SME
Grade 10 Science · Problem type
Beta decay
Use this for “Carbon-14 gives off a beta particle. What nucleus is left?”
Diagram
Mass numbers (top) and atomic numbers (bottom) add to the same on both sides.
A beta particle is an electron: a neutron turned into a proton.
Neutrons before: 8
This is an example. Type your own values to start a new problem.
X
→
Y
+
0
−1
e
N
Neutrons before
worked out (not typed)
Formulas
N
=
A
−
Z
8 = 14 − 6
A
′
=
A
14 = 14
Z
=
Z
′
−
1
6 = 7 − 1
Assumptions
•
The mass numbers (top) on the two sides add to the same total.
•
The atomic numbers (bottom) on the two sides add to the same total.
•
The beta particle carries away 0 in mass number and −1 in atomic number.
•
The new atomic number names the new element.
Step-by-step
WE KNOW
A = 14, Z = 6
FIND
neutrons before (N), mass number after (A′), atomic number after (Z′)
Step 1 · Find neutrons before (N)
Use N = A − Z
The nucleons that are not protons are neutrons.
N
=
14
−
6
N
=
8
Step 2 · Find mass number after (A′)
Use A′ = A
A beta particle has mass number 0, so the mass number stays the same.
A
′
=
14
Step 3 · Find atomic number after (Z′)
Use Z = Z′ − 1
The beta particle has atomic number −1: a neutron became a proton.
Z
′
=
Z
+
1
Z
′
=
6
+
1
Z
′
=
7
is
nitrogen:
N
-14
Z
′
=
7
Check
Put the numbers back in. Both sides should match.
8 = 14 − 6 ✓
14 = 14 ✓
6 = 7 − 1 ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.
Refresh
Related lessons
Nuclear chemistry: radioactive decay, half-life, fission and fusion
Main lesson
Alpha decay
Use this for “Uranium-238 gives off an alpha particle. What nucleus is left?”
Fission of uranium-235
Use this for “U-235 takes in a neutron and splits into Ba-141, a second nucleus and 3 neutrons. What is the second nucleus?”
The mass defect: where the energy comes from
Use this for “U-238 gives off an alpha particle. How much mass is lost, and how much energy is released?”
Alpha, beta, fission or fusion?
Use this for “Which equation shows fission?” and “Why is fusion a cleaner source of energy than fission?”