| 1. |
- Kamae, Tuneyoshi, et al.
(författare)
-
PoGOLite - A high sensitivity balloon-borne soft gamma-ray polarimeter
- 2008
-
Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 30:2, s. 72-84
-
Tidskriftsartikel (refereegranskat)abstract
- We describe a new balloon-borne instrument (PoGOLite) capable of detecting 10% polarisation from 200 mCrab point-like sources between 25 and 80 keV in one 6-h flight. Polarisation measurements in the soft gamma-ray band are expected to provide a powerful probe into high energy emission mechanisms as well as the distribution of magnetic fields, radiation fields and interstellar matter. Synchrotron radiation, inverse Compton scattering and propagation through high magnetic fields are likely to produce high degrees of polarisation in the energy band of the instrument. We demonstrate, through tests at accelerators, with radioactive sources and through computer simulations, that PoGOLite will be able to detect degrees of polarisation as predicted by models for several classes of high energy sources. At present, only exploratory polarisation measurements have been carried out in the soft gamma-ray band. Reduction of the large background produced by cosmic-ray particles while securing a large effective area has been the greatest challenge. PoGOLite uses Compton scattering and photo-absorption in an array of 217 well-type phoswich detector cells made of plastic and BGO scintillators surrounded by a BGO anticoincidence shield and a thick polyethylene neutron shield. The narrow Held of view (FWHM = 1.25 msr, 2.0 deg x 2.0 deg) obtained with detector cells and the use of thick background shields warrant a large effective area for polarisation measurements (similar to 228 cm(2) at E = 40 keV) without sacrificing the signal-to-noise ratio. Simulation studies for an atmospheric overburden of 3-4 g/cm(2) indicate that neutrons and gamma-rays entering the PDC assembly through the shields are dominant backgrounds. Off-line event selection based on recorded phototube waveforms and Compton kinematics reduce the background to that expected for a similar to 100 mCrab source between 25 and 50 keV. A 6-h observation of the Crab pulsar will differentiate between the Polar Cap/Slot Gap, Outer Gap, and Caustic models with greater than 5 sigma significance; and also cleanly identify the Compton reflection component in the Cygnus X-1 hard state. Long-duration flights will measure the dependence of the polarisation across the cyclotron absorption line in Hercules X-1. A scaled-down instrument will be flown as a pathfinder mission from the north of Sweden in 2010. The first science flight is planned to take place shortly thereafter.
|
|
| 2. |
- Larsson, Billy, 1956, et al.
(författare)
-
Similarities and differences between practitioners of psychotherapy in Sweden
- 2009
-
Ingår i: Journal of Psychotherapy Integration. ; 19:1, s. 34-66
-
Tidskriftsartikel (refereegranskat)abstract
- This study focuses on similarities and differences between Swedish psychotherapists of four orientations: psychodynamic, cognitive, cognitive–behavioral, and integrative therapy. The aim is to describe similarities and differences regarding (a) background factors, (b) focus in psychotherapy, (c) attitudes toward psychotherapy as art/craftsmanship, (d) scientific outlook, (e) what characterizes a good psychotherapist, and (f) how psychotherapy ought to be pursued. The therapists had very similar attitudes about the therapeutic relationship and rather similar attitudes about which effects psychotherapy ought to obtain. The greatest differences were related to psychotherapeutic techniques and science. The results are discussed with emphasis on the distance or proximity between the orientations. The conclusion is that there are differences between psychodynamic psychotherapy compared with cognitive and cognitive–behavioral therapies, which imply difficulties in integrating these orientations. However, the differences between the cognitive and cognitive–behavioral therapists are not of such a magnitude that they necessarily present an obstacle to integration.
|
|
| 3. |
- Larsson, Viktor, 1984, et al.
(författare)
-
Calculation of the neutron noise using the Analytical Nodal Method
- 2009
-
Ingår i: REACTOR PHYSICS CALCULATIONS IN THE NORDIC COUNTRIES.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this study, the neutron noise, i.e. the stationary fluctuations of the neutron flux around its mean value, iscalculated in 2-group diffusion theory for a 2-dimensional reactor using the Analytical Nodal Method. Abrief description of the calculation of the static flux is also included. The same calculational scheme for theneutron noise as for the static flux is used. As a benchmark, the calculated neutron noise for a 2-dimensionalfully homogeneous reactor is compared with the analytical solution which can easily be determined for homogeneousreactors. The result of the benchmark is that the numerically calculated neutron noise accuratelymatches the analytically calculated neutron noise.
|
|
| 4. |
- Larsson, Viktor, 1984, et al.
