| 61. |
- Rodushkin, Ilya, et al.
(författare)
-
Determination of plutonium concentrations and isotope ratios in environmental samples with a double-focusing sector field ICP-MS
- 1999
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 423:2-3, s. 472-479
-
Tidskriftsartikel (refereegranskat)abstract
- An analytical method for the ultratrace and isotopic analysis of plutonium in sediment samples using a double focusing sector field ICP mass spectrometer (ICP-SMS) is described. A detection limit for plutonium in the sub-fg ml-1 range was achieved. The ICP-SMS results were in acceptable agreement with alpha spectrometry. At the low fg ml-1 level a precision in isotope ratio measurements of 2-10% RSD was achieved. Accuracy of the results was assessed by 238U/235U and 205Tl/203Tl isotope ratio determinations using isotopic standards and a natural Tl standard solution, respectively. It was shown that correction for 238UH+ and 238UH2+ is necessary for both plutonium concentration and isotopic composition determinations. From a practical standpoint, the use of ICP-SMS for plutonium measurements is an attractive alternative to techniques such as alpha spectrometry and thermal ionization mass spectrometry (TIMS) due to its higher throughput and ability to measure both concentration and isotopic ratio on the same sample.
|
|
| 62. |
- Sipos, A., et al.
(författare)
-
Visualization of neutron and proton induced particle production in a CMOS image sensor
- 2003
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 509:03-jan, s. 328-332
-
Tidskriftsartikel (refereegranskat)abstract
- A commercially available off the shelf CMOS Image Sensor was irradiated with neutron and proton beams. The Image Sensor is equipped with standard video output. The data were collected on VHS videotapes and analyzed off-line after digitization. The camera chip with 110 000 pixels each having 12 x 12 mum(2) size, shows the nuclear reactions occurring in the sensitive layer as bright spots or tracks. Several applications are suggested based on the inexpensive CMOS Image Sensor.
|
|
| 63. |
- Slunga, E., et al.
(författare)
-
Scintillation response of BaF2 and YAlO3 : Ce (YAP : Ce) to energetic ions
- 2001
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 469:1, s. 70-76
-
Tidskriftsartikel (refereegranskat)abstract
- The scintillation response of BaF2 and YAP: Ce to protons. a particles, O-16 and Si-28 ions in the 5-30 MeV range has been investigated. The ratio between the fast and slow parts of the scintillator signal for BaF2 has been used to separate protons, a particles and heavier ions, and the dependence of this ratio on the particle energy has been studied. The time constants and intensities of the two components of the YAP: Ce signal were measured, as were the time constant and intensity of the weak component of the slow part of the BaF2 signal. Furthermore, the dependence of the light yield on the particle energy has been investigated for both BaF2 and YAP: Ce.
|
|
| 64. |
- Somsak, Dangtip, et al.
(författare)
-
Facility for measurements of nuclear cross sections for fast neutron cancer therapy
- 2000
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 452:3, s. 484-504
-
Tidskriftsartikel (refereegranskat)abstract
- A facility for measurements of neutron-induced double-differential light-ion production cross-sections, for application within, e.g., fast neutron cancer therapy, is described. The central detection elements are three-detector telescopes consisting of two silicon detectors and a CsI crystal. Use of ?E-?E-E techniques allows good particle identification for p, d, t, 3He and alpha particles over an energy range from a few MeV up to 100 MeV. Active plastic scintillator collimators are used to define the telescope solid angle. Measurements can be performed using up to eight telescopes at 20░ intervals simultaneously, thus covering a wide angular range. The performance of the equipment is illustrated using experimental data taken with a carbon target at En = 95 MeV. Distortions of the measured charged-particle spectra due to energy and particle losses in the target are corrected using a newly developed computer code. Results from such correction calculations are presented.
|
|
| 65. |
- Stanislaus, S., et al.
(författare)
-
Results from beam tests of MEGA's low-mass, high-rate cylindrical MWPCs
- 1992
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 323:1-2, s. 198-202
-
Tidskriftsartikel (refereegranskat)abstract
- One of the leading experimental projects at LAMPF has been the MEGA experiment. This is an experiment to search for the rare decay μ → eγ with a sensitivity of 10-13. A prime component of this project has been the design and construction of high-rate, low-mass MWPCs for the tracking of positrons from muon decay. With rate capabilities of 2 × 104 e+/mm2/s and a thickness of 3 × 10-4 radiation lengths, these chambers are state-of-the-art cylindrical MWPCs. Cylindrical chambers of this size (0.9 m2) and thinness have never been previously constructed. The MEGA project at LAMPF has recently succeeded in building chambers with these necessary performance characteristics as demonstrated by data taken from muon decays, cosmic rays, and sources. © 1992.
|
|
| 66. |
- Thungström, Göran, et al.
