1. Improving the radiation detection level and operational data of pre and post event monitoring systems
Alon Osovizky PhD.
Y. Ifergan, E. Vax, Y. Yehuda-zada, B. Sarussi, D. Smadja, Y. Levin, S. Dadon,
Y. Levin, Y. Knafo, T. Mazor, Y. Kadmon
Israel Atomic Energy Commission (IAEC)
6 December 2016
Vienna International Centre
Good after noon
My name is Alon Osovizky
And my talk presents segmented detection array with an ability to determine the direction of the radiation source
IAEA International Conference on Nuclear Security: Detection Equipment

2. Introduction
Worldwide effort to improve the performance of detection instrumentation
Goal – Angular response
Detector array configurations
Results
Discussion
There is a need to improve the performances of the radiation detection instrumentation.
Important Parameters such as power consumption, instrument dimensions and isotope identification have been addressed by many systems.
This work is focused on providing information on the direction of the source once the rate alarm is triggered
This information which enhanced operational data is obtained by dividing the detector into segments
During this talk I will present the detector array configurations the measured results the analysis method and will discuss our findings and our plans for future work.
IAEA International Conference on Nuclear Security: Detection Equipment

3. Pre and Post Events Deep space Environmental Monitoring HLS:
Pre Event – Fast Response
Post Event - Hot Spot
Systems for determine the direction of the source are needed for several applications like deep space investigation, environmental monitoring and nuclear security.
The ability to define the source direction enables faster response.
Fast response is a major advantages at pre events scenarios
the indication for the source direction provides an important operational data for the field security response team.
At post event scenarios hot spots can be identified faster therefore reducing the personnel dose exposure
Goal:
To provide the direction of the radiation source
IAEA International Conference on Nuclear Security: Detection Equipment

4. “Arc-Shape” – 2D Configuration
Experimental setup
Our setup is based on detector array where the method for identifying the radiation source direction is based on
the ratio between each of the detectors and the total counts.
Each of the detectors count rate is changing according to the source location because of the radiation attenuation by it’s neighbors detectors.
The first configuration that we have evaluated is The arc-shape which is a 2D configuration,
imagine that the detector array is monitor a room from the wall.
On the presented source location the detectors on the left would have a lower count rate then the group on the right because they are shielded by them
or monitoring ground while being installed on the bottom of flying object e.g. UAV.
Six Bi4Ge3O12 crystals
IAEA International Conference on Nuclear Security: Detection Equipment

5. “Flower-Shape” – 3D ConfigurationsX
The second configuration is a flower shape configuration
The flower shape configuration is aimed to provide the third dimension.
imagine monitor the same room but this time from the ceiling instead of the wall.
The room can be divided more easily into separate regions both on the floor and in different elevations
We have evaluate the angular response of configuration were all the detector are in the same height
and another configuration were the central detector is raised above the other detectors, like a sundial concept.
The source location was set by theta degree which is the elevation of the source and phi degree which is the azimuth
“Sundial”
Concept
Det.#1 in the center is in the same height as the other five detectors.
Det.#1 in the center is raised above the other five detectors.
IAEA International Conference on Nuclear Security: Detection Equipment

6. Simulation GEANT4 Step 1 – Correlation to measurements
Step 2 – Optimization
0° ≤ φ ≤ 360°
and
0° ≤ θ ≤ 90° steps of 15°
We have simulated our setup configurations.
The figures presents the flower shape
a side view on the right and an upper view on the left. The detectors array is in the center and all the location where the source was measured- the white dots.
As a first step we have looked for correlation between the measured and simulated results for validating our simulation results.
Then on the second step we investigated other detectors array configuration based only on simulation for optimizing the angular response
IAEA International Conference on Nuclear Security: Detection Equipment

