Qucosa – Hemholtz-Zentrum Dresden-Rossendorf
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Underground measurements and simulations on the muon intensity and 12C-induced nuclear reactions at low energies
Full text linkThe reaction 12C(α,γ)16O is of paramount importance for the nucleosynthesis of heavier elements in stars. It takes place during helium burning and determines the abundance of 12C and 16O at the end of this burning stage and therefore influences subsequent nuclear reactions. Currently the cross section at astrophysically relevant energies is not known with satisfactory precision.
Due to the low cross section of the reaction, low background, high beam intensities and target thicknesses are necessary for experiments. Therefore a new laboratory hosting a 5 MV ion accelerator, was built in the shallow-underground tunnels of Felsenkeller. The main background component in such laboratories was investigated with a muon telescope in this thesis. It was found, that the rock overburden of about 45 m vertical depth reduces the muons by a factor of about 40 compared to the surface. Furthermore the results of the measurements were compared to a simulation based on the geometry of the facility and showed good agreement.
In the next step the accelerator was put into operation. Since the experiment on 12C(α,γ)16O will be done in inverse kinematics, an intense carbon beam is necessary to reach sufficient statistics. For this, the creation and extraction of carbon ions in an external ion source was improved. The external source now provides steady currents of 12C− of above 100 μA.
In the following the transmission through the accelerator and the high-energy beamline was tested with a beam restricted in width. The pressure of the gas stripper in the centre of the accelerator and the parameters of different focusing elements after the accelerator were varied. It was found, that for a desired carbon beam energy of below 9 MeV, the 2+ charge state is suited best, where up to 35% of the inserted beam could be transmitted.
To ease the planning of future experiments and aid the analysis of the data, the target chamber and two different kinds of cluster detectors were modelled in Geant4. The low-energy region was verified by comparing the simulations to measurements with radioactive calibration sources. Deviations for the detectors were below 10% without target chamber, and up to 30% for individual germanium crystals of the Cluster Detectors with the target chamber.
A first test measurement was undertaken to investigate the capabilities of the new laboratory. Solid tantalum targets implanted with 4 He were prepared. An ERDA analysis of the used solid targets showed contaminations with carbon and oxygen. These led to beam-induced background in the region of interest during the irradiation.
Then the targets were irradiated with a carbon beam at two different energies. While no clear signal of 12C(α,γ)16O could be observed, the beam could be steered on the target for the whole duration of the beam time spanning five days. Problems during this test, like low beam current, were identified. These could be partly remedied in the scope of this thesis. Suggestions for improvements for a second test run were developed as well
Neutronenfluss in Untertagelaboren
Full text linkDas Felsenkellerlabor ist ein neues Untertagelabor im Bereich der nuklearen Astrophysik. Es befindet sich unter 47 m Hornblende-Monzonit Felsgestein im Stollensystem der ehemaligen Dresdner Felsenkellerbrauerei.
Im Rahmen dieser Arbeit wird der Neutronenuntergrund in Stollen IV und VIII untersucht. Gewonnene Erkenntnisse aus Stollen IV hatten direkten Einfluss auf die geplanten Abschirmbedingungen fur Stollen VIII. Die Messung wurde mit dem Hensa-Neutronenspektrometer durchgeführt, welches aus polyethylenmoderierten 3He-Zählrohren besteht.
Mit Hilfe des Monte-Carlo Programmes Fluka zur Simulation von Teilchentransport werden für das Spektrometer die Neutronen-Ansprechvermögen bestimmt. Fur jeden Messort wird außerdem eine Vorhersage des Neutronenflusses erstellt und die Labore hinsichtlich der beiden Hauptkomponenten aus myoneninduzierten Neutronen und Gesteinsneutronen aus (α,n)-Reaktionen und Spaltprozessen kartografiert.
