pmt notes

reason for thin gold foil

thicker foil would stop particles completely

advantages of alpha scattering

gives good estimate of upper limit, maths behind it is simple

disadvantages of alpha scattering

not accurate as it is always an overestimate, the alpha particles are assumed to have the same initial ke which may not be realistic

advantages of electron scattering

more accurate than alpha scattering, gives direct measurement of radius, not affected by strong nuclear force, no repulsion so can get closer to the nucleus, greater resolution as wavelength can be made very small

disadvantages of electron scattering

electrons must be accelerated to very high speeds to maximise resolution, electrons can be scattered by both protons and neutrons

what does a small amount of particles deflected at a large angle mean

centre of atom is positively charged

what does very few particles deflected by more than 90 degrees mean

the centre of the atom is very dense and very small

how to safely handle ionising radiation

use long handled tongs to move the source, storing the source in a lead-lined container, keeping the source as far away as possible from yourself, never pointing the source towards yourself or others

sources of background radiation

radon gas, nuclear weapons testing, nuclear meltdowns, cosmic rays, rocks

define decay constant

the probability of a nucleus decaying per unit time

activity

number of nuclei that decay per second

what happens when an element has too many neutrons

beta minus decay

what happens when an atom has too many protons

beta plus emission or electron capture

what happens when an atom has too many nucleons

alpha decay

what happens when an atom has too much energy

gamma emission

radius of nucleus from elelctron scattering formula

R=0.61(de broglie wavelength)/ sin(angle of first minimum)

nuclear fission

the splitting of a large nucleus into two daughter nuclei

nuclear fusion

where two smaller nuclei join together to form one larger nucleus

binding energy

the amount of energy required to split a nucleus into all its separate constituent nucleons. it is equivalent to the mass defect

contamination

the introduction of radioactive material to another object

moderator

slows down the neutrons released in fission reactions to thermal speeds

control rods

absorb neutrons in the reactor in order to control chain reactions

coolant

absorbs the heat released during fission reactions in the core of the reactor

why do nuclei have a lower mass than the combined mass of their separated nucleons

work must be done against the strong nuclear force to separate nucleus. the potential energy of individual nucleons is higher than the potential energy of nucleons in a nucleus

define induced fission

Fission caused by the absorption of a free neutron.

define critical mass

The minimum mass of fissile material needed to sustain a nuclear chain reaction.

To minimise the number of collisions needed to slow neutrons down to thermal neutrons, the nucleon number of moderator atoms should be…

low