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  • 1.
    Birgersson, Evert
    Örebro University, Department of Natural Sciences.
    Determination of binary fission-fragment yields in the reaction 251Cf(nth, f) and Verification of nuclear reaction theory predictions of fission-fragment distributions in the reaction 238U(n, f)2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Neutron-induced fission has been studied at different excitation energies of the compound nucleus by measurements on the two fissioning systems, 252Cf* and 239U*.

    For the first time, the light fission fragment yields from the reaction 251Cf(nth, f) have been measured with high resolution. This experiment was performed with the recoil mass spectrometer LOHENGRIN at ILL in Grenoble, France. When the results from this work, where the compound nucleus is at thermal excitation, are compared to the spontaneous fission of 252Cf, enhanced emission yields as well as an increased mean kinetic energy is observed around A = 115. This suggests the existence of an additional super-deformed fission mode in 252Cf.

    The reaction 238U(n, f) was studied using the 2E-technique with a double Frisch grid ionization chamber. Fission fragment mass, energy and angular distributions were determined for incident neutron energies between 0.9 and 2.0 MeV. The experiments were performed at the Van de Graaff accelerator of IRMM in Geel, Belgium. This is the first measurement of the mass distribution for incident neutron energies around 0.9 MeV. The motivation for studying 238U(n, f) was to verify theoretical predictions of the mass distribution at the vibrational resonance in the fission cross section at 0.9 MeV. However, the predicted changes in fission fragment distributions could not be confirmed.

    A precise modelling of the fission process for the minor actinides becomes very important for future generation IV and accelerator driven nuclear reactors. Since fission fragment distributions depend on the excitation of the fissioning system, so does the number of delayed neutrons, which are one of the safety parameters in a reactor.

    List of papers
    1. Binary fission-fragment yields from the reaction 251Cf(nth, f)
    Open this publication in new window or tab >>Binary fission-fragment yields from the reaction 251Cf(nth, f)
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    2005 (English)In: Nuclear fission and fission-product spectroscopy: 3rd international workshop on nuclear fission and fission-product spectroscopy, American Institute of Physics , 2005, p. 349-352Conference paper, Published paper (Refereed)
    Abstract [en]

    The recoil mass spectrometer LOHENGRIN of the Laue-Langevin Institute, Grenoble has been used to measure the light fission-fragment mass yield and kinetic energy distributions from neutron-induced 252Cf*, using 251Cf as target material. ©2005 American Institute of Physics

    Place, publisher, year, edition, pages
    American Institute of Physics, 2005
    National Category
    Subatomic Physics Natural Sciences Physical Sciences
    Research subject
    Physics
    Identifiers
    urn:nbn:se:oru:diva-11214 (URN)10.1063/1.2137266 (DOI)0-7354-0288-4 (ISBN)
    Conference
    The 3rd International Workshop on NUCLEAR FISSION AND FISSION-PRODUCT SPECTROSCOPY, Château de Cadarache, Saint Paul lez Durance, France, May 11-14, 2005
    Available from: 2007-09-03 Created: 2007-09-03 Last updated: 2017-10-18Bibliographically approved
    2. Light fission-fragment mass distribution from the reaction 251Cf(nth, f)
    Open this publication in new window or tab >>Light fission-fragment mass distribution from the reaction 251Cf(nth, f)
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    2007 (English)In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 791, no 1-2, p. 1-23Article in journal (Refereed) Published
    Abstract [en]

    For mass numbers A = 80 to 124 the recoil mass spectrometer LOHENGRIN of the Institute Laue-Langevin in Grenoble was used to measure with high resolution the light fission-fragment mass yields and kinetic energy distributions from thermal-neutron induced fission of 252Cf* for the first time, using 251Cf as target material. The obtained mean light fragment mass AL = (107 ± 2) and the corresponding mean kinetic energy Ek,L = (103±2) MeV are within the expected trend. Emission yields around A = 115 are enhanced and the corresponding mean kinetic energy is higher compared to spontaneous fission of 252Cf. This could be explained by the existence of an additional super-deformed fission mode.

