Abstract:
This thesis focuses on biological shielding calculations for a 10 MeV Rhodotron electron
beam accelerator operating in dual mode to produce a 10 MeV primary electron beam
and 7.5 MeV secondary X-rays, generated by hitting an optimized tantalum-73 (73Ta)
target with the primary electron beam.
The first part of this thesis describes the Rhodotron electron accelerator and its oper ating principle. A model is presented for the transverse optics of a TT-100 Rhodotron
accelerator. Potential industrial applications of a Rhodotron accelerator for Botswana
are highlighted, including sterilization of food products, medical devices, pharmaceuti cals, wastewater and sludge treatment, cargo screening and postal mail decontamination.
Sterilization of food reduces harmful micro-organisms, thus prolonging shelf-life and min imizing health risks to humans. A particular emphasis is placed on the sterilization of
meat for local consumption and export as the meat industry plays an important role in
Botswana’s economy and represents the country’s third main income earner.
The second and main part of this thesis focuses on designing an optimal biological radi ation shielding structure for the Rhodotron and irradiation vaults to protect the general
public, radiation workers and the environment from unnecessary radiation exposure in
compliance with recommendations by the International Commission on Radiological Pro tection (ICRP).
viTwo methods of shielding calculations are employed, namely analytical estimates using
empirical formulas from the literature and Monte Carlo (MC) predictions based on the
FLUktuierende KAscade (FLUKA) simulation package. FLUKA has the added advantage
that the transport of particles (photons and electrons in this project) and their interactions
with matter are included for complex geometrical shielding structures. On the other hand,
FLUKA simulations are numerically intensive and require more computational time.
After the primary beam strikes the target, the main biological dose rate is attributed to
the secondary photons. The shield is designed to reduce the biological dose equivalent
rates to less than 5 µSvh−1 during normal operation. The analytic calculations show that
an ordinary concrete wall with a thickness of approximately 2.1 m is sufficient to shield
the Rhodotron accelerator vault. Using the latter value as the input for FLUKA, the
thickness is varied in steps of 0.01 m from a lower limit of 1.9 m until the biological dose
rate of 5 µSvh−1
is achieved. The FLUKA results show that a 2 m thick ordinary concrete
wall, roof and slab are sufficient to shield both the accelerator and irradiation vaults to
permissible levels for optimal and safe operation.
