M. El Bouanani

Luminescent layers for ion-photon emission microscopy

Abstract Ion beam induced luminescence (IBIL) combined with ion beam induced charge collection (IBICC) is applied in a quantitative study of the IBIL generation yield and detection efficiency for several plastic phosphor materials. The main purpose of this study is to search for strongly luminescence materials that can be used to easily coat samples to be studied with ion-photon emission microscopy (IPEM). A special focus is given to plastic scintillation materials because thin films are easily prepared, and such films have already been used for single event triggering. The emission yield was found to be low for typical Bicron plastic phosphors (only ∼70 photons/ion/μm). The total collection, transmission and photon detection efficiency of the optical microscope used in this study was determined to be only ∼0.00003. For thin film plastic phosphors ∼20 μm thick, the detection efficiency was only 0.04 photons/ion. This means that using these plastics, IPEM would need to be performed with ∼20× more beam fluence to obtain data, such as IBICC, similar to a standard scanned nuclear microprobe. Improvements are discussed.

The high-energy heavy ion nuclear microprobe at the University of North Texas

Abstract The high-energy, heavy ion, microprobe recently installed at the University of North Texas (UNT) has a demagnification factor of ∼60. It has a probe-forming lens system with a new Russian quadruplet configuration. The microprobe is installed on a 3 MV NEC 9SDH-2 Pelletron tandem accelerator, which has ultra stable high energy for heavy ions ( ΔE / E ∼10 −4 ). Sputter and RF sources produce a variety of ions for microprobe applications. A resolution of ∼2 μm has been achieved for 2.0 MeV protons, 4.0 MeV C ions and 9.0 MeV α-particles with a current of about 50–100 pA. Materials characterization and failure analysis of microelectronics are discussed. Current limitations and future improvements to the system are outlined.

The effects of large angle plural scattering on heavy ion elastic recoil detection analysis

Heavy ion elastic recoil detection analysis (HIERDA) is becoming widely used to study a range of problems in materials science, however there is no standard methodology for the analysis of HIERDA spectra. Major impediments are the effects of multiple and plural scattering which are very significant, even for quite thin (∼100 nm) layers of very heavy elements. To examine the effects of multiple scattering a fast FORTRAN version of TRIM has been adapted to simulate the spectrum of backscattered and recoiled ions reaching the detector. The results of the simulations are compared with experimental measurements on well characterised samples including thin Au layers and pure elements beyond the single scattering critical angle performed using ToF-E HIERDA at Lucas Heights and show good agreement except in the long tails.

Ionoluminescence decay measured with single ions

A new ion beam analysis-based, single ion technique called the time to first photon has been developed to measure the decay of the luminescence signal of phosphors. Such measurements are currently needed to study luminescence decay mechanisms following high-density excitations and to identify strongly luminescent phosphor coatings with short lifetimes for ion photon emission microscopy (IPEM). The samples for this technique consist of thin phosphor layers placed or coated on the surface of PIN diodes. Single ions from an accelerator strike this sample and simultaneously create ion beam induced luminescence (IBIL) from the phosphor that is measured by a single-photon-detector, and an ion beam induced charge collection (IBICC) signal in the PIN diode. In this case, the IBICC signal provides the start pulse and the IBIL signal the stop pulse to a time to amplitude converter. It is straightforward to show that this approach also measures a signal proportional to activity versus time with an accuracy of 5% as long as the number of detected photons per ion is less than 0.1, which usually requires the use of absorbers for the IBIL detector or electronic discrimination for the IBIL signals. Details of the new analysis are given together with examples of luminescence decay measurements of several ceramic phosphors being considered to coat IPEM samples. IPEM is currently being developed at Sandia National Laboratory (SNL), the University of North Texas in Denton, and the Universities and INFN of Padova and Torino.

Diffusion-time-resolved ion-beam-induced charge collection from stripe-like test junctions induced by heavy-ion microbeams

Abstract To design more radiation-tolerant integrated circuits (ICs), it is necessary to design and test accurate models of ionizing-radiation-induced charge collection dynamics. A new technique, diffusion-time-resolved ion-beam-induced charge collection (DTRIBICC), is used to measure the average arrival time of the diffused charge, which is related to the average time of the arrival carrier density at the junction. Specially designed stripe-like test junctions are studied using a 12 MeV carbon microbeam with a spot size of ∼1 μm. The relative arrival time of ion-generated charge and the collected charge are measured using a multiple parameter data acquisition system. A 2-D device simulation code, MEDICI, is used to calculate the charge collection dynamics on the stripe-like test junctions. The simulations compare well with experimental microbeam measurements. The results show the importance of the diffused charge collection by junctions, which is especially significant for single-event upsets (SEUs) and multiple-event upsets (MEUs) in electronic devices. The charge sharing results also indicate that stripe-like junctions may be used as position-sensitive detectors with a resolution of ∼0.1 μm.

