Silicon detectors

The short penetration depth of UV/blue photons is the reason that frontside CCD detectors have very poor QE at the blue end of the spectrum. The frontside of a CCD is the side upon which the polysilicon wires that control charge collection and transfer are deposited. These wires are 0.25 to 0.5 /xm thick and will absorb all UV/blue photons before these photons reach the photosensitive volume of the CCD. For good UV/blue sensitivity, a silicon detector must allow the direct penetration of photons into the photosensitive volume. This is achieved by turning the CCD over and thinning the backside until the photosensitive region (the epitaxial layer) is exposed to incoming radiation. 

Instrumentation. Traditional methods of alpha and beta spectrometry instrumentation have changed little over the past decade. Alpha spectrometric methods typically rely on semi-conductor or lithium-drifted silicon detectors (Si(Li)), or more historically gridded ion chambers, and these detection systems are still widely used in various types of uranium-series nuclide measurement for health, environmental, and... 

All of the silicon detectors can be cooled to reduce the thermal noise that produces a background under all the induced signals. The thermal noise is created by random fluctuations that promote an electron across the bandgap into the conduction band resulting in an electron-hole pair. The number of promoted electrons will be proportional to a Boltzmann function containing the bandgap A and the temperature T ... 

For practical reasons, silicon detectors are usually cooled from room temperature down to approximately — 20°C cooling below — 60°C is not useful because the system noise becomes dominated by the external electronic circuit. Temperatures below — 20°C are not used also because the internal physical stresses from differences... 

Cooled silicon detectors are particularly useful in experiments in which the measured particles are expected to cause significant damage to the crystal lattice during the experiment. If the detector is not cooled, the thermal noise will dramatically change during the measurement and the detector resolution will decrease with time. 

The sample is then raster scanned through the focus spot, and the transmission in each image pixel is recorded. Among the variety of soft X-ray detectors are proportional counters and phosphors with photomultipliers. A recent development is a silicon detector with a segmented chip (Feser et al., 2003) allowing for dark and bright field as well as differential phase contrast imaging. 

Fig.2. Plot of m/q determined from deflection in the RPMS vs silicon detector particle identification parameter.

Fig.l. A silicon box. It consists of ten silicon detectors which take count of protons and alpha-particles emitted in each fusion events. 

The silicon box comprises ten silicon detectors surrounding the target with almost 4tt steradian, as shown in fig.l two of them are of an annular, square type and the others are plain, rectangular either of them has no marginal insensitive area. A half of the box subtends the front 2 with respect to the target and the other half the rear 2ir. Each silicon detector works as a partially depleted aE counter and discriminates between protons and alpha-particles. Its depletion depth is chosen such that the energies deposited by protons do not exceed the minimum energy deposited by alpha-particles. A typical depletion depth employed was 0.4 mm. 

The silicon detectors were made of n-typed single crystal of 1 mm thick. They have a MOS structure of gold, tungsten oxide, n-typed silicon and aluminum back contact. Since these layers can be deposited on the silicon wafer by evaporation techniques, the fabrication process is so simple as to be applicable to fabrication of the detectors for a special use. No surface treatment for passivation is given to them so that their performance is affected by ambient gases. For example, some good detectors show a leakage current of half micro-ampere at room temperature in the atmosphere, but a few micro-ampere in vacuum. So, in order to stabilize their performance, the silicon detectors were operated at the dry ice temterature. 

Holm, E., B. Oregoni, D. Vas, H. Pettersson, J. Rioseco, and U. Nilsson. 1990. Nickel-63 Radiochemical separation and measurement with an ion implanted silicon detector. J. Radioanal. Nucl. Chem. 138 111-118. 

Fig. 5. Calibration measurement of solid hydrogen film layer thickness via energy loss of a particles [27,28]. Americium a source is embedded on the surface of the gold-plated copper substrate, onto which hydrogen thin film is deposited by releasing the gas through porous sintered metal (diffuser). Silicon detector, mounted on the vertically movable diffuser, measured the a particle energy loss in the film, which is converted the thickness using the stopping power...

The presently used detector system is composed of three time-of-flight detectors, seven identical 16-strip silicon wafers, and germanium detectors [15]. A schematic view of the detector arrangement is shown in the focal plane of SHIP in Figure 1. Three secondary-electron foil detectors in front of the silicon detectors are used to measure the velocity of the particles [18]. They are mounted 150 mm apart from each other. The detector signals are also used to distinguish implantation from radioactive decays of previously implanted nuclei. Three detectors are used to increase the detection efficiency. 

A He(KCl)-jet transportation system was used for the transfer of the activities. The KC1 aerosol with the reaction products was collected by impaction on a Pt or Teflon slip for 60 or 90 s, was picked up with lOpL of the aqueous phase and was transferred to a 1 mL centrifuge cone containing 20 iL of the organic phase. The phases were mixed ultrasonically for 5 s and were centrifuged for 10 s for phase separation. The organic phase was transferred to a glass cover slip, was evaporated to dryness on a hot plate, and was placed over a passivated ion-implanted planar silicon detector (PIPS). This procedure took about 1 min. 

Adsorption of Hg nuclides on silicon detectors, as in the successful experiment with Hs04, proved experimentally not feasible, since Hg was adsorbed on quartz surfaces only at temperatures of -150 °C and below. However, Hg adsorbed quantitatively on Au, Pt, and Pd surfaces at room temperature. As little as 1 cm2 of Au or Pd surface was sufficient to adsorb Hg atoms nearly quantitatively from a stream of 1 1/min He. Therefore, detector chambers containing a pair of Au or Pd coated PIPS detectors were constructed. Eight detector chambers (6 Au and 2 Pd) were connected in series by Teflon tubing. The detector chambers were positioned inside an assembly of 84 3He filled neutron detectors (in a polyethylen moderator) in order to simultaneously detect neutrons accompanying spontaneous fission events, see Figure 27. 

---