1. Detector performance features Matthew Whyndham MSSL

2. 10 Oct 2000ReSIK Eng/Sci Meeting SRC Wroclaw 2 Detector effects Basic operation –quantum efficiency –pulse height distribution –gain vs HV Position sensitivity –linearity –digitisation effects Energy sensitivity –linearity –use of discriminators –RESIK high-order operation High rate operation –gain depression –image distortion

3. 10 Oct 2000ReSIK Eng/Sci Meeting SRC Wroclaw 3 window Readout cathode anodes Basic operation

4. 10 Oct 2000ReSIK Eng/Sci Meeting SRC Wroclaw 4 papers [1] M. W. Trow, ESA-SP 356, 1992 [2] Trow/Bento/Smith, Rate dependant image distortions in proportional counters, Nucl. Instr. Meth. A 328 (1994) (W. = Whyndham = Trow)

5. 10 Oct 2000ReSIK Eng/Sci Meeting SRC Wroclaw 5 Detection of photons Quantum efficiency peaks ~ 7 keV –low energy / long wavelength - drop due to window absorption –high energy - long range in gas pulse height distribution –FWHM ~14% @6 keV –Ar-K and Xe-L escape peaks possible Gain –logarithmic gain law log G = A + B.V –one HV step (30V) results in factor ~1.3 gain change –eight steps available in RAL HVU

6. 10 Oct 2000ReSIK Eng/Sci Meeting SRC Wroclaw 6 Position sensitivity 8-bit charge measurement ~ 256 bins in optimal case but SNR determines real performance position determination done by lookup table stretched bins 45 10 digitisation spikes near 1/2, 1/4, 3/4 more prominent if PHD restricted or low

7. 10 Oct 2000ReSIK Eng/Sci Meeting SRC Wroclaw 7 Energy sensitivity initial number of ion/electron pairs strictly proportional to energy –but gain not equal for all energies hence non-linear relation –fig 4 in PSD paper 2/3 order - reduce HV –order 1 still present! –study PHA –adjust discriminators

8. 10 Oct 2000ReSIK Eng/Sci Meeting SRC Wroclaw 8 Calibration data latest data taken at RAL summer 2000 scans of beam over detector length slot-mask - 300  m slots - defines positions beam normal to detector - minimal parallax all energies used by RESIK mostly low count rate ADCs in appropriate analog-card “best HV” in each case (Fe55 cal - lower HV) RESIK-A = BCS-B card (3,4) RESIK-B = BCS-A card (1,2)

9. 10 Oct 2000ReSIK Eng/Sci Meeting SRC Wroclaw 9 High rate operation deadtimes in electronics gain depression image distortion

10. 10 Oct 2000ReSIK Eng/Sci Meeting SRC Wroclaw 10 dead times in electronics –anti-pileup deadtime of position-encoding logic of 32  s –extendable (paralysable) –affects entire detector (1,2) (3,4) –accounted for in Yohkoh software

11. 10 Oct 2000ReSIK Eng/Sci Meeting SRC Wroclaw 11 gain depression –reduction in gain at high rate –effects pulse height distribution markedly- and therefore validity of discriminator settings –localised effect - wherever the intense line happens to be –function of charge (rate × gain × ph. Energy × conversion-constant) –operates at all rates but significant over 1000 c/s –compensate by raising HV or adjusting discriminators

12. 10 Oct 2000ReSIK Eng/Sci Meeting SRC Wroclaw 12 image distortion –“attraction” of counts towards areas of highest rate –caused by viz [2] fig 1. build-up of slow ions establishment of axial field distortion of electron path –total number of counts conserved –function of charge –probably detectable at all rates –significant over 10 3 c/s

13. 10 Oct 2000ReSIK Eng/Sci Meeting SRC Wroclaw 13 Summary Detector health –build plot of Fe55 cal fit params during pre-launch and mission position-calibration –data analysis required rate effects –deadtime : understood –gain depression / image distortion : complex picture high order operation –observe PHA carefully –build experience progressively