FLUKA simulation studies of ISAC targets at TRIUMF

                                 Mina Nozar
                                   TRIUMF

Abstract:
FLUKA has been extensively utilized at TRIUMF to study various target,
converter, and absorber designs for the upcoming ARIEL proton and electron
beams, to maximize isotope yields while minimizing power deposition in the
target.  In addition, time evolution of activities and residual dose rates have
been determined for shielding purposes.

FLUKA has also been used to optimize Sr-82 yields through modifications to the
beam energy, intensity, and target parameters in a 85Rb(p,4n)82Sr reaction.
Additional shielding requirements were determined and a proposed shielding
implementation was tested.

This talk will focus on a FLUKA study of six ISAC targets used between 2008 and
2010.  Of these, two are Low Power targets: Ta#27 and SiCGr#24,  using TM4
assembly (LP-TM1), and four are High Power targets: Ta#26, SiCGr#25, Nb#4, and
Nb#5, using TM4 assembly (HP-TM4). All targets were irradiated with 480 MeV
protons for approximately 600 hours.  Beam intensity was about 40 mA for Low
Power targets and 80 mA for High Power targets.  The target assemblies were
modelled to consist of seven main components: the target material itself and six
materials making up the target oven, the heat shield, and the ion extraction.

Using the one-step method, we determined the following quantities in the above
mentioned seven regions of interest:  isotope production rates, time evolution
of the residual nuclei and the corresponding activities,  as well as star
densities and deposited energies.  We also looked at the time evolution of
residual dose rates due to induced radioactivity in a detector placed radially 1
m from the center of the beam.

In order to determine residual dose rates in the presence of different shielding
scenarios, we used Stefan Roesler's two-step method.  In particular, we looked
at dose rates1 week after the EOB outside the Spent Target storage vault
shielding and 3 year after EOB outside the Target Transport Flask.

Since FLUKA is now capable of calculating activities using the analytical
solution of Bateman equation, we would like to discuss the feasibility of using
information about the activities for a given irradiation parameter and cooling
time to assess shielding configurations (eg. storage or transport) using the
standard FLUKA. This can also be achieved if one is able to include the
shielding configurations in the FLUKA run with assigning vacuum to the region
and shielding material to the decay material.