16 th international congress on neutron capture therapy june 14-19, helsinki, finland improvement of...

16th International Congress on Neutron Capture TherapyJune 14-19, Helsinki, Finland

Improvement of a PGNAA Facility for BNCT in THOR

C. K. Huang1, H. M. Liu2, J. J. Peir2, Y. S. Huang2, and S. H. Jiang1

1 Institute of Nuclear Engineering and Science, National Tsing Hua University 2 Nuclear Science and Technology Development Center, National Tsing Hua University

Taiwan


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


Introduction

- Reactor & Neutron Beam Tsing Hua Open-pool Reactor (THOR)


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: 228.76cm Diameter: 8-inch

Outside part Length: 158.75cm Diameter: 10-inch


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


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


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


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


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 10B(n, )α 7Li reaction.

Materials & Methods


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

unit: uSv/h

previous now previous now

#1 62.00 13.85 overload 25.00

#2 3.50 0.17 3.50 0.24

#3 1.00 0.32 4.50 0.35

#1 overload 70.00 overload 110.50

#2 6.25 0.49 10.25 0.65

#3 3.00 1.02 6.25 1.10

#1 overload 190.00 overload 260.00

#2 21.00 0.90 25.00 1.13

#3 6.25 2.39 11.50 2.25

1.2MW

ReactorPower

Position

Shutter Status

Close Open

100kw

500kw


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 ~4x107 neutrons-cm-2-sec-1 (meas.)

thermal (<0.4eV) 4.88E-03 1.55% 18.50%epithermal (0.4eV-10keV) 4.95E-03 1.56% 18.78%

fast (10keV-20MeV) 1.65E-02 0.81% 62.71%total 2.64E-02 0.65% 100.00%

RERelativeStrength

neutron energyflux per source

intensity


Results MCNP simulation with a phantom at different position

The “Booster”


Results


Results Phantom position: 30cm away from beam exit

Foil position: at 2cm depth in phantom

Thermal neutron flux is 3.66x107 neutrons-cm-2-sec-1

The net counting rate resulted from the 10B(n, )α 7Li reaction in boron sample is about 342 cpm.

The dead time of HPGe detector is ~32.8%


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: ~4x107 neutrons-cm-2-sec-1

At 32cm away from beam exit (with a phantom as a booster): 3.66x107

neutrons-cm-2-sec-1

The dead time problem for HPGe system is still a challenge due to severe scattering background contamination.


Acknowledgement

Mr. Yu-Shiang Huang

Dr. Hong-Ming Liu

Dr. Jin-Jer Peir

Dr. Fong-In Chou

Dr. Mei-Ya Wang


Thank you for your attention.

Taiwan

16 th international congress on neutron capture therapy june 14-19, helsinki, finland improvement of...

Documents

neutron capture therapyjune

epithermal neutron beam

beam exitwith

e2 beam design

radial neutron beams

original e2 beam exit

thor core

core calculation