| 1. |
- Keleta, S, et al.
(author)
-
Exclusive measurement of two-pion production in the dd -> He-4 pi pi reaction
- 2009
-
In: Nuclear Physics A. - : Elsevier BV. - 0375-9474 .- 1873-1554. ; 825:1-2, s. 71-90
-
Journal article (peer-reviewed)abstract
- The results from the first kinematically complete measurement of the dd -> He-4 pi pi reaction are reported. The aim was to investigate a long standing puzzle regarding the origin of the peculiar pi pi-invariant mass distributions appearing in double pion production in light ion collisions, the so-called ABC effect. The measurements were performed at the incident deuteron energies of 712 MeV and 1029 MeV. with the WASA detector assembly at CELSIUS in Uppsala, Sweden. We report the observation of a characteristic enhancement at low pi pi-invariant mass at 712 MeV, the lowest energy yet. At the higher energy, in addition to confirming previous experimental observations, Our results reveal a strong angular dependence of the pions in the overall centre of mass system. The results are qualitatively reproduced by a theoretical model, according to which the ABC effect is described as resulting from a kinematical enhancement in the production of the pion pairs from two parallel and independent NN -> d pi sub-processes. (C) 2009 Elsevier B.V. All rights reserved.
|
|
| 2. |
|
|
| 3. |
- Bargholtz, Chr., et al.
(author)
-
Measurement of the eta -> pi(+)pi(-)e(+)e(-) decay branching ratio
- 2007
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 644:5-6, s. 299-303
-
Journal article (peer-reviewed)abstract
- The reaction pd -> He-3 eta at threshold was used to provide a clean source of eta mesons for decay studies with the WASA detector at CELSIUS. The branching ratio of the decay eta -> pi(+)pi(-)e(+)e(-) is measured to be (4.3 +/- 1.3 +/- 0.4) x 10(-4).
|
|
| 4. |
- Bargholtz, Chr., et al.
(author)
-
Properties of the WASA pellet target and a stored intermediate-energy beam
- 2007
-
In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 587:2-3, s. 178-187
-
Journal article (peer-reviewed)abstract
- Experimental data from the reaction close to threshold have been used to investigate time-dependent properties of the WASA pellet target and the stored beam of 892.8 MeV protons in the CELSIUS accelerator. The detection of 3He ions in solid-state detectors provides an excellent almost background free trigger for η production. Pellet interactions with the surrounding material and with the beam lead to evaporation of deuterium gas into the beam pipe. Approximately 30% of the registered η decay events are due to interactions in deuterium gas outside the pellets. Due to beam–target interaction the beam is transversely heated and appears to acquire a component of a slightly lower energy.
|
|
| 5. |
- Berlowski, M., et al.
(author)
-
Measurement of eta meson decays into lepton-antilepton pairs
- 2008
-
In: Physical Review D. Particles and fields. - : American Physical Society. - 0556-2821 .- 1089-4918. ; 77:3, s. 032004-
-
Journal article (peer-reviewed)abstract
- A search for rare lepton decays of the eta meson was performed using the WASA detector at CELSIUS. Two candidates for double Dalitz decay eta -> e(+)e(-)e(+)e(-) events are reported with a background of 1.3 +/- 0.2 events. This allows to set an upper limit to the branching ratio of 9.7x10(-5) (90% CL). The branching ratio for the decay eta -> e(+)e(-)gamma is determined to (7.8 +/- 0.5(stat)+/- 0.8(syst))x10(-3) in agreement with world average value. An upper limit (90% CL) for the branching ratio for the eta -> e(+)e(-) decay is 2.7x10(-5) and a limit for the sum of the eta ->mu(+)mu(-)mu(+)mu(-) and eta ->pi(+)pi(-)mu(+)mu(-) decays is 3.6x10(-4).
|
|
| 6. |
- Petrén, Henrik, et al.
