An artificial neutron source has been built which is very stable in operation and flexible in use. Using the D—D reaction, target currents of more than 200 microamperes at 300 kv give a neutron yield of 10 grams radium‐beryllium equivalent. It has been found that voltage stability at these currents may be greatly improved by the use of special diaphragms, and that a reflux target cooling system is very satisfactory in maintaining a heavy water‐ice target. Electrostatic deflection of the ion beam has produced a neutron source which may be modulated at high frequencies or otherwise time‐controlled.