16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland Improvement of a PGNAA Facility for BNCT in THOR C. K. Huang 1, H. M. Liu 2, J. J. Peir 2, Y. S. Huang 2, and S. H. Jiang 1 1 Institute of Nuclear Engineering and Science, National Tsing Hua University 2 Nuclear Science and Technology Development Center, National Tsing Hua University

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland  The dose delivered during Boron Neutron Capture Therapy (BNCT) is highly depended on boron concentration accumulated in tumor region. Accordingly, the information of boron concentration in blood is essential.  In Taiwan, 17 BNCT clinic trials were performed  ICP-AES was used to determine the boron concentration in blood samples.  In order to not only accurately but rapidly measure boron concentration in blood samples, a Prompt Gamma Neutron Activation Analysis (PGNAA) facility is being under construction at E2 beam port of Tsing Hua Open-pool Reactor (THOR). Introduction

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland Introduction - Reactor & Neutron Beam  Tsing Hua Open-pool Reactor (THOR)

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland  Tsing Hua Open-pool Reactor (THOR)  A TRIGA-conversion research reactor with maximum thermal power of 2MW.  One epithermal neutron beam for BNCT and the other six radial neutron beams. Introduction - Reactor & Neutron Beam  E-2 beam  Inside part  Length: cm  Diameter: 8-inch  Outside part  Length: cm  Diameter: 10-inch

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland  Construction design of E2 beam was performed in previous work and the installation of beam collimation plug was completed subsequently.  A cylindrical concrete beam collimation plug with an aperture of 1 inch was adopted. Introduction - Reactor & Neutron Beam

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland  A tremendous amount of fast neutrons and gammas will come out directly from the core.  Therefore, these undesired contaminations result in high background dose rate surrounding the PGNAA facility and in addition, cause significant dead- time loss during prompt gamma ray measurement.  The objectives of this work are to reduce severe background contaminations as well as to maintain sufficient thermal neutron flux at sample position of the PGNAA facility. Introduction - Challenge & Aims

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland Materials & Methods  To lower background contaminations, a shielding assembly using lead and borated polyethylene was employed at a distance of ~50 cm away from E2 beam exit. System Shielding Beam capture Beam collimator

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland  MCNP was used for core calculation and E2 beam design.  A full core calculation was performed from THOR core firstly to establish a source plane near the original E2 beam exit.  Source term is a disk source positioned at ~40cm behind the beam exit  With a radius of 13cm  29 energy group from 0.01 to 20MeV.  The space distribution is basically divided into two group, inside(r<1.3cm) and outside(r=1.3-13cm), respectively.  Based on this spectrum, we calculate the flux at beam exit Materials & Methods

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland  Simulation on different scenarios were performed.  Free-in-air  Phantom as a thermal neutron “Booster”  Comparison between different position  To determine thermal neutron flux, a two-foil method was adopted.  An HPGe detector was used to measure the gamma spectrum, and to determine the peak area resulted from the 10 B(n,α) 7 Li reaction. Materials & Methods

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland Results  Background gamma dose rates were measured and compared.  A preliminary result showed that gamma dose rate surrounding the PGNAA facility decreased significantly, with 3 to 25 times lower depending on different measuring position. #2 #1 #3

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland Results  To determine thermal neutron flux at beam exit, a double-foil activation analysis was adopted and a MCNP simulation was also performed.  Thermal neutron flux at beam exit is ~4x10 7 neutrons-cm -2 -sec -1 (meas.)

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland Results  MCNP simulation with a phantom at different position  The “Booster”

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland Results

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland Results  Phantom position: 30cm away from beam exit  Foil position: at 2cm depth in phantom  Thermal neutron flux is 3.66x10 7 neutrons-cm -2 -sec -1  The net counting rate resulted from the 10 B(n,α) 7 Li reaction in boron sample is about 342 cpm.  The dead time of HPGe detector is ~32.8%

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland Summary  A PGNAA facility at E-2 beam in THOR is now under remodeling and a phantom as a booster is adopted.  The background dose rate at sample position is still not low enough for operation.  With a presence of booster, thermal neutron flux could possibly raises 5 times.  Thermal neutron flux is measured successfully:  At beam exit: ~4x10 7 neutrons-cm -2 -sec -1  At 32cm away from beam exit (with a phantom as a booster): 3.66x10 7 neutrons-cm -2 -sec -1  The dead time problem for HPGe system is still a challenge due to severe scattering background contamination.

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland Acknowledgement  Mr. Yu-Shiang Huang  Dr. Hong-Ming Liu  Dr. Jin-Jer Peir  Dr. Fong-In Chou  Dr. Mei-Ya Wang

16 th International Congress on Neutron Capture Therapy June 14-19, Helsinki, Finland Thank you for your attention.