2. ScintillationDet W. Udo Schröder, 2004 2 PM Operation Philips XP2041 5” dia cathode 14 dynodes + focussing electrodes Socket FE1120 pin connections Sockets PA a c PM schematic U(t) t Fast PM: pulse rise time ~2ns, gain: 3. 10 7 PM Voltage divider (progressive) U 0 =2000V PMSc mu-metal shield tube provides protection from external B field. mu metal soft iron

3. ScintillationDet W. Udo Schröder, 2004 3 Pre-Amplifiers Task: amplify weak detector signals (mV) to ~ 1V, transmit through cable. Main types: charge-sensitive or voltage-sensitive Charge sensitive preamps integrate charge Q(t)  E deposit from detector directly. Use for semiconductor diodes. Voltage sensitive preamps amplify U(t) = Q(t)/C, C = const.!  PM, PC Detector is essentially a capacitor C d, delivers a time dependent charge Q(t), current I=dQ/dt For E measurement, integrate Q For t measurement, differentiate Q Use operational amplifiers (op-amp) for both. + - U0U0 R R,C Q CdCd CdCd R C Replacement circuit for detector and decoupling

4. Basic Counting System Detector Ground Bias (U 0 ) R C -+ - - +-+ +- -+++ Pulse Height Analysis Digitization unipolar bipolar 0 R: Load resistor C: Insulate electronics from high voltage (bias) Pulse height 100 mV Charge sensitive preamplifier: Voltage output pulse height (1V) independent of detector C Amplifier/Shaper: differentiates (1x or 2x) Final amplitude 2-10V Binary data to computer Pre Amp Amp Shaper UU

5. ScintillationDet W. Udo Schröder, 2004 5 Operational Amplifiers Gain is very high (~10 6 ), inverting. Properties of amp can be determined by feedback circuit: Feeding back the negative of the input signal to the summation point cancels the signal at  Integrator G + - -Q-Q +Q·10 6 RfRf G + - R in  G + -  CfCf G + - C in  RfRf Differentiator

6. ScintillationDet W. Udo Schröder, 2004 6 Charge Sensitive Preamp Inverting, integrating preamp Pulse decay governed by t dec  1/R f C f. Additional amplifier necessary for pulse shaping and gain. G CfCf RfRf CdCd R in U t

7. ScintillationDet W. Udo Schröder, 2004 7 Main/Shaping Amplifiers Tasks: 1) Linear amplification to pulse heights of U  (1-10)V 2) Improvement of signal/noise ratio (integration) 3) Pulse shaping (Gaussian shape is best) C d1 R d1 RIRI CICI C d2 R d2 1 st diff integr 2 nd diff More versatility: RC-circuits  active filters

8. ScintillationDet W. Udo Schröder, 2004 8 NIM Signal Standards (National Instruments Methods) Linear analog NIM signals +10V 0V “1” “0” +10V 0V “1” +5V “0” 0V TTL-Logic Slow logical NIM (TTL) pulses:discriminators, gates,… -16mA -0.8V/50  2ns Fast logical NIM signals for fast timing/triggering NIM- gate/trigger signal

9. ScintillationDet W. Udo Schröder, 2004 9 Discriminator/Trigger R1R1 RfRf Mono Vibrator +10V U disc InputOutput Task: Produce a logical signal, whenever analog signal exceeds threshold U disc. Use for logical decisions (open acquisition,...). Exist for slow and fast pulses. For fast timing, use negative NIM logic units U disc U in t t U out

10. ScintillationDet W. Udo Schröder, 2004 10 Zero-Crossing Triggering t Produce fast, bipolar linear pulse. Possible: different gains for positive and negative parts  zero crossing at different time (fraction of time to maximum) Produce “saturated” uniform pulse Differentiate saturated pulse, use triplet pulse as input for trigger (negative pulse polarity). Trigger output appears at zero crossing (Internal delays neglected) t t U trig Trigger output signal t

11. ScintillationDet W. Udo Schröder, 2004 11 Constant-Fraction Discriminator U in Delay T d  U f =f·U in Trigger Zero crossing timing always at same physical time, independent of pulse amplitude for fixed pulse shape: no “walk” with energy U cftd amplitude dependent leading edge discr. output timing Can utilize for PSD! Pulse time jitter “walk” U disc

12. ScintillationDet W. Udo Schröder, 2004 12 Logic Modules U1U1 U2U2 U out = U 1 U 2 Overlap Coincidence U2U2 U1U1 Or (inclusive) U1U1 U2U2 U out t t t U1U1 U2U2 t t t U out = U 1 VU 2 Anti-Coincidence UU U complement U1U1 U2U2 U out = U 1 U 2 U2U2 For fast timing: use fast negative logic

13. ScintillationDet W. Udo Schröder, 2004 13 Signal Transmission inner conductor outer conductor/shield outer conductor dielectric medium outer casing Coaxial cables/transmission lines  traveling waves in cavity resonators Wave equation (R=0): z L: inductivity/length C: capacity/length depend on diameter and dielectric signal propagation speed (speed of light): typically c -1 =5 ns/m characteristic resistance Z 0 =Ohmic resistance! For R≠0, Z 0 () complex Z 0 = 50  or 93  used for timing, spectroscopy, resp.

14. ScintillationDet W. Udo Schröder, 2004 14 Impedance Matching RdRd R load RdRd sender receiver For impedance matching, R load =Z 0, cable looks infinitely long: no reflections from end. For mismatch, R load ≠ Z 0, reflection at end, traveling back, superimpose on signal Polarity of reflected signal R load =0, ∞

15. ScintillationDet W. Udo Schröder, 2004 15 Cable Reflections Receiver input impedance R load ≠ Z 0,  use additional Ohmic termination in parallel R load R term L L Open end: R load = ∞ Input and reflection equal polarity, overlap for t > 2T cable T cable = 2L/c Short: R load =0, Input and reflection opposite polarity, superposition = bipolar Multiple (n) reflections attenuated by R -n

16. ScintillationDet W. Udo Schröder, 2004 16