    Place, publisher, year, edition, pages
    Amsterdam: Elsevier, 2007
    Keywords
    Nuclear reactions, 251Cf(nth, f ), Californium-251, Neutron-induced fission, Fission modes, Minor Actinides, Transmutation, Fission-fragment spectroscopy
    National Category
    Subatomic Physics Natural Sciences Physical Sciences
    Research subject
    Physics
    Identifiers
    urn:nbn:se:oru:diva-4080 (URN)10.1016/j.nuclphysa.2007.04.018 (DOI)
    Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2017-12-14Bibliographically approved
    3. Properties of the reaction 238U(n, f) at the vibrational resonances
    Open this publication in new window or tab >>Properties of the reaction 238U(n, f) at the vibrational resonances
    2009 (English)In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 817, no 1-4, p. 1-34Article in journal (Refereed) Published
    Abstract [en]

    Recent fission cross-section calculations for the reaction 238U(n, f ), based on an extended statistical model, predict a significant change of fission fragment properties, such as the mean mass by A = 1.5 and a notable increase in total kinetic energy in the region of the vibrational resonance at an incident neutron energy En = 0.9 MeV. This model includes individual fission cross-sections by the asymmetric standard 1 (S1) and standard 2 (S2) as well as the symmetric super-long (SL) mode. In order to verify the model predictions, a dedicated experiment on 238U has been carried out to measure fission-fragment mass yield distributions for incident neutron energies from En = 2.0 MeV down to 0.9 MeV, where the fission characteristics at the vibrational resonance at En = 0.9 MeV were investigated for the first time. The previously reported distinct structure in the angular anisotropy around En = 1.2 and 1.6 MeV wasobserved at En = 0.9 MeV as well. The predicted large changes in fission fragment mass yield and total kinetic energy could not be confirmed. In the resonance the mean total kinetic energy is only about 0.5 MeV higher than at En = 1.8 MeV. At the same time, a slight decrease of the mean heavy fragment mass was observed, probably indicating a slightly increased contribution of the S1 fission mode.

    Place, publisher, year, edition, pages
    Amsterdam: Elsevier, 2009
    Keywords
    Nuclear reactions 238U(n, f ), E = 0.9–2.0 MeV; measured/analyzed fission fragment mass yields and
    National Category
    Subatomic Physics Physical Sciences
    Research subject
    Physics
    Identifiers
    urn:nbn:se:oru:diva-5485 (URN)10.1016/j.nuclphysa.2008.12.001 (DOI)000263449200001 ()2-s2.0-58149293406 (Scopus ID)
    Available from: 2009-02-12 Created: 2009-02-12 Last updated: 2017-12-14Bibliographically approved
  • 2.
    Norrman, Eva
    Örebro University, Department of Natural Sciences.
    Optimisation of radiographic imaging by means of factorial experiments2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the optimisation process of radiographic imaging, factorial designed experiments can be applied. The parameters (factors) are varied together instead of one at a time, making it possible to discover interactions between the factors as well as main influences of them on the result variable. A 2k design implies having k number of factors each one set to two different levels (low and high).

    A computer program, CoCIQ, designed to automatically analyse and evaluate test images of a contrast-detail phantom, was evaluated and adjusted to clinical situations using a flat panel detector. The program gives a quantified measurement of image quality by calculating an Image Quality Figure (IQF) for the X-ray image. It was shown that the program produces IQF with small variations. It was also found that there was a strong linear statistical relation between the computerised evaluation and the evaluation performed by human observers.

    2k factorial experiments were evaluated by investigating the influence of tube potential, tube loading, focus size and filtration on the result variables IQF, Kerma Area Product (KAP) and effective dose using a flat panel detector. It was found that the result variables were mainly influenced by tube loading, tube potential and filtration. Interactions between tube potential and filtration as well as between tube loading and filtration were observed, too. This work demonstrates that accepted knowledge was reproduced and that the effects of interactions between parameters were revealed.

    Extended 2k experiments were then applied at three different optimisation procedures. Two studies were performed using a flat panel detector for lumbar spine radiography. The aim was to find optimal settings for tube potential, system sensitivity and filtration for different sized patients and, in a separate study, to investigate the effect of the image post processing parameters and the possibility for dose reduction by adjusting these. The parameters are ROI (Region Of Interest) density, gamma, detail contrast enhancement, unsharp masking, kernel size and noise compensation.

    After determining the optimal settings from these experiments, X-ray images of the lumbar spine of an Alderson phantom were acquired and evaluated in a visual grading analysis (VGA).

    The results illustrated that the image quality was maintained at a lower effective dose by operating with a reduced tube potential and increased sensitivity of the X-ray system.

