Nuclear Reactions and Q-Values

Manual: General · Subject: Physics

Analyze reaction notation, conservation laws, thresholds, and energy balance in nuclear reactions.

Nuclear Reaction Basics

Reaction notation

A nuclear reaction is written in the form $a + A \rightarrow b + B$ , where incident and target nuclei produce outgoing particles and recoiling products. Conservation of charge, nucleon number, energy, momentum, and angular momentum constrains possible reactions.

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Q-value

The $Q$ -value is $Q=(m_{\text{initial}}-m_{\text{final}})c^2$ . If $Q>0$ , the reaction releases energy; if $Q<0$ , energy must be supplied.

Solving reaction-energy problems

1

Step 1: Write the balanced nuclear equation.
2

Step 2: Check conservation of $A$ and $Z$ .
3

Step 3: Use atomic or nuclear masses consistently.
4

Step 4: Compute $Q=(m_i-m_f)c^2$ .
5

Step 5: Interpret whether the reaction is exoergic or endoergic.

Common reaction types

Reaction type	Typical use
$(n,\gamma)$	Neutron capture and activation
$(\alpha,n)$	Neutron source production
Fission	Energy and reactor physics
Fusion	Light-element energy release

What does a negative Q-value mean?

Energy is released Energy must be supplied The reaction is impossible in all cases The product mass is zero

Write the formula for the Q-value of a reaction.

Which quantities must be conserved in any nuclear reaction?

Charge and nucleon number Only energy Only momentum Only mass

Why is angular momentum often important in reaction analysis?

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Nuclear Reactions and Q-Values

Nuclear Reaction Basics

Reaction notation

Solving reaction-energy problems