L. Giuntini

Evidence of light guiding in ion-implanted diamond.

We demonstrate the feasibility of fabricating light-waveguiding microstructures in bulk single-crystal diamond by means of direct ion implantation with a scanning microbeam, resulting in the modulation of the refractive index of the ion-beam damaged crystal. Direct evidence of waveguiding through such buried microchannels is obtained with a phase-shift micro-interferometric method allowing the study of the multimodal structure of the propagating electromagnetic field. The possibility of defining optical and photonic structures by direct ion writing opens a range of new possibilities in the design of quantum-optical devices in bulk single-crystal diamond.

Macro and Micro Full Field X-Ray Fluorescence with an X-Ray Pinhole Camera Presenting High Energy and High Spatial Resolution

This work describes a tabletop (50 cm × 25 cm × 25 cm) full field X-ray pinhole camera (FF-XPC) presenting high energy- and high spatial-resolution. The FF-XPC consists of a conventional charge-coupled device (CCD) detector coupled, in a coaxial geometry, to a pinhole collimator of small diameter. The X-ray fluorescence (XRF) is induced on the samples with an external low-power X-ray tube. The use of the CCD as an energy dispersive X-ray detector was obtained by adopting a multi-image acquisition in single photon counting and by developing a processing algorithm to be applied in real-time to each of the acquired image-frames. This approach allowed the measurement of X-ray spectra with an energy resolution down to 133 eV at the reference value of 5.9 keV. The detection of the X-ray fluorescence through the pinhole-collimator allowed the two-dimensional elemental mapping of the irradiated samples. Two magnifications (M), determined by the relative sample-pinhole-CCD distances, are used in the present setup. A low value of M (equal to 0.35×) allows the macro-FF-XRF of large area samples (up to 4 × 4 cm(2)) with a spatial resolution down to 140 μm; a large magnification (M equal to 6×) is used for the micro-FF-XRF of small area samples (2.5 × 2.5 mm(2)) with a spatial resolution down to 30 μm.

The external beam microprobe facility in Florence: Set-up and performance

Abstract An external beam microprobe facility, based on a quadrupole doublet supplied by Oxford Microbeam Ltd, has been installed on a new beamline at the 3 MV single-ended Van de Graaff accelerator in Florence. The goal was to obtain a beam with a spot size on target of 10–20 μm and a current in the order of at least 1 nA, in order to allow PIXE, PIGE and RBS elemental analysis in air or in a helium atmosphere. The beam was extracted from the vacuum lines through a 0.1 μm thick Si 3 N 4 window to minimise lateral straggling. The design goals have been successfully achieved; the measurements of the beam spot characteristics in vacuum as well as in air and in helium atmosphere, are here reported.

Proton elastic scattering cross-section on boron from 0.5 to 3.3 MeV

Abstract Using a set-up for simultaneous many-angle detection of backscattered particles, the proton elastic scattering cross-section on 10B and 11B has been measured for beam energies from 0.5 to 3.3 MeV and in the angular range from 100° to 170° in steps of 5°. The overall accuracy in the measured cross-section is estimated to be better than ±5% at all the beam energies and angles.

The differential PIXE set-up at the Van de Graaff laboratory in Florence

PIXE analysis performed with protons of different energies makes it possible to obtain information about the depth sequence of different elements within the analysed sample. In this paper we report on the differential PIXE set-up installed at the external-beam facility of the KN3000 accelerator in Florence. In order to change beam energy on the sample, our choice was to insert energy degraders between beam exit window and sample. 25 μm Upilex foils are used to degrade the beam: with 3 MeV protons, the energy loss is about 500 keV; higher energy losses are obtained by sandwiching more foils. Measurements of lateral beam profiles and of energy loss and straggling after the Upilex foils are reported, compared to those obtained with other materials such as aluminium and copper. We also investigated the possible damage to the foil due to beam irradiation. Preliminary applications of this set-up to the stratigraphic analysis of samples of archaeometrical interest are described.

