| 1. |
- Komaguchi, K, et al.
(författare)
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An ESR and ENDOR study of irradiated 6Li-formate
- 2007
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 66:3, s. 754-760
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Tidskriftsartikel (refereegranskat)abstract
- Lithium formate (6LiOOCH·H2O), 95% 6Li enrichment, combined with an exchange of crystallization water with D2O was investigated. The ESR spectrum of the radiation induced free radicals stable at room temperature consists of a singlet with a narrow line width, 0.92 mT. 6Li has smaller magnetic moment and nuclear spin, which resulted in the narrower line width accompanied with an increase in peak amplitude. In comparison with lithium formate with natural isotopic composition, 6Li (7.5%, I = 1) and 7Li (92.5%, I = 3/2), the sensitivity was increased by a factor of two. With optimised spectrometer settings 6Li formate had seven times higher sensitivity compared to alanine. Therefore this material is proposed as a dosimeter material in a dose range down to 0.1 Gy. The g and the 13C-hyperfine (hf) tensors of the CO2- radical anion, major paramagnetic products, were evaluated to be g = (2.0037, 1.9975, 2.0017), and A(13C) = (465.5, 447.5, 581.3) MHz for polycrystalline samples at room temperature. Furthermore, the 1H-hf and 6Li-hf tensors observed for the surroundings of CO2- by ENDOR technique were in fairly good agreement with DFT calculations. The CO2- radicals are found to be so stable that the formate is applicable to the ESR dosimetry, because of fully relaxing in a fully relaxed geometrical structure of the CO2- component and remaining tight binding with the surroundings after the H atom detachment from HCO2-. © 2006 Elsevier B.V. All rights reserved.
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| 2. |
- Lund, Anders, et al.
(författare)
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New materials for ESR dosimetry
- 2002
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - 1386-1425 .- 1873-3557. ; 58:6, s. 1301-1311
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Tidskriftsartikel (refereegranskat)abstract
- New materials for electron spin resonance (ESR) dosimetry have been investigated with the aim to find systems more sensitive than L-alanine accepted as a standard for high dose determinations. Among the investigated systems ammonium tartrate, 2-methylalanine, salts of formic acids and dithionates have been found to be more sensitive than alanine by a factor 2-10. The lower limit applies to tissue equivalent materials, while much higher sensitivities were obtained with formates and dithionates containing heavier atoms. The increased sensitivity was mainly attributed to suitable ESR properties of the room temperature stable radicals as regards spectral shape (narrow lines, little or no hyperfine structure) and microwave saturation properties (short relaxation times). The radical structures have when necessary been clarified by ENDOR spectroscopy, while the saturation properties have been screened by pulsed ESR measurements.
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| 3. |
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| 4. |
- Nilsson, Jonas, 1969-, et al.
(författare)
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The effects of UV-irradiation on the ESR-dosimetry of tooth enamel
- 2001
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Ingår i: Applied Radiation and Isotopes. - 0969-8043 .- 1872-9800. ; 54:1, s. 131-139
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Tidskriftsartikel (refereegranskat)abstract
- Tooth enamel has been shown to be an excellent dosimeter material for retrospective dosimetry. A complication is that it is sensitive to ultraviolet light (UV), creating a signal that interferes with the dosimetric signal. Irradiation of tooth enamel by UV-light induces a mixture of stable and unstable free radicals. The unstable radicals disappear in about three weeks. Stable radicals are created both at the dosimetric peak and at the same g-value as the native peak. The stable peak coinciding with the native peak shows saturation behavior both for UVA/B- and UVC-light. The signal intensity from the sun is roughly estimated to induce a signal comparable to 15 mGy/h from 60 kV X-rays. The blue lamps used by dentists when hardening plastic repairs contain a narrow tail in the UVA/B-region, and it is shown here that these lamps also contribute to the stable peak coincident with the native peak. The contribution to the dosimetry peak, though negligible, at least for the irradiation times is used in this work. Most of the problems with UVA/B-induced signal contributions can probably be avoided by not using front teeth and teeth close to plastic repairs. (C) 2000 Elsevier Science Ltd.Tooth enamel has been shown to be an excellent dosimeter material for retrospective dosimetry. A complication is that it is sensitive to ultraviolet light (UV), creating a signal that interferes with the dosimetric signal. Irradiation of tooth enamel by UV-light induces a mixture of stable and unstable free radicals. The unstable radicals disappear in about three weeks. Stable radicals are created both at the dosimetric peak and at the same g-value as the native peak. The stable peak coinciding with the native peak shows saturation behavior both for UVA/B- and UVC-light. The signal intensity from the sun is roughly estimated to induce a signal comparable to 15 mGy/h from 60 kV X-rays. The blue lamps used by dentists when hardening plastic repairs contain a narrow tail in the UVA/B-region, and it is shown here that these lamps also contribute to the stable peak coincident with the native peak. The contribution to the dosimetry peak, though negligible, at least for the irradiation times is used in this work. Most of the problems with UVA/B-induced signal contributions can probably be avoided by not using front teeth and teeth close to plastic repairs.