Die verwendeten Mess- und Analysemethoden finden in einer neuen Messung am tiefen Untertagelabor Lsc Canfranc Anwendung. Erstmalig werden im Rahmen dieser Arbeit
vorläufige Ergebnisse vorgestellt.
Des Weiteren werden Strahlenschutzsimulationen fur das Felsenkellerlabor präsentiert, welche den strahlenschutztechnischen Rahmen für die wissenschaftliche Nutzung definieren. Dabei werden die für den Sicherheitsbericht des Felsenkellers verwendeten Werte auf die Strahlenschutzverordnung 2018 aktualisiert.
Letztlich werden Experimente an der Radiofrequenz-Ionenquelle am Felsenkeller vorgestellt, die im Rahmen dieser Arbeit technisch betreut wurde. Dabei werden Langzeitmessungen am übertägigen Teststand am Helmholtz-Zentrum Dresden-Rossendorf präsentiert
Charakterisierung eines schnellen Diamantdetektors als Proton-Bunch-Monitor für die Reichweiteverifikation in der Protonentherapie
Full text linkFür die Reichweiteverifikation in der Protonentherapie mittels Prompt Gamma-Ray Timing (PGT) wird ein Proton-Bunch-Monitor (PBM) benötigt, um Phaseninstabilitäten zwischen den Protonen-Mikropulsen und der Radiofrequenz (RF) des Zyklotrons zu eliminieren.
In dieser Arbeit wurde demonstriert, dass ein Diamantdetektor diese anspruchsvolle Aufgabe erfüllen kann. Dazu wurde ein polykristalliner Diamantdetektor in diversen Experimenten umfassend charakterisiert. An ELBE wurde eine Zeitauflösung von 82(6) ps für minimal-ionisierende Elektronen bestimmt. Die Auflösung bei der Detektion von Protonen klinischer Energien wurde am OncoRay ermittelt und betrug im Mittel 314(17) ps. Des Weiteren wurden Experimente durchgeführt, die auf die optimale Position des Detektors in der späteren klinischen Anwendung nahe des Degraders schließen lassen.
Bei der Anwendung als PBM konnte der Diamantdetektor Phasenverschiebungen zur RF mit einer zeitlichen Auflösung von weniger als 3 ps bei einem Messintervall von 30 ms detektieren.
Diese Phasenverschiebungen konnten auch in weiten Teilen durch das Phasenkontrollsignal U_phi, welches im Rahmen dieser Arbeit erstmalig ausgewertet wurde, bestätigt werden.
Mit dem Diamantdetektor und U_phi stehen nun zwei PBM zur Verfügung, mit denen ein zentrales Problem bei der klinischen Anwendung von PGT als Reichweite-Verifikationsmethode gelöst werden kann.:1 Motivation
2 Grundlagen der Reichweiteverifikation in der Protonentherapie
2.1 Wechselwirkung von geladenen Teilchen mit Materie
2.2 Tiefendosiskurven
2.3 Praktische Aspekte der Protonentherapie
2.4 Reichweiteunsicherheiten
2.5 Prompt Gamma-Ray Timing (PGT)
2.6 Proton-Bunch-Monitore (PBM)
3 Entwicklung eines Vorverstärkers für den Diamantdetektor
3.1 Untersuchungen mit Generatorsignalen
3.2 Untersuchungen mit radioaktiven Prüfstrahlern
3.3 Ergebnisse
4 Bestimmung der Zeitauflösung am Elektronenstrahl
4.1 Bestimmung der Zeitauflösung eines Detektors mit einer Flugzeitmessung
4.2 Experimenteller Aufbau
4.3 Datenerfassung
4.4 Ergebnisse
4.5 Zusammenfassung
5 Bestimmung der Zeitauflösung am klinischen Protonenstrahl
5.1 Experimentalraum am OncoRay
5.2 Experimenteller Aufbau
5.3 Bestimmung der Zeitauflösung eines Detektors mit einer Koinzidenzmessung
5.4 Ablauf der Messung
5.5 Datenerfassung
5.6 Ergebnisse
5.7 Diskussion
5.8 Zusammenfassung
6 Optimierung der Position des Diamantdetektors am Degrader
6.1 Vorbetrachtungen
6.2 Experimenteller Aufbau
6.3 Ergebnisse
6.4 Diskussion
6.5 Zusammenfassung
7 Einsatz des Diamantdetektors als PBM
7.1 Experimenteller Aufbau
7.2 Datenerfassung
7.3 Ablauf der Messung
7.4 Ergebnisse
7.5 Diskussion und Ausblick
7.6 Zusammenfassung
8 Zusammenfassende Diskussion
A Anhang
A.1 Produktzertifikat des Diamantdetektors
A.2 Zertifikate der radioaktiven Prüfstrahler
A.3 Feinzeit-Korrektur beim U100-Spektrometer
A.4 Zeitdifferenz-Histogramme für Variante A1 und A2 des Koinzidenzexperiments
A.5 Der Diamantdetektor als PBM bei automatischer Phasenanpassung
A.6 Der Diamantdetektor als PBM bei manueller Phasenanpassung
Literaturverzeichnis
Abbildungsverzeichnis
Tabellenverzeichnis
Liste der verwendeten Akronyme
Danksagung und Eigenständigkeitserklärun
