Download Kandidatexamensarbete i fysik Valbara projekt

Kandidatexamensarbete i fysik
Valbara projekt VT2017
Samordnare: Pär Olsson ([email protected])
Version: 2016-10-25
Projektlista (se nedan för utförlig beskrivning samt kontaktuppgifter):
Reaktorfysik (RF)
RF1: Penetration of steam into dense-sintered uranium nitride
RF2: Strålskador i material för fissions- och fusionsreaktorer
Astro-partikelfysik (AP)
AP1: Selection of Active Galactic Nuclei
AP2: X-ray spectroscopy of Active Galactic Nuclei
AP3: Investigation of multiple phases of Active Galactic Nuclei activity using radio
interferometric data
AP4: Simuleringsstudie av meteorer och atmosfäriska event för Mini-EUSO
experimentet på ISS
Kärnfysik (KF)
KF1: Gamma-ray tracking with state-of-the-art AGATA detectors
KF2: Nuclear physics for charged particle therapy/hadron therapy
KF3: Computational approaches for advanced quantum mechanics problems and
Lattice QCD
KF4: Nuclear shell structure, its evolution and topological phase transitions
KF5: R-process simulation and heavy-Element Nucleosynthesis
RF1: Temperature dependence of novel nuclear fuel properties
Handledare: Mikael Jolkkonen ([email protected])
Uranium nitride is a novel nuclear fuel material with several attractive properties.
Unfortunately, it is attacked by hot steam/water, which has so far precluded its use in
conventional water-cooled reactors. It would be of great industrial importance to
understand and possibly counteract the mechanism of its degradation in aqueous
environments.
A series of studies has been performed at the Arfwedson Fuel Laboratory at KTH, showing
that in an early stage of attack, steam or oxygen penetrates into the material and leads to
internal oxidation, and hence volume increase, which causes the pellet to crack and
crumble, The newly exposed surfaces then result in an accelerated attack. For this reason,
exposed samples frequently lose their integrity to such extent that micrographic
investigation of e.g. penetration depth is difficult.
The proposed project will try to establish a method for masking off the surface of a UN
pellet, leaving only a pinhole where the pellet material is exposed. For this purpose, the
pellet will be embedded in a thermally cured sealant or a low-melting alloy. As a first step,
the efficacy of the sealant in protecting the surface will be evaluated. If this proves
satisfactory, samples with a tiny surface exposed will be prepared either by micro-drilling
down to the pellet surface, or by indentation before hardening.
The rationale of the study is that by protecting the main body of the pellet, the depth and
mode of a local attack can be studied by sectioning or progressive grinding of a pellet with
retained macroscopic integrity. The collected data is expected to include rates and depths
of penetration/oxidation, and information on the structures and phases present
(presumably original mononitride, uranium dioxide, and uranium sesquinitride formed in
the process). Since transport along grain boundaries is suspected, particular attention will
be given to intergranular surfaces, The direction of the continued work will then depend on
the findings made in this step, and on the available time.
RF2: Strålskador i material för fissions- och fusionsreaktorer
Handledare: Pär Olsson ([email protected])
Strålskador uppstår i material som finns nära härden i en fissionsreaktor eller
reaktionskammaren i en framtida fusionsreaktor. De snabba neutroner som frigörs i
kärnreaktionerna växelverkar med materialen och orsakar en mäng mikroskopiska och
makroskopiska effekter som kraftigt begränsar vilka material man kan använda och hur man
bör designa framtida strålningsbeständiga material. Material som utsätts för strålning blir
med tiden sprött, det kan svälla upp och det kan förvridas geometriskt. Det är mycket
avancerade fenomen som spänner över tidsskalor från femtosekunder till år och rymdskalor
på Ångström till meter. För att undersöka hur strålskador påverkar material kan man utöver
experiment använda olika typer av datorsimuleringar.
I det här projektet kommer ni att jobba med att optimera användandet av en
kvantmekanisk simuleringskod. Vi kan lösa en förenklad version av Schrödingerekvationen
för upp till ca 1000 atomer med hög noggrannhet men det är mycket resurskrävande. För
att simulera hur skador uppstår på den mest grundläggande nivån behöver vi den
storleksordningen atomer och även ca 1000 tidssteg (av storleksordningen femtosekunder).
