Table 2.

Radioactive isotopes of Na⁺, K⁺ (Rb⁺), and Cl

Isotope	Atomic No.	Half-Life	Decay Mode	Gamma Intensity
24Na	11	15 h	β− (1.39 MeV)	Yes
22Na	11	2.58 yr	β+ (89%, 0.54 MeV), ε (11%)	Yes
42K	19	12.4 h	β− (82%, 3.53 MeV) (18%, 2.03 MeV)	Low
43K	19	22.4 h	β− (0.83 MeV)	Yes
83Rb	37	83 days	ε (0.9 MeV)	Yes
86Rb	37	18.77 days	β− (1.77 MeV)	Low
36Cl	17	3 × 105 yr	β− (98%, 0.71 MeV), ε (2%)	No

Atomic number or number of protons in the nucleus of the atom. Half-life is the rate of radioactive decay or time it takes for activity to be reduced by ½. Decay mode: β⁻, negative beta emission or energetic electron; β⁺ positron emission, ε, orbital electron capture or absorption of an inner atomic electron. Energy of decay is given in parenthesis. Where more than one decay exists, separate energy values and distribution are given. The last column indicates whether gamma ray energy is released.