Atomic nucleus - Structure of matter

Question 1

What determines the total electric charge of nucleus?

Answer 1

Nuclei of atoms are formed by nucleons - protons and neutrons.

The main fetures of nucleus are:
Atomic number Z which determines the number of protons present in the nucleus.
Mass number A which determines the total number of nucleons.

Neuron number N for the number of neutrons.

Thus, A = Z + N

Total electric charge of nucleus is Z.1.6*10^-19C.

Question 2

Explain the mass of the atom.

Answer 2

Mass of atom is mostly present in its nucleus, since the nucleon mass is approcimately 1.10³ times higher than the electron mass.

The mass of atoms is usually expressed in mass units.

1 mass unit (m.u.) is represented by 1/12 mass of the carbon isotope ¹²C.

Numerically, 1 mass unit = 1.66*10^-27kg.

Its energy equivilent is 931MeV.

Mass of atoms can be estimated by ising mass spectrometers.

Question 3

What are isotopes?

Answer 3

Isotopes are types of nuclei with identical charge by of different mass (identical Z, different A).

There are about 280 stable isotopes in nature. Together with those produced artificially, their number exceeds 1100.

Question 4

What are isobars?

Answer 4

Isobars are called atoms whose nuclei contain identical number of nucleons but different number of protons (different Z, identical A).

Question 5

What are isomers?

Answer 5

Isomers are atoms with the same number of protons and neurons, but with different energies of nuclei.

Therefore they are not stable and after some time the excess energy is emitted in the form of quantum radiation.

Question 6

How can the nuclear radius be found?

Answer 6

Radius of proton is 1.23*10^-15m.

Radius of R_A of nucleu of heavy atoms can be calculated by

R_U = 1.23*10^-15.A^1/3(m)

See book p.19 for example.

Radii of nuclei increase from hydrogen to uranium only 6.2 times.

Extremely high values for density of nuclear mass (ρ~=10¹⁴ kg/m³) follow from this fact.

Question 7

Explain nuclear forces.

Answer 7

Nuclear forces are results of the strong interation and the range of their action does not exceed the radius of the nucleus.

Forces of the strong interation do not depend on the nucleon charge.

Their range is of 10^-15 m and, at this distance, these forces are the strongest forces known in nature.