För att optimera användandet av beräkningsresurserna kommer vi koppla den
kvantmekaniska koden till en kod som baserar sig på enklare Newtondynamik och sedan
utnyttja den snabbare modellen för att förutspå i vilken del av vår simuleringscell som vi
behöver använda den högsta noggrannheten. Detta kan ge oss upp till en faktor 20 i
effektivisering, vilket kan bli klart avgörande för vilka sorters studier man kan göra i
framtiden. Projektet kräver inte att ni förändrar de två simuleringskoder som vi kommer
använda, men att en mindre kod skrivs som läser information från den ena och matar in i
den andra, och vice-versa. Programmeringen kan ske i valfritt språk.
AP1: Selection of Active Galactic Nuclei
Supervisor: Serena Falocco ([email protected])
In some galaxies, the cores, called Active Galactic Nuclei (AGN), are extremely luminous and
emit in the broad energy band. The main fuel of AGN is accretion onto super massive black
holes (SMBH) in accretion disks. Variable emission over the full range of the
electromagnetic spectrum is one of the most peculiar properties of AGN: thanks to the
variability studies the evidence of SMBH in AGN has gone from circumstantial to universal.
The AGN studies in the time domain also provide the most compelling evidences of the
accretion disk existence.
There is strong evidence for a tight interplay between SMBH and the host galaxy evolution.
Thus, an extensive knowledge of the black hole demography is of primary importance to
increase our understanding of galaxy evolution over the cosmic timescales.
Several techniques have been developed to search AGN, exploiting their broad-band
emission. This is a strong advantage since one single identification technique might not be
sufficient to obtain an unbiased census of the AGN population. The emission in the optical
colors originates from the accretion disk, thus it is widely used to identify AGN, but it can be
strongly absorbed by material in the AGN itself. The hard X-ray emission instead is not
strongly absorbed even for the most obscured sources. Thus, the X-ray selection has the
strength to potentially include also a population of obscured AGN. A different technique to
overcome the bias introduced by obscuration is to use the infrared (IR) selection since the
absorbing material that makes AGN difficult to select in optical wavelengths emits radiation
in the IR.
AGN variability plays an important role adding one further dimension to complete the AGN
census in the Universe. It potentially allows to distinguish AGN from sources of similar
optical or IR colors (for example, different classes of non- active galaxies).
During this project the students will learn the most common AGN diagnostics based on
their broad band emission. They will compare the results from a variety of AGN selection
methods exploiting the broadest astronomical surveys to date.
AP2: X-ray spectroscopy of Active Galactic Nuclei
Supervisor: Serena Falocco ([email protected])
Active Galactic Nuclei (AGN) are the most luminous persistent sources in the Universe. In
the currently accepted picture the 'central engine' is an accretion disk where matter spirals
onto a Super Massive Black Hole (SMBH). X-rays can penetrate outward from very near the
SMBH, thus they offer unique insights into the physical processes occurring in these
regions. X-ray spectra turn out to be unique tools to explore special and general relativistic
effects due to the high velocities of matter in the AGN’s innermost regions and to the
strong gravitational field of the SMBH. This offers one of the most fascinating views of
matter in the relativistic regime; besides, it allows to get constrains on the accretion disc
properties and on the SMBH spin. Moreover, X-rayspectroscopic studies allow to investigate
the effects of obscuration and reflection from circum-nuclear regions in AGN, with the main
aim to and make predictions useful to understand the physical and morphological
properties of these structures.
In this project the students will learn the X-ray spectroscopic techniques to investigate the
physics and the morphology of AGN. X-ray data from the main current satellites will be
exploited to explore the AGN 'central engine' and its circumnuclear regions.
AP3: Investigation of multiple phases of Active Galactic Nuclei activity using radio
interferometric data
Supervisor: Sumana Nandi ([email protected])
The center of active galaxies, known as Active Galactic Nuclei (AGN), emit spectacular
radiation across the electromagnetic spectrum, from radio to gamma rays. The accretion of
matter onto the supermassive black holes at the center of the AGN generates energy with
high efficiency. Sometimes an AGN may go through two or more cycles of activity. However,
the number of such known events is small and the mechanism of the recurrent activity is
still unknown. The aim of this study is to identify AGN with episodic activity using multi
frequency radio data. During this project students will learn the basic techniques of radio
interferometry and radio continuum data processing obtained from radio interferometers.
Using spectral index analysis of these radio images they will define the multiple phases of
AGN activity.
