N5A4  Nuclear Measurement Techniques & Instrumentation

Friday, Nov. 6  08:30-10:10  Pacific Salon 3

Session Chair:  Daniel Stephens Jr., Pacific Northwest National Laboraotry, United States; Jason Hayward, University of Tennessee Department of Nuclear Engineering, United States

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(08:30) N5A4-1, Refurbishment of Fast Neutron Detectors at the TREAT Facility to Support Fuel Motion Monitoring

D. L. Chichester, S. M. Watson, J. T. Johnson

Idaho National Laboratory, Idaho Falls, Idaho, USA
Transient testing of nuclear fuel, i.e. testing fuel until it fails, is a required component in the development and qualification of new, innovative commercial nuclear power fuel systems. Work is now underway at Idaho National Laboratory to restart the 16,000-MW peak-power Transient Reactor test Facility (TREAT) to support this type of testing. One of several key diagnostic measurements made during transient testing is monitoring, in real time, the movement of fuel caused by fuel and cladding swelling, bowing, and melting. This information is needed to understand when and where a fuel's cladding is breached, to understand the physical and chemical mechanisms that impact the progression of an accident, and to understand how fuel movement and relocation affect coolant circulation around the fuel during an accident. At TREAT fuel motion monitoring is performed using a 360-channel line-of-sight hodoscope that uses fast-neutron detectors to record the location of fuel inside a test chamber. This system is sensitive to a minimum fuel volume of approximately 0.2 cm3 with a temporal resolution of 1-ms. Work is currently underway to refurbish the TREAT hodoscope and its fast neutron detectors, ZnS(Ag) scintillators embedded in Lucite. This paper will briefly present the TREAT facility and the transient testing program and then discuss work underway to refurbish its hodoscope detectors and to develop a new data acquisition system to support fuel motion monitoring.

(08:50) N5A4-2, Fast multiplicity counter featuring stilbene detectors for nondestructive assay of special nuclear material

A. Di Fulvio1, S. D. Clarke1, T. Jordan1, T. H. Shin1, C. S. Sosa1, M. M. Bourne1, D. L. Chichester2, S. A. Pozzi1

1Nuclear Engineering and Radiological Science, University of Michigan, Ann Arbor, Michigan, US
2Idaho National Laboratory, Idhao Falls, Idhao, US
The Treaty on the Nonproliferation of Nuclear Weapons demands for new instruments to prevent diversion of fissile material and safeguard controls. We present a fast neutron multiplicity counting system based on organic scintillators, i.e. liquid EJ-309 and stilbene. The system is able to detect fission correlated counts and photon and neutron multiplets, needed to quantify fissile mass, without the need of complex electronic circuitry and unfolding procedures, required in moderated systems. Moderated system, typically based on helium-3 detectors, feature a gate time of hundreds of microseconds. Conversely, the use of organic scintillators allows an exceptionally short gate time of hundreds of nanoseconds. This results in a reduction of accidental neutron coincidence. In our system, the superior gamma-neutron discrimination capabilities of stilbene scintillators allow to measure higher order multiplicities (> 3) and the inspection of complex source terms. This counter is thus also suitable for the assay of newer fuels containing plutonium and other fissionable actinides. A prototypal version of the well counter was assembled and tested at the University of Michigan, using a spontaneous fission and an (alfa,n) neutron source, i.e. 252Cf and PuBe respectively. Presented measured results show excellent agreement with simulations. The viability of the system to discriminate time correlated fission neutrons from random, uncorrelated neutrons was proved. An experimental campaign will be carried out at Idaho National Laboratory in August 2015 to characterize weapon grade plutonium samples.

(09:10) N5A4-3, Development of Flexible Alpha Camera and Actual Measurement of Plutonium Specimen

