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Silicon particle detectors made on Czochralski and float zone silicon materials were irradiated with 7 and 9 MeV protons at a temperature of 220 K. During the irradiations, the detectors were biased up to their operating voltage. Specific values for the fluence and flux of the irradiation were found to cause a sudden breakdown in the detectors. We studied the limits of the fluence and the flux in the breakdown as well as the behavior of the detector response function under high flux irradiations. The breakdown was shown to be an edge effect. Additionally, the buildup of an oxide charge is suggested to lead to an increased localized electric field, which in turn triggers a charge carrier multiplication. Furthermore, we studied the influences of the type of silicon material and the configuration of the detector guard rings. [ABSTRACT FROM AUTHOR]

After irradiation with 7 and 9 MeV protons, activation-induced effects were encountered in measurements of current-voltage (IV) and capacitance-voltage (CV) characteristics for Czochralski and float-zone grown silicon particle detectors prepared on printed circuit boards with copper electrodes. With the present detector construction, the 30Si(p,n)30P and 63Cu(p,n)63Zn reactions induce dominant interference in such measurements. The daughter nuclides are positron emitters with half-lives of 2.5 and 38.5 min, respectively, and the slowing down of the emitted positrons generates a significantly large concentration of electron-hole pairs in the detector volume increasing the leakage current level and decreasing the breakdown voltage. The observed time-dependent characteristics were verified by modeling the activation of the detector structure and the resulting leakage current. As a result, the electrical measurements cannot be performed immediately after irradiation due to silicon activation, and, generally, materials becoming easily activated should be avoided in the detector concept. [ABSTRACT FROM AUTHOR]

The stopping powers of polycarbonate for protons of energy 0.6-5.9 MeV and α particles of energy 2.0-24.0 MeV have been measured in a transmission experiment employing thin-foil targets. The essence of the novel experimental method employed in the present measurements is to record both projectile energy and time of flight while constantly alternating measurements with and without the target foil in place. The accuracies of the proton data and α-particle data range from 2.0% to 3.0% and 2.2% to 2.7%, respectively. All of the resulting measurements were analyzed in terms of modified Bethe-Bloch theory in order to extract values of the target mean excitation energy (I) and Barkas-effect parameter (b). The composite results for the two projectiles are that I = 71.52 eV and b = 1.13, the former value lying about one standard deviation below the additivity value and the latter value lying about one standard deviation below the expected value of 1.4 ± 0.1. Previous measurements of the stopping power of polycarbonate for [sup 7]Li ions were analyzed by the same method, but with the inclusion of an effective charge parameter (δ). The proton and α-particle data, with a few lower-energy points included, were analyzed for a three-parameter fit, also. Results for the three projectiles studied indicate both internal consistency and agreement with expectations based on modified Bethe-Bloch theory. [ABSTRACT FROM AUTHOR]

Focuses on the measurement of the cross section for elastic scattering of protons through the use of natural copper (Cu), molybdenum (Mo), silver (Ag) and tin (Sn) near the Coulomb barrier. Determination of the threshold energies; Identification of those threshold energies ascertained; Experimental cross section ratios given for the elements of Cu, Mo, Ag and Sn; Information on the film thicknesses.

In this Rapid Communication, we report positron annihilation results on in-grown and proton irradiation-induced vacancies and their decoration in aluminium nitride (A1N) single crystals. By combining positron lifetime and coincidence Doppler measurements with ab initia calculations, we identify ingrown VAI-ON complexes in the concentration range 1018 cm-3 as the dominant form of VAI in the AIN single crystals, while isolated VAI were introduced by irradiation. Further, we identify the UV absorption feature at around 360 nm that involves VAI. [ABSTRACT FROM AUTHOR]