Characterization of River Sand from and Gombak as wall Radiation Shield for Mobile Hot Cell Muhammad Hannan Bin Bahrin Bahagian Sokongan Teknikal (BST) Unit : Pusat Pembangunan Logi dan Prototaip Megat Harun Al Rashid Megat Ahmad, Hasni Hasan, Anwar Abdul Rahman, Azraf Azman, Mohd Zaid Hassan, Mohd Rizal B. Mamat, Shalina Sheikh Muhamad , Mohd Arif Hamzah , Rafhayudi Jamro, Yii Mei Wo and Nurliyana Hamssin

Acknowledgements

 Ministry of Science, Technology and Innovation (MOSTI), Funding under RMK10, 4TH rolling. Project Technology Development and local engineering in radioactive sources management. Development of Mobile Hot Cell and Nuclear equipment / Gamma Irradiation sources [Project code: P30009001003006].  Kumpulan Radiokimia dan Alam Sekitar (RAS), Bahagian Teknologi Sisa dan Alam Sekitar (BAS), Agensi Nuklear .  Kumpulan Teknologi Bahan (M TeG), Bahagian Teknologi Industri (BTI), Agensi Nuklear Malaysia.  Pusat Pembangunan Logi dan Prototaip (PDC), Bahagian Sokongan Teknikal (BST), Agensi Nuklear Malaysia. Introduction

Mobile Hot Cell (MHC) • Mobile Hot Cell (MHC) are designed to handle and manage seal sources of Spent High Activity Radioactive Sources (SHARS) such as irradiators and teletherapy heads.

Mobile Hot Cell sand shielding

Definition: Sand is a soil particle size between 0.05 and 2.00mm in diameter.

Glossary of terms in soil science

Type of sands: • Very coarse sand • Coarse sand (typical) • Medium sand • Fine sand (typical) • Very fine sand

River sands are filled and compacted between internal compartment and outer wall of MHC.

Advantages of using sands are: • Its availability everywhere which suit the MHC purpose. • It is not permanent, it can be transferred, cleaned or replaced. Details Coarse sand Fine sand

Sand particle size 0.5 – 1.0 mm 125 – 250 µm

Coarse sand Coarse sand Fine sand Fine sand Sample Kajang Gombak Kajang Gombak

River sand from Kajang is obtain from: The Living Depot (Bangi) Price: RM10/ gunny sack River sand from Gombak is obtain from: Greenwood City Furniture , Price: RM12 / gunny sack Objectives

• To test the linear variation of attenuation coefficient, μ on different sample of river sand at 661.7 keV gamma radiation from sealed source Caesium – 137 (137Cs) • To estimate build-up factor value for each sample using Berger formula at the actual shielding thickness.

The mass attenuation coefficient

Photons can be only scattered or absorbed. Photon absorption is an interaction process when the photon disappears and all its energy is transferred to atoms of the material or to secondary particles.

Exponential attenuate on law:

= - Emerges with intensity, I −휇휇 - Incident intensity, Io Rearrange퐼 퐼0 푒 equation: - Penetrating of material with mass thickness, r - Linear Attenuation Coefficient, μ = + - Build-up factor, B

Real푙푙 퐼 condition−휇휇 equation:푙푙 퐼표

= −휇휇 퐼 퐵퐼0 푒 River sand sample preparation

Sample are dry into furnace at 110oC for 6hour. The moisture contain are low, between 4% to 6%.

Coarse sand Kajang (PKK) Coarse sand Gombak (PKG)

Fine sand Kajang (PHK) Fine sand Gombak (PHG) Methodology

Information of source used: Cs-137(because of simple spectrum) - Current activity (July 2016): 7.98µCi

Ervin B. Podgoršak, Modes of Radioactive Decay, Radiation Physics for Medical Physicists (2010) Page: 475 Linear attenuation coefficient determination using Gamma Spectrometer

Disk Model 747 sources CANBERRA Cs-137 Lead Shield

Screw

Model 7500SL CANBERRA Vertical Slimline Shielding thickness Cryrostat level (2cm to 10cm) Detector: High-purity germanium (HPGe) Gamma Spectrometer Gamma spectrometer data result

= 1 cos 1 + 퐸훾 퐸훾′ − 휃 퐸훾 2 푚표푐

Hannan et al , Nustec 2016, August 8-10, Comparison of photopeaks between shielding material (H2O) and without shielding material Data fitting

1. Gaussian function (photopeak):

( ) = 2 − 푥−푏 2 2푐 푓 푥 푎푒 2. Minimizing sum of least-square method 3. Levensberg-Marquadt Algorithm Kajang coarse sand at photopeak Value of linear attenuation coefficient, μ of sand sample

휇 푁�푁푁 휌 푤푤푤푤�

= −휇휇 is퐼 linear퐼0푒 attenuation coefficient 휇

Sample Density, ρ (g/cm3) µ experiment (cm-1) µ NIST (cm-1) Water 1 0.0862 0.0862 Gombak fine sand (PHG) 1.58 0.1353 No information Kajang fine sand (PHK) 1.59 0.1304 No information Gombak coarse sand (PKG) 1.72 0.1417 No information Kajang coarse sand (PKK) 1.85 0.1508 No information Build-up factor

Berger formula: *Build-up factor (J. R. Lamarsh) , = 1 + ( ) ( ) 푏 퐸 휇휇 ( ) and ( ) have been determined퐵 by퐸 fitting휇휇 the results푎 퐸 휇휇 of 푒calculations to this analytical expression. 푎 퐸 푏 퐸 Calculating dose reduction based on first principle = 풆풆 풂풂풂 −흁� Example dose value inside containment wall: 푩풌풌풌 흁 ⁄흆 Dose rate푫 at wall, ퟐ 풆Dose with Shielding Buildퟒ흅� up µSv/hr (without build up  e.g: inside is 1000 Ci of Cs-137 material factor, B build-up) (µSv/hr )

Water, H2O 2.857 555 1.58e3

Gombak fine 5185 9.38 sand (PHG) 1.80e-3

Kajang fine 1074 4.05 sand (PHK) 3.76e-3

Gombak coarse sand 0.69e-3 3868 2.68 (PKG) Without considering build-up factor and skyshine effect. Kajang coarse 1883 1.30 sand (PKK) 0.18e-3 Conclusion

• Coarse sand Kajang is found to the most suitable for mobile hot cell biological shield. • Gamma spectrum can provide accurate value of linear attenuation coefficient as well as estimation of radiation build-up especially Compton scattering. • Build-up of radiation at lower energies from photopeak is clearly visible. • Berger formula can provide an estimation of build-up factor for sand sample at the desire shielding thickness. Future works

• Determine spectrum and linear attenuation coefficient for 60Co. • Evaluate build-up factor according to collimated and wide beam dose experiment. • Mathematically unfolding the measured data to access real spectrum and obtain better build-up factor value. • To correlate with MCNP computations (possibly also with our own Markov- Chain Monte Carlo random walk method especially if MCNP fails). References • J. H. Hubbell, Int. J. Appl. Radiat. Isot. 33, 1269 (1982). • The National Institute of Standards and Technology (NIST) • N. Tsoulfanidis, S Landsberger, Measurement and detection of radiation, P311, 3rd edition, (2011) • J. R Lamarsh, A. J. Baratta, Introduction to nuclear Engineering, 3rd edition, (2001) • Dhlomo S V, Swart H S, Evaluation and Verification of a Biological Shield in a SHARS Unit (2008) Thank you