University of Milano INFN Milano Department of Physics

JRA 02 - AGATA Time-over-Threshold (TOT) technique for AGATA preamplifiers

The issue of ADC saturation & system dead time Exotic nuclei are to be

Mixed reset technique: continuous + pulsed JRA 02 - AGATA Saturated output without pulsed-reset

Fast-reset device PACAGA 5 A (GANIL) AGATA_ core-pulser (KOELN) PB-B 1 - MI (MILANO)

Time-Over-Threshold (TOT) technique second-order time-energy relation E = energy of the large signal T

Time-Over-Threshold (TOT) technique second-order time-energy relation offset term contribution of the tail due to

Experimental setup with the AGATA capsule JRA 02 - AGATA Encapsulated AGATA HPGe crystal

Calibration procedure Parameters calculated by a fitting procedure Parabolic fitting curve Calibration pulser signals

TOT technique applied to overthreshold pulser signals (1) Pulser signal @ 5. 97 Me.

TOT technique applied to overthreshold pulser signals (2) 60 Co background rate = 1.

TOT technique applied to overthreshold pulser signals (3) Background event rate = 800 Hz

Experimental setup: 241 Am+Be AGATA capsule at LNL 241 Am+Be source with Ni target

241 Am+Be spectrum in pulse-height mode Energy Resolution (fwhm) in “pulse-height” mode 1. 1732

241 Am+Be spectrum “reset” mode (by TOT technique) Energy Resolution (fwhm) in pulse-height mode

Comparison on the 8. 99 Me. V Ni line “pulse-height” mode FWHM = 15

The ideal acquisition chain: “dual -range” core preamplifier JRA 02 - AGATA Reset threshold

First results with an ASIC preamplifier for Ge detectors

The realized JFET-CMOS preamplifier DC-coupled, optimized for negative signals (hole signals), fully functional at

The proposed CMOS output stage: a selfadjusting constant-current source follower M 2 (n-MOS) is

First test-bench characterization Negative output voltage swing of -2. 5 V against a negative

The BF 862 JFET at T=300 K and T=77 K T= 300 K From

Measurement results with HPGe detector Rise time ~ 16 ns Cdet ~ 60 p.

Summarized preamplifier performance T = 77 °K Energy sensitivity (CF = 0. 2 p.

Conclusions JRA 02 - AGATA l A TOT technique has been adopted for AGATA

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University of Milano INFN - Milano Department of Physics JRA 02 - AGATA Going beyond the ADC limit in AGATA with a Time-over-Threshold technique and first results with an ASIC preamplifier for Ge detectors Francesca Zocca FREEDAC meeting Ljubljana 2008, May 28 th

JRA 02 - AGATA Time-over-Threshold (TOT) technique for AGATA preamplifiers

The issue of ADC saturation & system dead time Exotic nuclei are to be disentangled in a hostile environment of high background radioactivity: (Bremsstrahlung, neutrons, charged particles…) g ( 1 -10 Me V) Background of energetic particles JRA 02 - AGATA HPGe segmented detector p K ( 10 -100 Core Me. V) The preamplifier output signals are directly digitized: shaping, filtering and pulse shape analysis are made on the digitized signals Segments charge preamplifier From detector Second stage charge loop Antialias ADC Individual highly energetic events or bursts of piled-up events could easily cause ADC SATURATION and introduce a significant SYSTEM DEAD TIME

Mixed reset technique: continuous + pulsed JRA 02 - AGATA Saturated output without pulsed-reset Ideal non-saturated output without pulsed-reset ADC overflow voltage level Preamplifier output with continuous-reset (50 s decay time constant) An ADC overflow condition would saturate the system for a long while Output with pulsed-reset A fast-reset mechanism allows a fast recovery of the output quiescent value, so minimizing the system dead time

Fast-reset device PACAGA 5 A (GANIL) AGATA_ core-pulser (KOELN) PB-B 1 - MI (MILANO)

Time-Over-Threshold (TOT) technique

Time-Over-Threshold (TOT) technique second-order time-energy relation E = energy of the large signal T = reset time offset term

Time-Over-Threshold (TOT) technique second-order time-energy relation offset term contribution of the tail due to previous events E = energy of the large signal T = reset time V 1 , V 2 = pre-pulse and post-pulse baselines b 1 , b 2 , k 1 , E 0 = fitting parameters Within ADC range standard “pulse-height mode” spectroscopy Beyond ADC range new “reset mode” spectroscopy

