Design of a cavity ion source with high ion yield for nuclear applications

Cavity ionization is an alternative highly sensitive technique to the more general Thermal Ionisation(TI), for precise isotopic ratio measurement in nuclear technology. Some of the limitations in TI eg., poor precision for low abundant isotopes and also for elements with high ionization potential, can be addressed using this hot cavity ionization source. The cavity consists of cylindrical rhenium (or similar material with high work function) tube with suitable length and diameter and is heated to 2000° - 2500°C. The sample, deposited inside the cavity, gets evaporated followed by ionization by collisions with the hot metal surface by thermal ionization. The multiple collisions of the vapours with the hot cavity lead to high ionization efficiency. The confinement of the sample within the cavity reduces the losses thus allowing sufficient ion yield for very small quantities typically a few nanograms of analyte material. The design involves computer simulations using SIMION 8.0 software. Various models namely wall collision and ionization and reflection models were used to study the ionization probability of the sample particles inside the cavity. An attempt has been made to understand the mechanism and most important parameter(s) leading to enhanced ionisation. The paper will discuss the effect of various design parameters of the cavity on ionization efficiency and optimisation of the design using comparison study among different configurations