Y. Morishita1, S. Yamamoto1, K. Izaki2, J. H. Kaneko3, N. Nemoto2, Y. Kashimura4

1Nagoya University Graduate School of Medicine, 1-1-20 Daiko-Minami, Higashi-ku, Nagoya City, Aichi Prefecture, Japan
2Japan Atomic Energy Agency, 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki, Japan
3Hokkaido University Graduate School of Engineering, Kita 17, Nishi 8, Kita-ku, Sapporo, Hokkaido, Japan
4Inspection Development Company, 4-33 Muramatsu, Tokai-mura, Naka-gun, Ibaraki, Japan
Such nuclear fuel materials as uranium and plutonium are handled at nuclear fuel facilities. The prompt detection of contamination from these materials is important to prevent exposure to workers. A ZnS(Ag) (silver-doped zinc sulfide) scintillation detector, which measures alpha particles, has been widely used to detect these materials. In general, its window area is approximately 100 cm2, and there is a narrow spaces that cannot be measured directly, such as inside of pipes, filter interspaces, and so on. The direct measurement of alpha particles in narrow spaces is useful for contamination source identification. A ZnS(Ag) scintillation detector only obtains count-rate information about alpha particles and does not have the ability to distinguish nuclear fuel materials from such naturally occurring alpha emitters as radon daughters. Both alpha auto-radiography and a Si surface barrier detector (SSBD) are used to distinguish plutonium from radon daughters. However, these methods are not suitable for the flexible measurement of narrow spaces at nuclear work sites. To solve this problem, we developed a new imaging detector called a flexible alpha camera that can flexibly measure a narrow spaces at work sites. We measured a plutonium specimen and radon daughters with our flexible alpha camera. The 2-dimensional distribution result imaged the plutonium specimen as a point. The plutonium specimen’s spatial resolution was only 0.36-mm FWHM, calculated by Gaussian fitting. On the other hand, the radon daughters were uniformly imaged in the field-of-view. The plutonium specimen’s energy spectrum was confirmed from 30 to 80 channels, and its energy resolution was ~70.97%, calculated by Gaussian fitting. On the other hand, the energy spectrum of the radon daughters was confirmed from 30 to 120 channels. Plutonium was distinguished from the radon daughters based on the differences of the 2-dimensional distribution and the energy. Our flexible alpha camera is also compact and adaptable to distinguish plutonium for narrow spaces at work sites.

(09:30) N5A4-4, Radiation Hard Imaging and Tracking System Based on Coincident Detection of Secondary Electrons with Pixel Detector Timepix

J. Jakubek1, M. Jakubek1, J. Tous2

1Institute of Experimental and Applied Physics of the Czech Technical University in Prague, Prague, Czech Republic
2CRYTUR s.r.o., Turnov, Czech Republic
In this contribution we present novel imaging or tracking system based on coincident detection of secondary electrons emitted from thin metallic foil or photocathode after interaction with ionizing radiation. The system can be used for imaging or tracking of charged particles, neutrons or gamma rays (with scintillator and photocathode). The small vacuum detector system consists of metallic foil electrode placed in front of the hybrid pixel detector Timepix (256 x 256 pixels with pitch of 55 µm) with optimized silicon sensor (100 µm thick, no electrode the top). The negative acceleration voltage of 15-20 kV is applied to the electrode. Two additional field shaping electrodes are placed between the foil and detector. When ionizing particle interacts with the foil it often recoils few secondary electrons. These secondary electrons recoil further electrons. Emitted electrons are accelerated by electric field towards the pixel detector and detected in coincidence. The initial energy of electrons leaving the foil can vary very much but many of them are just slightly over the work function (units of eV) of used metal. These electrons are therefore projected to the small area of the pixel detector (focused by longitudinal magnetic field). The primary radiation itself can either hit the pixel detector as well or miss it in tilted geometry (which is intended in high flux cases). The coincident detection of emitted secondary electrons allows for full suppression of the signal due to thermo-electrons. If the primary particle is detected as well then its direction can be determined (tracking). Since the primary detecting medium of the system is a metallic foil, its radiation hardness can be very high. This property makes the method very promising for imaging of beam profiles for particle accelerators. In this case the system is tilted to avoid irradiation of the semiconductor detector. This work is carried out in frame of the Medipix Collaboration.

(09:50) N5A4-5, On-Chip Detection of Radioactivity via Silcion-Based Sensors for the Quality Control Testing of Radiopharmaceuticals

L. F. Thompson1, S. J. Archibald2, T. Deakin1,3, M. M. N. Esfahani4, N. Pamme2, M. P. Taggart1, M. D. Tarn3

1Department of Physics and Astronomy, University of Sheffield, Sheffield, United Kingdom
2Department of Chemistry, University of Hull, Hull, United Kingdom
3Lablogic Systems Ltd., Sheffield, United Kingdom
4Department of Engineering, University of Hull, Hull, United Kingdom
Current positron emission tomography (PET) methods are dependent on short-lived radiotracers such as such as 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG). It is necessary to perform detailed quality control (QC) on these compounds before they can be administered to patients. Current QC methods involve several instruments, use significant volumes of the radiotracer and require measurement times of order an appreciable fraction of the 18F half-life. This paper discusses novel methods under investigation to perform the radio analysis part of the overall QC process using microfluidic techniques in a ‘lab on-a-chip’ context suitable for use with small volumes (typically nl) of samples. Microcells have been fabricated in a number of different substrate materials. Detector systems using inorganic scintillators and SiPMs have been employed to detect Cerenkov radiation, scintillation light and gammas produced by the radiotracer. Results from these studies will be presented which indicate that, for a range of substrate materials, a suitable count rate monitoring mechanism can be devised using SiPMs closely coupled to the microfluidic cell.