Department of Physics

Nuclear and Accelerator-Based Physics Seminars

Suggestions for speakers are most welcome! Contact or .

Upcoming Seminars

    Past Seminars

    • June 29, 2017, at 10:15 in FYS3. Israel Mardor (Tel Aviv University): Neutron-rich isotope research at SARAF via neutron induced fission

      In this talk, I will give a brief overview of SARAF with emphasis on the liquid-lithium target, describe its potential regarding neutron-rich isotopes, and conclude with possible collaboration topics.

    • June 20, 2017, at 14:15 in FYS3. Emanuel Ydrefors (Instituto Tecnológico de Aeoronáutica (ITA), Brazil): Relativistic studies of few-body systems using the Bethe-Salpeter approach

      From a general point of view, understanding the interaction in terms of the fundamental degrees of freedom is very important for nuclear and particle non-perturbative physics. Since that is a very difficult problem, simple models are of great value for understanding the crucial qualitative features of the solution with more realistic kernels. For example, ladder and cross-ladder diagrams for two-body systems, and effective three-body forces in the case of three-body systems. It is well-known that in the non-relativistic approach the binding energy of this system is not bounded from below, what is known as Thomas collapse. As it was discovered in the light-front dynamics (LFD) [2,3], the relativistic repulsion prevent the Thomas collapse in the non-relativistic sense.

      The Bethe-Salpeter equation provides an approach to perform non-perturbative studies of few-body systems in Minkowski space. In this contribution we will briefly review some recent results [1,2] computed for two- and three-boson systems using the aforementioned formalism. We present results computed in Minkowski space and they are compared with Euclidean calculations.

      For the two-body system we will discuss the response to cross-ladder exchanges in the interaction kernel, and in addition the two-body current contribution to the elastic electromagnetic form factor [3]. Regarding the three-body system having a zero-range interaction we discuss the response of to higher Fock components, and thus effective three-body forces [4]. We present results for systems where two of the particles can form a bound state, and in addition for so-called Borromean systems, where no two-body bound state exists. The latter kind of systems was not treated in previous works [1,2] and our results show that these papers were not treating the true ground state. We show that the Thomas collapse is also prevented in the Bethe-Salpeter approach by the relativistic repulsion at small distances. Further counterparts of other well-known phenomena in non-relativistic physics, as the popular Efimov physics, is also briefly discussed.

      [1] T. Frederico, Phys. Lett. B 282 (1992) 409

      [2] J. Carbonell and V. A. Karmanov, Phys. Rev. C 67 (2003) 037001

      [3] V. Gigante, J. H. Alvarenga Nogueira, E. Ydrefors, C. Gutierrez, V. A. Karmanov and T. Frederico, Phys. Rev. D 95 (2017), 056012.

      [4] E. Ydrefors et al, Phys. Lett. B 770 (2017) 131.

    • June 15, 2017, at 14:15 in FYS3. Beyhan Bastin (GANIL): Study of explosive H-burning processes : direct and indirect measurements with SPIRAL 1 & 2 beams

      During the seminar we will present and discuss experimental programs concerning the H-burning processes carried out and foreseen at the existing SPIRAL1 and the new SPIRAL2 facilities. In the first part of the seminar we will focus more particularly the discussion on the novae astrophysical scenario. We will give details on an experiment realized with the VAMOS spectrometer and a 19Ne beam produced and post-accelerated with SPIRAL1. In this experiment, a new broad resonance below the proton threshold has been observed in 19Ne and impact significantly the destruction rate of 18F. The latter is one of the main beta emitters produced during the thermonuclear explosion. The consequence on the space observational programs based on low energy gamma ray detection (below 10 MeV) with Satellites will be discussed. In the second part, the new opportunities offered by the SPIRAL1-upgrade and SPIRAL2 facilities for the study of novae and X-ray bursters will be shortly presented as well.

    • June 8, 2017, at 14:15 in FYS3. José Barea (Universidad de Concepción, Chile): Single particle levels and double beta decay matrix elements in the microscopic interacting boson model

      The Interacting Boson Model is introduced and how it is connected with the Shell Model. The calculation of the double beta decay matrix element using this model is explained and how are affected when the energies of single particle levels are changed.

