Some of the important properties of atomic nucleus are given below :
(a) Nuclear charge : The charge on the nucleus is due to protons contained in it. The charge on each proton is + 1.6 x 10-19 coulomb which is equal in magnitude to thecharge of an electron. Taking the charge of a proton as one unit, the total charge on the nucleus is numerically equal to the numberof protons. For example, a hydrogen nucleus (i.e., proton) carries a single unit charge.
(b) Nuclear mass : As we may know that the mass of the nucleus is the sum of the masses of the neutrons and protons contained in it. This is expressed in terms of atomic mass unit (a.m.u.). One a.m.u. = 1.66 x 10-27 kg. For example 6C12 nucleus has a mass of 12 a.m.u. so that its mass number A = 12.
It is assumed that the mass of the nucleus should be
Z mp + N mn
where mp and mn are the masses of proton and neutron respectively
and Z is atomic number and N is the number of neutron.
Experimentally, it has been observed that
real nuclear mass < Z mp + N mn
The difference is assumed and real mass is called as mass defect.
(c) Nuclear Radius : Rutherford with his experiment on α – particle scattering by thin metallic foils, concluded that the distance of the closest approach of the α – particle to the nucleus of the scatterer can be regarded as a measure of the size of the nucleus. He found this distance of the order of 10-14 m.
It has been observed that volume of the nucleus is directly proportional to the number of nucleons A, i.e.
Volume α A
Or 4/3 π r3 α A
or r3 α (3/4 π) A
or r α (3/4 π)1/3 A1/3 = C (3/4π)1/3 A1/3
or r = r1 A1/3
where r1 is a linear constant and has an average value of 14 x 10-15m. A is mass number of the nucleus. Radius of the nuclei of the carbon elements are given below:
Carbon (A = 12)
r = 1.4 x 10-15 x (12)1/3 = 3.21 x 10-15 m
These are the 3 important properties of nucleus. Next time we will discuss more properties of laser.
You may also read earlier article: Parts of nucleus.