63-66;Radioactivity

Question 1

how was scale model of atom discovered

Answer 1

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

Question 2

nature of nucleus

Answer 2

nucleus of atom contain 99% of mass of atom

Question 3

nuclear radiation

Answer 3

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

Question 4

alpha radiation

Answer 4

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

Question 5

beta radiation

Answer 5

e-

greater range of penetration = less penetrating than gamma rays = hazardous if ingested

Question 6

gamma radiation

Answer 6

electromagnetic ray

comes from nucleus = very penetrating = useful for radiation therapy but MOST hazardous due to its ability to penetrate large thickness

Question 7

radioactivity

Answer 7

result of nuclear instability

nucleus emits particle that is transformed into nucleus of different chem element

Question 8

positron

Answer 8

anti-particle of e-

when positron encounters e- = annihilate w/ production of 2 gamma ray photons = conversion of mass to energy

Question 9

radioactive decay

Answer 9

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

Question 10

decay curve

Answer 10

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

Question 11

half life

Answer 11

time for 1 half of nuclei to decay

Question 12

radioisotope

Answer 12

measured in curie

1 curie=1g of radium

Question 13

medical radioisotopes

Answer 13

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

Question 14

detection of radiation

Answer 14

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

Question 15

biological effect of IR

Answer 15

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

Question 16

radiation exposure standards

Answer 16

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

Question 17

minimise exposure

Answer 17

max distance btw u and source

minimize time spent near source

use shielding EG Pb

use film badge/monitoring device to record dose received

Question 18

radiation therapy

Answer 18

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

Question 19

diagnostic use of radioisotopes

Answer 19

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

Question 20

nuclear fission

Answer 20

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

Question 21

nuclear fusion

Answer 21

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