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| 5. |
- Olsson, Sara, 1970-, et al.
(författare)
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Ammonium tartrate as an ESR dosimeter material
- 1999
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Ingår i: Applied Radiation and Isotopes. - 0969-8043 .- 1872-9800. ; 50:5, s. 955-965
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Tidskriftsartikel (refereegranskat)abstract
- This study is one step in the search for an ESR dosimeter material with a higher signal intensity than the commonly used l-α-alanine, to be useful in the clinical dose range (approximately 0.1–20 Gy). The substance ammonium tartrate was found and investigated regarding signal intensity, radical stability, dose response and dose resolution. The ESR signal intensity of ammonium tartrate was shown to be more than twice the intensity of the alanine signal. The data indicate that an unstable radiation induced radical contributes to the ESR signal initially; after a couple of hours it has converted to a secondary radical which has a decay slow enough to be considered stable during the first two weeks after irradiation. Ammonium tartrate has a linear dose response in the investigated range of 0.5–4000 Gy and a dose resolution of 0.1 Gy at the 0.5 Gy level where, as a comparison, the corresponding value for alanine is 0.3 Gy. We thus find the substance suitable for clinical dosimetry.
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| 6. |
- Olsson, Sara K., 1970-, et al.
(författare)
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Development of ammonium tartrate as an ESR dosimeter material for clinical purposes
- 2000
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Ingår i: Applied Radiation and Isotopes. - 0969-8043 .- 1872-9800. ; 52:5, s. 1235-1241
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Tidskriftsartikel (refereegranskat)abstract
- The crystalline substance ammonium tartrate is investigated with respect to its suitability as a clinical dosimetry material. The properties investigated are: the radical stability for absorbed doses relevant for clinical use, the improvement in sensitivity when the crystals are deuterated and the linear electron tranfer (LET)-dependence. After photon irradiation to an absorbed dose of 20 Gy, the signal increases rapidly during the first 6 h. After this period, the changes are more moderate and can be corrected for. The signal-to-noise ratio of irradiated ammonium tartrate is twice the corresponding value of alanine. By deuterating the crystals, the sensitivity can be further improved by a factor of 1.4. As expected, the signal decreases with increasing LET of the radiation, but no changes in the spectrum shape was observed.
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| 7. |
- Olsson, Sara, 1970-, et al.
(författare)
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Radiation dose measurements with alanine/agarose gel and thin alanine films around a 192Ir brachytherapy source, using ESR spectroscopy
- 2002
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Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 47:8, s. 1333-1356
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Tidskriftsartikel (refereegranskat)abstract
- Alanine/agarose gel and alanine films in stacks have been used for measurements of absorbed dose around an HDR 192Ir source in a vaginal cylinder-applicator, with and without a 180° tungsten shield. The gel and the films were analysed by means of ESR spectroscopy and calibrated against an ion chamber in a 4 MV photon beam to obtain absolute dose values. The gel serves as both dosimeter and phantom material, and the thin (130 μm) films are used to achieve an improved spatial resolution in the dose estimations.Experimental values were compared with Monte Carlo simulations using two different codes. Results from the measurements generally agree with the simulations to within 5%, for both the alanine/agarose gel and the alanine films.
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| 8. |
- Sastry, M, et al.
