atom, nucleus, radioactivity Flashcards
ernest rutherford
scientist from NZ, 1911 gold foil experiment, proposed nuclear model of atom, approximated size of nucleus (order of 10^-15m)
gold foil experiment
bombarded alpha particles (known to be pos.) at thin piece of gold foil
-most undeflected + passed straight through
-some deflected through small angles
- very small number turned back by angles >90 deg.
Niels bohr
danish, 1913, proposed model describing how electrons are arranged in orbits around the nucleus using emission spectra
emission spectrum
pattern produced when light from a luminous source undergoes dispersion
-continuous
-line spectrum
continuous spectrum
produced by an incandescent solid or liquid. all visible wavelengths produced no matter the object
line spectrum
produced when a gaseous element gives out light and is then passed through a prism/diff. grating. bright and dark lines formed for each element
spectroscopy
where the analysis of a mixture of gases can use line spectrums to identify each element and relative amounts of each
energy level
fixed energy value that an electron can have in an atom
-if atom given energy it can move to orbit of higher energy level (excited state)
-electron will eventually fall back to original orbit + emit energy (photon)
- hf = E2 - E1
lasers
light amplification by stimulated emission of radiation
-in laser many atoms have electrons in excited state
-all of these atoms stimulated by light of certain freq. –> electrons fall to o.g. orbit
-photons emitted in intense beam
uses of lasers
-phone lines (optical fibres)
-burn cancer cells, correct eyesight, remove birthmarks
-cutting + welding in industry
atomic number (Z)
no. of protons an element has
(no. protons = no. electrons)
mass number (A)
no. of protons + neutrons an element has (atomic weight)
No. neutrons = A - Z
isotope
atoms of an element that have the same no. of protons but different no. of neutrons e.g. Hydrogen (1), Deuterium (2)
Henri Becquerel
french, 1896 noticed that uranium salt caused nearby plate to go black (exposed)
-concluded salt must be giving out radiation
(discovered radioactivity)
radioactivity (nuclear radiation)
the disintegration of the nuclei of certain atoms with the emission of 1 or more types of radiation
-occurs when nuclei of certain isotopes are unstable (excess energy)
1. alpha α
2. beta β
3. gamma γ
radioactive
this is when a source’s nucleus emits radiation (excess energy) e.g. uranium, radon etc.
alpha radiation
fast moving helium nuclei ejected from the nuclei of radioactive atoms i.e. a-particle = 2 protons + 2 neutrons
-greatest ionising ability
-least penetration ability (stopped by paper)
-charge +2
-deflected same as pos. charge
beta radiation
fast moving electrons ejected from the nuclei of radioactive atoms i.e. 1 b-particle = 1 electron
-ionising ability less than a-radiation
-penetration ability more than a-radiation (mm)
-charge -1
-deflected as neg. charge
gamma radiation
high freq. electromagnetic radiation in the range of 3x10^-19Hz
emission of gamma rays does not affect structure of nucleus however it loses energy and hence becomes more stable
-least ionising ability
-most penetrating power (cm) lead
-no charge
-undeflected
paul villard
french, 1900 discovered gamma radiation.
named by rutherford
activity
no. of nuclei in a radioactive substance decaying per sec.
unit: becquerel (Bq) -> 1Bq = 1 radioactive decay per sec
law of radioactive decay
-states no. of nuclei decaying per sec (activity) is directly proportional to the no. of nuclei undecayed (N)
i.e. A ∝ N
A = λN
λ = decay constant (unit = s^-1)
decay is a random process
half life
time taken for half of the undecayed atoms of a radioactive isotope to undergo decay
in general after n half lives 1/2^n of the original sample remain
-also time taken for activity to decrease by half
-does not depend on size of sample
T1/2 = ln2/λ
decay series
series of isotopes formed when an isotope undergoes radioactive decay. process continues until stable isotope formed