(författare)
-
Processing of silicon UV-photodetectors
- 2001
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 460:1, s. 165-184
-
Tidskriftsartikel (refereegranskat)abstract
- UV-enhanced photodetectors of both n+-p and p+-n type have been processed in silicon. Photodetectors of the p+-n type display a responsivity close to the theoretical limit with an antireflective coating of either thermally grown dry silicon dioxide or deposited oxide (TEOS), followed by a short wet oxidizing step. This holds, irrespective of whether the detector window is doped by boron through ion implantation or diffusion from a solid source. However, for p+-n photodiodes with a TEOS-oxide in the as-deposited state the responsivity decreases substantially for wavelenghts below 500 nm compared to the theoretical predictions. This is attributed to a high recombination velocity at the silicon dioxide/silicon interface, as supported by computer simulations of the detector performance. In contrast, n+-p photodiodes are found to be rather insensitive with respect to the properties of the silicon dioxide/silicon interface. These results provide the first experimental demonstration that high built in electric fields, caused by abrupt dopant profiles, can suppress the influence of a high interface carrier recombination velocity.
|
|
| 67. |
- van der Marel, J, et al.
(författare)
-
Backtracking as a way to reconstruct Compton scattered gamma-rays
- 1999
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 437:2-3, s. 538-551
-
Tidskriftsartikel (refereegranskat)abstract
- A method has been developed to reconstruct the tracks of gamma-rays that have undergone Compton scattering in a high-resolution detector system. The development of this method is focussed on applications in nuclear gamma-ray spectroscopy. In nuclear in-beam gamma-ray spectroscopy a number of (position-sensitive) germanium detectors are placed around a target where the nuclei under investigation are produced. The gamma-rays emitted by the nuclei can have energies up to several MeVs. The nuclear reactions in the target can cause emission of up to 25 coincident gamma-rays and sometimes even more. In order to resolve the individual gamma-rays from such events the detector systems currently under development will have such a high granularity that the energy of scattered gamma-ray will be deposited in several different detector segments. Therefore, in order to determine the initial energies and the first interaction positions, the tracks have to be reconstructed. The reconstruction method presented in this paper is based on the observation that the energy deposition of the final photoelectric interaction after scattering usually falls in a narrow energy band. Starting from points in this energy range attempts are made to reconstruct the tracks using the photoelectric and Compton interaction probabilities and the Compton scattering formula. The method has been tested on simulated events with up to 25 coincident gamma-rays of various energies and with different detector position resolutions. Reconstruction efficiencies of up to 84% have been achieved. (C) 1999 Elsevier Science B.V. All rights reserved.
|
|
| 68. |
- van der Marel, J., et al.
(författare)
-
Collimatorless imaging of gamma rays with help of gamma-ray tracking
- 2001
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 471:02-jan, s. 276-280
-
Tidskriftsartikel (refereegranskat)abstract
- In many gamma-ray detector systems that are built for imaging purposes Compton scattered photons are suppressed as much as possible. However, the information from photons that scattered inside a detector system can be used to reconstruct the tracks of the photons with help of gamma-ray tracking. Estimates of the incident directions of the photons can be made and an image can be created. Examples of potential applications for this technique are the use as a gamma-camera in medical imaging (e.g. SPECT) or as a detector for PET. Due to the omission of collimators, much higher detection efficiencies can be achieved, reducing the doses required for an image. A gamma-ray tracking method, called backtracking, has been developed for nuclear spectroscopy. The method tracks gamma-rays originating from a point source in the center of a spherical detector system consisting of position-sensitive germanium detectors. This method can also be used as a tracking technique for imaging of an unknown source distribution. With help of Monte Carlo simulations the method has been investigated for simple test cases with one or two planar detectors and one or two point sources. The results-show that the sources can be located accurately in three dimensions.
|
|
| 69. |
- van der Marel, J., et al.
(författare)
-
gamma-ray tracking in germanium : the backtracking method
- 2002
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 477:03-jan, s. 391-396
-
Tidskriftsartikel (refereegranskat)abstract
- In the framework of a European TMR network project the concept for a gamma-ray tracking array is being developed for nuclear physics spectroscopy in the energy range of similar to 10 keV up to several MeV. The tracking array will consist of a large number of position-sensitive germanium detectors in a spherical geometry around a target. Due to the high segmentation, a Compton scattered gamma-ray will deposit energy in several different segments. A method has been developed to reconstruct the tracks of multiple coincident gamma-rays and to find their initial energies. By starting from the final point the track can be reconstructed backwards to the origin with the help of the photoelectric and Compton cross-sections and the Compton scatter formula. Every reconstructed track is given a figure of merit, thus allowing suppression of wrongly reconstructed tracks and gamma-rays that have scattered out of the detector system. This so-called backtracking method has been tested on simulated events in a shell-like geometry for germanium and in planar geometries for silicon, germanium and CdTe.
|
|
| 70. |
- Wallmark, M., et al.
(författare)
-
Operating range of a gas electron multiplier for portal imaging
- 2001
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 471:02-jan, s. 151-155
-
Tidskriftsartikel (refereegranskat)abstract
- At the Karolinska Institute in Stockholm, Sweden a new detector for portal imaging is under development, which could greatly improve the alignment of the radiation beam with respect to the tumor during radiation treatment. The detector is based on solid converters combined with gas electron multipliers (GEMs) as an amplification structure. The detector has a large area and will be operated in a very high rate environment in the presence of heavy ionizing particles. As was discovered recently high rates and alpha particles could cause discharges in GEM and discharge propagation from GEM to GEM and to the readout electronics. Since reliability is one of the main requirements for the portal imaging device, we performed systematic studies to find a safe operating range of the device, free from typical high rate problems, such as discharges.
|
|