(författare)
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51V(n,β)52Cr reaction for neutron dosimetry : Development and assessment of a spectrophotometric method for determination of Cr in vanadium at sub ppm level
- 2004
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Ingår i: Spectrochimica Acta Part A - Molecular and Biomolecular Spectroscopy. - : Elsevier BV. - 1386-1425 .- 1873-3557. ; 60:10, s. 2363-2367
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Tidskriftsartikel (refereegranskat)abstract
- With a view to monitoring the changes in coloration caused by the nuclear reaction 51V(n,β)52Cr in solution of vanadyl sulphate and using it for neutron dosimetry, electronic absorption spectra of vanadyl sulphate solutions were investigated at different concentrations of chromate impurity in micromolar range. It was observed that the presence of chromate enhances the absorptivity over a wide wavelength range serving essentially as a colouring agent for vanadium matrix, presumably due to charge transfer process. The absorbance at 380nm varied linearly over a wide concentration range. The limit of detection of chromate obtained is shown to be adequate for detecting neutron-induced chemical transmutation of vanadium to chromium under standard reactor conditions, when used with long path length cells. It was observed that the absorbance does not change on electron irradiation, suggesting that radiolytic effects due to beta decay, if any, do not interfere in the measurement of neutron-induced changes. In addition to its potential for neutron dosimetry, this is the first report of a simple and direct method of estimation of Cr in vanadium matrix at sub ppm level.
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| 9. |
- Adolfsson, Emelie, 1985-, et al.
(författare)
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Response of Lithium Formate EPR Dosimeters at Photon Energies Relelvant to Brachytherapy
- 2009
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Ingår i: IFMBE Proceedings. - Heidelberg : Springer Berlin Heidelberg. - 9783642034725 - 9783642034749 ; , s. 236-239
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- After development of sensitive dosimeter materials Electron Paramagnetic Resonance EPR dosimetry has been successfully used also in radiation therapy. The intensity of the EPR-signal is a measure of the amount of free radicals created by ionizing radiation which is proportional to the absorbed dose in the dosimeter. Lithium formate monohydrate is a dosimeter material with 2-6 times higher sensitivity than alanine, a linear dose response over a wide dose range and mass-energy absorption properties similar to water. These properties make lithium formate promising for verification of absorbed doses around high dose rate brachytherapy sources where the dose gradient is steep and the photon energy distribution changing with distance from the source. Calibration of the dosimeters is performed in 60Co or MV photon beams where high dosimetric accuracy is feasible. The use in brachytherapy field relies on the assumption that the production of free radicals per mean absorbed dose in the dosimeter is similar at the lower photon energies present there. The aim of this work was to test that assumption. The response of the dosimeters as a function of photon energy was determined by irradiations with four x-ray qualities in the range 100-250 kV and 137Cs, relative to the response when irradiated with 60Co, all photon beams with well-known air kerma rates at the Swedish Secondary Standards Dosimetry Laboratory. Monte Carlo simulations were used to convert air kerma free in air to mean absorbed dose to the dosimeter. The measured response relative 60Co as a function of photon energy was below unity for all qualities. The maximum deviation from unity was 2.5% (100 kV, 135 kV) with a relative standard deviation of 1.5% (k = 1).
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| 10. |
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| 11. |
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| 12. |
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| 13. |
- Gerdle, Björn, et al.
(författare)
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Decreased muscle concentrations of ATP and PCR in the quadriceps muscle of fibromyalgia patients – A 31P-MRS study
- 2013
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Ingår i: European Journal of Pain. - : John Wiley & Sons. - 1090-3801 .- 1532-2149. ; 17:8, s. 1205-1215
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND METHODS:Fibromyalgia (FMS) has a prevalence of approximately 2% in the population. Central alterations have been described in FMS, but there is not consensus with respect to the role of peripheral factors for the maintenance of FMS. 31P magnetic resonance spectroscopy (31P-MRS) has been used to investigate the metabolism of phosphagens in muscles of FMS patients, but the results in the literature are not in consensus. The aim was to investigate the quantitative content of phosphagens and pH in resting quadriceps muscle of patients with FMS (n = 19) and in healthy controls (Controls; n = 14) using (31) P-MRS. It was also investigated whether the concentrations of these substances correlated with measures of pain and/or physical capacity.RESULTS:Significantly lower concentrations of adenosine triphosphate (ATP) and phosphocreatinine (PCr; 28-29% lower) were found in FMS. No significant group differences existed with respect to inorganic phosphate (Pi), Pi/PCr and pH. The quadriceps muscle fat content was significantly higher in FMS than in Controls [FMS: 9.0 ± 0.5% vs. Controls: 6.6 ± 0.6%; (mean ± standard error); P = 0.005]. FMS had significantly lower hand and leg capacity according to specific physical test, but there were no group differences in body mass index, subjective activity level and in aerobic fitness. In FMS, the specific physical capacity in the leg and the hand correlated positively with the concentrations of ATP and PCr; no significant correlations were found with pain intensities.CONCLUSIONS:Alterations in intramuscular ATP, PCr and fat content in FMS probably reflect a combination of inactivity related to pain and dysfunction of muscle mitochondria.