    • May 23, 2017, at 14:15 in FYS3. Antoine de Roubin (University of Jyväskylä): Nuclear deformation of strontium and rubidium isotopes in the region of A = 100

      The ion trap mass spectrometer ISOLTRAP, located at CERN-ISOLDE, was used to extend the atomic mass surface in the region A=100. The mass of isotopes 100-102Sr and 100-102Rb were measured, including the first direct mass determination of 102Sr and 101,102Rb. Through those measurements the continuation of the region of deformation with the increase of the neutron number was confirmed. Additionally, a comparison between experimental values and beyond mean-field calculations results, available in the literature, is shown in order to interpret the shape evolution in the strontium isotopic chain and a possible onset of deformation in heavier krypton isotopes. To complete this study, Hartree-Fock-Bogoliubov calculations for even and odd isotopes were performed, highlighting the competition of nuclear shapes in the region. 

    • May 18, 2017, at 10:15 in FYS3. Karim Bennaceur (Université Claude Bernard Lyon, University of Jyväskylä, Helsinki Institute of Physics): Regularized pseudopotential for nuclear structure calculations

      In this seminar, I will discuss the properties of existing effective interactions used in mean-field and beyond-mean-field calculations. I will also explain why some ambiguities and pathologies have lead us to develop a new form of effective interaction that we call a regularized pseudopotential.

      This pseudopotential has a two-body part which takes the form of a finite-range interaction containing derivative terms with a gaussian form factor whose range is a regularization scale. This particular form gives us a potential of building an order-by-order correctible theory.

      I will explain why the necessity to reproduce the canonical value of the nucleon effective mass in infinite nuclear matter imposes to complement the two-body pseudopotential with a non-local zero-range three-body term. The parameters of this pseudopotential were adjusted so as to reproduce infinite nuclear matter properties and binding energies of magic and open shell spherical nuclei using a newly developed code, FINRES4, which solves the Hartree-Fock-Bogolyubov equations on a space-coordinate mesh with a finite-range interaction. The implementation of this new pseudopotential in the codes for deformed nuclei HFODD and HFBTEMP is under development.

      I will present results of mean-field calculations for closed and open shell nuclei obtained with this pseudopotential and discuss the strategy we consider for future developments.

    • May 11, 2017, at 14:15 in FYS3. Dr. Mikael Reponen (University of Jyväskylä): Towards precision mass measurements and in-source laser spectroscopy of neutron-deficient silver isotopes

       The radioactive neutron deficient silver isotopes around the N=Z region have been of considerable interest for several years. In particular, N=Z 94Ag may exhibit the most unique isomer in existence. In addition to a low-spin (7+) beta- delayed-proton decaying isomer, 94Ag has been identified as having a spin trap isomer with the highest spin, (21+), ever observed for β-decaying nuclei. The isomer’s long half-life of 0.39(4) s [1], high excitation energy [2] and high spin [3] are matched by an unparalleled selection of decay modes including, among others, β decay [3] and one- proton [4] decay. However, the claimed existence of the most exotic form of decay in 94mAg(21+), namely two-proton emission, has been questioned [5]. One piece of the puzzle is the energy of the isomer. Mass measurements of 92Rh and 94Pd, the respective two-proton and β-decay daughters of 94Ag, have been performed at JYFLTRAP which, when combined with the original spectroscopic decay data, lead to a 1.4 MeV contradiction in the deducted isomer energy [6].

      A project is underway at the Accelerator Laboratory of the University of Jyväskylä aiming to investigate the neutron-deficient isotopes of silver. The project will commence with the resonance ionization spectroscopy (RIS) of 101−97Ag, produced using the 92Mo(14N,2pxn)104−xAg heavy-ion fusion-evaporation reaction in order to extract and confirm the nuclear spins and magnetic dipole moments measured at KU Leuven [7]. The ultimate goal is a high precision mass measurement study in the region of the isotope 94Ag, aimed for direct measurements of 93Pd (the 1 proton decay channel), 94Ag and 94mAg(21+) masses in order to unambiguously determine of the energy of isomer.

      I will present the status of the project which has seen the commissioning of an inductively-heated hot cavity catcher [8], a device to be used in the production of silver isotopes. Recent results and new ion source developments will be discussed.

      [1] I. Mukha et al., Physical Review C 70, 044311 (2004).

      [2] I. Mukha et al., Nature 439, 298 (2006).

