Evaluation of the in-situ Performance of Neutron Detectors based on EJ-426 Scintillator Screens for Spent Fuel Characterization

The reliable detection of neutrons in a harsh gamma-ray environment is an important aspect of establishing non-destructive methods for the characterization of spent nuclear fuel. In this study, we present results from extended in-situ monitoring of detector systems consisting of commercially available components: EJ-426, a $^6$Li-enriched solid-state scintillator material sensitive to thermal neutrons, and two different types of Hamamatsu photomultiplier tubes (PMT). Over the period of eight months, these detectors were operated in close vicinity to spent nuclear fuel stored at the interim storage facility CLAB, Oskarshamn, Sweden. At the measurement position the detectors were continuously exposed to an estimated neutron flux of approx. 280 n/s $\cdot$ cm$^2$ and a gamma-ray dose rate of approx. 6 Sv/h. Using offline software algorithms, neutron pulses were identified in the data. Over the entire investigated dose range of up to 35 kGr, the detector systems were functioning and were delivering detectable neutron signals. Their performance as measured by the number of identified neutrons degrades down to about 30% of the initial value. Investigations of the irradiated components suggest that this degradation is a result of reduced optical transparency of the involved materials as well as a reduction of PMT gain due to the continuous high currents. Increasing the gain of the PMT through step-ups of the applied high voltage allowed to partially compensate for this loss in detection sensitivity. The integrated neutron fluence during the measurement was experimentally verified to be in the order of $5 \cdot 10^9$ n/cm$^2$. The results were interpreted with the help of MCNP6.2 simulations of the setup and the neutron flux

Blind Benchmark Exercise for Spent Nuclear Fuel Decay Heat

The decay heat rate of five spent nuclear fuel assemblies of the pressurized water reactor type were measured by calorimetry at the interim storage for spent nuclear fuel in Sweden. Calculations of the decay heat rate of the five assemblies were performed by 20 organizations using different codes and nuclear data libraries resulting in 31 results for each assembly, spanning most of the current state-of-the-art practice. The calculations were based on a selected subset of information, such as reactor operating history and fuel assembly properties. The relative difference between the measured and average calculated decay heat rate ranged from 0.6% to 3.3% for the five assemblies. The standard deviation of these relative differences ranged from 1.9% to 2.4%

A Detector System for Light–Element Analysis using a Nuclear Microprobe : for Applications in Geoscience

I detta arbete har två analysmetoder med mycket hög känslighet för att mäta väte och bor utvecklats. Dessa har tillämpats på geologiska material där de kan vara ett verktyg i att svara på frågeställningar gällande b.la. jordskorpans utveckling och flödet av vatten på jorden. Metoderna kan mäta en väte- eller bor-atom bland en miljon andra atomer. Jonstråleanalys är ett fält inom den tillämpade fysiken som använder sig av strålar med laddade partiklar, vanligtvis protoner (väteatomkärnor) eller alfapartiklar (heliumatomkärnor) med hög energi för att genomföra grundämnesanalys av prover. De laddade partiklarna accelereras med hjälp av en accelerator upp till en energi av ca 3 MeV, vilket motsvaras av att partikeln har accelererats av det elektriska fältet från en spänning på 3 miljoner volt över en sträcka på en meter. Då dessa partiklar skjuts in i provet sker en mängd reaktioner och kollisioner med både atomernas elektroner och med atomkärnorna i provet. I en del av dessa reaktioner uppstår högenergetisk elektromagnetiskstrålning, i form av röntgen- eller gamma-strålning. Det kan också sändas ut laddade partiklar från provet, antingen i form av kärnreaktionsprodukter eller spridda partiklar från jonstrålen. Med rätt detektorutrustning kan denna strålning mätas och slutsatser kan dras om provets massfördelning och koncentrationen av olika grundämnen. Jonstrålen kan fokuseras ner till en tusendels millimeter och flyttas över provet, och på så vis bestrålas endast en liten del av provet åt gången. Genom att sedan flytta strålen över provet kan kartor över provets grundämneskoncentration och massfördelning skapas. I de flesta fall går det även att få ut på vilket djup i provet som grundämnet befinner på. Med hjälp av denna tredimensionella information kan man t.ex. studera hur olika ämnen fördelar sig i provet.Jonstråleanalysmetoderna kan med lätthet detektera de flesta grundämnena i det periodiska systemet. De svåra grundämnena är de som är lättare än aluminium. Dessa grundämnen är svåra eftersom sannolikheten för att de laddade partiklarna växelverkar med de lätta atomerna är liten för de reaktioner som används av de vanligaste jonanalysmetoderna.Målet med detta arbete är att utveckla redan existerande jonstråletekniker för att mäta väte, tungt väte (en vätekärna med en extra neutron) och bor. Analysen av förhållandet mellan väte och tungt väte utförs genom att en tung-vätekärna skjuts in i provet och om den kolliderar med en väteatom (vanligt väte eller tungt väte) så sprids både den inkommande väteatomkärnan och väteatomen ut genom provet och detekteras samtidigt parvis i två av de 2048 detektorerna som finns bakom provet. Boranalysen genomförs istället genom att en proton sänds in i provet och när denna stöter på en boratom så sker en kärnreaktion i provet. Vid kärnreaktionen bildas tre stycken högenergetiska heliumkärnor. Genom att detektera dessa kan koncentrationen av bor bestämmas