Monte Carlo simulations and experimental studies of yttrium-90 production using a 33 MeV linac

The purpose of this research is the investigation of the 90Zr(n,p)90Y reaction as an alternative method to the traditional fission product based on the 90Sr/90Y generator. The fast neutrons necessary to activate 90Zr are generated through (p,xn) reactions during 33 MeV proton irradiation of natural tungsten or other targets. Since 90Y is a pure beta emitter, the gamma-rays from the 90Zr(n,2n)59Zr reaction were used to quantify the neutron flux incident on the 90Zr sample. Using the simulation code MCNPX (Monte Carlo N-Particle System), the angular and energy distributions of neutrons incident on the Zr target were calculated. Based on the MCNPX neutron flux predictions, the 90Y activity was determined.

Heavy ion microbeam studies of diffusion time resolved charge collection from p-n junctions

The knowledge of (diffusion, drift, and funneling assisted) charge collection within electronic devices is essential to design radiation hardened Integrated Circuits (ICs). In the present work, diffusion time resolved charge collection studies were performed on stripe-like junctions using 12 MeV carbon and 28 MeV silicon microbeams and MEDICI simulation calculations. The relative average arrival time of the diffused charge on the junctions was measured along with the amount of charge collection by the junctions. The average arrival time of the diffused charge is related to the first moment (or the average time) of the arrival carrier density on the junction. The experimental results and MEDICI (a 2D-device simulator) calculations support this interpretation. These results show the importance of the diffusive charge collection by junctions, which is especially significant in accounting for Single Event Upsets (SEUs) and Multiple Bit Upset (MBUs) in digital devices.

A compact Ultra-High Vacuum (UHV) compatible instrument for time of flight-energy measurements of slow heavy reaction products

A compact Ultra-High Vacuum (UHV) compatible instrument for time of flight-energy measurements of slow heavy reaction products from nuclear reactions has been designed and tested at the CELSIUS storage ring in Uppsala. The construction is based on MicroCh

Complementary scattered and recoiled ion data from ToF-E heavy ion elastic recoil detection analysis

Abstract The advantage of Time of Flight and Energy (ToF- E ) Heavy Ion Elastic Recoil Detection Analysis (HIERDA) over Rutherford Backscattering (RBS) analysis is its mass and energy dispersive capabilities. RBS cannot separate signals from very heavy elements; the limitation is a result of physical principles of the two-body collision process. The mass resolution of ToF- E HIERDA deteriorates for very heavy elements; the limitation is related to the poor energy resolution of Si detectors for heavy ions. Very high ion energies improve the energy resolution and consequently the mass resolution of HIERDA, but significantly lower the cross section. Usually the energy spectra from ToF- E HIERDA data are used to extract depth profiles. In this work, the benefits of using the time spectra of both the recoiled and the scattered ions are discussed. The advantages are: (i) improved depth resolution by using the time spectra, and (ii) although the energy of very heavy recoils decreases with increasing mass, the energies of scattered ions increase. Time and energy projections of spectra, which have overlapping signals provide complementary data for analysis.

The effects of multiple and plural scattering on Heavy Ion Elastic Recoil Detection Analysis

An increasing number of groups use Heavy Ion Elastic Recoil Detection Analysis (HIERDA) to study a wide range of problems in materials science, however there is no accurate and reliable methodology for the analysis of HIERDA spectra. Major impediments are the effects of multiple and plural scattering which are very significant, even for quite thin (∼100 nm) layers of very heavy elements. To examine the effects of multiple scattering, a fast FORTRAN version of TRIM has been adapted to simulate the spectrum of backscattered and recoiled ions reaching the detector. The results of the simulations will be compared with experimental measurements on well characterized samples of thin Au layers on Si performed using ToF-E HIERDA at the Lucas Heights Laboratories of the Australian Nuclear Science and Technology Organization.