   Chapter 11, Problem 85CP ### University Physics Volume 3

17th Edition
William Moebs + 1 other
ISBN: 9781938168185

#### Solutions ### University Physics Volume 3

17th Edition
William Moebs + 1 other
ISBN: 9781938168185
Textbook Problem

# (a) A panicle and its antiparticle are at rest relative to an observer and annihilate (completely destroying both masses), creating two y rays of equal energy. What is the characteristic y -ray energy you would look for if searching for evidence of proton-antiproton annihilation? (The fact that such radiation is rarely observed is evidence that there is very little antimatter in the universe.) (b) How does this compare with the 0.511-MeV energy associated with electron-positron annihilation?

To determine

(a)

The characteristic γ - ray energy that will be produced after proton-antiproton annihilation.

Explanation

Given:

A particle and anti particle annihilate and produced two γ - rays.

Formula used:

When a proton and antiproton annihilate each other, their masses are completely destroyed and transformed into energy. This energy can be calculated using the equation,

E=mc2, where m is the mass of the proton (or antiproton) and c is the speed of light.

Calculation:

When proton-antiproton annihilation occurs, both particles completely lose their mass and produce two γ - rays. Each γ -ray will have the same amount of energy, which can be calculated by,

E=mc2

We know, the mass of the proton ( m ) = 1.672×1027 kg, and speed of light ( c ) = 3×108 m/s

To determine

(b)

The comparison between 939 MeV of γ - ray energy produced by proton-antiproton annihilation, with the 0.511 MeV energy produced by electron-positron annihilation.

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