A tailored 200 parameter VME based data acquisition system for IBA at the Lund Ion Beam Analysis Facility - Hardware and software

With the recent advances towards modern Ion Beam Analysis (IBA), going from one- or few-parameter detector systems to multi-parameter systems, it has been necessary to expand and replace the more than twenty years old CAMAC based system. A new VME multi-parameter (presently up to 200 channels) data acquisition and control system has been developed and implemented at the Lund Ion Beam Analysis Facility (LIBAF). The system is based on the VX-511 Single Board Computer (SBC), acting as master with arbiter functionality and consists of standard VME modules like Analog to Digital Converters (ADC's), Charge to Digital Converters (QDC's), Time to Digital Converters (TDC's), scaler's, IO-cards, high voltage and waveform units. The modules have been specially selected to support all of the present detector systems in the laboratory, with the option of future expansion. Typically, the detector systems consist of silicon strip detectors, silicon drift detectors and scintillator detectors, for detection of charged particles, X-rays and γ-rays. The data flow of the raw data buffers out from the VME bus to the final storage place on a 16 terabyte network attached storage disc (NAS-disc) is described. The acquisition process, remotely controlled over one of the SBCs ethernet channels, is also discussed. The user interface is written in the Kmax software package, and is used to control the acquisition process as well as for advanced online and offline data analysis through a user-friendly graphical user interface (GUI). In this work the system implementation, layout and performance are presented. The user interface and possibilities for advanced offline analysis are also discussed and illustrated

Radiation tolerance of ultra-thin PIN silicon detectors evaluated with a MeV proton microbeam

A focused MeV proton beam at the Lund Ion Beam Analysis Facility has been used to induce radiation damage in transmission semiconductor detectors. The damage alters the response of detectors and degrades their charge transport properties. In this work, the radiation tolerance of ultra-thin silicon PIN detectors was studied as a function of proton fluences and detector thickness using a scanning proton microprobe. The investigated detectors had thicknesses ranging between 6.5 and 22 mu m, and different selected regions of each detector were irradiated with fluence up to 2 x 10(15) protons/cm(2). The results show that the charge collection efficiency (CCE) decreases as a function of the proton fluence. Compared with non-irradiated regions, the CCE was above 94% at the lowest fluence of 2 x 10(12) protons/cm(2) for all the detectors studied. Degradation of the devices caused spectral peak shifting toward lower energies. The highest possible fluence of 2.55 MeV protons that could be used, causing only minor radiation damage, was 2 x 10(13) cm(-2) for the thinnest detectors (6.5 and 10 mu m) and 2 x 10(12) cm(-2) for the thickest detectors (15 and 22 mu m)

Hydrogen concentration analysis in clinopyroxene using proton-proton scattering analysis

Traditional methods to measure water in nominally anhydrous minerals (NAMs) are, for example, Fourier transformed infrared (FTIR) spectroscopy or secondary ion mass spectrometry (SIMS). Both well-established methods provide a low detection limit as well as high spatial resolution yet may require elaborate sample orientation or destructive sample preparation. Here we analyze the water content in erupted volcanic clinopyroxene phenocrysts by proton-proton scattering and reproduce water contents measured by FTIR spectroscopy. We show that this technique provides significant advantages over other methods as it can provide a three-dimensional distribution of hydrogen within a crystal, making the identification of potential inclusions possible as well as elimination of surface contamination. The sample analysis is also independent of crystal structure and orientation and independent of matrix effects other than sample density. The results are used to validate the accuracy of wavenumber-dependent vs. mineral-specific molar absorption coefficients in FTIR spectroscopy. In addition, we present a new method for the sample preparation of very thin crystals suitable for proton-proton scattering analysis using relatively low accelerator potentials

Lithium analysis using a double-sided silicon strip detector at LIBAF

Quantification and mapping possibilities of lithium in geological material, by Nuclear Reaction Analysis (NRA), was evaluated at the Lund Ion Beam Analysis Facility (LIBAF). LiF and two Standard Reference Materials, (SRM 610 and SRM 612) were used in the investigation. The main part of the data was obtained at the beam energy 635keV studying the high Q-value reaction 7Li(p, α)4He, but reaction yield and detection limits were also briefly investigated as a function of the energy. A double-sided silicon strip detector (DSSSD) was used to detect the α-particles emitted in the reaction in the backward direction. The combination of the high Q-value, a reasonably good cross-section and the possibility to use a high beam current have been demonstrated to allow for measurement of concentrations down below 50ppm. Proton energies below 800keV were demonstrated to be appropriate energies for extracting lithium in combination with boron analysis

Deuterium/hydrogen microscopy in astrogeological material using an elastic recoil approach

A new experimental setup for quantitative hydrogen isotopic-ratio microscopy in thin samples (up to 12 mu m) is under development at the Lund Ion Beam Analysis Facility. This technique is derived from the proton-proton scattering technique and has been proven to have the same beneficial features, namely a detection limit below 1 wt-ppm and a depth resolution better than 1 mu m. The method gives absolute quantitative information about H or D content in atoms per cm(2) and does not depend on the structure, chemical environment or other so called "matrix effects". This work presents an evaluation of the developed technique through measurements on unique material from samples from the Tagish Lake meteorite, which has been suggested to be one of the most primitive solar system materials yet studied. We discuss the capabilities of the technique through the results from measurements on a geological standard. (C) 2014 Elsevier B.V. All rights reserved