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P7 Radioactivity (Nuclear Radiation (Radioactivity Dangers (Radiation Type…

- - - - forces not in balance with electrostatic repulsion of protons)
        
        nuclei become stable by radioactive decay
        
        a random process not affected by external conditions
        
        cannot be predicted
        
        cannot be sped up (e.g. by temperature or pressure)
        
        emitting radiation
  - - - idea of atoms before nucleus discovered
        
        a sphere of diffuse positive charge
        
        with electrons embedded inside
    - - Alpha particle Scattering experiment
        
        Ernest Rutherford, Hans Geiger and Marsden
        
        fired alpha particles at a very thin gold foil
        
        source of alpha particles contained in a lead box
        
        experiment done in a vacuum
        
        alpha particles only travel a few cm in air
        
        most α particles passed straight through
        
        most of atom is empty space
        
        nucleus is small
        
        some α particles deflected through small angles
        
        nucleus is positively charged
        
        small number of α particles deflected at large angles
        
        nucleus contains a concentrated mass
      - predicted existence of neutrons
    - - electrons orbit nucleus at specific energy levels
        
        electrons absorb electromagnetic radiation
        
        to move away from nucleus
        
        electrons emit electromagnetic radiation (as photon)
        
        to move closer to nucleus
    - - found direct experimental evidence for neutrons
        
        uncharged particle to account for mass of nucleus
  - - - atomic number
        
        Z
        
        no. of protons
      - mass number
        
        total no. of nucleons (protons and neutrons)
        
        A
      - chemical symbol
        
        X
    - - same no. of protons
      - different no. of neutrons
  - - - radiation knock electrons out of atoms
        
        atoms become positively charged
    - - objects exposed to ionising radiation are irradiated
        
        *object does not become radioactive
    - - unwanted presence of radioactive atoms on other materials
        
        when radioactive substances contacts other materials
        
        would cause damage over a long time period
    - - Chernobyl
        
        no high-speed shutdown system
        
        operators ignored safety instructions
    - - alpha
        
        very dangerous inside body
        
        affects all surrounding tissue
        
        some danger outside body
        
        absorbed and damages skin, retinal cells
      - beta and gamma
        
        dangerous
        
        reaches cells throughout body
    - - bigger the risk of cancer
        
        high radiation doses kill living cells
- - - - no. of counts per second
  - - - from atmosphere and materials around us
        
        radon gas
        
        decay product of uranium
        
        causes lung cancer
        
        emits alpha particles
        
        damaging when breathed inside body
        
        seeps from radioactive rocks underground
        
        soil, air, rocks, vegetation
        
        cosmic rays
        
        from outer space
  - - - unit of activity is Becquerel (Bq)
        
        1 decay per second
  - - - always takes the same time for sample to halve
        
        half-life is the average time of decay rate
        
        for count rate from isotope to halve its initial value
        
        count rate (after n half-lives) = initial count rate ÷ 2^n
        
        for no. of nuclei of the in sample (so mass) to halve
        
        no. of unstable nuclei (after n half-lives) = initial no. of unstable nuclei ÷ 2^n
    - - has the most unstable nuclei
        
        emit a lot of radiation in a short time
- - - - gamma detector monitors isotope movement form outside of body
      - radioactive iodine
        
        half-life
        
        decays (almost completely) shortly after
        
        avoids unnecessary radiation exposure
        
        long enough to complete imaging or treatment
        
        emits gamma radiation
        
        can be detected outside of body
        
        decays into a stable product
  - - - isotope absorbed by organ
        
        gamma camera detects radiation from directly in front
        
        computer builds up image
  - - - half-life of 5 years
        
        continuous sufficient dose
        
        not exposed to high levels for many years
      - gamma radiation penetrates deep into body
  - - - long half lives
        
        to irradiate tumour in given time
        
        short enough to mostly decay afterwards
- - - - energy - gamma radiation emitted
        
        Induced Fission
        
        nucleus absorbs a neutron fired at it
        
        Spontaneous Fission
        
        fission without absorbing a neutron
  - - - naturally occurring uranium contains >99% Uranium-238
        
        nuclear reactor use enriched (2-3%) Uranium-235
        
        U-238 is non fissionable
        
        can change into other heavier nuclei
        
        e.g. plutonium-239 (fissionable)
    - - used in a separate reactor to U-235 reactors
        
        less commonly used
  - - - cause other fission events to ocuur
  - - - Control rods
        
        absorb surplus neutrons
        
        without undergoing fission
        
        controlled fission
        
        keeps chain reaction under control
        
        one neutron per fission causes chain reaction
        
        rod depth adjusted
        
        to maintain steady chain reaction
      - Moderator
        
        water molecules collide with fission neutrons
        
        slow high-speed neutrons to be more readily absorbed
        
        fast neutrons don't cause further fission
      - Coolant
        
        water cools heating fuel rods
        
        transfers heat from core to heat exchanger
        
        circulates through sealed pipes
        
        water is pressurized
        
        prevent it boiling in the reactor
        
        potential explosion
        
        water turns to steam in secondary chamber
        
        steam from heat exchanger turns turbines
      - thick steel vessel
        
        withstands high temperature and pressure of core
      - enclosed by thick concrete walls
        
        absorbs and limits radiation escaping
    - - with long half-lives
        
        unused uranium and plutonium removed for future use
        
        to be stored securely for many years
- - - - process by which stars release energy
      - energy carried away as KE of product nucleus and particles
    - - heating to high temperatures and pressures
        
        passing an big electric current through
        
        plasma contained using a magnetic field
        
        stops plasma touching container edges and cooling
        
        gas heated to plasma of small nuclei
        
        nuclei with no electrons
        
        energy needs to be inputted
        
        attempts so far use more energy than released
        
        fusion reactors still being developed
      - colliding nuclei at very high speed
    - - deuterium + tritium → helium + neutron
  - - - deuterium extracted from water
      - tritium is made from lithium
    - - produce large amounts of energy per mass
    - - no greenhouse or pollutant emissions
    - - no chain reactions to control
    - - products are not radioactive
      - reactor walls absorb neutrons and become radioactive
    - - products not suitable for making nuclear weapons
- - - - a neutron changes >> a proton and an electron
        
        beta particle emitted
        
        high speed electron
        
        smaller and faster
        
        less ionising (less collisions)
        
        more penetrating (travel further)
        
        2 more items...
        
        relative mass is 0
        
        mass number remains same
        
        relative charge is -1
        
        large deflection by magnetic and electric field
        
        proton stays in nucleus
        
        atomic number += 1
    - - gamma ray
        
        an electromagnetic wave
        
        weakly ionising
        
        highly penetrating (travels long way)
        
        absorbed by thick lead (cm)/ concrete (m)
        
        unlimited range in air
        
        no charge and no mass
        
        no change in atomic or mass number
        
        not deflected by magnetic or electric field
    - - alpha particle emitted
        
        2 protons 2 neutrons
        
        helium nucleus
        
        largest
        
        strongly ionising (many collisions)
        
        least penetrating
        
        2 more items...
        
        relative mass is 4
        
        mass number - 4
        
        relative charge is +2
        
        atomic number - 2
        
        small deflection by magnetic and electric field
    - - when alpha particles collide with unstable nuclei
        
        nuclei becomes more unstable
        
        a neutron emitted
        
        uncharged
        
        pass through substances easier than α or β