63-66;Radioactivity Flashcards
how was scale model of atom discovered
By Sir Rutherford = bombarded thin metal foils w/ alpha particles (Helium) stripped of their 2 e-s = scattering of charged particles by metal atoms
established that mass and positive charges aren’t even distributed but conc in vol v small to vol of atom = nuclear model of atom
nature of nucleus
nucleus of atom contain 99% of mass of atom
nuclear radiation
particles/waves that emanate from atomic nucleus
E associated w/ this radiation = ionising radiation = large enough E to strip e-s from atoms to alter structures
alpha radiation
2 protons and 2 neutrons
Helium nucleus
large mass = short range inside body = not suitable for radiation therapy = hazardous when ingested due to great destructive power
beta radiation
e-
greater range of penetration = less penetrating than gamma rays = hazardous if ingested
gamma radiation
electromagnetic ray
comes from nucleus = very penetrating = useful for radiation therapy but MOST hazardous due to its ability to penetrate large thickness
radioactivity
result of nuclear instability
nucleus emits particle that is transformed into nucleus of different chem element
positron
anti-particle of e-
when positron encounters e- = annihilate w/ production of 2 gamma ray photons = conversion of mass to energy
radioactive decay
For each no. of protons = there’s optimum no. of neutrons for max stability of nucleus
if neutron no. too small/big = particles are emitted from nucleus = until stable configuration = emission is radioactivity/radioactive decay
more unstable the species = larger % of nuclei emits radiation is given time period = more radioactive
decay curve
shows radioactive decay process via exponential decay relationship of amount of radioactive substance (grams on y-axis) vs time (days on x axis)
half-life used
when alpha/beta emission involved = radioactive transformation process easily studied due to different chemical element daughter nucleus left behind after particle is emitted
half life
time for 1 half of nuclei to decay
radioisotope
measured in curie
1 curie=1g of radium
medical radioisotopes
administered internally, chosen on basis of
- type + energy of radiation
- half life
- rapidity + completeness of excretion
EG RADIUM
- alpha decay emission = produces radioactive gas Radon and other radioisotopes w/ short half lives after successive decays
these artificially produced isotopes used for diagnostic applications = short half lives + ease of introduction into chem compounds utilised by body EG albumin and Vit B12
detection of radiation
since high energy radiation ionises atoms + molecules in materials it passes thru
- photographic film
= blackening proportional to amount of IR received - TLD/ThermoLuminescent Dosimetry crystals
= amount of IR emitted proportional to radiation dose received - Ionisation chambers
= sealed tube containing ionisable gas + electrode w/ fairly low V
1. ions produced by radiation doesn’t gain enough energy from V to produce further ions by collision = counters used to identify type of radiation and radiation energy
X low sensitivity
- Scintillation Counter
= IR absorbed by crystal = emission of light flash = counted to indicate no. of absorption events = intensity of radiation
biological effect of IR
X/Gama R = photoionises molecule = causes compton scattering and ionises other atoms
Produces v active chem species = disables cellular components/produces toxins, can break chromosome chains, mutate cells, cancer
radiation exposure standards
measurable ionisation effects and amount of energy transferred to tissue
Curie/Ci = strength of radioactive sample
Becquerel/Bq = unit for source of activity
1Ci=3.7 x 10^10 Bq
Roentgen/R= radiation exposure for X/Gamma rays, to calibrate output of XR machines
minimise exposure
max distance btw u and source
minimize time spent near source
use shielding EG Pb
use film badge/monitoring device to record dose received
radiation therapy
X/G R to treat cancer but will also damage normal tissue cells
therapeutic ratio=cancer cells killed:normal cells kille
to increase TR = inject boron into tumour = irradiate low energy neutrons so higher dose to tumour
diagnostic use of radioisotopes
Tracer principle
= radioisotope molecules are the same as those that follow normal metabolic pathway (Ca, Na and P) = we can trace the pathway to be detected and analysed outside of the body
nuclear fission
release of energy by splitting of heavy element’s nuclei into 2 or more lighter nuclei EG Uranium but U is scarce, expensive, produced radioactive waste materials
nuclear fusion
light nuclei combined to form intermediate nuclei = total mass is reduced and energy released
produces more energy for given mass/fuel, uses cheap/abundant fuel and no radioactive waste produced BUT not possible to initiate and control fusion process to produce useful energy
requires T of millions of degrees, no material can w/i stand it