(author)
-
eta-meson production in proton-proton collisions at excess energies of 40 and 72 MeV
- 2010
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 82:5, s. 055206-
-
Journal article (peer-reviewed)abstract
- The production of eta mesons in proton-proton collisions has been studied using the WASA detector at the CELSIUS storage ring at excess energies of Q = 40 MeV and Q = 72 MeV. The eta was detected through its 2 gamma decay in a near-4 pi electromagnetic calorimeter, whereas the protons were measured by a combination of straw chambers and plastic scintillator planes in the forward hemisphere. About 6.9 x 10(4) and 9.3 x 10(4) events were found at Q = 40 MeV and Q = 72 MeV, respectively, with background contributions of less than 5%. A simple parametrization of the production cross section in terms of low partial waves was used to evaluate the acceptance corrections. Strong evidence was found for the influence of higher partial waves. The Dalitz plots show the presence of p waves in both the pp and the eta {pp} systems and the angular distributions of the eta in the center-of-mass frame suggest the influence of d-wave eta mesons.
|
|
| 7. |
- Schönning, Karin, et al.
(author)
-
Polarisation of the omega meson in the pd -> He-3 omega reaction at 1360 and 1450 MeV
- 2008
-
In: Physics Letters B. - elsevier : Elsevier BV. - 0370-2693 .- 1873-2445. ; 668:4, s. 258-262
-
Journal article (peer-reviewed)abstract
- The tensor polarisation of omega mesons produced in the pd -> He-3 omega reaction has been studied at two energies near threshold. The 3 He nuclei were detected in coincidence with the pi(0)pi(+)pi(-) or pi(0)gamma decay products of the omega. in contrast to the case of phi-meson production, the omega mesons are found to be unpolarised. This brings into question the applicability of the Okubo-Zweig-lizuka rule when comparing the production of vector mesons in low energy hadronic reactions.
|
|
| 8. |
- Schönning, Karin, et al.
(author)
-
Production of eta and 3 pi mesons in the pd -> (HeX)-He-3 reaction at 1360 and 1450 MeV
- 2010
-
In: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 45:1, s. 11-21
-
Journal article (peer-reviewed)abstract
- The cross-sections of the pd -> He-3 eta, pd -> He-3 pi(0)pi(0)pi(0) and pd -> He-3 pi(+)pi(-)pi(0) reactions have been measured at the beam kinetic energies T-p = 1360 MeV and T-p = 1450 MeV using the CELSIUS/WASA detector setup. At both energies, the differential cross-section d sigma/d Omega of the eta meson in the pd -> He-3 eta reaction shows a strong forward-backward asymmetry in the CMS. The ratio between the pd -> He-3 pi(+)pi(-)pi(0) and pd -> He-3 pi(0)pi(0)pi(0) cross-sections has been analysed in terms of isospin amplitudes. The reconstructed invariant-mass distributions of the pi pi, He-3 pi and (3)He2 pi systems provide hints on the role of nucleon resonances in the 3 pi production process.
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
|
|
| 12. |
|
|
| 13. |
|
|
| 14. |
- Bargholtz, Christoph, et al.
(author)
-
Production of the ω meson in the pd -> 3He ω reaction at 1450 MeV and 1360 MeV
- 2009
-
In: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 79:4, s. 044002-
-
Journal article (peer-reviewed)abstract
- The production of ω mesons in the pd→3Heω reaction has been studied at two energies near the kinematic threshold, Tp=1450 MeV and Tp=1360 MeV. The differential cross section was measured as a function of the ω c.m. angle at both energies over the whole angular range. Whereas the results at 1360 MeV are consistent with isotropy, strong rises are observed near both the forward and backward directions at 1450 MeV. Calculations made using a two-step model with an intermediate pion fail to reproduce the shapes of the measured angular distributions and also underestimate the total cross sections
|
|
| 15. |
|
|
| 16. |
|
|
| 17. |
|
|
| 18. |
|
|
| 19. |
- Gerén, Linda, 1962-
(author)
-
Pionic Fusion Study of the 6He Halo
- 2006
-
Doctoral thesis (other academic/artistic)abstract
- The structure of the halo nucleus 6He has been investigated in a pionic fusion experiment at the CELSIUS storage ring facility in Uppsala. The 4He(d, 6He)π+ reaction was studied 0.6 - 5.0 MeV above threshold in the centre-of-mass frame with a deuteron beam incident on a 4He gas target. The 6He ions were detected in a ΔE - E solid-state detector telescope inserted into the CELSIUS ring. The results for the total and differential cross section are presented and compared to results for the analogue reaction producing the 3.56 MeV analogue state in 6Li. A simple model of the reaction gives results consistent with earlier findings of 6He as having a spatial extent considerably exceeding that of the alpha particle. It is also shown that information about the high momentum part of the halo wave function can be extracted from the results of this pionic fusion measurement.
|
|
| 20. |
|
|
| 21. |
- Kastlander, Johan, et al.
