Question

A beam of alpha particles produces a current of 10.14 A in an ionization chamber for 8 seconds. The chamber contains air at STP (36 eV/ip), where ip means ion pair.

(a) How many ion pairs are produced?
(b) How much energy did the beam deposit in the chamber?
(c) If the chamber volume is 240 cc, what is the energy absorbed per unit mass in units of gray? (1 gray absorbed dose = 1 J/kg)

Answer 1

(a) The total charge =

I = current = 10.14 Amp

Q = 81.12 Coloumb

number of ions pair = n =Q/e = 81.12/(1.6*10-19) = 50.7*1019 = 5.07*1020 ions

where e = charge of 1 electron

(b) Since the energy per ion-beam =w= 36 eV

then energy deposited in the chamber = E = nw= 5.07*1020*36 eV =182.52*1020 eV = 1.82*1022 eV =

1.82*1022*1.6*10-19 J = 2912 Joule

(c) let the density =

so mass of the gas =

where V = volume of the chamber = 240 CC = 2.4*10-4 m3

kg

Absorbed dose = E/m = J/kg = = gray

Please provide the density of alpha particles, in the above formula and find the answer.