lose energy and have a short range * short range makes them relatively harmless if handled carefully but can be dangerous if the alpha emitter enters the body

Question 38

Ionisation of beta particles

Answer 38

Beta particles are moderately ionising * create less dense trail of ions, have a longer range * more dangerous than alpha because they are able to travel further and penetrate the skin

Question 39

Ionisation of gamma rays

Answer 39

Gamma is the least ionising form of radiation (although it is still dangerous) * don't produce as many ions, they are more penetrating and have a greater range * can make them hazardous in large amounts

Question 40

What does ionising effects depend on?

Answer 40

* The kinetic energy of the type of radiation: the higher the kinetic energy of the radiation, the more ionising it is * alpha has the greatest mass, gamma has virtually no mass * The charge: the greater the charge of the radiation, the more ionising it is

Question 41

Parent and daughter nucleus

Answer 41

During α-decay or β-decay, the nucleus changes to a different element * The initial nucleus is called the parent nucleus * The nucleus of the new element is called the daughter nucleus

Question 42

Alpha decay (and equation)

Answer 42

Alpha symbol added to element (remember this is a new element) with a 4 as the mass number (top) and two as proton number (bottom) * Mass number decreases by 4 * Atomic number decreases by 2

Question 43

Beta decay (and equation)

Answer 43

Beta symbol added to completely new element with 0 as mass number (top) and -1 as atomic number (bottom) * a neutron changes into a proton and an electron, e is emitted and p remains in nuclei * mass number stays the same * atomic number increases by 1

Question 44

Gamma decay

Answer 44

Gamma symbol added to the same element * ray is emitted from an unstable nucleus which lessens its enegry but does not change its structure * no change in mass number * no change in atomic number

Question 45

Half-life

Answer 45

The time taken for half the nuclei of that isotope in any sample to decay * it is constant for a particular isotope to decrease from 100% to 50% to 25% etc.

Question 46

How to calculate the half-life froma sample in a graph? (4 steps)

Answer 46

1. Check the original activity (where the line crosses the y-axies) 2. Halve this value and look for this activity 3. Go across from the halved value (on the y-axis) to the best fit curve, and then straight down to the x-axis 4. The point where you reach the x-axis should be the half-life

Question 47

Uses of radiation (name 4)

Answer 47

* Medical procedures including diagnosis and treatment of cancer * Sterilising food (irradiating food to kill bacteria) * Sterilising medical equipment (using gamma rays) * Determining the age of ancient artefacts * Checking the thickness of materials * Smoke detectors (alarms)

Question 48

How is radiation used in smoke detectors?

Answer 48

* Alpha particles are used in smoke detectors * The alpha radiation will normally ionise the air within the detector, creating a current * The alpha emitter is blocked when smoke enters the detector * The alarm is triggered by a microchip when the sensor no longer detects alpha

Question 49

How is radiation used in measuring the thickness of materials

Answer 49

Beta particles can be used for tracing and gauging thickness * As material moves above the beta source, the particles are able to penetrate it can be monitored using a detector * If the material gets thicker, more particles will be absorbed, meaning that less will get through * If the material gets thinner the opposite happens

Question 50

How is radiation used in diagnosis and treatment of cancer?

Answer 50

Gamma rays can be used in radiotherapy * They are directed at the cancerous tumour and are moved around to minimise harm to healthy tissue whilst being aimed at the tumour and kill its cells

Question 51

How is radiation used in sterilising food and medical equipment?

Answer 51

Gamma rays are used widely to sterilise medical equipment * It is the most suitable because: * It is the most penetrating out of all the types of radiation * It is penetrating enough to irradiate all sides of the instruments * Instruments can be sterilised without removing the packaging

Question 52

How can ionising radiation cause damage? (4)

Answer 52

* Cell death * Tissue damage * Mutations * Cancer

Question 53

What can acute radiation exposure cause?

Answer 53

* It can cause skin burns, similar to severe sunburn * Radiation can reduce the amount of white blood cells in the body, making a person more susceptible to infections by lowering their immune system

Question 54

How to handle radioactive sources safely (for students)? (name 4)

Answer 54

* Keep the source in a lead lined container until the time it is needed * Use tongs to move the source, rather than handling it directly * The source should be kept at as far a distance from the student as possible during the experiment * The time that the source is being used should be minimised * After the experiment the student should wash their hands * The date and the time that the radiation has been used for should be recorded

Question 55

How is radioactive waste disposed of?

Answer 55

Radioactive waste with a long half-life is buried underground to provenet it from being released into the environment