7. Direction estimation - Initial phase{ , ,… ,
,…,
Direction estimation - Initial phase
Measuring the angular response function:
Measure the detectors array angular response: a(φ,θ)
Normalize each detector measurements: Di / Total counts
Interpolate the angular response to 2o steps: {a(0,0), a(0,2),…,a(2,0),a(2,2),…,a(90,0),…, a(90,358)}
The analysis process was based on few steps.
On the first step the detectors reading at each of the testing points (the white dots presented on the previous slide) was record
and normalized by dividing each detector counts by the total counts
then we interpolate the angular response to 2deg step between the measured points.
For each measuring point (specified by theta and phi) a vector A of the normalized detectors counts was documented.
IAEA International Conference on Nuclear Security: Detection Equipment

8. Direction Estimation - Algorithm
Finding the direction that outputs maximum correlation to the angular response by using a spatial matched filter (“Beam Former”)
Where :
 Sampled Auto Covariance (6x6 matrix)
 Known Normalized Angular Response (6x1 vector)
Calculate the estimation error.
On the second step the measured data from an unknown direction was analyzed by applying “Beam Forming” method.
Beam forming is a classical spatial signal processing methods, developed for radar antenna arrays to identify the electric signal direction.
The analysis algorithm is matching between the measured data from unknown angle and the premeasured database from the known directions.
A scalar is calculated by multiplying the vector A (theta and phi) at a known position by the sampled covariance matrix and the transposed vector.
This search process is done repeatedly over all the half sphere vectors saved in the database to find the maximum scalar value.
High scalar value implies on a good matching between the measured data and the evaluated direction.
IAEA International Conference on Nuclear Security: Detection Equipment

9. Evaluation Method
Estimation error – a tool for comparing between array configurations.
Estimation error = True direction - Estimated direction
Reading statistic affects the direction estimation error.
Qualitative comparison by adding noise and evaluating the error statistics of the estimated source direction.
Quantifying the angular systematic error of measurements at unknown locations for predefined working conditions.
The Estimation error is a tool for comparing between array configurations
The Estimation error equal to the True direction minus the Estimated direction
The reading statistics (source intensity and measuring time SNR) affects the direction estimation error.
Hence, the method utilized for qualitative comparison between the various configurations was based on
adding statistical noise to the measured/simulated data and evaluate the mean error (bias) of the estimated source direction relative to the known source direction.
This bias error provides an indicator for comparing between the angular error of different detector configurations and for the time period required for achieving the similar accuracy. Once the optimal configuration will be selected, measurements at unknown location will be performed for quantify the angular systematic error at predefine working conditions.
The calculated angular error is used to compare between detectors array configurations.
estimation error is the difference between the True direction to the Estimated direction.
IAEA International Conference on Nuclear Security: Detection Equipment

10. “Arc-Shape” – 2D Configuration
THIS SLIDE PRESENTS THE ARC SHAPE results
We can see that the ratio between each of the detector counts and the total counts has an angle dependence.
It can be seen that the “arc-shape” configuration succeeds in estimating the true direction of the source over the range of 0° ≤ θ ≤ 180° with high accuracy
for noise levels of 1, 5, 10 and 25%
Error bars are equal to the STD error
The ratio Di/Σdi has an angle dependence
IAEA International Conference on Nuclear Security: Detection Equipment

11. “Flower-Shape” – Experiment vs. Simulation
Measured Response
Theta = 72 deg
Simulated Response
Theta = 72 deg
The normalized ratio Di/Σdi has an angle dependence
IAEA International Conference on Nuclear Security: Detection Equipment

12. “Flower-Shape” – Experiment vs. Simulation
Measured Response
Theta = 18 deg
Simulated Response
Theta = 18 deg
The results measured and simulated for theta of 18 degree presents the obstacle for determine the source location.
When the Ratio of all the detectors is 0.16 (1/6 of the readings) that means uniform reading
Furthermore the detectors have same ratio over the 360 deg of the azimuth PHI t
hat means that the vector A stored in the database for all the PHI points at theta of 18 deg are the same
And that we will have a large error in defining the source location
Ratio of 0.16 (1/6) means uniform reading
Uniform readings - less information to estimate the source azimuth
IAEA International Conference on Nuclear Security: Detection Equipment

