The Radioactive Decay of Tritium

DOE-HDBK-1132-99

The names, commonly used symbols, atomic masses, and relative natural

abundances of the hydrogen isotopes are summarized in Table II.

TABLE II. The isotopes of hydrogen.

Natural

Name

Chemical

Atomic Mass

Natural

Abundance

Symbol

Abundance

(x:H Ratio)

(Percent)

Protium

1.007 825 03

99.985 %

1:1

Deuterium

2.014 101 78

0.015 %

1:6,600

1:1017

Tritium

3.016 049 26*

very low

* Calculated

2.10.4

The Radioactive Decay of Tritium .

Generic . As the lightest of the pure beta emitters, tritium decays with the

emission of a low-energy beta particle and an anti-neutrino; i.e.,

Η e + β + ν.

(2)

Tritium decays with a half-life of 12.3232 0.0043 mean solar years or, using

365.2425 mean solar (days) per mean solar year, 4,500.96 1.57 days. The

specific activity of tritium is approximately 9,619 Ci/g, and/or 1.040 10 -4 g/Ci.

In addition, the activity density (i.e., the specific activity per unit volume) for

tritium gas (T2) is 2.589 Ci/cm3, under standard temperature and pressure

(STP) conditions (i.e., 1 atmosphere of pressure at 0 EC), and/or 2.372 Ci/cm3

at 25EC. Under STP conditions, it can also be shown that these values

translate to 58,023 Ci/g-mole and 29,012 Ci/g-atom, respectively.

Beta Emissions. Beta particles interact with matter by colliding with bound

electrons in the surrounding medium. In each collision, the beta particle loses

energy as electrons are stripped from molecular fragments (ionization) or

promoted to an excited state (bremsstrahlung production). Because the rate

I-90