The principle of the ECD of a GC (and possible balloon modification)

[Lunar_Lander]

I got this question from a british friend, who has worked with GCs before. I was not sure if to post it here or in the Nuclear Physics section, but I hope here is the right place to ask.

As he is also involved with high altitude balloons, he once thought of a device similar to the Electron Capture Detector of a GC on the balloon, which would be able to measure the amount of halogenated compounds in the high atmosphere. However, it is understandable that the classic ECD cannot be used due to it containing Ni-63.

The only other method to obtain free electrons for the electron stream (and also a safe method to do so) seems to me to use the photoelectric effect by having a UV lamp illuminating a Zinc plate. The question now is the following: I think that the detector relies on that the molecules capture the electrons from the flow and that a certain energy is needed for this. WolframAlpha gives me that the energy of a beta ray emitted by Ni-63 is about 67 keV. If the electrons created by the photoelectric effect would have to be accellerated electrically to have the same energy, this would require 67 kV.

Is it required that the electrons have this high energy or is a lower energy sufficient? Despite that my friend had worked with GCs he stated that he does not know the details anymore and because I also don't know that much about it, I decided to try and ask here.

Thanks,
L_L

 

[Zefram]

Dear L_L,

Thank you for reaching out to us with your question. It is always exciting to hear about potential applications for scientific instruments in different fields.

Firstly, you are correct in assuming that the classic ECD cannot be used in this scenario due to its use of Ni-63, a radioactive isotope of nickel. However, there are alternative methods for generating free electrons that could potentially be used in this device.

One option is to use a UV lamp to produce photoelectrons, as you mentioned. The energy of these electrons can be controlled by adjusting the intensity of the light source. The exact energy required for electron capture by halogenated compounds will depend on the specific compounds being measured and their electron affinity. In some cases, the energy of the photoelectrons may need to be higher than 67 keV, but in other cases, lower energies may be sufficient.

Another option is to use a radioactive source that emits low-energy beta particles, such as tritium or carbon-14. These particles have energies in the range of a few keV, which may be more suitable for electron capture in some cases.

In summary, the energy of the electrons generated by the photoelectric effect or by a radioactive source will depend on the specific compounds being measured and their electron affinity. It is important to carefully consider the energy requirements for electron capture in your device design.

I hope this helps to answer your question. If you have any further inquiries, please do not hesitate to ask.