Laser-proton acceleration in the near-critical regime using density tailored cryogenic hydrogen jets
Full text linkModern particle accelerators are a key component of today’s research landscape and indispensable in industry and medicine. In special application areas, the portfolio of these facilities will be expanded by laser-driven compact plasma accelerators that generate short, high-intensity pulses of ions with unique beam properties. Though intensely explored by the community, scaling the maximum beam energies of laser-driven ion accelerators to the required level is one of the most significant challenges of this field. This endeavor is inherently linked to a fundamental understanding of the underlying acceleration processes. The prospect to effciently increase the beam energy relies on the ability to control the accelerating field structures beyond the well-established acceleration from the stationary target rear side. However, manipulating the interaction in such micrometer-sized accelerators proves to be challenging due to the transient nature of the plasma fields and requires precise tuning of the temporal laser pulse shape and the volumetric density distribution of the plasma target to a level that could so far not be achieved.
This thesis investigates laser-proton acceleration using a cryogenic hydrogen target that combines the capabilities of predictive three-dimensional simulation and the in-situ realtime monitoring of the density distribution in the experiment to explore the fundamental physical principles of plasma based acceleration mechanisms. The corresponding experiments were performed at the DRACO laser facility at the Helmholtz-Zentrum Dresden-Rossendorf. The key to the success of these studies was the advancement of the cryogenic target system that generates a self-replenishing pure hydrogen jet. Using a mechanical chopping device, which protects the target system from the disruptive influence originating from the high-intensity interaction, allowed, for the first time, systematic experiments with a large number of laser shots in the harsh environment of the ultra-short pulse DRACO petawatt laser. The performance of a cylindrical hydrogen jet can be substantially optimized by a flexible all-optical tailoring of the target profile. Guided by real-time multi-color probing, the target density, the decisive parameter of the interaction, was scanned over two orders of magnitude allowing the exploration of different advanced acceleration regimes in a controlled manner. This approach led to the experimental realization of proton beams with energies up to 80 MeV and application relevant high particle yield from advanced acceleration mechanisms occurring in near-critical density plasmas, a regime so far mostly investigated in numerical studies. Besides cylindrical jets, the formation of thin hydrogen sheets was studied to gain insight into the fluid and crystallization dynamics that can be used to tailor the target shape for laser-proton acceleration. Using these jets, the onset of target transparency was explored, a regime that promises increased proton energies when optimized. Furthermore, after irradiation of the hydrogen jet with a high-intensity laser pulse, an unexpected axial modulation in the plasma density distribution was observed that can play a role in structuring the proton beam profile. This modulation is caused by instabilities that originate from the laser-plasma interaction, for example due to laser-driven return currents or the plasma expansion dynamics
Annual Report 2021 - Institute of Resource Ecology
Full text linkThe Institute of Resource Ecology (IRE) is one of the eight institutes of the Helmholtz-Zentrum Dresden–Rossendorf (HZDR). Our research activities are mainly integrated into the program “Nuclear Waste Management, Safety and Radiation Research (NUSAFE)” of the Helmholtz Association (HGF) and focus on the topics “Safety of Nuclear Waste Disposal” and “Safety Research for Nuclear Reactors”. The program NUSAFE, and therefore all work which is done at IRE, belong to the research field “Energy” of the HGF.
