Question

In the medical diagnostic technique known as positron emission tomography (PET), a positron and an electron annihilate each other and two γ–ray photons are emitted. What is the angle between the momentum vectors of the two photons?

a. Zero degrees

b. 45°

c. Any angle is possible

d. 90°

e. 180°

Answer 1

when a positron and electron are collide each other thenelectron positron annihilation occur

when they collide then two gama photon are produced

at high energy some other particle are created

in the collision

total electric charge conserved

linear momentum and angular momentum and total energy conserved

after collision the gama photon are emitted in opposite direction

if they emitt any angle so there is change in momentum so the momentum conservation will not followed

so it must that the generate gama photon are emitted in opposite direction

so the angle between two gama photon will 180^o

so option (e) is correct Ans