AP4: Simuleringsstudie av meteorer och atmosfäriska event för Mini-EUSO
experimentet på ISS
Handledare: Christer Fuglesang ([email protected])
Mini-EUSO är ett instrument som ska skickas upp till ISS i slutet av 2017. Huvudsyftet är att
testa teknologi och metod för framtida stora experiment som ska studera extremt
högenergetisk kosmisk strålning genom att detektera den UV-strålning dessa orsakar I
atmosfären. Mini-EUSO är inte tillräckligt känslig för detta men kan ändå göra en del
experimentell vetenskap, bland annat detektera meteorer och studera atmosfäriska blixtar
på hög höjd, s.k. ”transient luminous events” (TLE). Detta KEX går ut på att använda det
simuleringspaket som existerar för Mini-EUSO och undersöka hur instrumentet kan
användas för studier av meteorer och/eller TLEs. Specifika frågor kan vara hur många
meteorer kan man förväntas sig? Hur starka måste de vara för att kunna observeras? Vilken
typ av TLE (det finns fler olika) kan detekteras?
KF1: Gamma-ray tracking with state-of-the-art AGATA detectors
Handledare: Ayşe Ataç Nyberg ([email protected])
We plan to carry out an experiment in order to study the structure of the magic nucleus
102Sn. So far, not much is known about the excited states of this nucleus. The experiment
may also reveal valuable information about the neighbouring tin isotopes like 103Sn and
the doubly magic nucleus 100Sn. This experiment will be performed at the accelerator
centre GANIL (Grand Accélérateur National d'Ions Lourds) which is located in Caen, France.
During this experiment, we plan to use AGATA (The Advanced Gamma Tracking Array) in
order to measure the gamma-rays emitted after the nuclear reaction. Gamma-ray tracking is
a new technique developed within the AGATA project. With this technique, the
experimental sensitivity for detection of gamma rays is expected to increase by several
orders of magnitude, compared to what is possible today.
Our experiment is planned to take place in year 2018, however, the preperations will start
already in 2017. In this project, the student will take part in the preparations, like cross
section calculations, testing all the possible target and beam combinations and making
count rate estimates. These investigations will increase the chances of success during the
experiment. The student will also get a chance to learn and test the newly developed
gamma-ray tracking technique. This work will be done mainly by using existing computer
codes, however, the student may also need to modify the codes if necessary. The aim of the
project is to give the students the skill to work with a complex system involving different
type of detectors, to combine their physics knowlegde with the new technology and
programming.
KF2: Nuclear physics for charged particle therapy/hadron therapy
Supervisors: Bo Cederwall ([email protected]), Torbjörn Bäck ([email protected]),
Chong Qi ([email protected])
The use of charged particles like proton and heavier ions (helium, carbon, …) in
cancer/tumor therapy is one of many highly successful applications of physics in medicine.
Its advantage over the traditional treatments with photons or electrons lies in its efficient
end precise irradiation of the tumor thanks to the sharp “Bragg peak” at the end of the
charged particle range which makes it possible to irradiate cancer tumors with much higher
dose without detrimental effects on the surrounding healthy tissues. Proton therapy was
proposed as early as 1946. The first treatments were performed in nuclear physics labs at
Berkeley and Uppsala in 1950s. Since then, the The Swedberg Laboratory in Uppsala has
continued to provide proton therapy for a limited range of special cases suitable for
treatments with a single beam of relatively low energy. Nowadays, full-scale facilities with a
wide range of energies and precision rotating gantries are developing around the world and
the number of treatments has increased dramatically in the past few years. In particular, the
Skandion Clinic (Skandionkliniken) in Uppsala, Sweden is operating since 2015 which makes
Sweden the first Nordic country with a full-scale facility for proton treatments.
Despite its well proven efficiency one has to be aware that the effectiveness of the hadron
therapy treatment can be influenced by the limited understanding of the nuclear reactions
involved and the underlying nuclear interactions. In this project the students are expected
to get an overview on nuclear physics in hadron therapy and understand the uncertainties in
relation to dosimetry and particle stopping, nucleus-nucleus reactions and the
fragmentation cross sections. Using information available in scientific data bases and in the
literature the students will identify the key reaction cross-sections and secondary particle
(neutron or charged particle) distributions where experimental data and theoretical
frameworks need to be updated. Test experiments at the Skandion clinic will be discussed
in collaboration with the Skandion clinic team. The students will also become acquainted
with and learn to run existing Monte Carlo simulation codes (The GEANT4 CERN software
and other packages).
KF3: Computational approaches for advanced quantum mechanics problems and Lattice
QCD
Supervisors: Chong Qi ([email protected]), Karl Sallmén ([email protected]), Daniel Karlsson
([email protected])
Solving quantum mechanical problems is full of fun but get challenging for large systems.