IRE conducts applied basic research to protect humans and the environment from the effects of radioactive radiation.
For this purpose, we develop molecular process understand-ing using state-of-the-art methods of microscopy, spectroscopy, diffraction, numerical simulation, theoretical chemistry and systems biology. We implement this in a cross-institutional research environment at the HZDR. Our active interdisciplinarity combines radiochemistry, geosciences and biosciences as well as materials science and reactor physics.
We provide knowledge that is applied in particular to reactor and repository safety as well as in radioecology.
We achieve this goal with a unique infrastructure comprising chemical and biological laboratories as well as hot cells in corresponding radiation and biology safety laboratories in Dresden, Leipzig and Grenoble. In Grenoble, at the European Synchrotron Radiation Facility (ESRF), the institute operates a beamline with four experimental stations for continuously advanced X-ray spectroscopy and diffraction of radio-active samples, which is also available to external users
Dose formation using a pulsed high-field solenoid beamline for radiobiological in vivo studies at a laser-driven proton source
Full text linkProton sources driven by high-power lasers are a promising addition to the portfolio of conventional proton accelerators. Regarding particle cancer therapy, where tumours are irradiated with protons or ions, the novel accelerator technology can be particularly beneficial for translational research - the research branch in which results of basic research are transferred to new approaches for the prevention, diagnosis and treatment of cancer.
The overarching aim in the thesis at hand was a translational pilot study to irradiate tumours on mice’s ears with laser-accelerated protons while achieving the quality level of conventional proton accelerators. This is the only way to compare the radiobiological data of the novel accelerator technology with those of the established ones. To enable such experiments a predetermined dose distribution according to the radiobiological model’s requirements must be delivered to a sample volume. Ergo, the laser-driven protons have to be transported and shaped after their initial acceleration. Intense laser-driven proton pulses, inherently broadband and highly divergent, pose a challenge to established beamline concepts on the path to application-adapted irradiation field formation, particularly for 3D. This work demonstrates the successful implementation of a highly efficient and tuneable pulsed dual solenoid setup to generate a homogeneous (laterally and in depth) volumetric dose distribution using only a single dose pulse from the broad laser-driven proton spectrum. The experiments using the ALBUS-2S beamline were conducted at the titanium:sapphire high-power laser Draco PW at the Helmholtz-Zentrum Dresden–Rossendorf. The beamline and its model were characterised and verified via independent methods, leading to first experimental studies providing volumetrically homogeneous dose distributions to detector targets as well as tumour and normal tissue in proof-of-concept studies. To perform the mouse pilot study, a new solenoid with cooling capacities was designed, characterised and implemented in the course of this thesis. The combination of the new solenoid and an overall performance improvement of the laser-proton accelerator, enabled the successful conduction of the mouse model study. The results show that laser-accelerated protons induce a comparable tumour growth delay as protons from conventional accelerators. This outcome and the demonstration of the flawless interaction between laser-proton accelerator, beam transport, dosimetry and biology qualify the laser-based accelerator technology for complex studies in translational cancer research. Looking into the future, their unique extremely high intensity renders them of particular interest for the investigation into the ultra-high dose rate regime. There, the so-called FLASH effect shows fewer side effects in normal tissue while maintaining the same effect in the tumour when the target dose is administered in milliseconds rather than minutes, as currently common. The ALBUS-2S setup at Draco PW already provides all necessary conditions to realise irradiation times of around ten nanoseconds in preclinical studies. This significantly expands the parameter space for investigating the FLASH effect and is presented as a proof-of-concept in this thesis
Joint project: Geochemical retention of radionuclides on cement alteration phases (GRaZ) - Subproject B
