Rough identification of a recoil nucleus

From this original picture:

Noyau de recul


We can make an estimate about KE2 :

cloud chamber alpha scattering


Atom present in cloud chamber : H, C, N, O

Energy of the alpha at the time of collision ?


4 MeV initial, so about 3.5 MeV during collision.

Ke1 = 3.5 MeV.

Excel calculus :

excel calc

 So we have to simulate the energy loss in air for H, C, N, O recoil nucleus, with their KE2 calculated. For that, we will use the marvelous SRIM software which calculus the range of ions in matter ( 

If the nucleus is hydrogen, with Ke2 = 0.56 MeV : 


 Recoil range is > 4 mm, or we observe something in a mm range. Can’t be a recoiling hydrogen nucleus.


If the nucleus is  carbon , with Ke2 = 0.65 MeV : 

carbonRange is compatible with observations


If the nucleus is nitrogen , with Ke2 = 0.60 MeV : 


Range is compatible with observations 


If the nucleus is oxygen , with Ke2 = 0.56 MeV :


 Less range. Much more compatible with observations. 


What the alpha will statistically encounter more ?


+ add more carbon from the alcohol molecule, but still low, so excluded.

Nitrogen or oxygen are much more probable to scatter an incoming alpha particle. So in a pure statistical view, this is the recoiling of a Nitrogen nucleus. We can’t know much.