Optimizing The Pulse Processing Algorithm; Overview Of The Fpga Algorithm; Regions Of Interest - Pyramid D100 User Manual

Digital pulse processor

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PSI System Controls and Diagnostics

11 Optimizing the Pulse Processing Algorithm

The energy required to create a scintillation photon in sodium iodide crystal is nearly constant at

25 eV per photon. Combined with the linear response of the photomultiplier, this means that the

energy of the original ionizing particle or photon is encoded in the amount of charge in the pulse

delivered from the anode of the multiplier. The task of the D100 is thus to integrate the current

pulses, making corrections as necessary for background offsets and overlapping pulses. The

algorithm running in the D100 FPGA is designed to extract the best energy resolution even when

there is the potential for degradation due to pulse overlap at high input rates. Pulses which have

been compromised by overlap are not included in the energy spectrum, but they can still be

counted.

Note that all processing at the FPGA level is done on raw binary numbers for speed. Conversion

to an absolute energy scale in eV is a function of the host software.

When pulses have been discriminated and integrated, the D100 can assign them in real time to a

region of interest (ROI) according to their integral. This process is also called histogramming. It

is of course equivalent to putting the pulses into energy bins.

The normal D100 operation mode delivers 1024 channels of energy resolved spectral data to the

host over the bi-directional message channel between the D100 and the host. This allows a

conventional energy spectrum display, and is convenient for making the translation to an

absolute energy scale.

An alternate, fast pathway is available that allows pulses to be discriminated and delivered to the

A500 processor in real-time via dedicated fibers. It is only available when you are using the

A500 real-time controller to interface the D100. Up to ten D100 boards can be placed in this

mode per A500. The regions of interest for this fast energy discrimination mode are defined in

the host software in a standard file interface and downloaded to the D100. The file is a sequence

of 50 integers separated by carriage return, line feed. The entries must be in ascending order.

The first must be 0 and the last 65535, so covering the full available energy range. The regions

of interest are contiguous but do not have to be the same width.

Note that these ROIs are not the same as the regions that can be defined in the energy spectrum

in the PSI Diagnostic host software.

D100 User Manual

D100_UM_081027

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