1. Apr 20, 2014

### vanceEE

"Radium-226 has a half-life of 1,620 years, which means that half of a given sample of radium-226 will decay into lead by the end of 1,620 years. In the next 1,620 years, half of the remaining sample will decay into lead, leaving one-fourth of the original amount of radium-226."(1)

Wouldn't half of the Radium-226 decay into Radon-222 instead of Lead? I am new to this but my previous knowledge of decay from Physics tells me that Radium would would first decay to Radon by the end of 1,620 years which can be described by the equation below:
$\stackrel{226}{86}Ra→ \stackrel{222}{84}Rn + \stackrel{4}{2}He$

Is (1) a misprint or am I missing the half-life concept?

2. Apr 20, 2014

### snorkack

The main branch daughters of radium are:
So all non-lead daughters of radium have a combined half-life of under 148 days. Over the 1600 year half-life of radium, almost all that has decayed into radium emanation has gone on to lead.

3. Apr 20, 2014

### Staff: Mentor

I think it should be more like

^{226}_{\phantom{0}88}Ra \rightarrow {}^{222}_{\phantom{0}86}Ba + ^{4}_{2}He

Edit: this is wrong, idiotic mistake. See below.

What they mean is most likely that there is a long decay chain which ends with Pb. If most steps are faster, that's effectively as if the Ra was decaying into Pb with a given half life.

Last edited: Apr 21, 2014
4. Apr 20, 2014

### DrDu

Are you really sure about Barium?

5. Apr 21, 2014

### Staff: Mentor

Sigh, I copy pasted nice LaTeX from another post - and I corrected atomic masses, but got distracted and left Ba from the original code

$$^{226}_{\phantom{0}88}Ra \rightarrow {}^{222}_{\phantom{0}86}Rn + ^{4}_{2}He$$

6. Apr 21, 2014

### DrDu

:-)
$$\mathrm{^{226}_{\phantom{0}88}Ra \rightarrow {}^{222}_{\phantom{0}86}Rn + ^{4}_{2}He}$$?