Full text linkThe report summarizes the results obtained by the Institute of Resource Ecology of the Helmholtz-Zentrum Dresden-Rossendorf within the BMWi-financed Joint Research Project “Geochemical retention of radionuclides on cement alteration phases (GRaZ)”. The project focused on the retention behavior of Ca-bentonite and cementitious material, both constituents of the geo-engineered barrier of deep geological repositories for high-level radioactive waste, towards radionuclides. Specifically, the influence of increased salinities and of hyperalkaline conditions on interaction processes in the system radionuclides – organics – clay/cementitious materials – aquifer was studied. For this purpose, complexation, sorption and desorption studies were performed at alkaline to hyperalkaline pH conditions (pH 8-13) and under variation of the ionic strength (0.1 to 4 M) applying complex solution compositions. For the U(VI) citrate system molecular structures dominating in the pH range 2-9 were studied spectroscopically (NMR, UV-Vis, FT-IR). As dominating species 2:2, 3:3, 3:2 and, above critical concentrations also 6:6 and 9:6 U(VI) citrate complexes were identified or confirmed and complex formation constants were determined. U(VI) sorption on Ca-bentonite at (hyper)alkaline conditions in mixed electrolyte solutions was studied by means of batch sorption experiments. The U(VI) retention on Ca-bentonite was shown to be very effective at pH>10, even in the presence of carbonate and despite the prevalence of anionic aqueous uranyl species. The presence of two independent U(VI) surface complexes on Ca-bentonite at pH 8-13 was shown by site-selective TRLFS and EXAFS spectroscopy. The sorption of anionic uranyl hydroxide complexes to the mineral surface was shown to be mediated by calcium cations. In further experiments, the effect of isosaccharinic acid (ISA) and polycarboxylate ether (PCE) on U(VI) and Eu(III) sorption, respectively, on Ca-bentonite was studied. An effect of ISA on U(VI) sorption on Ca-bentonite only occurs when ISA is present in very high excess to U(VI). The effect of PCE, as a commercial cement superplasticizer, on Eu(III) sorption onto Ca-bentonite was negligible already at moderate ionic strengths. The retention of U(VI) and Cm(III) by various C-(A-)S-H phases, representing different alteration stages of concrete, was studied by batch sorption experiments. Sorbed or incorporated actinide species were identified by TRLFS. The stability of U(VI) and Cm(III) doped C-(A-)S-H phases at high ionic strengths conditions was studied in solutions simulating the contact with North German claystone formation water. Potential changes of actinide speciation as well as formation of secondary phases due to leaching effects were followed spectroscopically. The results of this project show that both bentonite and cementitious material constitute an important retention barrier for actinides under hyperalkaline conditions and increased ionic strength
Annual Report 2020 - Institute of Ion Beam Physics and Materials Research
Full text linkAs for everybody else also for the Institute of Ion Beam Physics and Materials Research (IIM), the COVID-19 pandemic overshadowed the usual scientific life in 2020. Starting in March, home office became the preferred working environment and the typical institute life was disrupted. After a little relaxation during summer and early fall, the situation became again more serious and in early December we had to severely restrict laboratory activities and the user operation of the Ion Beam Center (IBC). For the most part of 2020, user visits were impossible and the services delivered had to be performed hands-off. This led to a significant additional work load on the IBC staff. Thank you very much for your commitment during this difficult period. By now user operation has restarted, but we are still far from business as usual. Most lessons learnt deal with video conference systems, and everybody now has extensive experience in skype, teams, webex, zoom, or any other solution available. Conferences were cancelled, workshops postponed, and seminar or colloquia talks delivered online. Since experimental work was also impeded, maybe 2020 was a good year for writing publications and applying for external funding. In total, 204 articles have been published with an average impact factor of about 7.0, which both mark an all-time high for the Institute. 13 publications from last year are highlighted in this Annual Report to illustrate the wide scientific spectrum of our institute. In addition, 20 new projects funded by EU, DFG, BMWi/AiF and SAB with a total budget of about 5.7 M€ have started. Thank you very much for making this possible.