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| 14. |
- Gustafsson, Håkan, 1976-, et al.
(författare)
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Visualizing the dose distribution and linear energy transfer by ID and 2D ESR imaging : A potassium dithionate dosimeter irradiated with C6+ and N7+ ions
- 2008
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 112:29, s. 8437-8442
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Tidskriftsartikel (refereegranskat)abstract
- We report the application of one- and two-dimensional (1D and 2D) spectral-spatial electron spin resonance imaging (ESRI) for visualizing the dose distribution and linear energy transfer (LET) in a potassium dithionate, K 2S2O6 (PDT), dosimeter irradiated with the heavy ions C6+ and N7+. The ESR spectrum in the irradiated PDT consists of a superposition of two isotropic signals assigned to two ·SO3- radicals, R1 and R2, with no hyperfine splittings and slightly different g values. The ID ESRI profiles clearly indicate the spatial penetration of the beams and the location of the sharp maximum dose, the "Bragg peak", detected for each beam. The depth penetrations are different: ≈2.3 mm for C6+ and ≈1.8 mm for N7+ beams, ±0.1 mm, beyond these limits, no radicals were detected. 2D spectral-spatial ESRI images reflect both the dose distribution and the spatial dependence of the relative intensities of radicals R1 and R2, an effect that is assigned to the depth variation of the LET. This study has demonstrated that ESRI is a promising new method for dose and LET determination. Of particular interest are applications in the field of radiotherapy with heavy ions, because in this case the Bragg peak is pronounced and the dose can be focused at specific depths while the surrounding areas are protected. © 2008 American Chemical Society.
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| 15. |
- Lindström, Jan
(författare)
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Radioluminescence : A simple model for fluorescent layers - analysis and applications
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A phosphor or scintillator is a material that will emit visible light when struck by ionising radiation. In the early days of diagnostic radiology, it was discovered that the radiation dose needed to get an image on a film, could be greatly reduced by inserting a fluorescent layer of a phosphor in direct contact with the film. Thus, introducing the step of converting the ionising radiation to light in a first step. Going forward in time, film has been replaced with photodetectors and there is now a variety of imaging x-ray systems, still based on phosphors and scintillators. There is continuous research going on to optimise between the radiation dose needed and a sufficient image quality. These factors tend to be in opposition to each other. It is a complicated task to optimise these imaging system and new phosphor materials emerges regularly. One of the key factors is the efficiency of the conversion from xrays to light. In this work this is denoted “extrinsic efficiency”. It is important since it largely determines the final dose to the patient needed for the imaging task. Most imaging x-ray detectors are based on phosphor or scintillator types where their imaging performance has been improved through tweaking of various parameters (light guide structure, higher density, light emission spectrum matching to photodetectors, delayed fluorescence quenching etc) One key factor that largely determines the extrinsic efficiency of a specific phosphor is the particle size. Larger particles result in a higher luminance of the phosphor for the same radiation dose as does as a thicker phosphor layer (to a limit). There exists already a battery of models describing various phosphor qualities. However, particle size and thickness have not been treated as a fully independent variables in previous model works. Indirectly, the influence of these parameters is accounted for, but the existing models were either considered too general, containing several complex parameters and factors to cover all kind of cases or too highly specialised to be easily applicable to fluorescent detectors in diagnostic radiology. The aim of this thesis is therefore to describe and assess a simple model denoted the “LAC-model” (after the original authors Lindström and Alm Carlsson), developed for a fluorescent layer using individual sub-layers defined by the particle size diameter. The model is thought to be a tool for quickly evaluating various particle size and fluorescent layer thickness combinations for a chosen phosphor and design. It may also serve as a more intuitive description of the underlying parameters influencing the final extrinsic efficiency. Further tests affirmed the validity of the model through measurements. The LACmodel produced results deviating a maximum of +5 % from luminescence measurements. During the development of the model various assumptions and simplifications were made. One assumption was the absence of a so called “dead layer”. This is a layer supposedly surrounding each particle