stable and unstable nuclei Flashcards
what are the two already known forces acting on the nucleons in a nucleus
electrostatic forces from the protons electric charge and gravitational forces due to the masses of particles
what is significant about those two forces
the repulsion from electrostatic force is much bigger than the gravitational attraction
why does there have to be another force
if these were the only forces acting on a nucleus, the nucleons would fly apart
how strong is the strong force
to hold the nucleus together, it must be an attractive force thats stronger than the electrostatic force
what is significant about the strong force’s range
it is very short. it can only hold a nucleus together when they’re separated by a few femtometres
what is significant about the strong force’s strength
it quickly falls beyond its range
what else is significant about the strong force
works equally between all nucleons. the size of the force is the same for proton-proton, neutron-proton, etc
is the strong force repulsive
at very small separations the strong force must e repulsive or it would crush the nucleus to a point
draw a sketch graph showing the vary in strength of the strong nuclear force
ok
where does alpha emission happen
only in very big nuclei
why does alpha emission happen to big nuclei
they are too massive for the strong nuclear force to keep them stable
what happens when an alpha particle is emitted
proton number decreases by two and the nucleon number decreases by four
what is significant about alpha particles’ range
they have a very short range, only a few cm in air.
how can this be seen
by observing the tracks left by alpha particles in a cloud chamber or use the Geiger counter (a device that measures the amount of ionising radiation). bring it up close to the alpha source then move it away slowly and observe how the count rate drops
what is beta emission
beta decay is the emission of an electron from the nucleus along with an antineutrino
where does beta decay happen
in isotopes that are unstable due to having too many more neutrons than protons (neutron rich)
what happens when a nucleus ejects a beta particle
one of the neutrons changes into a proton
what happens in beta emission
the proton number increases by one, and the nucleon number stays the same
what are antineutrinos
tiny neutral particles released in beta emission. it carries away some energy and momentum
why were neutrinos first hypothesized
due to observations in beta decay
what did scientists originally think
the only particle emitted from the nucleus during beta decay was an electron
what disproved it
observations showed that the energy of the particles after the beta decay was less than it was before which didnt fit the principle of conservation of energy
what did pauli wolfgang suggest in 1930
another particle was being emitted and it carried away the missing energy
what did this particle have to be
it had to be neutral (or charge wouldn’t be conserved in beta decay) and had to have 0 or almost 0 mass (as it has never been detected)