      [3] C. Plettner et al., Nuclear Physics A 733, 20 (2004).

      [4] I. Mukha et al., Physical Review Letters 95, 022501 (2005).

      [5] O.L. Pechenaya et al., Physical Review C 76, 011304 (2007).

      [6] A. Kankainen et al., Physical Review Letters 101, 142503 (2008).

      [7] R. Ferrer et al., Physics Letters B 728, 191 (2014).

      [8] M. Reponen et al., Review of Scientific Instruments 86, 123501 (2015).

    • April 20, 2017, at 14:15 in FYS2. David Sharp (University of Manchester): Nucleon occupancies of neutrinoless double beta decay systems and transfer reactions in inverse kinematics with a solenoid - the ISOLDE Solenoid Spectrometer

      Nuclear structure information, such as the ground state nucleon occupancies, can provide data against which NME calculations relevant to neutrinoless double beta decay can be benchmarked and improved. Transfer reactions, as a probe of the single-particle nature of nuclear states, are ideal for extracting the nucleon occupancies. An overview of a campaign of measurements aimed at extracting nucleon occupancies for a number of 0ν2β decay candidates will be presented.

      Some time will be spent detailing a new spectrometer, the ISOLDE Solenoidal Spectrometer (ISS), being commissioned to exploit the available radioactive beams from HIE-ISOLDE. This spectrometer is based on the HELIOS concept, which has been successfully exploited for transfer reaction studies at Argonne National Laboratory. This presentation will provide an update on the current status of the ISS project and the science proposals for early implementation of the spectrometer.

    • April 18, 2017, at 14:15 in FYS3. Jack Henderson (TRIUMF): Transition strengths in 22,23Mg as tests of ab initio theory

      The calculation of E2 transition strengths can prove complicated within traditional nuclear models, often requiring phenomenological adjustments to the nucleon charges in order to reproduce experimental data. In recent years, ab initio nuclear theory has become readily applicable in mid-mass nuclei and in principle, may allow for the reproduction of transition strengths without requiring the use of effective charges. Two experiments were performed using the TIGRESS gamma- ray spectrometer at the TRIUMF-ISAC facility, with the goal of providing improved transition strength information on 22,23Mg for comparison with such models. The results of these experiments will be presented and compared to calculations using the in-medium similarity-renormalization- group (IM-SRG) and symplectic no-core shell model (NCSpM) ab initio methodologies.

    • April 6, 2017, at 14:15 in FYS3. Prof. Natalie Jachowicz (Ghent University, Belgium): Modeling  neutrino-nucleus scattering for accelerator-based neutrino experiments 

      Neutrino-oscillation experiments rely on neutrino-nucleus scattering to detect the neutrinos carrying the oscillation signal. A precise understanding of the mechanisms underlying the interaction of the neutrino with an atomic nucleus is hence mandatory to disentangle the oscillation pattern. This quest for the precise determination of oscillation parameters is complicated by the fact that monochromatic neutrino beams are not available, and neutrinos are produced with a broad energy distribution. The signal in a detector is the superposition of different reaction mechanisms : quasi-elastic, multi-nucleon emission, pion-production etc., which all need to be understood. 

      I will present the present status of our models for the description of neutrino-nucleus cross sections, including quasi-elastic excitations, multinucleon knockout and neutrino-induced pionproduction.

    • March 28, 2017, at 14:15 in FYS3. Wafa Almosly (University of Jyväskylä): Nuclear response to supernova neutrino

      Realistic estimates of neutrino-nucleus interactions in various nuclei are essential for many application in nuclear and astrophysics.

      The neutrino-nucleus and antineutrino-nucleus cross sections are calculated for the stable cadmium isotopes and lead isotopes. The considered energies are appropriate for the detection of supernova neutrino. The nuclear responses are computed by folding the computed cross sections with realistic energy spectra for the incoming (anti)neutrino.

      The Donnelly-Walecka method was adopted for the cross sections calculations. The required wave function are constructed using quasiparticle random-phase approximation for the even-mass target nuclei and microscopic quasiparticle phonon model for the odd-mass ones.

