radioactivity Flashcards
conclusions of gold foil experiment
- most of the space in an atom is empty (most alpha particles passed through w/o any deviation)
- the enthire +ve charge of an atom is placed in the centrally located nucleus
- enthire mass of the atom is also concentrated within the nucleus. the elctrons revolve around the nucleus in circular orbits.
A (mass number)
the total number of nucleons present within the nucleus of an atom
Z (proton number)
total number of protons present within the nucleus of an atom
N (neutron number)
total number of neutrons present within the nucleus of the atom
isotope
nucleus of the same element having the same proton number, but a difference neutron number (and hence a diff. mass number)
H-1→ nucleus = proton, atom = protium
H-2 → nucleus = deuteron, atom = deuterium
H-3 → nucleus = triton, atom = tritium
strong nuclear force
force present within the nucleus due to which protons and neutrons attract themselves and each other in the nucleus.
this does not mean that there is no repulsive force. there is repulsive force, however, dominating that repulsive force is the strong nuclear force.
but because repulsive forces still exist, the nucleus might be unstable.
radioactivity
the process through which an unstable nucleus undergoes decay in order to attain stability
alpha decay
A = -4
Z = -2
N = -2
in end + helium nucleus (4,2)
beta decay
A = no change
Z = +1
N = -1
in end + beta minus particle + anti neutrino
gamma decay
parent nucleus = star
daughter nucleus = more stable = no star
in end + gamma radiation
law of radioactive decay
the number of nuclei undergoing decay per unit time is directly proportional to the number of undecayed/unstable nuclei.
∆N/∆t ∝ -N
properties of radioactive decay
- spontaneous reaction (no need to interfere to start the reaction)
- random process - cannot predict when it happens, which nuclei undergoes decay, cant predict shit unpredictable ahh
half life
time taken for half of the unstable nuclei to undergo decay
N = (1/2)^(t/T_1/2)*N_0
fission
large unstable nucleus breaks down into two or more fragments.
moderator
substance used to bring down the energy of the neutron given at the time of the fission reaction
- heavey water
- graphite
control rod
used to control the rate at which energy is relased in the chain reaction, to avoid making it an uncontrolled reaction
- cadmium
- boron
fusion
two or more fragments fuse to form a larger, more stable nucleus.
properties of alpha/beta particles + gamma radiation
ionizing:
alpha > beta > gamma
penetrating power:
gamma > beta > alpha
alpha = stopped by paper
beta = stopped by aluminum
gamma = stopped by lead/concrete
proton-proton cycle
H+H → H (deuterium isotope)
H (deuterium isotope) + H → He (3 isotope)
H+H → H (deuterium isotope)
H (deuterium isotope) + H → He (3 isotope)
He (3 isotope) + He (3 isotope) → He + H + H
possible cause of error in determining half life
presence of background radiation
if GM counter returns a value even in the absence of any radioactive material, it is because of this background radiation.
before bringing radioactive material close to GM counter, turn on the counter and leave it on for 2-3 minutes. this will return a value if there is any background radiation. make a note of it. bring the radioactive material close. now it will return a final value - the actual count of radioactive from that material will then be the second value - the first reading from the GM counter. (to ensure that we don’t consider background radiation)
geiger müller counter (GM counter)
used to measure radiation
