Answer to Question #280549 in Atomic and Nuclear Physics for BIGIRMANA Elie

Question

(a) Compute the energy released from a pair production reaction. [2 marks]

(b) Using the line of stability curve, briefly explain why Helium 6

2He is unstable and would

eventually decay into 6

3Li. Indicate the corresponding decay reaction equation. [4 marks]

(c) The Figure bellow represents a typical X-ray spectrum from a tungsten target. Explain the

behaviour of the observed spectrum as far the mechanism of X-ray production is concerned.

[4 marks] .

Answer 1

a)

$E=\Delta m c^2=2 ⋅ 511~ keV = 1.022~ MeV.$

b)

What are the nuclear processes which originate the huge thermonuclear energy of the Sun, and that has last 4.6×10⁹ years (the assumed age of the Sun)? It cannot be the simple

fusion of two protons, or of α-particles, or even the fusion of protons with α-particles, since neither ²He₂,

⁸Be₄, or ⁵Li₃, are not stable. The only possibility is the proton-proton fusion in the form p + p → d + e⁺ + ν_e, which occurs via the β-decay, i.e., due to the weak-interaction.

c)

The results obtained show that with a specific thickness, the target material itself can act as filter, which enables generation of X-rays with a limited energy. Because of its properties such as high atomic number and high melting point (3422 °C), tungsten is used as the target material in X-ray tubes.