Ion source with cathode having an array of nano-sized projections

A well logging instrument comprising:

• a sonde housing;
• a radiation generator carried by the sonde housing and comprising an ion source comprising at least one cathode comprising a substrate supporting an insulating layer having an array of holes formed therein, an array of nano-sized projections, respective projections of the array of nano-sized projections being positioned in corresponding holes of the array of holes, and an array of gates opposite the array of nano-sized projections and supported by the insulating layer, the array of nano-sized projections and the array of gates having a first voltage difference such that a resultant electric field between respective projections and gates causes electrons to be emitted from the array of nano-sized projections and accelerated away from the at least one cathode;
• and an ion source electrode downstream of the at least one cathode;
• the at least one cathode and the ion source electrode having the same voltage applied such that the electrons enter the opening of the ion source electrode, some of the electrons as they travel downstream through the opening of the ion source electrode striking an ionizable gas to create ions;
• an extractor electrode downstream of the ion source electrode;
• the ion source electrode and the extractor electrode having a second voltage difference such that the ions are accelerated toward the extractor electrode;
• a suppressor electrode downstream of the ion source;
• and a target downstream of the suppressor electrode;
• the extractor electrode and the suppressor electrode having a voltage difference such that a resultant electric field between the extractor electrode and suppressor electrode accelerates the ions generated by the ion source toward the target.