Electron scattering Flashcards
Why is electron scattering more accurate than alpha particle scattering
Electrons are leptons and so do not interact with the SNF but interact with electrostatic force which is better understood compared to the SNF meaning it is a more accurate method for estimating the nuclear radius
Why can electrons be diffracted
because they have a wave-particle duality
When a beam of high energy electrons are directed at at a thin metal, the incident electrons are
diffracted by the nuclei of the atoms in the foil
The beam of electrons is produced by
accelerating electrons through a very high pd so at high speeds their de Broglie wavelength, = h/mv will be small enough to be similar to the size of the nuclear radius ~ 1fm for maximum diffraction
A detector measures
the number of electrons per second diffracted through different angles
The beam of electrons are fired through… causing
The beam of electrons are fired through an atomic lattice causing them to scatter and form a diffraction pattern with a central bright circular maxima surrounded by other rings of dimmer maximima
Scattering of the beam of electrons occurs because of
their charge and their de Broglie wavelength
Difference between the scattering of electrons and alpha particles
Scattering of the beam electrons by the nuclei occurs due to their charge. This is the same as alpha-scattering except the electrons are attracted not repelled causing intensity to decrease as charge or angle of diffraction increases
In every reaction, what is conserved
energy, momentum and charge
Intensity =
number of electrons per second
First minimum (theta min) appears when
sinX = 0.61*lambda/Radius of nuelcus
Graph of intensity (y) against angle of diffraction (x) (one quadrant)
starts at top of y axis and decreases 1/x style to a non-zero minimum then increases to a peak then decreases 1/x style
non-zero min at (theta min, y)
Graph of intensity (y) against angle of diffraction (x) (two quadrants)
big central peak symmetrical about intensity axis then symmetrical decreases non-zero peaks
Explain what happens to the intensity as the angle of diffraction increases
The graph shows that as the angle from the source to the zero order beam is increases, the number of electrons per second = intensity of the beam diffracted decreases then increases slightly then decreases again
How is a diffraction pattern formed and how is this used to calculate the nuclear radius
Diffraction of the beam electrons by each nucleus causes maxima and minima to be superimposed. This happens provided the de Broglie wavelength of the electrons in the beam is no greater than the dimensions of the nucleus. The angle of the first minimum from the centre is measured and used to calculate the diameter of the nucleus
