Analytical model for release calculations in solid thin-foils ISOL targets

Abstract

A detailed analytical model has been developed to simulate isotope-releasecurves from thin-foils ISOL targets. It involves the separate modeling of diffusion and effusion inside the target.The former has been modeled using both first and second Fick'slaw.The latter,effusion from the surface of the target material to the end of the ionizer, was simulated with the Monte Carlo code Mol Flowþ. The calculated delay-time distribution for this process was then fitted using a double-exponential function. There lease curve obtained from the convolution of diffusion and effusion shows good agreement with experimental data from two different target geometries used at ISOLDE. Moreover, the experimental yields are well re- produced when combining there lease fraction with calculated in-target production

Computational Studies of Solid Stoppers for Generating Intense Exotic Radioactive Ion Beams at FRIB

“…For example, the finite elements codes ANSYS [6, -] and COMSOL [7] were used to calculate the temperature distributions in ISOL target assemblies due to beam heating, applied heating, and external cooling [8,15]. The diffusion delays were calculated by analytically solving Fick's equations for simple planar, cylindrical, and spherical geometries [9,10] or with a finite-difference code [9,11], while the effusion process was simulated using a Monte Carlo code such as GEANT4 [12,13], MolFlow+ [14],…”

“…( 13). The effusion release rate fe (t) is obtained by taking the histogram of the particle release times from effusion simulations and fitting the data to the following function [10]:…”

“…( 24). To calculate the convolution analytically [10,33], we used the first 50 terms in Eq. ( 13) for the diffusion function…”