Transcript Document

Introduction to the Radioactive Ion Beam Optimiser: RIBO
Applications to EURISOL and SPES
Mario Santana Leitner
References
[1] M. Santana Leitner, A Monte Carlo Code to Optimize
the Production of Radioactive Ion Beams by the ISOL
Technique, PhD. Thesis, UPC-ETSEIB / CERN.
[2] J. Crank, The Mathematics of Diffusion, Clarendon
Press (1956).
[3] The TARGISOL Project, www.csic.es/targisol
[4] K. Torrance, E. Sparrow, Theory for off-specular
reflection from rough surfaces, Journal of the Optical
Society of America, 57 (1967) 1105-1114.
[5] A. Siber, Theory of Thermal Energy Inert Atom
Scattering from Surface Vibrations, Phd. Institute of
Physics, Zagreb (2000).
[6] U. Koester, Yields and Spectroscopy of Radioactive
Isotopes at LOHENGRIN and ISOLDE, PhD thesis, Phys.
Dpt. Technischen Universitaet Muenchen,
[7] Persistance of Vision Pty. Ltd, www.povray.org
[8] A. Andrighetto, MC Calculation in UCx Target at 40
MeV incident energy, Presentation at Orsay, 13/05/2005
[9] A. Andrighetto, M. Barbui, M. Cinusero, F. Gramengna,
G. Prete (LNL), C. M. Antonucci, S.Cevolani, C. Petrovich
(ENEA Bologna), M. Santana (CERN), Uranium Carbide
Fision Disc Targets for the SPES Project, an Update, The
European Phys. Jour. A (in preparation).
http://www.cern.ch/RIBO
[email protected]
MAXIMIZATION OF RIB EXTRACTION
New facilities aim at more intense RIB’s. Most of the
effort is put to increase the generation with bigger targets
and powerful primary beams I(Y).
DIFFUSION IN SOLIDS. RIBO-diffuse
The first occurring process, and often the dominant one.
Atoms diffuse driven by a ‘concentration repulsive force’[2]:
RIBO-diffuse is a finite method
code that computes diffusion for
particles, fibers and foils with:
However, large targets may entail long diffusion, effusion
and sticking times, and thus, the most exotic isotopes may
decay before extraction; the extraction efficiency (εr) is
hindered.
The Monte Carlo code RIBO [1] integrates all phenomena
linked to extraction, for its prediction + optimization.
EFFUSION IN POWDERS AND FIBERS
Just like normal effusion, except that individual
objects can’t be described geometrically. Instead, the
media are taken as continue, and a statistical approach is
used.
• An average flight path
FP between collisions
is fitted.
• Macro steps are used.
• Variable D, D(x)
• Time varying D, D(x,t)
• Pulsed beams.
• Source/sink terms.
Diffusion release
profile x,t for a nonhomogeneous
starting
concentration
Additional features: invert the diffusion function [3] and sample
diffusion times.
IONIZATION & ION TRANSPORT
Individual trajectories are simulated for molecular and
quasi-molecular flows. Collisions usually follow the cosine law
[4]. These are the features of the effusion module:
• Unlimited full 3-D
combinatorial geometry.
• Multiple source features.
• Adsorption in walls.
• Absorption in walls
(transmission studies).
Scheme input file MK7
• Collisions with residual gas
(hard-sphere) model.
• Several collision modes
(Snell, Lambert, Isotropic)
• Computation of impedances.
Random walk in Ta-129 target
• Time-share analysis.
• Moving walls (valves): New studies underway.
• Effusion through crystals [5] (semi-classic phonon theory).
APPLICATION TO THE UC DISCS TARGET FOR THE SPES PROJECT AT LNL
RIBO tracks effusion up to and including ionization.
Surface Ionization [6]:
Features 1-6 of RIBO are
used in series with MCNPX
to estimate the production of
n-rich radioisotopes in the
SPES-RIB project at INFN.
Simulations concern the
“multi-thin” target [8,9], with
7 UC 6-cm diameter pills.
The different parameters are stored in “sion.dat”, “workf.dat”
The preliminary results yield these release fractions (RF):
Plasma Ionization probability pI:
The cross section σ is read from “plION.dat”; tr is the effusion
time in the ion source.
The FP, D and sticking time
are fitted against real data.
For example, after fitting
these results are obtained.
EFFUSION.
SPES target (7pills +5 dumps) design
view and RIBO input file view, the
latter produced with RIBORAY
Transport of ions (k=q·dt/m):
MORE ABOUT RIBO (www.cern.ch/ribo)
1. Scripts:
• “3D-RIBO” exports geometry to POVRAY [7] ray
tracer.
• “Trace” plots (through PAW) individual trajectories.
2. Output post-processing:
• Direct fit of test effusion release functions to statistical
momenta <t>, <t2>, …, of results.
• Computation of Release Fraction for a grid of values
{T1/2, tsticking, Diffusion} through Laplace transforms.
RIBO computes the trajectory of ions with B{x,y,z},
E{x,y,z} and {x,y,z}0, {vx,vy,vz}0
Recombination and emittance computations also included.
DRF is the diffusion release fraction. 3 Different time diffusion time constants and 3 different
sticking times have been tested for 6 half-lifes. Mass was A=95, and <FP> = 15 micrometer.
Remarks:
• The reference diffusion time constant is 9 s [1]table A.6
• 2.3 % of the effusion time spent in each pill.
• Average free flight = 160 m
• 105 collisions in the powder, i.e. 95% of total.