Evaluation Study of High Purity Germanium HPGe based

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

• Introduction • Study - Objectives - Detector & Materials • Findings • Conclusions • Further study

• 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 Steel Cargo Container can provide shielding to radioactive materials : Detection & identification of nuclides : Isotope identification can be challenging for low level radiation 3

HPGe detector HPGe Na. I Resolution of Th-232 detection, HPGe and Na. I detectors side by side. HPGe detector has the ability to resolve the gamma peaks, providing higher resolution detection. • HPGe field deployment - Reduce size, complexity, operating power, cost of electronics - Low power, reliable mechanical cryogenic coolers 4

• Objective To evaluate the potential use of the HPGe detector for cargo container scanning • Detector & Materials – – HPGe Detector (Falcon 5000®) ISO 20 foot shipping cargo container Safe Radioisotope discs NORMs 5

Safe Source & NORMs used in Study Isotope Discs Emission Activity * 1 u. Ci = 3. 7 x 104 Bq Cs-137 Gamma 21. 2 µci (7. 84 x 105 Bq) NORMs (used as masking agents) Readings on Identi. Finder (handheld device) at close distance to sources Identification (Isotopes) Soil 0. 67 u. Sv/hr Th-232/U-232 Rock 36. 11 u. Sv/hr Ra-226 Antique aircraft camera 1. 01 u. Sv/hr Th-232/U-232

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

– Background at Location A, B & C collected (Count time of 3, 600 s). 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 Na. I detector. The safe source was placed inside the container. No alarm detected B A – C

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

Background Data Location A Counts Location B Location C Energy (ke. V) • 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

Background Data Net Count Rate cps Common Energy Lines present in the background locations Energy (ke. V) Nuclide Origin 352 PB-214 Uranium Series 583. 2 TL-208 Thorium Series 609. 3 BI-214 Uranium Series 911. 1 AC-228 Thorium Series 968. 9 AC-228 Thorium Series 1120. 1 BI-214 Uranium Series 1460. 7 K-40 Natural 1764. 3 BI-214 Uranium Series 2614. 2 TL-208 Thorium Series Energy (ke. V) • 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

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

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

• HPGe detector can provide information about the presence of γradioactivity 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

• To test out the capability of the technology with other isotopes/mixed isotopes • Optimizing the placement of the detector using a customized mobile cart 15

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 CANBERRA Samson Yang Deon Lim Greg Landry, CHP Jonathan Coleman-Zheng