    The experiments on image post process parameters revealed their influence on image quality and indicated that image quality could be improved by changing the settings of the process parameters.

    Factorial experiments were also performed, using a multislice CT scanner to investigate the possibility for dose reduction at paediatric head examinations. An anthropomorphic phantom simulating a one-year-old child was scanned using different settings of tube potential, tube loading and reconstruction filter.

    The study showed that a 25 % reduction of dose was possible with maintained image quality by reducing the tube loading.

    Factorial designed experiments provide an effective method to simultaneously predict the influence of various parameters on image quality and radiation dose in the optimisation in diagnostic radiology.

    List of papers
    1. A clinical evaluation of the image quality computer program, CoCIQ
    Open this publication in new window or tab >>A clinical evaluation of the image quality computer program, CoCIQ
    2005 (English)In: Journal of digital imaging, ISSN 0897-1889, E-ISSN 1618-727X, Vol. 18, no 2, p. 138-144Article in journal (Refereed) Published
    Abstract [en]

    To provide an objective way of measuring image quality, a computer program was designed that automatically analyzes the test images of a contrast-detail (CD) phantom. The program gives a quantified measurement of image quality by calculating an Image Quality Figure (IQF). The aim of this work was to evaluate the program and adjust it to clinical situations in order to find the detectable level where the program gives a reliable figure of the contrast resolution. The program was applied on a large variety of images with lumbar spine and urographic parameters, from very low to very high image qualities. It was shown that the computer program produces IQFs with small variations and there were a strong linear statistical relation between the computerized evaluation and the evaluation performed by human observers (R2 = 0.98). This method offers a fast and easy way of conducting image quality evaluations.

    National Category
    Physical Sciences
    Research subject
    Physics
    Identifiers
    urn:nbn:se:oru:diva-2863 (URN)10.1007/s10278-004-1036-0 (DOI)
    Available from: 2007-12-28 Created: 2007-12-28 Last updated: 2017-12-14Bibliographically approved
    2. A factorial experiment on image quality and radiation dose
    Open this publication in new window or tab >>A factorial experiment on image quality and radiation dose
    2005 (English)In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 114, no 1-3, p. 246-252Article in journal (Refereed) Published
    Abstract [en]

    To find if factorial experiments can be used in the optimisation of diagnostic imaging, a factorial experiment was performed to investigate some of the factors that influence image quality, kerma area product (KAP) and effective dose (E). In a factorial experiment the factors are varied together instead of one at a time, making it possible to discover interactions between the factors as well as major effects. The factors studied were tube potential, tube loading, focus size and filtration. Each factor was set to two levels (low and high). The influence of the factors on the response variables (image quality, KAP and E) was studied using a direct digital detector. The major effects of each factor on the response variables were estimated as well as the interaction effects between factors. The image quality, KAP and E were mainly influenced by tube loading, tube potential and filtration. There were some active interactions, for example, between tube potential and filtration and between tube loading and filtration. The study shows that factorial experiments can be used to predict the influence of various parameters on image quality and radiation dose.

    National Category
    Physical Sciences
    Research subject
    Physics
    Identifiers
    urn:nbn:se:oru:diva-2864 (URN)10.1093/rpd/nch557 (DOI)
    Available from: 2007-12-28 Created: 2007-12-28 Last updated: 2017-12-14Bibliographically approved
    3. Optimising the tube potential for lumbar spine radiography using a flat-panel digital detector
    Open this publication in new window or tab >>Optimising the tube potential for lumbar spine radiography using a flat-panel digital detector
    (English)Manuscript (preprint) (Other academic)
    National Category
    Physical Sciences
    Research subject
    Physics
    Identifiers
    urn:nbn:se:oru:diva-2865 (URN)
    Available from: 2007-12-28 Created: 2007-12-28 Last updated: 2017-10-18Bibliographically approved
    4. Optimization of image process parameters through factorial experiments using a flat panel detector
    Open this publication in new window or tab >>Optimization of image process parameters through factorial experiments using a flat panel detector
    2007 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 52, no 17, p. 5263-5276Article in journal (Refereed) Published
    Abstract [en]

