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Log out of Readcube. Click on an option below to access. Log out of ReadCube. The experimental results agree very closely with those obtained by Rauch and Heer and are in good accord with the theoretical estimates the theoretical results are reported in brackets.

Volume 69 , Issue 2.

Electronic Defect States in Alkali Halides Effects of Interaction with Molecular Ions Springer Tract

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Log in to Wiley Online Library. Purchase Instant Access. View Preview. Learn more Check out. The With such penetration depths, we can obtain the alkali halide single crystals can be colored with ener- distribution profiles of the defects along the whole getic ion bombardment and the optical absorption path of the incident ions in the target, using a micro- bands responsible for this coloration are characteris- spectrophotometric technique. We have studied the tic of the different defects created in the crystals.

F and F-aggregate center profiles versus the incident Most of these defects created by irradiation processes ion dose at room temperature and the F and I center are well known. It is possible to distinguish three kinds profiles at low temperature L. The colloidal of defects: center profiles in heavily irradiated and thermally - The anionic defects corresponding to F, F-aggregate annealed samples have also been studied.

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To explain the experimental results concerning the - The cationic defects corresponding to I type centers F-center production, we have compared the defect in LiF1. The - The colloidal defects which result from the agglom- F-center concentrations are very sensitive to the eration of the atoms of the matrix intrinsic colloids 2 density of dissipated energy. A model of interaction or from the agglomeration of the implanted ions core surrounding the ion path in which the energy is themselves extrinsic colloids 3.

Using ion and the target. We know that the anionic defects these distributions and the F-center creation efficiency are created by electronic processes 4 and their creation by a delta-ray mechanism, it has been possible to will be connected to the electronic stopping power. These calculated The I centers are created by direct displacements of the results are in good agreement with the experimental alkali ions of the matrix1. All these defects may be ones. In particular we obtain with rather good pre- then used as detectors of the particle-matter inter- cision the F-center growth curves for all the incident actions.

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Another interest of alkali halides is that these ion energies higher than the Bragg peak energy. Experimental procedure as absorption or emission. The beams of 56 MeV alpha-particles and 28 MeV To perform the study we have essentially used deuterons were produced in the synchrocyclotron accel- V. The beam cur- multiplier. The irradiations were performed in type of defect, it is possible to calculate the concen- the direction. The irradiated samples were cleaved into 8 plates of 0. These plates were scanned in the micro- spectrophotometer in the penetration direction of the incident ions.

The light beam of the microspectro- photometer which passes through the sample was 10 pm wide.

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For penetration depths of about 1 or 2 ram, the spatial resolution of the defect profiles is rather good. On the other hand the samples were thin enough Fig. Microspectrophotometric set-up. For focussing of the image 6 sample, 7 photomultiplier, 8 synchronous amplifier, on the face of the sample we used a microscope 9 recorder. These energies have where f is the oscillator strength, n the index of refrac- been plotted from the range curves which are given tion of the host material, W the absorption band full- in section 4.

Bragg's curve behaviour analogous to that of the At room temperature in LiF, the F-band is located electronic stopping power of the ions. These results are shown The LiF samples studied at room temperature have in figs. We have chosen the energies of 14, 10, 5, 2.

Controlled production of F centers in alkali halide crystals ..|INIS

The irradiation doses were between 0. After irradiation the distri- characteristic zones of the F-center profiles. On the y-axis we have plotted.. F-center profiles in L i F irradiated at r o o m temperature with 56 M e V alpha-particles. F-center growth curves in LiF irradiated at r o o m tempera- 2 1. PEREZ et al. Gaussian of the two fluctuations. The results con- energy is at the top of the F-center peak. This law is applied F-center creation efficiencies for the incident ions. We have also drawn nucl.

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Calculated electronic stopping powers The irradiations with protons have been performed and comparison with the F-center profiles We have used Benton's method 7 for the calculation of electronic stopping powers in LiF between 0. For energies lower than 0. These electronic stopping powers are available for one particle. We have found that the energetic distribution of the ions was approximately Gaussian in shape with a fwhm of 0. Calculated electronic stopping powersl,Z ; and range distributions 3,4 vs energy per nucleon for alpha-particle and deuteron in LiF. Corrected electronic stopping powers for alpha-particles s and deuteronsG.

F-center growth curves in LiF irradiated at room tempera- ture with 28 MeV deuterons. F-center creation efficiencies as a function o f the electronic 2 2. Using the Physique Nucl6aire de Grenoble". Such protons have uncertainty principle and the atomic excitation cross a penetration depth of 15 mm in LiF. For alpha-particles and quasi-linear in a large part of the ion range. However, deuterons in LiF we find the mean radius to be of the we observe a saturation of the F-center creation near order of magnitude of the atomic radius.

In addition, the peak of the F-center profile which corresponds from the ionization and excitation cross sections, to the Bragg's peak of the energy loss profile. Such an we have calculated the percentages of the total energy effect has also been observed by Arnold et al. For radiophotoluminescent glass. NF I dxAe' 5.

From a classical theory, Fain's calcu- lations 5 allow us to obtain the energy and angle We can also deduce the mean energies dissipated distributions of the ejected electrons. The results of several particles respectively. In fact, we know given by Berger 14 in water and above l0 keV the that the energy dissipated by an ion can be propagated around its trajectory by a delta-ray mechanism.

The 10 2 energy deposited is then localized in core surrounding the ion path. The radius of this core is a function of the incident ion and of its energy. To explain our experi- m mental results we are then brought to consider a model of the core which will allow us to calculate the spatial.. Spatial energy distribution around the ion path in LiF 10 -4 We have used the model of Fain et ai.

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This model is valid in the region where the electronic energy loss is predominant. Distribution o f the secondary energy deposition around 5.

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This energy is nucl. We have taken into account the density only. In the case of an ion beam it is necessary to correction due to the different materials in order to consider the overlaps of the cores as a function of obtain a complete curve for LiF in the whole energy the incident ion dose.

To obtain the spatial distributions for an ion beam We know then the energy and angular distri- we have performed a calculation supposing that in butions of the emitted electrons and also the energy first approximation the particles are homogeneously deposition by the electrons. It suffices to integrate distributed on the bombarded face. We have considered these results for all the energies E and the angles 0 a regular geometrical distribution with cubic symmetry of the secondary electrons to obtain the distributions and a particle-particle distance a. The results obtained mean distance a between each particle.

In a square a 2 in LiF for alpha-particles and deuterons with the surrounding one particle we can calculate the total energies of 14, 10, 5, 2. Taking into account the total energy with energies of 14, 10, 5, 2. Calculation of the F-center creation Using the spatial energy deposition around the ion path, it is possible to calculate the created F-center concentrations.

Distribution o f the secondary energy deposition around a deuteron in LiF. Distribution o f the secondary energy deposition around direction perpendicular to this trajectory. We know then the energy dissipated at each point of the crystal; it is necessary now to convert the energy density into F-center concentration. For that purpose we must know the F-center creation efficiency by a delta-ray mechanism.

In this case the F-center pro- i duction is truly that of a delta-ray mechanism. This error is not very important taking into tration for each dissipated energy density. The calculated F-center con- the ion path into F-center distribution. By integrating Centrations are systematically lower than the measured this distribution we obtain the number of F-centers ones.

This can be due to the fact that we have con- per particle for the considered energy and dose.