Question

Fusion in stars often proceeds via the p-p cycle, which combines 4 protons and two electrons to form an alpha particle. In this process, neutrinos and gamma rays are also produced. How many gamma rays are produced in one p-p cycle?

a. 12

b. 4

c. 2

d. 1

e. 8

f. 6

Answer 1

In one complete proton-proton cycle, a total of six gamma rays are produced from the fusion of four protons into one alpha particle, emission of two positrons (which later produce gamma rays upon annihilation with electrons), and the release of two neutrinos.

Step-by-step explanation:

The proton-proton cycle, a set of nuclear reactions that produces energy in stars like the Sun, generates multiple forms of radiation, including gamma rays and neutrinos. In one complete cycle, four protons are fused into one alpha particle, two positrons are released (which will eventually annihilate with electrons to create additional gamma rays), and two neutrinos are emitted. Specifically, one p-p cycle results in the creation of six gamma rays.

The reactions within this cycle are initiated by two hydrogen nuclei (¹H) coming together to form deuterium (²H), which in turn reacts with another ¹H to form helium-3 (³He). This process releases one gamma ray each time it occurs and must happen twice for the next reaction, where two ³He nuclei combine to form helium-4 along with two protons being released back. The annihilation of the two positrons with electrons produces an additional four gamma rays. Hence, throughout one p-p cycle, six gamma rays are produced in total.