    In the optimization process of lumbar spine examinations, factorial experiments were performed addressing the question of whether the effective dose can be reduced and the image quality maintained by adjusting the image processing parameters. A 2(k)-factorial design was used which is a systematic and effective method of investigating the influence of many parameters on a result variable. Radiographic images of a Contrast Detail phantom were exposed using the default settings of the process parameters for lumbar spine examinations. The image was processed using different settings of the process parameters. The parameters studied were ROI density, gamma, detail contrast enhancement (DCE), noise compensation, unsharp masking and unsharp masking kernel (UMK). The images were computer analysed and an image quality figure (IQF) was calculated and used as a measurement of the image quality. The parameters with the largest influence on image quality were noise compensation, unsharp masking, unsharp masking kernel and detail contrast enhancement. There was an interaction between unsharp masking and kernel indicating that increasing the unsharp masking improved the image quality when combined with a large kernel size. Combined with a small kernel size however the unsharp masking had a deteriorating effect. Performing a factorial experiment gave an overview of how the image quality was influenced by image processing. By adjusting the level of noise compensation, unsharp masking and kernel, the IQF was improved to a 30% lower effective dose.

    Place, publisher, year, edition, pages
    Bristol: IOP publishing, 2007
    Keywords
    Quality, Coefficients, Radiography, Reduction, Urography
    National Category
    Natural Sciences Physical Sciences Medical and Health Sciences Physiology Radiology, Nuclear Medicine and Medical Imaging
    Research subject
    Physics; Medicine; Radio Physics
    Identifiers
    urn:nbn:se:oru:diva-2866 (URN)10.1088/0031-9155/52/17/011 (DOI)
    Available from: 2007-12-28 Created: 2007-12-28 Last updated: 2018-01-13Bibliographically approved
    5. Optimisation of paediatric CT head examinations through factorial experiments
    Open this publication in new window or tab >>Optimisation of paediatric CT head examinations through factorial experiments
    (English)Manuscript (Other academic)
    National Category
    Physical Sciences
    Research subject
    Physics
    Identifiers
    urn:nbn:se:oru:diva-2867 (URN)
    Available from: 2007-12-28 Created: 2007-12-28 Last updated: 2017-10-18Bibliographically approved
  • 3.
    Tovesson, Fredrik
    Örebro University, Department of Natural Sciences.
    The neutron-induced fission cross section of 233Pa: and the quest for clean and safe nuclear energy2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Neutron-induced fission of 233Pa has been investigated between 1.0 and 8.5 MeV, and the reaction cross section was determined. Due to the short half-life of 233Pa for β-decay, fission events from the daughter product 233U affect the analysis of the protactinium experiment. In order to be able to correct for this contamination by ingrowing 233U, its fission cross section was measured as well in the same energy region.

    The result for the 233Pa(n,f) cross section is compared with previous theoretical evaluations and indirect cross section estimations extracted from fission probability data. The cross section data that were measured in this work are lower than all other values for this isotope. The 233U(n,f) cross section values are also compared to evaluations. The evaluations for the neutron-induced fission cross section of 233U(n,f) are based on a large set of experimental values, and are thus considered to be very accurate. A good agreement between the results obtained in this work and the evaluations is observed in this case.

    New model calculations, based on the statistical model for nuclear reactions, are compared to the experimental results for the 233Pa(n,f) cross section. These theoretical calculations describe the experimental results very accurately, and can be used to extract information about the fissioning system.

    The main motivation for this work is its relevance for the thorium-based nuclear fuel cycle, which has been proposed for advanced reactor facilities intended for safe power supply and transmutation of nuclear waste.

    List of papers
    1. Neutron-induced fission cross section of 233Pa between 1.0 and 3.0 MeV
    Open this publication in new window or tab >>Neutron-induced fission cross section of 233Pa between 1.0 and 3.0 MeV
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    2002 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 88, no 6, p. 062502-Article in journal (Refereed) Published
    Abstract [en]

    The energy dependent neutron-induced fission cross section of 233Pa has for the first time been measured directly with monoenergetic neutrons. This nuclide is an important intermediary in a thorium based fuel cycle, and its fission cross section is a key parameter in the modeling of future advanced fuel and reactor concepts. A first experiment resulted in four cross section values between 1.0 and 3.0 MeV, establishing a fission threshold in excess of 1 MeV. Significant discrepancies were found with a previous indirect experimental determination and with model estimates.