13. “Flower-Shape” – Raised vs. Flat Raised Central Detector
Measured Response
Flat Central Detector
Theta = 36 deg
Measured Response
Raised Central Detector
Theta = 36 deg
On this slide the angular response for a central detector raised above the his surrounding detectors (the sundial concept) and the results for a flat central detector configuration at angle of 36 degree are presented
as shown The configuration with a raised central detector yielded a Major change of the ratio between each of the detectors and the total counts
And improved the accuracy for identifying the direction
Major change of the ratio between each of the detectors and the total counts
IAEA International Conference on Nuclear Security: Detection Equipment

14. “Flower-Shape”- Central Detector, Flat vs. Raised
Tradeoff
The measured results for the configuration with a raised central detector versus a confutation where the central detector is in the same height as the other detectors around him presented two main conclusions:
First the angular error at low angles (theta below 35 deg) where the source is above the detectors was dramatically reduced
Second – by raising the central detector it has reduced the shielding provided by the central detector at high angles (theta close to 70 deg) therefore increasing the error
IAEA International Conference on Nuclear Security: Detection Equipment

15. Larger surface (Sensitivity)
Optimization
Based on our measured results with the flower shaped configuration two more configuration were evaluated by simulation
On the first configuration we have added another detector 7 detector instead of six
On the second configuration we have replaced the detector cylindrical shape by a trapezoid one in order to increase the detector surface and improve the shielding created by each detector to its neighbors one (reducing the “dead space”)
Higher resolution
Larger surface (Sensitivity)
Improved attenuation
The diameter of the circumcircle is the same
IAEA International Conference on Nuclear Security: Detection Equipment

16. Simulation for angular estimation error for all detector configurations
The simulated results from all six configurations
3 detectors array once with a flat central detector and once with a raised central detector are presented the graph presented that the majority improvement in the estimation error is gain by the sundial concept.
With the trapezoid shape a flat low estimation error was obtained over all the half sphere range
IAEA International Conference on Nuclear Security: Detection Equipment

17. Conclusions
“Arc-shaped" - good identification of the source direction over 180°.
“Flower-shaped" - identify the source location over a spherical aspect area (three dimensions).
A major improvement when the central detector was raised up (sundial concept).
Segments detector - Directional performance without the cost of reduced sensitivity, same detector volume
IAEA International Conference on Nuclear Security: Detection Equipment

18. Future Study Detector configuration Light sensor Electronics
Energy response
Hand-held device
IAEA International Conference on Nuclear Security: Detection Equipment

19. Thank you
IAEA International Conference on Nuclear Security: Detection Equipment

20. “Sundial” Concept Sun ~ Radiation Source Gnomon ~ Radiation detector
Shadow ~ Absorption
Dial ~ Direction
IAEA International Conference on Nuclear Security: Detection Equipment

21. Estimation Error
angular error is depended on the detectors count rate.
count rate affects the accuracy for defining the direction.
same statistic should be used for evaluating different detector array configurations.
The method utilized for comparing the response-time of the various configurations was based on adding statistical noise to the measured/simulated data and calculate the bias of the estimated source direction relative to the known source direction.
This bias provides an indicator for the statistical error and for the time period required for achieving the similar accuracy. Once the optimal configuration is selected, measurements at unknown location are required for characterizing the angular systematic error at predefine working conditions.
The intensity of the source affects the error for defining the direction of the radiation.
the angular errors is depended on the detectors count rate. Hence, for evaluating the angular error of different detector arrays the same statistic should be used. The method utilized for comparing the response-time of the various configurations was based on adding statistical noise to the measured/simulated data and calculate the bias of the estimated source direction relative to the known source direction. This bias provides an indicator for the statistical error and for the time period required for achieving the similar accuracy. Once the optimal configuration is selected, measurements at unknown location are required for characterizing the angular systematic error at predefine working conditions.