    • March 13, 2017, 13:15 at FYS1. Prof. Abuduwayiti Aierken (The Xinjiang Technical Institute of Physics & Chemistry, CAS): Radiation Hardened High Efficiency Solar Cells for Space Application
      Currently used space solar cells are GaAs based lattice matched three junction solar cells which conversion efficiency around 28-29%, but it hardly matches the nowadays higher criteria of high efficiency and radiation hardened for space application. In order to increase the cell efficiency, theoretically, increase the number of subcells is the conventional way, however, it is difficult to find proper materials fitting the both lattice matching and current matching requirement between the sub-cells.
      In our research, we overcome the lattice mismatch problem between the sub-cells by semiconductor wafer bounding technology, fabricated GaInP/GaAs//GaInAsP/InGaAs four junction full spectra solar cell with conversion efficiency up to 32% under AM0 and the degradation of efficiency is less than 15% after 1MeV electron irradiation with fluence of 10^15 e/cm2.
      I will also introduce the Laboratory of Electronic Component Radiation Effects, Xinjiang Technical Institute of Phys. & Chems., Chinese Academy of Sciences.
    • March 3, 2017, 10:15 at FYS3. Prof. Bo Cederwall (KTH): Lifetime measurements for sensitive tests of nuclear structure theories
       The advantage of lifetime measurements as a tool to constrain nuclear theory will be illustrated with a few examples, including some recent work at JYFL.
    • February 28, 2017, 15:15 at FYS3. Prof. Eiji Ideguchi (Osaka University): Nuclear structure programs at RCNP and RIKEN
      Some topics of nuclear structure studies at RCNP, Osaka University and RIBF at RIKEN Nishina Center will be presented.
      At RCNP, a cyclotron facility is utilized for various nuclear structure studies. There are mainly two beam lines used for these studies. One is EN beam line where unstable nuclear beams can be produced by utilizing projectile fragmentation reactions. The other is WS beam line where high-resolution spectrometer, Grand Raiden, is available. Recently, we have started CAGRA project to combine Ge Clover array (CAGRA) with EN and Grand Raiden spectrometer. Two CAGRA campaign experiments at both beam lines have been successfully performed.
      At RIBF, world highest-intensity RI beams are available using BigRIPS fragment separator. A number of in-beam gamma-ray spectroscopy experiments are performed using NaI based array DALI2 and also experiments using stopped RI beams utilizing EURICA gamma-ray spectrometer were performed. In addition, superheavy element search experiments have been performed and new element, Z=113, was successfully identified and it was named as Nh recently. Some experimental results at RIBF will be introduced. In addition, a new project, OEDO, has been started at SHARAQ beam line by CNS, the University of Tokyo, where low-energy RI beams will be used for gamma-ray spectroscopy. In this project, CAGRA spectrometer can be combined with OEDO to perform high-spin gamma-ray spectroscopy of unstable nuclei.
      Future prospects of our project will be discussed.
    • February 14, 2017, 14:15 at FYS3. Marc Schuh (Max-Planck-Institut für Kernphysik, Heidelberg): The Tritium-Helium-Trap
      THe-Trap is a Penning-trap mass spectrometer designed to measure the mass ratio of tritium and helium-3 with a relative uncertainty of 10-11. The resulting mass difference, i.e. Q-value, will be of help for the KArlsruhe TRItium Neutrino (KATRIN) experiment to measure the endpoint of the tritium beta-decay energy spectrum with a precision better than 0.2 eV. I will give a general overview over THe-Trap and point towards a current problem: In 2015 two groups [1],[2] published mass values of helium-3 that deviate by 4σ from each other. The groups used different techniques for detecting the ion eigenfrequencies in a Penning trap. On its way to the mass measurement of tritium THe-Trap will investigate both methods to show if their results are consistent. 
      [1] Myers, E. G. et al., Phys. Rev. Lett., 114, 1 (2015) 
      [2] S.L. Zafonte and R.S. VanDyck, Metrologia, 52, 280 (2015) 
    • February 3, 2017, 10:15 at FYS3. Ruben de Groote (Instituut voor Kern- en Stralingsfysica, KU Leuven): Collinear Resonance Ionization Spectroscopy as a sensitive probe of nuclear structure