Experimental setup with the AGATA capsule JRA 02 - AGATA Encapsulated AGATA HPGe crystal at LNL built-in pulser Core preamplifier

Calibration procedure Parameters calculated by a fitting procedure Parabolic fitting curve Calibration pulser signals are completely disentangled from the background

TOT technique applied to overthreshold pulser signals (1) Pulser signal @ 5. 97 Me. V 60 Co background rate = 1. 3 k. Hz 60 Co background rate = 14. 5 k. Hz

TOT technique applied to overthreshold pulser signals (2) 60 Co background rate = 1. 3 k. Hz Resolution @ 5. 97 Me. V = 10. 5 ke. V (0. 18 %) 60 Co background rate = 14. 5 k. Hz Resolution @ 5. 97 Me. V= 15. 2 ke. V (0. 25 %)

TOT technique applied to overthreshold pulser signals (3) Background event rate = 800 Hz Pulser line energy Resolution (fwhm) E 1 = 3. 3501 Me. V 11. 68 ke. V 0. 35 % E 2 = 5. 9720 Me. V 11. 42 ke. V 0. 19 % E 3 = 10. 656 Me. V 11. 28 ke. V 0. 11 % E 4 = 18. 797 Me. V 12. 55 ke. V 0. 067 % E 5 = 33. 369 Me. V 14. 33 ke. V 0. 043 % E 6 = 49. 434 Me. V 19. 16 ke. V 0. 039 % Better than 0. 4% over the full range Pulser energy = 5. 97 Me. V Pulser energy = 10. 65 Me. V Pulser energy = 18. 8 Me. V Event rate Resolution (fwhm) 1. 3 k. Hz 10. 50 ke. V 0. 18 % 1. 2 k. Hz 12. 07 ke. V 0. 11 % 1. 3 k. Hz 12. 94 ke. V 0. 069 % 2. 3 k. Hz 11. 79 ke. V 0. 20 % 2. 4 k. Hz 12. 97 ke. V 0. 12 % 2. 3 k. Hz 15. 56 ke. V 0. 083 % 4. 2 k. Hz 12. 57 ke. V 0. 21 % 4. 2 k. Hz 14. 02 ke. V 0. 13 % 4. 2 k. Hz 18. 64 ke. V 0. 10 % 8. 2 k. Hz 13. 23 ke. V 0. 22 % 8. 2 k. Hz 17. 87 ke. V 0. 17 % 8. 2 k. Hz ~ 30 ke. V 0. 16 % 14. 5 k. Hz 15. 18 ke. V 0. 25 % 14. 5 k. Hz 22. 56 ke. V 0. 21 % 14. 2 k. Hz ~ 40 ke. V 0. 21 %

Experimental setup: 241 Am+Be AGATA capsule at LNL 241 Am+Be source with Ni target Fast neutrons thermalized in paraffin and captured by natural metallic nickel g-photons produced in the 4 to 9 Me. V range source

241 Am+Be spectrum in pulse-height mode Energy Resolution (fwhm) in “pulse-height” mode 1. 1732 Me. V (60 Co) 2. 99 ke. V 0. 25 % 1. 3325 Me. V (60 Co) 3. 24 ke. V 0. 24 % 2. 2233 Me. V (H) 4. 51 ke. V 0. 20 % 4. 440 Me. V (12 C) 104 ke. V 2. 34 % 7. 6312 Me. V (Fe) 11 ke. V 0. 14 % 7. 6456 Me. V (Fe) 11 ke. V 0. 14 % 8. 9984 Me. V (Ni) 15 ke. V 0. 17 %

241 Am+Be spectrum in reset mode

241 Am+Be spectrum “reset” mode (by TOT technique) Energy Resolution (fwhm) in pulse-height mode Resolution (fwhm) in reset mode 4. 440 Me. V (12 C) 104 ke. V 2. 34 % ~5. 6 Me. V 10. 5 ke. V 0. 14 % 18. 8 ke. V 0. 34 % ~6. 1 Me. V 15. 1 ke. V 0. 17 % 17. 1 ke. V 0. 28 % 7. 6312 Me. V (Fe) 11 ke. V 0. 14 % 7. 6456 Me. V (Fe) 11 ke. V 0. 14 % 18. 8 ke. V (29. 4 ke. V for the doublepeak) 0. 25 % (0. 38 % for the doublepeak) 8. 9984 Me. V (Ni) 15 ke. V 0. 17 % 18. 9 ke. V 0. 21 % “pulse-height” mode (by ADC)