(författare)
-
Comparative study of 2-group P1 and diffusion theories for the calculation of the neutron noise in 1D 2-region systems
- 2009
-
Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 36:10, s. 1574-1587
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the neutron noise, i.e. the stationary fluctuations of the neutron flux around its meanvalue, is calculated in 2-group P1 and diffusion theories for a 2-region slab reactor using Green’sfunction technique. The applicability of diffusion theory for different types and locations of the perturbation,as well as different frequencies, is assessed. Material data, i.e. nuclear cross-sections and kineticparameters, representative of a Light Water Reactor (LWR) and of a Heavy Water Reactor (HWR),respectively, are used in this work. It is demonstrated that for practical situations in LWRs and HWRs,there is no significant advantage to use P1 theory since diffusion theory gives acceptable results. Thelargest deviations between the two formalisms are observed in regions of large gradients of the staticneutron flux, such as close to the reflector interface and close to the perturbation. Such observationsare in agreement with theoretical expectations. This study also indicates that neglecting the effect ofcross-section perturbation on the diffusion coefficient gives a rather small impact on the solution. Thisallows drastically simplifying the determination of the neutron noise. When using numericaltechniques for such a determination the memory requirements and computational effort can be significantlyreduced.
|
|
| 5. |
- Larsson, Viktor, 1984
(författare)
-
Development of a Numerical Tool for Estimating the Neutron Noise in Nuclear Reactors
- 2009
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The neutron noise, i.e. the time-variations of the neutron flux around its meanvalue, can be used for obtaining important safety parameters in a nuclear reactor,e.g. the decay ratio for a boiling water reactor and the moderator temperature coefficientfor a pressurized water reactor. The main benefit of using the neutron noiseis that it can be taken from the existing detectors and there is therefore no need forperturbing reactor operation. It would thus be advantageous to be able to calculatethe neutron noise with a relatively simple model with a relatively small computationaleffort, a work initiated earlier at the Department of Nuclear Engineering,Chalmers University of Technology.The objectives of this report are thus to validate some of the assumptions inthe previously developed model and to evaluate various ways of improving it. Acomparison is thus conducted between P1 and diffusion theories with two energygroups for a 1-dimensional 2-region reactor. The previous model used the FiniteDifference Method, a method which is simple and easy to implement for spatialdiscretization of the equations. The drawback is that the accuracy is low unlessthe size of the nodes of the reactor model is small. To enhance the neutronics whilekeeping the size of the nodes in the range of 15-20 cm, theAnalytical Nodal Methodwas implemented for the calculation of the neutron noise.The results fromthis study are that there is no need in practical situations for usinghigher order theory for neutron noise calculations since diffusion theory givesresults that are accurate enough. The implemented Analytical Nodal Method alsoshows high agreement with the analytically calculated neutron noise.
|
|
| 6. |
- Larsson, Viktor, 1984, et al.
(författare)
-
Parametric study of the influence of heterogeneous boron concentration and coolant density on cross section generation in BWRs
- 2008
-
Ingår i: International Conference on the Physics of Reactors 2008, PHYSOR 08; Interlaken; Switzerland; 14 September 2008 through 19 September 2008. - 9781617821219 ; 2, s. 966-973
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we investigate the effect of heterogeneous boron concentration and coolant density distribution on nodal macroscopic cross sections, which could potentially arise in an Anticipated Transient Without Control rods of a boiling water reactor. All calculations are made with the 2-D transport code PHOENIX4. Full core simulators, such as POLCA7, often have simple models for handling such heterogeneities with the basic requirement that conservative results are obtained simulating such core conditions. We have found that this is not always the case and that the errors can potentially be quite high.
|
|
| 7. |
- Larsson, Viktor, 1984, et al.
(författare)
-
Semi-analytical calculations of the neutron noise in 2-group theory for 1-D homogeneous systems
- 2008
-
Ingår i: International Conference on the Physics of Reactors 2008, PHYSOR 08; Interlaken; Switzerland; 14 September 2008 through 19 September 2008. - 9781617821219 ; 2, s. 1235-1242
-
Konferensbidrag (refereegranskat)abstract
- In this paper, 2-group diffusion and P1 theories are compared via semi-analytical calculations of the neutronnoise in a 1-D 2-region slab reactor using the Green’s function technique. The neutron noise, i.e. the timevariationsof the neutron flux around its mean value, is useful for core diagnostics and monitoring of a reactor.For a 2-region system, the Green’s function can be calculated in a semi-analytical manner as a function offrequency and space, for various positions of the perturbation. This work demonstrates that for practicalsituations in a Light Water Reactor, there is no significant advantage to use P1 theory since diffusion theorygives acceptable results. The largest deviations between the two formalisms are observed in the reflector region.This study also shows that neglecting the effect of cross-section perturbations on the diffusion coefficient has arather strong impact on the solution in the reflector.
|
|
