12.7 Nuclear Radii And Distance of Closest Approach

Question 1

What happens when an alpha particle of electric charge 2e and kinetic energy Ek is directed head on at a nucleus of atomic number z?

Answer 1

The alpha particle will come to rest for an instance a distacen d form the centre of the nucleus where
Ek = k((2e)(Ze))/d —> d = ((2e)(Ze))/Ek and will then be repelled. We see that the kinetic energy of the alpha particle gets transformed entirely to electrical potential energy at the point of closest approach.

Question 2

How is it possible to obtain estimates of nuclear radii?

Answer 2

By scattering electrons or neutrons from nuclei.

Question 3

What is the advantages of using electrons?

Answer 3

The strong forces does not act upon them and so they can approach the nucleus very closely.

Question 4

What is the advantages of using neutrons?

Answer 4

Being neutral they can penetrate deep into matter and get very close to the nucleus.

Question 5

What does the scattering of electrons and neutrons form nuclei show?

Answer 5

Diffraction minima - that is angles at which the number of scattered particles is small. These angles are given by sin@ = lambda/b where b is the diameter of the nucleus and lambda is the de Broglie wavelength of the scattered particle.