Comparison on the 8. 99 Me. V Ni line “pulse-height” mode FWHM = 15 ke. V ( 0. 17 % ) “reset” mode FWHM = 19 ke. V ( 0. 21 % ) At high energies the performance in reset mode approaches the performance in pulse-height mode

The ideal acquisition chain: “dual -range” core preamplifier JRA 02 - AGATA Reset threshold ~ 10 Me. V ~ 5 Me. V 1 st channel 2 nd channel ~ 20 Me. V Result : Pulse-height mode (ADC ~ 5 Me. V) Pulse-height mode (ADC ~ 20 Me. V) Reset mode (from ~ 20 Me. V on)

First results with an ASIC preamplifier for Ge detectors

The realized JFET-CMOS preamplifier DC-coupled, optimized for negative signals (hole signals), fully functional at cryogenic temperature 5 V 0. 8 m CMOS technology provided by Austria Micro Systems M 3 holes for mounting VD test 23 mm Inspired to that proposed in : J. Gal et al. “Realization of charge sensitive preamplifiers using current feedback operational amplifier”, Nucl. Instrum. And Meth. , Vol. A 366, pp. 145 -147, 1995 det out Integrated circuit and discrete devices as mounted on a Printed Circuit Board of 0. 8 mm teflon (PTFE) laminate VEE VCC 47 mm

The proposed CMOS output stage: a selfadjusting constant-current source follower M 2 (n-MOS) is the “sourcefollower” transistor, whose current is kept constant by the negative feedback loop M 1 (n-MOS) acts as a “driver” transistor, and provides the load current whenever a negative output signal is present Inserted into the loop of a negative feedback amplifier to guarantee the best overall circuit linearity (mandatory for gamma-ray spectroscopy)

First test-bench characterization Negative output voltage swing of -2. 5 V against a negative power supply of -2. 7 V CF = 0. 2 p. F dynamic energy range = ~ 8. 6 Me. V (CF= 1 p. F dynamic energy range = ~ 45 Me. V) Rise time of ~ 13 ns (1 m 50 W terminated cable) Rise time of ~ 15 ns (10 m 50 W terminated cable) Cdetector = 15 p. F Minimum ENC ~ 110 e- rms (0. 76 ke. V fwhm in HPGe) both at 300 K and 77 K

The BF 862 JFET at T=300 K and T=77 K T= 300 K From 300 K to 77 K the drain current and so the transconductance value decrease of a factor of 3 T= 77 K

Measurement results with HPGe detector Rise time ~ 16 ns Cdet ~ 60 p. F Shaping time Measurement made in Milano, April 2008, with detector setup “SUB” of GERDA experiment 0. 5 s 1 s 2 s 3 s 6 s 10 s Pulser line resolution ( ke. V fwhm) 3. 90 3. 16 2. 15 1. 99 1. 61 1. 60 60 Co line resolution (ke. V fwhm) 8. 37 4. 14 2. 85 2. 56 2. 25 2. 17

Summarized preamplifier performance T = 77 °K Energy sensitivity (CF = 0. 2 p. F) ~ 290 m. V/Me. V at preamp output ~ 217 m. V/Me. V after 150 W termination Negative output voltage swing ~ 2. 5 V Input dynamic range ~ 8. 6 Me. V Rise time ~ 16 ns with ~ 5 m coaxial cable Fall time ~ 250 s ( RF = 1. 2 GW ) Resolution 2. 2 ke. V @ 1. 332 Me. V ( 60 Co ) 1. 6 ke. V on pulser line Power required 23. 4 m. W (VFET = +4 V ID = 2 m. A VCC= +3. 6 V VEE = -2. 8 V) low value of the feedback capacitance, for maximization of the signal-to-noise ratio (even if at the expense of the dynamic range) very low power consumption: JFET bias point: VD= 2. 32 V ID= 2. 1 m. A PJFET = 8. 3 m. W PASIC = 15. 1 m. W

Conclusions JRA 02 - AGATA l A TOT technique has been adopted for AGATA preamplifiers and demonstrated with an AGATA capsule and a 241 Am+Be source. The obtained resolution in “reset mode” is of < 0. 4 % in all the tested range on pulser signals from 3 Me. V to 50 Me. V. A remarkable resolution of 0. 21 % was obtained on the Ni spectrum line at the energy of 8. 998 Me. V. The energy measurement range can be extended of more than one order of magnitude l A JFET-CMOS preamplifier, able to operate at cryogenic temperatures, has been realized and tested with a HPGe detector. The output stage provides at the same time a low output impedance and a large voltage swing. Future development: integration of the fast reset device in CMOS technology