The pulsed beam facility at the 3 MV Van de Graaff accelerator in Florence: Overview and examples of applications

Abstract An electrostatic chopper has been installed at the KN 3000 accelerator in Florence to obtain short beam pulses with a number of particles per pulse whose average value can be chosen by varying the current intensity at the deflector plates input. Beam pulses can be obtained containing an average number of particles per pulse from less than one to thousands. The transmitted beam pulses can be as short as 200 ps FWHM, at a repetition rate up to about 100 kHz. Among the many applications of the facility, the direct measurement of energy loss and straggling of protons in Kapton and aluminium is reported. In this measurement, the facility has been tuned for transmission of mainly single-proton pulses; the beam energy is directly measured downstream with a good energy-resolution detector, without and with absorbers in front. In general, measurements of this kind can be directed both to study the basic processes of charged particles interactions in materials, or more practically to obtain the effective values of energy parameters useful in many IBA applications, avoiding the need to rely on simulations or theoretical estimates. Also briefly described is an application to Si-detector testing. In this case, the facility has been tuned for transmission of pulses containing many hundreds of protons of energy E p =2.5 MeV and the detector is directly exposed to the pulses. Spectra containing equally spaced peaks at energies multiple of E p are obtained and the response linearity of the detector plus electronics system can thus be checked.

Complex refractive index variation in proton-damaged diamond

An accurate control of the optical properties of single crystal diamond during microfabrication processes such as ion implantation plays a crucial role in the engineering of integrated photonic devices. In this work we present a systematic study of the variation of both real and imaginary parts of the refractive index of single crystal diamond, when damaged with 2 and 3 MeV protons at low-medium fluences (range: 10(15) - 10(17) cm(-2)). After implanting in 125 × 125 μm(2) areas with a scanning ion microbeam, the variation of optical pathlength of the implanted regions was measured with laser interferometric microscopy, while their optical transmission was studied using a spectrometric set-up with micrometric spatial resolution. On the basis of a model taking into account the strongly non-uniform damage profile in the bulk sample, the variation of the complex refractive index as a function of damage density was evaluated.

Proton elastic scattering cross section on carbon from 350 keV to 3 MeV

Abstract Using our set-up for the simultaneous many-angle detection of backscattered particles [1], we have measured the proton elastic scattering cross section on carbon, in the angular range from 100° to 170° (in steps of 5°) and for beam energies from 350 keV to 3 MeV. Thin self-supporting natural carbon foils have been used, ∼ 13 μg/cm2 for the measurements from 350 to 700 keV, ∼ 50 μg/cm2 above 700 keV. A scattering spectrum was also simultaneously recorded at 15° (purely Rutherford cross section at all energies) for normalisation purposes. Thanks to the simultaneous acquisition of this spectrum, the uncertainties in the effective target thickness and in the integrated beam charge do not affect the deduced backscattering cross section values, whose overall accuracy is estimated to be ±4% (maximum error) at all the beam energies and angles.

Proton elastic scattering cross-section on aluminium from 0.8 to 3 MeV

Abstract Using a set-up for simultaneous many-angle detection of backscattered particles, the proton elastic scattering cross-section on aluminium has been measured for beam energies from 0.8 to 3.0 MeV and in the angular range from 100° to 170° in steps of 5°. A scattering spectrum is also simultaneously recorded at 15° for normalization purposes. The overall accuracy in the measured cross-section is estimated to be ±2.5% at all measured beam energies and angles.

External beam RBS in an unenclosed helium environment

Abstract The external beam facility installed at the KN-3000 accelerator in Florence, formerly used for PIXE measurements, has been exploited also for RBS analysis. A particle detector has been placed at 135° in a setup structure which also includes the two Si(Li) detectors simultaneously used for PIXE. A helium flow is kept in front of the particle detector and of the one used for low-energy X rays, as well as in the region between the beam exit window and the target; no chamber is used for gas containment, in order to allow us the most complete freedom for target size and for its handling. Gas leaks upwards are limited by a soft rubber lid which is kept in contact with the target itself. Helium saturation of the volume in front of the target and of the detectors is attained with a gas flow of less than 1 l atm min . All the “user-friendly” features of the existing PIXE facility have been maintained: in particular, video-monitoring the sample with a remotely controlled camera, checking beam position with laser aiming and sampling beam current with a rotating chopper are still possible and easy to perform. Particular care has been taken of particle-detector mounting and detection geometry in order to obtain the best possible energy resolution. The present setup gives an overall system resolution of about 28 keV FWHM, when bombarding ultra thin targets with 1.5 to 3 MeV protons. Further improvements are in progress. Preliminary applications have been performed on samples which may not be placed under vacuum; in particular, combined PIXE-RBS measurements have been done to clarify some problems connected with ancient inks analysis (thickness determination, penetration within the underlying paper or parchment), and to check composition of thin standards evaporated onto polymeric supports.