Fill in the blank in the given nuclear reaction. 

____ + 

Write a balanced nuclear reaction showing emission of a β- particle by 90Th²³⁴ (Symbol of daughter nucleus formed in the process is Pa.)

When the cold junction of a certain thermo-couple was maintained at 20°C, its neutral temperature was found to be 180°C. Find its temperature of inversion.

Q_n = 

Here, 

Q_n = 180^o C ; Q_c = 20^o C 

180^o =   
Q_i = 360 - 20 = 340^o C 

Alpha particles having kinetic energy of 1.8 MeV each are incident on a thin gold foil, form a large distance. Applying the principle of conservation of energy, find the closest distance of approach of the alpha particle from the gold nucleus.