Atoms and Nuclear Radiation

• Radioactive DECAY

  • most atoms have stable nucleus- not radioactive
  • some atomic nucleus are unstable
  • the nucleus gives out radiation as it changes to become more stable
• Activity

  • number of unstable nuclei of a source that decay each second (also called the rate at which nuclei decay)
  • measures in becquerels (Bq) which is 1 decay per sec.
  • as nuclei in a source decay and become stable, activity decreases since the number of radioactive nuclei decreases
• Count Rate

  • number of decays recorded each second by a detector
  • proportional to activity of a source, depending on detector distance from source - so count rate decreases with time
• Geiger Muller Tube

  • alpha or beta radiation enters tube, creates IONS between the WIRE and TUBE
  • the effect is like a PULSE of current that the counter registers
• Photographic Film

  • 'blackened' by radiation
  • more exposure, blacker film
• ALPHA

  • stopped by: 5CM OF AIR / SKIN / THIN METAL
  • very ionising as it has a large mass and charge
  • charge: +2e
  • speed: heavy and slow (mass of 4)
  • atom type: helium nucleus, 2P / 2N / 0E
• BETA

  • stopped by: METAL / 5MM ALUMINIUM / 2-3MM LEAD / 1M AIR
  • medium ionising ability (lower mass and weaker charge than alpha_
  • charge: -1e
  • speed: quite fast + light (negligible mass)
  • atom type: 1 high speed electron (0P / 0N / 1E)
• GAMMA

  • stopped by: SEVERAL CM OF LEAD / 1M CONCRETE / UNLIMITED IN AIR, WON'T BE STOPPED
  • not very ionising, has no mass or charge
  • charge: none, it's neutral
  • speed: 3x10^8 m/s
  • atom type: wave (on electromagnetic spectrum) NOT AN ATOM
• NEUTRON

  • stopped by: HYDROGEN RICH SUBSTANCES, LIKE CONRETE OR WATER / 100s or 1000s OF M IN AIR
  • unable to ionise an atom directly due to lack of charge - they're absorbed by a stable atom to become unstable and therefore radioactive
  • charge: neutral
  • speed: N/A
  • atom type: sub-particle
• Alpha decay

  • cause nucleus to lose 2 protons and 2 neutrons - atomic number decreases by 2, atomic mass by 4 and relative charge to reduce by 2
  • the element moves up 2 places in the periodic table
• Beta Decay

  • cause a neutron to turn into a proton in the nucleus, so gain 1 proton and lose 1 neutron
  • atomic number increase by 1, atomic mass stays same and relative charge of nucleus increases by 1
  • the element moves a place down in the periodic table
• Gamma

  • a wave not a particle, so no radioactive decay equation
  • element doesn't change as atomic number and mass stay the same
• Neutron

  • emission of a neutron causes atomic number to stay the same, atomic mass reduces by 1 and relative charge of nucleus to stay same
  • the element doesn't change
• HALF LIVES

  • radioactive decay is spontaneous, it's also not affected by temperature (external conditions)
  • the half life of a radioactive isotope is the average time is takes for the number of unstable nuclei of the isotope in a sample to HALVE.

  
• • nuclei with shorter half lives are more unstable
• HALF LIFE FORMULA

  • C = initial count rate OR mass / 2 to the power of half lives
  • C is count rate/mass after () half lives
• Contamination

  • the unwanted presence of materials containing radioactive nuclei
  • the hazard from this is due to the decay of the contaminating atoms
• example of CHERNOBYL

  • 1986 an accident occurred in a reactor causing the core to overheat and create a steam explosion which breached its containment building
• IRRADIATION

  • the exposure to nuclear radiation
  • the irradiated object doesn't become radioactive, eg sterilising food or medical equipment
  • they're exposed to radioactivity to kill bacteria
• Why irradiate food?

  • insect disinfestation - pulses, fish
  • quarantine - fruits
  • pathogen reduction
  • shelf life extension
  • sprout inhibition
• Examples of irradiation

  • cancer patient is exposed to external radioactivity to kill cancer cells during radiotherapy - doesn't become radioactive
• Dangers of contamination and irradiation

  • high doses can kill living cells
  • lower doses causes ionisation of living cells which can lead to mutations and cancer
• Dangers of contamination and irradiation

  • irradiation poses risk when process is occurring, but materials or people exposed don't become radioactive if there's no contamination
  • dangers of exposure to materials emitting radioactivity and electromagnetic waves such as X-rays - benefit has to outweigh risk
• reduce exposure to ionising radiation

  • keep safe distance from radioactive source (tongs, etc)
  • minimise time of exposure
  • use shielding like led aprons or concrete/brick walls between sources and personnel
  • danger also relates to the radiation type, eg alpha is quite harmless outside the body
• Why does information need to be peer reviewed?

  • there may be factors in addition to those studied
  • evidence may not be valid or there may not be sufficient evidence to draw a correct conclusion
  • there may be an incomplete understanding of the process