Nuclear Data
The research in Nuclear Data is focusing on fundamental research about nuclear data and nuclear reactions. Knowledge about this is important for applications such as cancer treatments or transmutation of used nuclear fuel.
The group is active in the field of nuclear data research. We measure various observables for neutron-induced reactions and contribute to model development. Our aim is to improve the understanding of the influence of microscopic nuclear data on large scale systems. Examples are:
- dosimetry and fast neutron cancer therapy
- radiation effects in microelectronics
- nuclear power reactors, especially fast reactors within Generation IV.
This means in practice that we
- measure cross-sections for light-ion production and fission, as well as fragment mass distributions
- improve theoretical models describing nuclear reactions
- calculate parameters and their uncertainties for large systems such as fast reactors, in dependence of nuclear data.
Projects
Fission yield, i.e. the new nuclei created as fragments of a fission process, tells us a lot about what happens in the reaction itself. By measuring properties such as mass, energy, and emission angle, we learn more about what happens in the splitting of a nucleus. We also measure reaction cross sections for various nuclear reactions.
It is also important to understand uncertainties in nuclear reaction data, and how these uncertainties affect the result of simulations and calculations of realistic situations. We work with nuclear data libraries and nuclear model codes such as TALYS.
Learn more about our research projects by following the links to the right.
Past projects
Some things the group has worked with earlier.
The AVKOK project was a part of the thesis work of John Loberg, PhD. AVKOK is Avancerad Void-monitorering i KOKvattenreaktorer (Advanced void monitoring in boiling water reactors) and is covered in chapter 4 in John Loberg's doctoral thesis: Novel Diagnostics and Computational Methods of Neutron Fluxes in Boiling Water Reactors (2010).
A related project within the division, also using neutrons to detect the void fraction in boiling water reactors, is Studies of void distributions using neutron tomography.
The work of John Loberg is also part of the background to the project Core monitoring in lead-cooled fast reactors.
In the spring of 2013 we hosted the meeting Uncertainties in the fuel cycle. On the meeting archive page you can find the presentations from both of the days of the meeting.
AIFONS
AlFONS (Accurate fission data for nuclear safety) is a project to make precision measurements of fission yields, i.e. the ratios of various fission products.
For this end, we are using the mass separation facility IGISOL at the University of Jyväskylä. Fission is induced in actinides by neutrons, thermal and high energy, and the result is studied.
We have developed a special neutron source for these experiments, utilizing the 30 MeV proton beam available in Jyväskylä. The protons collide with a beryllium target, inducing nuclear reactions that emit neutrons.
It is important to improve the understanding of the fundamental physics in the fission process. Better data for fission yields make it possible to improve predictions of the composition of nuclear fuel, and therefore also improve the neutron economy of a reactor. Calculations of this and other parameters in a nuclear reactor are at present depending on corrections using data from measurements during the monitoring of the reactor in operation. To reduce the uncertainties in the calculations of the fuel history inside the reactor core can improve the reactor safety as well as economy.
Better data is also important for considerations around final storage, and for development of new reactors of Generation IV. Fission yields determine the inventory of fission products, and hence the remaining decay heat in the used fuel during the first decades after removal from a reactor.
Fission Yield Measurements
We study properties of fragments produced in fission of heavy nuclei like 234,238U and 232Th – properties such as mass yields and energy- and angular distributions, as a function of excitation energy.
These explorations are relevant for both basic nuclear physics and for nuclear applications. Despite the vast amount of measurements historically devoted to nuclear fission we still lack the full insight into the complex physics at the moment of scission. The interplay of the fundamental forces is a challenge to the existing models.
Many questions are yet to be answered, for example:
- What drives the fissioning nucleus to select between symmetric and asymmetric mass split?
- Why do we see a strong angular preference (i.e. anisotropy phenomenon) in the fission fragments emission?
- How do resonance in the cross section influence the mass, energy and angular distributions?
- What are the characteristics of the fission barrier?
- What determines the neutron and gamma multiplicities and how are those values dependent on the mass and energy of the fission fragment?
The group has also interest in the development of detectors and data acquisition systems.
Medley
Preparation of the Medley setup.
Cross section measurements at NFS
Cross section measurements are the crucial input parameters for data evaluations and nuclear reaction model development.
A key ingredient in nuclear models is the optical potential describing interactions of a nucleon with a nucleus.
Data on elastic scattering is needed to form the optical potential. Light-ion production is another ingredient, and, last-not-least, knowledge of reference cross-sections is needed.
The Nuclear reactions research group is working with the Neutrons For Science (NFS) facility at the GANIL accelerator laboratory. The plan is to make measurements of
- light-ion production in neutron induced reaction with various target nuclei
- elastic (n,p) and (n,d) scattering
- fission fragment angular distributions
with a setup called Medley.
An arrangement of eight three-element detectors is mounted inside a scattering chamber. The chamber is evacuated during experimental runs.
Detection is based on DE-DE-E technique, using silicon surface barrier and CsI detectors. An optional collimator can be mounted in front of each telescope. The principle is shown in the figure below.
Nuclear Data Evaluation and Uncertainty Quantification
Total Monte Carlo (TMC) is a method to propagate nuclear data uncertainties to different applications, such as fission reactors, fusion reactors and shielding applications.
The basic idea is to use a state-of-the-art nuclear model code like TALYS and randomize the input parameters within a reasonable range. This range may be defined as fixed. Alternatively a feedback-loop may be used, which compares the resulting calculated cross sections with the existing data-set in the EXFOR database of nuclear reaction data, in order to decide whether the current parameter set leads to acceptable results.
In this way several hundred possible cross-section datasets are generated. TENDL is the TALYS Evaluated Nuclear Data Library.
These datasets are, after proper formatting, feed into a simulation code for the system (e.g. a reactor). In this way the macroscopic parameters and their corresponding uncertainties are calculated in direct dependence of basic nuclear physics input parameters. Since this is done “event-by-event” (parameter-set by parameter-set) the results are traceable back to the input data opening up for sensitivity analysis, studies of correlations, etc.
The TMC uncertainty propagation and TENDL production. In the TMC processes the final result is a spread in a macroscopic parameter. This spread is the systematic uncertainty in the calculation due to ND in the investigated parameter.
Contact
- Programme Professor
- Stephan Pomp
- Head of Division
- Henrik Sjöstrand
- Visiting adress: Ångströmlaboratoriet, house 9, floor 1, Lägerhyddsvägen 1, Uppsala