Mass–Energy, Nuclear Reactions & Radiation Evidence — Practice · Grade 12 Science

Chapter: Modern Physics

What this practice covers

By the end of Mass–Energy, Nuclear Reactions & Radiation Evidence you should be able to:

8 questions, numeric and written answer, each with a worked explanation.

Vocabulary used: mass defect, absorbed dose, binding energy.

Problem 1

Mass difference.002u with 931.5 MeV/u gives what energy?
Hints

Write the relationship first; substitute with consistent units.

Answer and explanation

1.863 MeV

.002×931.5.

Problem 2

Why distinguish activity from dose?
Answer and explanation

Activity is source decay rate; dose depends on energy deposited per mass and exposure conditions.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 3

Using 931.5 MeV/u, find energy for .004 u modeled mass loss.
Hints

List the given quantities, select a relationship, and check units before substituting.

Answer and explanation

3.726 MeV

.004×931.5=3.726.

Problem 4

Does rest-mass reduction violate energy conservation?
Answer and explanation

No; the difference appears as other forms of energy, with total energy conserved.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the calculation or mechanism that supports it.
  • Include units, conditions, or limits where relevant.

Problem 5

Find energy for mass difference 1.0×10⁻³⁰ kg using the same c. Show the reasoning, not just the conclusion.
Hints

Compare complete initial and final rest-mass accounting.

Answer and explanation

9.0×10⁻¹⁴ J.

Problem 6

Why do nuclear reaction equations require both nucleon and charge-number checks?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

They constrain particle accounting; emitted particles must be included to balance the complete reaction model.

Problem 7

Energy per event, event rate and total output are different scalesEnergy per event, event rate and total output are different scalesScaleCalculationResultOne event2 MeV×1.602×10⁻¹³ J/MeV3.204×10⁻¹³ J10¹² eventsMultiply by event count0.3204 JPowerEnergy / elapsed timeNeeds a timeintervalLarge energy per event does not alone determine device output.
Original event-count scaling for a hypothetical 2 MeV channel, not an operating reactor record.
Interpret the supplied visual. What power corresponds to 0.3204 J released steadily in 2 s?
Answer and explanation

0.1602 W before any useful-output losses are applied.

A reaction’s energy per event must be multiplied by event number to obtain total energy. Power additionally needs event rate or duration and a useful-output efficiency. A large nuclear energy per event therefore does not by itself specify a power plant’s output or a sample’s radiation signal. Include how much material participates, what fraction reacts, and where released energy goes. Compare like energy services rather than isolated per-event numbers.

0.1602 W before any useful-output losses are applied.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the physical or environmental relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 8

A supplied reaction releases 0.0015 u of rest-mass equivalent per event. Estimate energy in MeV, then explain why a detector count rate cannot directly give absorbed dose.
Answer and explanation

Energy≈0.0015×931.5=1.397 MeV/event. Dose also needs energy deposited, exposed mass, radiation characteristics and geometry; count rate includes detector efficiency/background and is not dose.

Energy≈0.0015×931.5=1.397 MeV/event.

Dose also needs energy deposited, exposed mass, radiation characteristics and geometry; count rate includes detector efficiency/background and is not dose.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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