A person with lymphoma receives a dose of 45 Gy in the form of γ radiation during a course of radiotherapy. Most of this dose is absorbed in 18 g of cancerous lymphatic tissue. (a) How much energy is absorbed by the cancerous tissue? (b) If this treatment consists of five 20 minute sessions per week over the course of 5 weeks and just 1% of the γ photons in the γ ray beam are absorbed, what is the power of the γ ray beam? (c) If the γ ray beam consists of just 0.5% of the γ photons emitted by the γ source, each of which has energy of 0.03MeV, what is the activity (in Ci) of the γ ray source?

Explanation:

a)  Energy absorbed by cancerous tissue E = R x M

R is the radiation dosage

M is the mass of the lymphatic

Energy absorbed by cancerous tissue

b) If only 1% of the total energy Et is absorbed over 20min session for 5 weeks = E

And the time of the period of the course is t = 20 x 5 = 100 min

E = 0.01Et

Total energy of gamma ray beam

Et = E x 100

= 810 x 10⁻³ x 100

= 8100J

Power of gamma ray beam is P

c) The total activity

The Number of decays dN = Es Total energy emitted at sourse per seconds / energy emitted per day

The Energy source Es per seconds = 0.05Ps

P= 0,0135W

The Power emitted at source

The Energy emitted per decay = 0.03MeV