Signal filters for the Gamma spectrometry
The filter that you see in this simulation is part of the first research, definitive patterns of PmtAdapter are here: www.theremino.com/technical/schematics
The three pulses (negatives) visible in the simulation are:
RED: impulse produced by the photomultiplier tube ( 1uS – 10 Volts )
WHITE: boost after the first cell goes down ( about 10 uS – 1 Volts )
GREEN: boost after the second low pass cell ( about 300 uS – 20 MV )
Only the third impulse ( sometimes called “Gaussian” because of its shape ) can be sampled accurately from a sound card. The second pulse, as far as slowed, still has the sharp tip and only rarely will a sample exactly on its tip. The inaccurate sampling produces a widening of the rows. This effect is minimized by impulses with form “Gaussian”, They provide a broad horizontal area, to minimize errors even at 48 KHz.
When watching the pulses with software viewers these forms are very dull, due to the limited bandwidth of your sound card, and also seem wide enough (tens of microseconds) but don't get your hopes up: without a double filter RC incoming impulses to the sound card are narrow and sharp. Then spread out but, Although their characteristics not seen more, the damage they have already made.
Comparison with the filters and the ADC hardware from the last century.
How beautiful are these hardware modules of Flintstones!
Too bad that after a while’ for years the potentiometers are beginning to scratch, switches make contact only on Thursday and that, even under the best conditions, the results are lower than those in software.
Questi ADC hardware sono velocissimi (ma serve a poco) ma in compenso hanno un rapporto segnale rumore di soli 60 dB contro i 110 dB raggiungibili con gli ADC della schede audio recenti (e questi servono davvero)
Inoltre i loro alimentatori sono rumorosissimi (from 5 MV to 50 MV pep) in confronto agli alimentatori che usiamo attualmente (sotto i 200 uV pep)
Non si tratta solo di spendere tanto o poco, ci sono di mezzo 30 anni di miglioramenti.
Of course you can leave comments, questions and advice.