decreasing the efficiency of converting x-rays to light. It is not completely “dead” as in inactive but is thought to have a reduced efficiency. This phenomenon was struggled with, when historically designing electron beam stimulated phosphors for various applications (i.e. displays, TV tubes etc). There are also articles reporting dead layer influence for x-ray detectors (usually spectrometers i.e. not for imaging). By introducing a dead layer in the LAC-model the effect of the layer was investigated and was found to result in a change of less than 8% for the extrinsic efficiency. It was also noted that sometimes a dead layer effect may emerge at surfaces of a scintillator slab but not necessarily connected to the phosphor particles themselves. Due to differences between phosphor material and the surroundings, an interface effect arose to compete with the process of inherent dead layers of the individual particles. It was found to be mostly negligible for x-rays in the studied energy and material range. However, an effect was shown for electrons as incident ionising radiation which could shed some light on the strangely neglected apparent dead layer created this way. Finally, applications, one involving developing a prototype for checking the light field radiation field coincidence, were evaluated for overall performance and the optimisation level of the applied fluorescent layer. Interesting findings were made during the development process: for the first time to the knowledge of the author, focus shift wandering was quantified in the corresponding movement of the x-ray field edge and a non-trivial discussion on the concept of an apparent light field edge resulted in a modified definition of the same.
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| 16. |
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| 17. |
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| 18. |
- Lund, Eva, 1944-, et al.
(författare)
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Muscle metabolism in fibromyalgia studied by P-31 magnetic resonance spectroscopy during aerobic and anaerobic exercise
- 2003
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Ingår i: Scandinavian Journal of Rheumatology. - : Informa UK Limited. - 0300-9742 .- 1502-7732. ; 32:3, s. 138-145
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Tidskriftsartikel (refereegranskat)abstract
- Objective: To investigate mechanisms underlying the reduced work capacity of fibromyalgia (FM) patients were compared to healthy controls at specified workloads, using P-31 magnetic resonance spectroscopy (MRS). Methods: The forearm flexor muscle group was examined with MRS at rest, at sub maximal and at maximal controlled dynamic work as well as at maximal isometric contraction. Aerobic fitness was determined by bicycle ergonometry. Results: Metabolite concentrations and muscle pH were similar for patients and controls at lower workloads. At maximal dynamic and static contractions the concentration of inorganic phosphate was lower and at static contractions the pH decrease was smaller in patients. The performed work by patients was only 50% compared to controls and the patients experienced more pain. Maximal oxygen uptake was lower in the fibromyalgia group. Expired gas-analysis in this group showed ventilatory equivalents at similar relative levels of maximal work capacity. Conclusion: Fibromyalgia patients seem to utilise less of the energy rich phosphorous metabolites at maximal work despite pH reduction. They seemed to be less aerobic fitted and reached the anaerobic threshold earlier than the controls.
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| 19. |
- Lund, Eva, 1944-, et al.
(författare)
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Performance testing of personal dosemeters from eleven dosimetry services in Sweden
- 2001
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Ingår i: Radiation Protection Dosimetry. - 0144-8420 .- 1742-3406. ; 96:1-3, s. 99-103
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Tidskriftsartikel (refereegranskat)abstract
- The Swedish regulation, SSI FS 98:5, requires that radiological workers of category A use dosemeters from an approved personal dosimetry service. The 11 services operating in Sweden at the moment use five different types of dosemeter. All have been tested for their ability to determine Hp(10) and some of them to determine Hp(0.07) according to the European Commission report Radiation Protection 73, EUR 14852, of 1994. The five unique systems have been tested regarding the angular and energy dependence of the response of the dosemeters. The test points for the determination of Hp(10) are all, except one, within the trumpet curve and for the unique systems it is shown that the uncertainty related to angular response at three different energies is within the required ▒40% except for the lowest X ray quality 40 kV. The energy dependence dominates over the directional dependence and the choice of radiation quality for calibration is of great importance for the system performance.
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