    National Category
    Physical Sciences
    Research subject
    Physics
    Identifiers
    urn:nbn:se:oru:diva-3089 (URN)10.1103/PhysRevLett.88.062502 (DOI)11863801 (PubMedID)
    Available from: 2003-11-21 Created: 2003-11-21 Last updated: 2017-12-14Bibliographically approved
    2. The Pa-233 fission cross section
    Open this publication in new window or tab >>The Pa-233 fission cross section
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    2002 (English)In: Journal of Nuclear Science and Technology, ISSN 0022-3131, E-ISSN 1881-1248, Vol. Supplement 2, p. 210-213Article in journal (Refereed) Published
    Abstract [en]

    The energy dependent neutron-induced fission cross section of 233Pa has for the first time been measured directly with mono-energetic neutrons. This isotope is produced in the thorium fuel cycle and serves as an intermediate step between the 232Th source material and the 233U fuel material. Four neutron energies between 1.0 and 3.0 MeV have been measured in a first campaign. Some preliminary results are presented and compared to literature.

    National Category
    Physical Sciences
    Research subject
    Physics
    Identifiers
    urn:nbn:se:oru:diva-3090 (URN)
    Available from: 2003-11-21 Created: 2003-11-21 Last updated: 2017-12-14Bibliographically approved
    3. 233Pa(n, f) cross section up to En=8.5 MeV
    Open this publication in new window or tab >>233Pa(n, f) cross section up to En=8.5 MeV
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    2004 (English)In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 733, no 1-2, p. 3-19Article in journal (Refereed) Published
    Abstract [en]

    The energy dependence of the neutron-induced fission cross section of 233Pa has been measured directly for the first time from the fission threshold up to En=8.5 MeV. This reaction plays an important role in the thorium-uranium fuel cycle, and is thus of interest for the design and modeling of advanced reactor and transmutation facilities. The existing information in the ENDF/B-VI and JENDL-3.3 evaluated nuclear data files differ by a factor of two for the 233Pa(n, f) cross section values and show different fission threshold energies. Our new experimental data give lower cross section values than both evaluations and resolves the question about the threshold energy. In addition to the experimental investigation, also a new theoretical calculation of the reaction cross section has been performed with the statistical model code STATIS, showing a good agreement with the experimental data.

    National Category
    Subatomic Physics
    Research subject
    Physics
    Identifiers
    urn:nbn:se:oru:diva-3091 (URN)10.1016/j.nuclphysa.2003.11.054 (DOI)
    Available from: 2003-11-21 Created: 2003-11-21 Last updated: 2017-12-14Bibliographically approved
    4. Fission fragment properties and the problem of the pulse height defect
    Open this publication in new window or tab >>Fission fragment properties and the problem of the pulse height defect
    2002 (English)In: Journal of Nuclear Science and Technology, ISSN 0022-3131, E-ISSN 1881-1248, Vol. Supplement 2, p. 673-676Article in journal (Refereed) Published
    Abstract [en]

    The pulse height defect (PHD) has been investigated for three different counting gases commonly used in ionization chambers. The PHD introduces an underestimation of the kinetic energy of a charged particle detected with an ionization chamber. Thus, in some cases it is of crucial importance to correct for this effect, e.g. when studying fission fragment properties. A now method was used, applying a waveform digitizer, to study the PHD. The fission fragment properties from spontaneous fission of 252Cf where determined using different counting gases and different ways of correcting for the PHD were evaluated.

    National Category
    Physical Sciences
    Research subject
    Physics
    Identifiers
    urn:nbn:se:oru:diva-3092 (URN)
    Available from: 2003-11-21 Created: 2003-11-21 Last updated: 2017-12-14Bibliographically approved
    5. Calculation of the neutron-induced fission cross section of 233Pa
    Open this publication in new window or tab >>Calculation of the neutron-induced fission cross section of 233Pa
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    2004 (English)In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 69, no 2, p. 021604-Article in journal (Refereed) Published
    Abstract [en]

    Since very recently, experimental data for the energy dependence of the 233Pa(n,f) cross section are finally available. This has stimulated a new, self-consistent cross section evaluation for the system n+233Pa in the incident neutron energy range 0.01–6 MeV. The results are quite different compared to earlier evaluation attempts. Since 233Pa is an important intermediary in the thorium based fuel cycle, its neutron reaction cross sections are key parameters in the modeling of future advanced reactor concepts.

    National Category
    Physical Sciences
    Research subject
    Physics
    Identifiers
    urn:nbn:se:oru:diva-3093 (URN)10.1103/PhysRevC.69.021604 (DOI)
    Available from: 2003-11-21 Created: 2003-11-21 Last updated: 2017-12-14Bibliographically approved
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