在核聚变过程中，观察到当两个氢原子融合形成一个氦原子时，会存在质量损失 M。 下表中给出了一个氢原子和一个氦原子的原子质量。质量以原子质量单位 (u) 给出。

1. Find the mass of two hydrogen atoms and subtract the mass of one helium atom.

Mass of two hydrogen atoms:
$2 \times 2.0141 = 4.0282\text{ u}$
Mass lost:
$M = 4.0282 - 4.0026 = 0.0256\text{ u}$

2. Write the mass loss in standard form.

$0.0256 = 2.56 \times 10^{-2}$

1. Form the percentage using mass loss as a fraction of the helium atomic mass.

From part (a), $M=2.56\times 10^{-2}=0.0256$ u.

$\text{Percentage}=\frac{M}{\text{atomic mass of one helium atom}}\times 100\%$

$=\frac{0.0256}{4.0026}\times 100\%$

2. Calculate and round the percentage appropriately.

$\frac{0.0256}{4.0026}\times 100=0.639584\ldots$

$\approx 0.640$

1. Convert the mass loss from atomic mass units to kilograms.

From part (a),
$M=2.56\times 10^{-2}\text{ u}.$
Given $1\text{ u}=1.66\times 10^{-27}\text{ kg}$,
$M=(2.56\times 10^{-2})(1.66\times 10^{-27})$
$=4.2496\times 10^{-29}\text{ kg}$
$\approx 4.25\times 10^{-29}\text{ kg}.$