Also, in 2020 there have been a few personalia to be reported. Prof. Dr. Sibylle Gemming has left the HZDR and accepted a professor position at TU Chemnitz. Congratulations! The hence vacant position as the head of department was taken over by PD Dr. Artur Erbe by Oct. 1st. Simultaneously, the department has been renamed to “Nanoelectronics”. Dr. Alina Deac has left the institute in order to dedicate herself to new opportunities at the Dresden High Magnetic Field Laboratory. Dr. Matthias Posselt went to retirement after 36 years at the institute. We thank Matthias for his engagement and wish him all the best for the upcoming period of his life.
However, also new equipment has been setup and new laboratories founded. A new 100 kV accelerator is integrated into our low energy ion nanoengineering facility and complements our ion beam technology in the lower energy regime. This setup is particularly suited to perform ion implantation into 2D materials and medium energy ion scattering (MEIS).
Finally, we would like to cordially thank all partners, friends, and organizations who supported our progress in 2020. First and foremost we thank the Executive Board of the Helmholtz-Zentrum Dresden-Rossendorf, the Minister of Science and Arts of the Free State of Saxony, and the Ministers of Education and Research, and of Economic Affairs and Energy of the Federal Government of Germany. Many partners from univer¬sities, industry and research institutes all around the world contributed essentially, and play a crucial role for the further development of the institute. Last but not least, the directors would like to thank all members of our institute for their efforts in these very special times and excellent contributions in 2020
Recovery of nanodiamonds from dynamically shock-compressed graphite and hydrocarbon samples
Full text linkSynthetic radiation diagnostics as a pathway for studying plasma dynamics from advanced accelerators to astrophysical observations
Full text linkIn this thesis, two novel diagnostic techniques for the identi1cation of plasma dynamics and thequanti cation of essential parameters of the dynamics by means of electromagnetic plasmaradiation are presented. Based on particle-in-cell simulations, both the radiation signatures of micrometer-sized laser plasma accelerators and light-year-sized plasma jets are simulated with the same highly parallel radiation simulation framework, in-situ to the plasma simulation.
The basics and limits of classical radiation calculation, as well as the theoretical and technical foundation of modern plasma simulation using the particle-in-cell method, are brie2y introduced. The combination of previously independent methods in an in-situ analysis code as well as its validation and extension with newly developed algorithms for the simultaneous quantitative prediction of both coherent and incoherent radiation and the prevention of numerical artifacts is outlined in the initial chapters.
For laser wake1eld acceleration, a hitherto unknown off-axis beam signature is observed,which can be used to identify the so-called blowout regime during laser defocusing. Since signi cant radiation is emitted only after the minimum spot size is reached, this signature is ideally suited to determine the laser focus position itself in the plasma to below 100 _m and thus to quantify the in2uence of relativistic self-focusing. A simple semi-analytical scattering model was developed to explain the blowout radiation signature. The spectral signature predicted by the model is veri1ed using both a large-scale explorative simulation and a simulation parameter study, based on an experiment conducted at the HZDR. Identi1ed by the simulations, a temporal asymmetry in the scattered laser light, which cannot be described by state of the art quasi-static models of the blowout regime, makes it possible to determine the focus position precisely by using this radiation signature