Evaluation Study of High Purity Germanium (HPGe) based Technology in Detection of Radiation Sources in Container Ng Bee Ling, Ngoh Li Ee, Gordon Lee, Jerome Koh, Danny Ng, May Ong, Lee Fook Kay Office of the Chief Science and Technology Officer (OCSTO) Ministry of Home Affairs, Singapore

Scope of Presentation Introduction Study Findings Conclusions - Objectives - Detector & Materials Findings Conclusions Further study

Steel Cargo Container can provide shielding to radioactive materials INTRODUCTION Challenges during Container scanning - Radiation Portal Monitor (RPM) and many handheld identifiers are used in field operations RPM : Detection (Plastic scintillator detectors with no ability to resolve gamma peaks) : High Efficiency/low resolution : Can “alarm” quite often Handheld detector : Detection & identification of nuclides : Isotope identification can be challenging for low level radiation Steel Cargo Container can provide shielding to radioactive materials

INTRODUCTION HPGe detector HPGe field deployment NaI Resolution of Th-232 detection, HPGe and NaI detectors side by side. HPGe detector has the ability to resolve the gamma peaks, providing higher resolution detection. Reduce size, complexity, operating power, cost of electronics Low power, reliable mechanical cryogenic coolers HPGe field deployment

Study Objective Detector & Materials To evaluate the potential use of the HPGe detector for cargo container scanning Detector & Materials NORMs HPGe Detector (Falcon 5000®) ISO 20 foot shipping cargo container Safe Radioisotope discs

(used as masking agents) Antique aircraft camera Safe Source & NORMs used in Study Isotope Discs Emission Activity * 1uCi = 3.7 x 104  Bq Cs-137   Gamma 21.2 µci (7.84 x 105 Bq) NORMs (used as masking agents) Readings on IdentiFinder (handheld device) at close distance to sources Identification (Isotopes) Soil 0.67 uSv/hr   Th-232/U-232 Rock 36.11 uSv/hr  Ra-226 Antique aircraft camera 1.01 uSv/hr

DIST. BETWEEN DETECTOR & CONTAINER LOCATION OF RADIOACTIVE SOURCE Test variables A B C LOCATION OF DETECTOR Data collected at Location A, B & C. DIST. BETWEEN DETECTOR & CONTAINER 20cm and 1m from detector to container. Study set-up MASKING WITH NORMs Buried in soil Hid under box LOCATION OF RADIOACTIVE SOURCE IN CONTAINER middle Floor At end wall, away from container doors

Study Background at Location A,B & C collected (Count time of 3,600s). Measurements were made to aid choosing a standard location to perform environmental background counts during normal operations Screening was performed on the container with the handheld NaI detector. The safe source was placed inside the container. No alarm detected B C A

Study Detection capability was evaluated by correct identification of the radiation source placed in different geometries in the container. Count times,300s, 600s, 1200s & 3600s Each detection was repeated at least twice Detector user interfaces Energy Spectrum Mode for location NID mode Dose mode

Background Data Many peaks in the unshielded background Location A Location B Location C Counts Energy (keV) Many peaks in the unshielded background Generally, the background rate at each location is quite similar However, it was observed that the background at Location B gave a poorer detection sensitivity than Location A and C

Common Energy Lines present in the background locations Background Data Common Energy Lines present in the background locations Energy (keV) Nuclide Origin 352 PB-214 Uranium Series 583.2 TL-208 Thorium Series 609.3 BI-214 911.1 AC-228 968.9 1120.1 1460.7 K-40 Natural 1764.3 2614.2 Net Count Rate cps Energy (keV) Net count distributions from background peaks are subtracted from normal measurements during routine analysis Principally from K-40, and three natural decay series: Uranium, Thorium and Actinium

Position of safe source inside container Findings Position of detector Position of safe source inside container Masking Detection Results Observations A   20cm and 1m from container doors Middle and floor of container No Yes Cs-137 detected within 300s At end wall, away from container doors Cs-137 detected at 3600s 20cm from container door Middle of container (safe source buried in a box of soil) No nuclide detected. But Cs-137 was detected within 300s at Location X (safe source hidden under a box of 20kg soil) Cs-137 detected at 3600s. X Container A Container doors End wall

Findings C Position of detector Position of safe source inside container Masking Detection Results Observations C On the mezzanine (high above container)   Middle and floor of container No Yes Cs-137 detected within 300s At end wall, away from container doors Cs-137 detected at 600s Middle of container (safe source buried in a box of soil) Cs-137 detected at 1200s Cs-137 detected at 3600s (safe source hidden under a box of 20kg soil) No nuclide detected. But Cs-137 was detected within 300s at location X  C X Container

Conclusions HPGe detector can provide information about the presence of γ-radioactivity and isotopes emitting radiation in the cargo container The distance between the source and the detector could affect scan time required to identify the source. The placement of the detector is an important factor when deploying HPGe detector In the various masking scenarios, the HPGe detector could identify the radioactive source that was placed in the container Background collection at the deployment locations is preferred for subsequent background subtraction Overall, this study has demonstrated that HPGe detector can accurately identify and ascertain if radiological dangers are present

Further Study To test out the capability of the technology with other isotopes/mixed isotopes Optimizing the placement of the detector using a customized mobile cart

Acknowledgements Office of the Chief Science and Technology Officer Oh Hue Kian Su Hui Yun Goh Jia Feng Phua Xu Mei Zhang Jinhua SECOM (Singapore) Pte Ltd Samson Yang Deon Lim CANBERRA Greg Landry, CHP Jonathan Coleman-Zheng