old Units

[Peter-1]

hello,
Who has an idea how I can convert a radiation source with radium from an old emanation apparatus with an indication of 25000 ME (Mache) into a current unit? I don't mean the familiar conversion.

1 ME = 3,64 Eman = 3,64×10−10 Ci/l = 13,4545 Bq/l

What I am looking for is the activity of the source in Bq.
Who has a tip?
Peter

[GigaBecquerel]

Hello Peter,

I am not sure what you're asking here.
You have 25000 ME, that's 336362.5 Bq/l.
Multiply that with the volume of your sample and you have the activity

[Peter-1]

I do not want to know the Bq / liter, but rather whether it is possible to calculate the activity of the source that generates this ME units.

[GigaBecquerel]

I got that, but if you have the volume-specific activity you multiply by volume and have the actual activity.

336 kBq/l times 1 l of sample is 336 kBq, 336 kBq/l times half a liter is 168 kBq.

Due to the high difference in half life you can assume that the Rn activity is the same as the Ra activity

[jneilson]

I know this is an older question but it looked interesting and although Gigabecq's answer seems largely correct to me, it also seems that the context is incomplete. Yes, Mache converts to a Bq/L value, and dimensionally, multiplying by volume gives activity - but it's perhaps not obvious what volume that relates to without some thought about the device in question; it's not quite the same thing as the usual context you'll find Bq/L when taking a water sample for environmental or process monitoring - the radium source itself is not part of a liquid.

However, thinking about what a radium emanation apparatus is (at least from my understanding), it's one of the early radium craze quackery things, designed to infuse drinking water with the radium emanations (radon and daughters), which would supposedly have health benefits when drunk. I imagine the standard operation would involve a volume of water being left to collect the radon emanations, which would gradually build up in the water as the radon was released from the radium and dissolved in the water. Thus presumably the rated Mache number is the activity concentration in the water the apparatus would produce when following its standard procedure, rather than directly relating to the source.

The activity in the water will build up until it reaches a steady value when the amount of radon being added from the radium decay matches the loss from decay and radon escape. If you assume all the radon migrates from the source to the water, and escape is negligible, you'd expect water to reach close to the equilibrium point after a few days, when the decay chain approximates secular equilibrium, and the activity of Rn in the water will be the same as the activity of Ra in the source. If you assume the Mache number is based on that activity being dissolved in a standard volume of water (the vessel size), then multiplying the converted Mache number by the vessel volume gives you Bq of Rn-222 in the water, and thus by secular equilibrium the Bq of Ra-226 in the source.

However, there's a few assumptions being made here that are not necessarily accurate - perhaps the Mache number is based on a different concentration than secular equilibrium, especially if there's significant Rn trapped in the source or escaping from the water to account for, or the standard use was to take the water after a shorter time before secular equilibrium was reached.

Of course, there's also decay to factor in as to the activity now, although the 1600yr half life of Ra-226 would mean the activity today, even around a century onward, will still be pretty similar to the original activity.