The development of computational approaches played an essential role in our
understanding of many-body systems like atom and molecular, condensed matter, quantum
chemistry and atomic nuclei. The computational physics is in particular becoming a third leg,
besides experiment and theory, supporting nuclear physics.
In this project the students will get an overview on the most popular computational
approaches that are applied in state of the art many body physics eigenvalue calculations.
We will then study simple systems like atoms, molecules and nuclei by solving the
Schrödinger equations. On top of the single-particle states derived, we will be able to
construct many-body bases and the corresponding Hamiltonian matrix. Then the students
will see that the complex many-body problem becomes a simple eigenvalue problem. The
students can choose from several advanced projects:
The diagonalization of large matrix through exact diagonalization (with Matlab, C++,
Fortran or Python) and by implementing iterative algorithms like Lanczos and JacobiDavidson. The students will also get access to high performance computation on
supercomputers through parallel implementations of the algorithm using MPI and/or
openMP. One will solve exactly the nuclear pairing Hamiltonian with the algorithm
developed.
The students will also learn how to implement lattice QCD and how to derive accurate
Nucleon-Nucleon and hyperon-nucleon potentials from it. From a computational
perspective one will see that the main challenge is actually to inverse a matrix.
The students can also work density functional theory studies of nuclear and atomic
properties. A challenge there is how to optimize the potentials (e.g., nucleon-nucleon
interactions) and to treat the influence of the continuum.
KF4: Nuclear shell structure, its evolution and topological phase transitions
Supervisor: Chong Qi ([email protected])
The shell structure is a common and distinct feature of many finite quantum systems
including atomic nuclei. In particular, the nucleus represents a unique self-organized object
characterized by the appearance of magic numbers that correspond to a specific shell
structure driven by the spin-orbit force as proposed by the Nobel laureates Goeppert Mayer
and Jensen. What is even more fascinating is that the magic numbers will change
depending on the ratio of neutron and proton numbers, N/Z, i.e., when we move from
nuclei in the vicinity of the β-stability line towards the particle driplines. This has attracted
worldwide attention in the past decade and demands for an improved modeling of the
nuclear structure.
In this project the students are expected to study systematically the shell characters of
both stable and unstable atomic nuclei and model its evolution as a function of N/Z ratio
within the simple independent particle model. The students will also be able to solve the
Schrödinger and/or Dirac equations with general potentials. Moreover, the students are
expected to run advanced many-body Hartree-Fock approaches, where the 2016 Nobel
Prize winner Thouless also played an esstential role, to simulate the shell structure of
atomic nuclei and/or atoms.
The students will also pioneer the possibility to see topological orders and phase
transitions in simple many-body systems like atomic nuclei in relation to the new Noble
prize. Atomic nuclei are known to exhibit different phases like nuclear shape, superfluidity,
halo and clustering but the the possibility to have topological orders is still not clear.
KF5: R-process simulation and heavy-Element Nucleosynthesis
Supervisors: Chong Qi ([email protected]), Daniel Karlsson ([email protected])
The so-called rapid neutron capture process (or the r-process) in nuclear astrophysics is
believed to be the mechanism for the nucleosynthesis of many stable heavy and superheavy
nuclei heavier than Iron. This process is not fully understood from a theoretical point of
view and the observed abundance of r-process elements still cannot be properly
reproduced. In this project a systematic calculation will be done to simulate the abundance
of heavy nuclei under different conditions based on theoretical estimations of nuclear
masses and decay half-lives. In particular, we would like to explore the influence of the
uncertainties in nuclear masses in our abundance predictions.
The r process codes ‘r-Java’ (Java) and ‘nucnet’ (C language) will be used for the simulation.
The project will thus not involve heavy programming. It is hoped that, after the project, the
student will have an overall understanding of the structures and decays of atomic nuclei as
well as the various nuclear astrophysical processes and be able to perform basic
calculations.
Alternatively, the students may get an overview of the different categories of gravitational
waves and their candidate sources including compact object binaries, core-collapse
supernovae as well as neutron stars. In particular, the core collapse supernovae and neutron
star mergers are the leading candidate sites for the unknown r-process. One will also
understand how gravitational-wave data can be inverted to infer the properties of neutron
stars and the general conditions in the merger environment from which one can tell
whether mergers are a significant r-process source or not. The detection of gravitational
radiation could thus have profound implications for nuclear astrophysics.