Atoms, Molecules and Nuclei Test - 4

The substance used for electron emission is known as an emitter or cathode. The cathode is heated in an evacuated space to emit electrons. If the cathode were heated to the required temperature in open air, it would burn up because of the presence of oxygen in the air. A cathode should have the following properties:
(i) Low work function: The substance selected as cathode should have low work function so that electron emission takes place by applying small amount of heat energy, i.e. at low temperature.
(ii) High melting point: As electron emission takes place at very high temperatures (> 1500°C), the substance used as a cathode should have high melting point.
Note:Oxides of any alkaline earth metals (e.g. calcium, strontium, barium etc.) have very good emission characteristics.

For ionising for a hydrogen atom in the ground state the energy required is 13.6 eV because E = -13.6/n², where n = 1.
For an atom in the excited state the ionization energy will be less than 13.6 eV, depending on the excited energy level in which the hydrogen atom is present.

For us to work safely, radioactive matter should reach the permissible value of radiation.
N/N_o = (1/2)^t/T
1/64 = (1/2)^t/T
(1/2)⁶ = (1/2)^t/T
t/T = 6
t = 12 h (Given: T = 2 h)
So, after 12 h, it is permissible to work in the given conditions.

When ₃Li⁷ nuclei are bombarded by protons, following reaction takes place:

₃Li⁷ + ₁H¹ → ₄Be⁸ + _aX^y

a = (4 - 1 - 3) = 0
y = (8 - 1 - 7) = 0

Since both a and y are zero, X comes out to be a gamma photon.

For the given reaction , we have

¹⁴N₇ + ⁴He₂ → ¹⁶O₈ + ¹p₁

Hence proton is emitted.