# Ionization energy in Geiger counters

Geiger counters can detect radioactivity because nuclear radiation consists of particles or radiation of sufficiently high energy to eject electrons from atoms. Consequently, this type of radiation is called "ionizing radiation." What is the longest wavelength of radiation that can be detected by a Geiger counter using neon gas as the ionizing medium?

I know the ionization energy of neon is $\pu{2080 kJ/mol}$, or $\pu{3.46*10^{-18} J/atom}$ of Ne (calculated by dividing the I.E. by avogadro's number).

Since $E = \frac{hc}{\lambda}$, I can calculate $\lambda$ to be $57.3$ nm. However, the textbook's answer is $3.64$ nm. I'm not sure why.

• I get your answer too. 3.64 nm is about 340 ev or 32,800 kJ/mole. I have no idea where that value is coming from. I assume that the problem answer is just wrong. // P.S. The sensitivity of a real Geiger counter depends on window thickness too. Seems like an awful thin window. – MaxW Jun 22 '18 at 4:06
• Commonly a GM tube can detect photons as a result of electrons being ejected from the steel of the tube or lead shielding around the tube as a result of the photoelectron or Compton effects. I think you should consider these effects as well as the ionization of the gas in the tube. – Nuclear Chemist Jun 22 '18 at 6:13
• @NuclearChemist - I looked at various x-ray absorption edges and ionization energies assuming that the fill gas had been changed. Nothing seems to fit. // I also tried to see if there was some simple math error. // The resolution cannot have anything to do with some hypothetical wall composition. The textbook's answer is just wrong. I can't figure out why. – MaxW Jun 22 '18 at 17:58
• You shouldn't use the ionization energy of Ne (21.6 eV); you should use the energy that is required to form one ion pair in neon (36.2 eV). However, that still doesn't lead to the textbook result. – Loong Jun 23 '18 at 15:43