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High Energy Accelerator Tomography

Objective

The primary goal of the project is the development through design, testing and demonstration of a non-destructive technique for the generation of tomographic images of highly radioactive objects such as glass monoliths of high level radioactive waste.
The project builds on the tomography expertise developed over a number of years at BAM and the expertise in detector design and operation in AEA Technology.
The primary goal of the project is the development through design, testing and demonstration of a nondestructive technique for the generation of tomographic images of highly radioactive objects such as glass monoliths of high level radioactive waste. The technique is based on the measurement of gamma ray transmissions with an electron linear accelerator as the photon source. The novel aspect of the technique is the use of Cerenkov counters for the detection of the transmitted gamma rays. Such detectors have a gamma ray energy response that exhibits a low energy threshold and a non-linear response up to gamma ray energies of several MeV. The use of detectors wthi such a response has important potential advantages in the context of tomography of highly radioactive objects. The intrinsically low sensitivity of the detectors to the low energy portion of the bremsstrahlung spectrum reduces the undesirable beam hardening effects which result from the rapid attenuation of this portion of the spectrum. It also provides discrimination against the low energy background from the objects, therby significantly improving the signal to background ratio in measurements.

The project involved work on all the amjor componets of the CT system, the detectors, collomators, data acquisition system and linac.

Following commissioning of the complete CT system trial tomograms were made of a simulated HLW glass monolith. These tomograms demonstrated the operation of the Cerenkov detector system and demonstrated that beam hardening artefacts, which were quite severe in the case of scintillation detector images, were absent in the images obtained with the Cerenkov detectors.
Work programme:

The novel aspect of the technique is the used of Cerenkov counters for the detection of the transmitted gamma-rays. Such detectors have a gamma-ray energy response that exhibits a low energy threshold and a non-linear response up to gamma-ray energies of several MeV.
The detectors to the low energy portion of the Bremsstrahlung spectrum should reduce the beam hardening effects which result from the rapid attenuation of this portion of the spectrum by waste packages.
There are three main phases in the development of the HEAT technique:

- The design construction and testing of Cerenkov counters, collimators and a Bremsstrahlung converter.
- The optimisation of counter performance for tomographic measurements.
- The demonstration of HEAT on simulated waste.

These three phases are further subdivided into:

- Design and construction of Cerenkov detectors followed by testing.
- Design and manufacture of collimators and bremsstrahlung converter.
- Set up Harwell linac tomography tests.
- Assess implementation of HEAT at BAM.
- Transport counters to BAM and set up followed by demonstration with simulated waste.
- Assessment of technique.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

AEA Technology plc
Address
Harwell Laboratory
OX11 0RA Didcot
United Kingdom

Participants (1)

FEDERAL INSTITUTE FOR MATERIAL RESEARCH AND TESTING
Germany
Address
87,Unter Der Eichen 87
12205 Berlin