Isodiaphers are atoms (nuclides) that have the same neutron excess, i.e., the same value of (N − Z), where N is the number of neutrons and Z is the number of protons (atomic number). They are also called isodiaphere pairs.
Isodiaphers are related by alpha decay — when a nucleus emits an alpha particle (₂⁴He, which has N-Z=0), the parent and daughter nuclei have the same neutron excess and are thus isodiaphers of each other.
The neutron excess = N − Z = (Mass Number − Atomic Number) − Atomic Number = A − 2Z
Example:
Another example: ³H (Tritium, N-Z=2) and ⁷Li (Lithium, N-Z=4... wait let me recalculate)
| Term | Same Property |
|---|---|
| Isotopes | Same atomic number (Z), different mass number |
| Isobars | Same mass number (A), different atomic number |
| Isotones | Same number of neutrons (N) |
| Isoelectronic | Same number of electrons |
| Isodiaphers | Same neutron excess (N − Z) |
When a nucleus emits an alpha particle (2 protons + 2 neutrons), both N and Z decrease by 2, so N-Z remains the same. Therefore, parent and daughter nuclei in alpha decay are always isodiaphers.
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