Akihiro Nohtomi

A new viewing theory on centroid finding for patterned position sensitive detectors (PPSD)

A study of a new viewing theory (surface viewing theory) on position sensing is described. The viewing that the infinite height cathode strips is based on it (linear viewing theory), limits the width of the readout channel to a severe narrow strip. Therefore, the number of channels for long length position sensing increases. The surface viewing theory, removes this limitation by shortening the heights and broadening the widths of the readout channels (cathode strips). In the surface viewing theory since the surface of the affected area is used for position determination, it is possible to broader sensing area comparing with the cathode strip, Preliminary designs and experiments show that the optimum sensing area (OPSA) based on the surface viewing theory decreases at least 10 times in number of the readout channels without any degradation in linearity comparing with the single cathode strip. Increasing the signal to noise ratio in sake of a better resolution is possible with vertical cascading of the OPSA. Two type combinations of the OPSA result in extended OPSAs that correspond to suitable patterns long length position sensitive detectors.

Severe hazards in two dimensional position sensing using wedge & strip and backgammon based patterns

The most unfavorable phenomenon in 2D position sensing is the readout dependence of the two independent dimensions (X, Y). The patterned cathodes, such as the wedge-and-strip, backgammon, chevron and triple charge division patterns, are very sensitive to the source displacement perpendicular to their position sensitive directions (X). This sensitivity results in severe dependance for the horizontal readout to the vertical readout. The predicted deviation due to vertical displacements of a given source, which Is experimentally confirmed shows that the deviation varies with the source displacement along the X axes. This deviation has a maximum value (about 10% of the full length) at the center of the pattern. Since the deviation varies along the X direction, finding a transfer function for correcting the readout is impossible. Using the patterned cathodes in multi wire proportional counters are possible if the wire spacing is a multiple of the pattern width. Also, these cathodes can be used for two dimensional position sensing, without any limitation, if the readout position in the other dimension is done using drift times of the primary electrons. Using this combination, a high resolution (0.25 mm) safe 2D ray trace type patterned telescope was manufactured for particle detection with low threshold energy.

Realization of a passive RTC (Ratio to Time Converter) using a new conversion technique for charge division readout

A dynamic conversion method is introduced to realize a novel RTC (passive RTC) for the charge division readout position sensing. Almost all the methods used for ratio to time conversion are static methods and start the conversion process after the signal peak sensing. Then, the static RTCs are monopolar input converters. The dynamic conversion performs the conversion process during the position signal forming and is based on the ratio to time responses of delay transmission lines. Then, the dynamic RTCs based on this method are bipolar converters. For the dynamic conversion method the ratio can be converted to time at any adjustable moment on the leading edges of the signals decreases the conversion dead time for on-line readouts. A delay line, using this conversion method, is substituted for a conventional RTC which includes at least 20 active elements. Since the delay line is a passive element, it is possible to install it within the position sensitive chambers. Using the dynamic conversion method, the signals of a Backgammon pattern are converted to position and position resolution of about 2% to the full length were achieved.

Modification of backgammon shape cathode and graded charge division readout method for a novel triple charge division centroid finding method

The triple charge division (TCD) centred finding method that uses a modified pattern of a backgammon shape cathode (MBSC) is introduced for medium range length position sensitive detectors with optimum numbers of cathode segments. The MBSC pattern has three separated areas and uses sawtooth like insulator gaps for separating the areas. The side areas of the MBSC pattern are severed by a central common area. The size of the central area is twice the size of both sides. Whereas the central area is the widest area among three, both sides areas have the main role in position sensing. With the same resolution and linearity, the active region of the original backgammon pattern increases twice by using the MBSC pattern, and with the same length, the linearity of TCD centred finding is much better than the backgammon charge division readout method. The linearity prediction of TCD centred finding and experimental results necessitated us to find an optimum truncation of the apices of the MBCS pattern in the central area. The TCD centred finding has a special readout method since charges must be collected from two segments in both sides and from three segments in the central area of the MBSC pattern. The so called graded charge division (GCD) is the special readout method for TCD. The GCD readout is a combination of the charge division readout and sequence grading of serial segments. Position sensing with TCD centred finding and GCD readout were done by two sizes of MBSC patterns (200 mm and 80 mm) and a spatial resolution of about 1% of the detector length is achieved.