      The Collinear Resonance Ionization Spectroscopy experiment (CRIS) at ISOLDE combines the high sensitivity and the universal applicability of resonance ionization spectroscopy with the high resolution offered by conventional collinear laser spectroscopy. This makes it an ideal tool to study the (ground-state) electromagnetic moments, radii and nuclear spins of nuclei far from stability. In this seminar, I will give an overview of the technical requirements of high-sensitivity CRIS measurements and the developments that were made to enhance the resolution of the technique. During this discussion, results obtained on e.g. neutron-deficient Fr beams and neutron-rich copper beams will be presented. The recent results on 76-78Cu will also be briefly interpreted through comparison with large-scale shell model calculations. Finally, future possibilities and technical challenges of the CRIS technique will be discussed.
    • December 15, 2016, 13:15 at FYS2. Prof. Bob Wadsworth (The University of York): Study of the N = Z nucleus 96Cd via Fragmentation
      Studies of N = Z nuclei in the 100Sn region have provided important data to test nuclear shell model predictions in the region. A particular focus in recent years has been the emergence of new data from the fragmentation facilities, which has enabled emphasis to be placed on the interactions and model spaces used to interpret the data. N = Z nuclei are also of interest because neutrons and protons occupy the same orbitals, which can lead to strong np correlations of both isovector and isoscalar type. The presentation will focus on new decay properties of the known 16+ spin-gap isomer in 96Cd [1] and the first evidence for an isomeric gamma decaying state in this nucleus, the latter of which results allows a tentative decay scheme to be deduced for the low-lying states following comparison with shell model calculations.
      [1] B. S. Nara Singh et al., Phys. Rev. Lett. 107, 172502 (2011)
    • December 13, 2016, 15:15 at FYS3. Prof. Matti Leino (University of Jyväskylä): Recent developments regarding the discovery of elements 115 and 117, and the role of physicists/chemists, or IUPAP/IUPAC
      Early this year, the IUPAC/IUPAP Joint Working Party (JWP) gave out the results of its assessment [1] of the discovery claims of man-made elements 113, 115, and 117, and accordingly gave permission to the discoverers to suggest names for these three elements. The proposed names were made public in June, and the five-month period granted for making comments regarding the suggested names came to an end on November 8th. IUPAC approved the names (also for 118) on Nov. 28th.
      Meanwhile, the research collaboration headed by scientists from the University of Lund challenged on statistical grounds the interpretation of the JWP regarding the so called cross reaction argument connecting the discovery of elements 115 and 117 [2].
      I will briefly discuss the element naming procedures and in somewhat more detail the Lund work regarding the decay chains of 117 and 115. This is simply a question of the mutual compatibility of two or more data sets in the special case of radioactive decay law.
      Not totally irrelevant is the question of the role of IUPAP and IUPAC in the naming. I will also briefly discuss this.
      Both the scientific 117/115 case and the naming practices were discussed in a lively manner in the recent Nobel Symposium NS160 dealing with superheavy element physics and chemistry, theory as well as experiments, held at the Bäckaskog castle in Sweden. My presentation is based on the relevant publications and on these NS160 discussions.
      [1] Paul J. Karol et al., Pure Appl. Chem. 2016; 88(1-2): 139
      [2] U. Forsberg et al., Phys. Lett. B 760 (2016) 293
    • December 9, 2016, 12:15 at FYS3. Dr. Ali Al-Adili (Upsala University): Uppsala University and the investigation program on Nuclear Fission
      This seminar gives a survey of the nuclear-fission research conducted by Uppsala University. Albeit 75 years of intense research, the community still lacks a complete fission model. Efforts are put by the nuclear-reactions group to understand the dynamics of the fission process.
      Experiments are performed on high-precision cross section experiments, fission yields, isomeric yields, prompt fission neutrons and gammas. During this talk, particular focus is put on the collaborations with JRC-GEEL in Belgium. Fission fragment spectroscopy increases the knowledge of the scission configuration and reveals hidden properties of the fission barrier. Especially if excitation energy is allowed to vary. Two different techniques are utilized to study the fission fragments (so-called 2-E and 2E-2v). Once the highly excited fragments are created, they de-excite promptly. These processes are highly affected by nuclear structure and they unwrap the information of energy sharing at scission. Our group also studies prompt fission neutron emission at different excitation energies. Lately we also got involved in prompt fission gamma measurements.
      The final part of the seminar will be dedicated to the IGISOL ion guide simulations done at Uppsala.
