P5 - nuclear physics Flashcards
define isotope
-atoms of the same element with the same number of protons & electrons but different numbers of neutrons
-most elements have them with 1 or 2 stable ones
-the unstable isotopes decay & emit radiation
similarities & differences between different isotopes
same:
-no. protons
-no. electrons
-charge
different:
-heavier
-diff. mass no.
-no. neutrons
nucleus
-contains the proton & neutron
-where the mass is concentrated
charge of the nucleus
positive because of the proton
atomic number
-proton number
-nuclide notation: Z
mass number
-nucleon number
-nuclide notation: A
nuclide notation
A
element
Z
what is fission & fusion
-fission - large nucleus splits into daughter nuclei; chain reaction eg. nuclear power station
-fusion - 2 small nuclei join into a heavier nucleus eg. stars
-both produce lots of energy
evidence of the atomic structure: Rutherford, Geiger, Mursden
-Alpha particles are sent to an atom
-particles either deflected fully, deflected slightly or bound off from the nucleus
-conclusion: atom is mostly an empty space & most of its mass is concentrated at its nucleus
background radiation
-radiation in the surroundings all the time
define radioactive substance
substance that decays by emitting radiation from its atonic nuclei
2 harmful ways radioactive substances touch us
1) contamination - radioactive substance gets inside the body
2) irradiation - radiation/ radioactive substance hits our bodies
natural sources of radiation
1) radon - radioactive gas that comes from radioactive uranium rocks underground
2) ground & rocks - contains radioactive substances; use materials form the ground to build buildings & houses
3) space - cosmic rays
artificial sources of radiation
medical sources:
1) X rays
2) Gamma rays - to destroy cancer cells
3) medical radiographers
nuclear power stations:
how to detect radiation
-use a Geiger’s counter
-records the rate of radiation (count rate)
-counts per seconds/ minutes
how does Geiger’s counter work
-when radioactive particle enters the tube, it ionizes the gas inside & triggers an electrical discharge with a click sound
-signal is sent to the electronic counter that registers the number of clicks
Geiger’s counter disadvantage
-count rates includes background radiation & the radioactive source
-correct count rate = measured count rate - background count rate
define radioactive decay
- random process when an unstable nucleus gives out
radiation to become more stable
-random process, direction of emission is random
-not affected by external factors eg. temp
when does a nucleus become unstable
1) too many protons
2) too many neutrons
how does radiation ionizing nuclear radiation
-radiation may knock electrons out of atoms
-ions are formed
Alpha particle:
-symbol
-made of
-charge
-in an electric field
-in a magnetic field
-symbol = α
-made of = 2 protons + 2 neutrons (helium)
-charge = +2
-in an electric field = towards the negatively charged plate
-in a magnetic field = Fleming’s left hand rule
range in air = a few cm
Beta particle:
-symbol
-made of
-charge
-in an electric field
-in a magnetic field
-symbol = β
-made of = an electron
-charge = -1
-in an electric field = towards the positively charged plate
-in a magnetic field = Fleming’s left hand rule
range in air = a few 10’s of cm
Gamma rays:
-symbol
-made of
-charge
-in an electric field
-in a magnetic field
-symbol = γ
-made of = electromagnetic radiation
-charge = neutral
-in an electric field = not deflected; uncharged
-in a magnetic field = not moved; uncharged
range in air = infinite
Penetrating power among alpha, beta & gamma
Alpha: weak penetration
-absorbed most easily
-absorbed by a thin sheet of paper
-cannot penetrate skin
Beta:
-easily travels through air/ paper
-absorbed by a few mm of metal eg. aluminum
Gamma: strong penetration
-takes several cm of lead/ concrete to absorb
which material absorbs all types of radiation
lead
ionizing effect among alpha, beta & gamma
Alpha: most ionizing
-speed = 3 x 10^7 m/s (slowest)
-mass = 4
-charge = +2
-slowest moving
-highest charge among them
Beta:
-speed = 2.9 x 10^8 m/s
-mass = 1/ 2000
-charge = -1
-medium moving; more likely to travel past air molecule without interacting with it
-can travel far
Gamma: least ionizing
-speed = 3 x 10^8 m/s (fastest)
-mass = 0
-charge = 0
-fastest moving
-lowest charge among them
Alpha decay equation
-remove 4 from the mass no. & 2 from the atomic no.
-write it in terms of the new element + helium + energy
eg. 241 237 4
Am —-> U + He + energy
94 92 2
Beta decay equation
-add 1 to atomic number (gain 1 proton since 1 electron is removed)
-write in terms of new element + electron + energy
eg. 14 14 0
C ——> N + e + energy
6 7 -1
define activity
-rate of a radioactive source’s nuclei decay
- fewer unstable nuclei with time = activity decreases with time
define half time
-average time taken for half the atoms of a sample to decay
-time taken for its activity to half
Uses of radio isotopes
1) smoke detectors
2) thickness measurement
3) cancer treatment
4) food irradiation
5) sterilization
6) medicine
7) engineering
8) radiocarbon dating
how does smoke detector work using radio isotopes
-smoke detector has a small amount of radioactive material
-alpha particles are emitted which ionize the air in the smoke detector
-smoke particle disrupt the ion flow & trigger the alarm
how does thickness measurement work using radio isotopes
-beta particles are aimed at the paper
-radiation that passes through the paper is detected & measured
-if paper is too thick, radiation passing through will be low
-paper thickness is then adjusted
how does cancer treatment work using radio isotopes
-gamma rays targeted cancer cells to destroy tumors
-source is moved around to ensure the other tissues receive minimal expose to radiation
how does food irradiation work using radio isotopes (preserve food)
-gamma rays kill microbes that cause food decay; sterile food
-used in space or hospitals to prevent infection for patient
how does sterilization work using radio isotopes
-gamma rays on medical devices to kill microbes
-gamma rays can penetrate through plastic = ensures all parts are thoroughly sterilized
how does medicine work using radio isotopes
-to diagnose a blockage in the kidney
-inject a radioactive tracer (technetium -99) in the bloodstream; if it doesn’t pass = blockage
-technetium -99 has a short half life, so safe to use
how does engineering work using radio isotopes
-prevents toxic water from waste contaminating local water supply
-inject water with a radioactive chemical into a hole in the ground.
-movement of water through the cracks is monitored using gamma ray detector from ground level
-allows engineers to track the flow of water & identify pathways that could lead to contamination
how does radiocarbon dating work using radio isotopes
-Carbon 14 in the body decays when living organisms die
-over time, the no. of carbon 14 reduces
-you can measure the amount of carbon on the body & estimate the time it was alive using Carbon 14 half life
-used in archaeology
1) use Geiger’s counter; activity of sample
2) use mass spectrometer; no. of atoms in the sample
3 ways radiation damaged living cells
1) kills a cell
2) causes cancer
3) causes genetic mutations
-either through penetrating or ionization
safety precautions & explanations
1) wear protective suits; radiation if absorbed by suit
2) radioactive hazard signs; inform people about the hazard
3) photographic film dosimeter badges; tracks the amount of radiation a person is exposed to, workers need to be relocated to prevent further exposure
ways to reduce radiation a person can absorb
-minimize exposure time
-maximize distance of person from the substance
-prevent contamination
