1
Homework 1
1.
In a process known as beta decay, a neutron (charge 0) in an unstable atomic nucleus becomes a proton (charge +e), ejecting an
electron (charge –e) and an antineutrino. (a) Use conservation of charge to determine the charge of an antineutrino. (b) Sixty
billion neutrinos (mostly from the Sun) pass through every square centimeter on Earth every second. They are hardly noticeable
due to their negligible mass and weak interaction with matter. When a neutrino and an antineutrino collide, however, they
annihilate each other and produce two (electrically neutral) gamma rays (charge 0) traveling in opposite directions. What is the
charge of a neutrino?
Step 1, formulas or related concepts.
Charge conservation.
Step 2, known quantities.
Charges of n (neutron) is 0, p (proton) +
e
, e (electron) –
e
, gamma 0.
Step 3, direct application of the formulas/concept or the condition to form an equation.
Based on charge conservation, and the reactions described, we have the following equations:
(a) n
p + e + antineutrino
(b) neutrino + antineutrino
gamma + gamma
Charge (in unit of
e
)
0 = +1
1
?
?
0
=
0
0
From equation (a), the charge of antineutrino is 0. Apply this result to equation (b), the charge of neutrino has to be 0 as well.
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 Spring '08
 Ye
 Electron, Charge, Magnetism, Work, Neutron, Electric charge

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