    • November 24, 2016, 10:15 at FYS2. Dr. Oliver Kirsebon (Aarhus University): Bringing an old magnetic spectrometer back out of retirement
      A powerful intermediate-image magnetic spectrometer, built in Jyväskylä in the 1980s and capable of focusing 8 MeV electrons, is currently being refurbished with the aim of measuring the end point of the beta-decay spectrum of 20F with high precision. In the seminar, I will review the current status of the project, discuss the astrophysical motivation behind it, and provide an outlook.
    • November 8, 2016, 15:15 at FYS3. Dr. Jenni Kotila (University of Jyväskylä): Towards more reliable double beta decay nuclear matrix elements: Obtaining directions from occupation probabilities
      The discovery that neutrinos have finite rest mass has led to wide renewed interest in neutrinoless double beta decay (0νββ), since it offers a sensitive probe to fundamental open questions about neutrino nature and absolute mass scale. The development of large-scale experiments to search for 0νββ-decay has increased the probability of a credible observation of the process in the near future. Thus, the reliability of the calculations of the associated nuclear matrix elements is likely soon to become a critical issue. A better understanding of nuclear structure can offer important constraints on the calculation of 0νββ-decay nuclear matrix elements. A simple way to consider differences between initial and final states of 0νββ-decay candidates is to look at the ground state occupation probabilities of initial and final nuclei. As is well known, the microscopic interacting boson model (IBM-2) has found to be very useful in the description of detailed aspects of nuclear structure. In this talk I will present results for ground state occupation probabilities obtained using IBM-2 for several interesting candidates of 0νββ-decay. Comparison with recent experimental results is also made.
    • October 13, 2016, 13:15 at FYS3. Dr. Panu Ruotsalainen (University of Jyväskylä): Isospin symmetry in the lower sd shell
      Traditionally isospin symmetry and its breaking has been investigated by comparing the energies of excited states in mirror nuclei. Nuclear shell model has been an essential tool in understanding the mechanisms leading to isospin symmetry breaking. Recently, the USD interaction was modified to reproduce the mirror energy difference systematics for T = 1, T = 2 and T = 3/2 sd shell nuclei. It was also used to reproduce the B(E2) values for these nuclei. Experimentally the B(E2) values are relatively well known for the T = 1 and T = 2 sd shell nuclei, which are in good agreement with the recent calculation. For the T = 3/2 sd shell mirror pairs, however, until now only one experimental B(E2) value has been available at A = 33. In this this seminar I will present the recent results from a Coulomb excitation study of T_z = -3/2 nucleus Mg-21 performed at TRIUMF, Vancouver. This new data puts the successful USD interaction to a stringent test by providing a second data point for the B(E2) systematics in the case of T = 3/2 sd shell nuclei.
    • August 16, 2016, 15:15 at FYS2. Prof. Andrey Andreyev (The University of York): Low-energy fission in the lead region: the synergy of beta-delayed, Coulex-induced and fusion-fission approaches
      In the last decade, through technological, experimental and theoretical advances, the situation in experimental low-energy fission studies has changed dramatically. With the use of advanced production and detection techniques, much more detailed fission information can be obtained for traditional regions of fission research and, very importantly, new regions of nuclei have become accessible for fission studies.
      The talk will give a review of recent low-energy fission experiments in very proton-rich nuclei in the lead region. Three complementary methods of fission studies in this region will be discussed:  beta-delayed fission [1,2,3], Coulex-induced fission [4] and fusion-fission reactions induced by charged particles [5,6]. 
      Recent theoretical efforts in respect of low-energy fission calculations in this region of nuclei will also be reviewed.
      The talk will also briefly present the results of the recent (June -July 2016) experiment at ISOLDE in which both beta-delayed fission in 188Bi  and charge radii in the long chain of bismuth isotopes have been studied.
      1.   A. N. Andreyev et al., Phys. Rev. Lett. 105, 252502 (2010)
      2.   L. Ghys et al., Phys. Rev. C90, 041301(R) (2014)
      3.   A.N. Andreyev, M. Huyse, P. Van Duppen, Reviews of Modern Physics, 85, 1541 (2013)
      4. J.-F. Martin et al, Eur. Phys. J. A51, 174 (2015)
      5. K. Nishio et al. Phys. Lett. B, 748, 89 (2015)
      6. E. Prasad et al., Phys. Rev. C 91, 064605 (2015)