(author)
-
Development of methods to use CdTe detectors in field measurements
- 2006
-
In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 41, s. 523-526
-
Journal article (peer-reviewed)abstract
- We are currently investigating the possibility to use CdTe detectors for in situ determinations of radionuclide concentration in soil. Buried activity can be reliably determined by a comparison of the count rate in the photo peak and the region between the photo peak and Compton edge. However, the pulse-height spectrum from CdTe detectors is severely deteriorated, due to poor charge collection, in particular for high gamma-ray energies. Our efforts have, therefore, been concentrated on improving the peak to valley ratio for such detectors. A simple, non-discriminating, algorithm for the analysis of output from two amplifiers with different shaping times is described. By means of this algorithm the peak-tovalley ratio for a small planar CdTe detector is improved by more than a factor of six compared to the uncorrected ratio without loss of efficiency.
|
|
| 22. |
- Kastlander, Johan, et al.
(author)
-
Efficient in situ method to determine radionuclide concentration in soil
- 2005
-
In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 547:2-3, s. 400-410
-
Journal article (peer-reviewed)abstract
- A simple realisation of the so-called peak-to-valley method is described combining simulations of photon transport in soil with measured detector properties. Comparisons regarding the total activity of Cs-137 determined from gamma spectra recorded in situ to results from soil sampling show excellent agreement for six different sites in Sweden with different surface properties and activities ranging from 15 to 1000 kBq/m(2). These results are quite insensitive to assumptions regarding soil composition. Our results for the burial depth are more sensitive to assumptions regarding soil composition, however, still in general agreement with the results from the soil samples.
|
|
| 23. |
- Kastlander, Johan, 1976-
(author)
-
In situ measurements of radionuclide concentration in soil : An investigation into detector properties and methods
- 2010
-
Doctoral thesis (other academic/artistic)abstract
- In case of a release of radioactive nuclides into the environment it is necessary to have reliable methods to estimate the potential effect on people and the ecosystem. In this context the total activity deposited, the elemental composition and the depth distribution are of importance. An efficient in situ method to estimate the average contamination over larger areas using high purity germanium (HPGe) detectors has been developed. The method combines simulation of photon transport with measured detector properties. The total activity of 137Cs determined from gamma-ray spectra recorded in situ are compared to results from soil sampling. Another in situ method has been developed to determine the depth distribution of a radionuclide contamination, using an array of small detectors inserted into the ground, as an alternative to the standard procedure of soil sampling. The possibility to use cadmium telluride (CdTe) detectors as well as lanthanum bromide (LaBr3) detectors has been investigated. As a demonstration of the developed method the small-scale variation of the activity distributions in an area covering 350 m2 have been measured and is compared to results obtained by other methods.
|
|
| 24. |
- Kastlander, Johan, et al.
(author)
-
In-situ method to determine depth distribution of buried activity
- 2011
-
In: Applied Radiation and Isotopes. - : Elsevier BV. - 0969-8043 .- 1872-9800. ; 69:5, s. 773-779
-
Journal article (peer-reviewed)abstract
- A method is described to determine the depth distribution of buried activity offering an alternative to conventional soil sampling and laboratory analysis by in-situ measurements with small detectors inserted into the ground. As ad demonstration of the method small-scale variations in the distribution of Cs-137 in a riparian marsh in central-eastern Sweden are determined using lanthanum bromide detectors (LaBr3). The results show variations of the activity ranging between 400 and 2200 kBq/m^2 over an area not exceeding 350 m^2. The decrease of the average activity since 2003 coincides with the physical decay indicating that no net redistribution of activity into this part of the marsh has occurred during the inter weening years.
|
|
| 25. |
- Kastlander, Johan, et al.
(author)
-
Investigation into the properties of CdTe detectors for in-situ measurements
- 2008
-
In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 596:3, s. 409-416
-
Journal article (peer-reviewed)abstract
- As part of a program investigating means to improve gamma-ray spectra obtained with CdTe detectors, we report results obtained with two 10×10×5 mm^3 CdTe detectors, one planar the other of quasi-hemispheric geometry. Applying a combination of cooling and pulse rise-time discrimination with the quasi-hemispheric detector, we obtain a resolution of 4 percent at 662 keV and a peak-to-valley ratio of 92 at a loss of approximately 25 percent of the counts in the full-energy region.
|
|
