90 research outputs found
Determination of New Radical Species in Ammonium Tartrate Dosimeters by CW- and Pulsed-EPR Techniques
No full textSamples of ammonium tartrate irradiated with doses of about 0.1–1 kGy by different beams of ionizing radiation (60Co–γ, 19 MeV protons and 62 MeV per nucleon carbon ions) were studied by continuous-wave electron paramagnetic resonance (cw-EPR) and by pulse-EPR techniques. Careful analysis of the cw-EPR and of the echo-detected EPR spectra allowed the identification of a second radical in the system besides the already known radical formed at high temperature by an hydrogen elimination at C(2) position [M. Brustolon et al., Res. Chem. Int 4:359, 1996]. The spectrum of the radical is compatible with that of a radical obtained by hydroxyl elimination
Radiation quality discrimination by continuous and pulse ESR techniques
No full textThe biological damages produced by ionizing radiations in tissues and cells depend on the radiation quality, besides on the dose. The discrimination of the radiation quality, which is related to the linear energy transfer (LET), interests various fields such as radiobiology, astronautic space research, radiotherapy research and accidental dosimetry.
In this work we have applied continuous wave ESR (cw-ESR) and pulse ESR techniques to ammonium tartrate samples with the aim of developing procedures able to discriminate radiation quality whose knowledge is fundamental for rabiobiological considerations. We have chosen the ammonium tartrate because it is a promising compound for the measurement of the absorbed ionizing radiation dose [1, 2, 3]. The compound is particularly competitive to standard alanine in the detection of ionizing radiation other than high energy gamma photons, such as low energy X photons, electrons, protons, thermal neutrons.
At the same time cw-ESR and the Electron Spin Echo (ESE) decay techniques and Double Electron-Electron Resonance (DEER) can be used to obtain from average to local distributions of spins. CW-ESR is particular suited for the determination of total spin (macroscopic) concentration, whereas ESE is suited for the determination of local concentration. A new insight into the knowledge of the complex distribution of free radicals inside the dosimeters can be obtained by DEER. This technique is very useful for our purpose because it is able to measure distance between radicals in solids in the range of approximately 1.5-8 nm by analyzing the dipolar coupling between two electron spins.
In this work we analyze the spatial distributions of the free radicals produced after exposure of ammonium tartrate dosimeters to various radiation beams (21 MeV protons, 60Co γ-photons, thermal neutrons).
By measuring the differences between the local radical concentrations and the macroscopic one, and the distributions of radical-radical distances obtained with DEER, this study has given details on the differences between the distributions of radicals created by the radiation-matter energy transfer for the different ionizing radiations.
Differences and analogies are discussed in terms of differences and analogies in the LET and type of particles involved.
References
[1] S. K. Olsson, S. Bagherian, E. Lund, G. A. Carlsson, A. Lund, Appl. Radiat. Isot. 1999, 50, 95565.
[2] M. Brustolon, A. Zoleo and A. Lund, J. Magn. Reson., 1999, 137, 389-396.
[3] A. Bartolotta, M. C. D'Oca, M. Brai, V. Caputo, V. De Caro, L. I. Giannola, Phys. Med. Biol., 2001, 46, 461-471
What can be studied with Electron Paramagnetic Resonance?
No full textEPR spectroscopy detects only paramagnetic species, i.e. species with unpaired electrons. Owing to its selectivity, an EPR study has the main advantage of providing insights into the nature of the paramagnetic centre, while also revealing detailed information on its environment and on the dynamical processes in which it is involved. In this chapter we will describe and provide a few examples of the various paramagnetic species that are studied using EPR methods for various experimental purposes
ENDOR of Fremy's salt
No full textThe 14N ENDOR of the radical anion (SO3)2NO= has been observed in fluid solutions in water and in water-ethanol mixtures, and trapped in irradiated single crystals of potassium hydroxylamine disulphonate. The quadrupole coupling has been estimated from the solid-state spectra and it is argued that this interaction is too weak to provide a significant relaxation mechanism for the radical in solution. Spectra have been calculated assuming relaxation occurs through modulation of the g and dipolar tensors and the spin-rotation coupling, together with Heisenberg exchange, and the results agree quite well with the spectra observed for the radical in water. An additional relaxation mechanism seems to operate in the water-ethanol mixtures
Echo detected EPR as a tool for detecting radiation-induced defect signals in pottery
No full textArchaeological fragments of pottery have been investigated by using CW-EPR and Echo Detected EPR (EDEPR). EDEPR allows to remove the CW-EPR dominant Fe(III) background spectrum, hiding much weaker signals potentially useful for dating purpose. EDEPR spectra attributed to a methyl radical and to feldspar defects have been recorded at room and low temperature for an Iron Age cooking ware (700 B.C.). A study on the dependence of EDEPR intensity over absorbed dose on a series of gamma-irradiated brick samples (estimated age of 562 +/- 140 B.C.) has confirmed the potential efficacy of the proposed method for spotting defect signals out of the strong iron background. (C) 2011 Elsevier Ltd. All rights reserved
Interaction between Starburst Dendrimers and SDS Micelles Studied by Continuous-Wave and Pulsed Electron Spin Resonance
No full textSTRUCTURE AND DYNAMICS OF RADICALS IN SOLIDS BY EPR AND ENDOR SPECTROSCOPIES
No full textEPR and ENDOR (Electron Nuclear DOuble Resonance) spectroscopies give complementary information in the study of paramagnetic species in solids. The ENDOR technique allows the determination of hyperfine tensors an order of magnitude smaller with respect to the EPR one. The molecular motions in solids affect the relaxation of both the transverse and longitudinal magnetization of the paramagnetic probe. The measurement of the transverse relaxation time is traditionally available by the EPR Lineshape analysis. Population variations due to the longitudinal relaxation processes can be monitored by the study of the amplitude of the ENDOR spectra
Structural Modifications of DMPC Vesicles upon Interaction with Poly(amidoamine) Dendrimers Studied by cw-Electron Paramagnetic Resonance and Electron Spin Echo Techniques
No full text
- …
