C.V. Nguyen, A.P.J. van Deursen

Transcription

1 MeV γ s from Long Leaders in STP Air C.V. Nguyen, A.P.J. van Deursen Group EPS, Technische Universiteit Eindhoven P.O. Box 513, 56 MB Eindhoven, The Netherlands C.V.Nguyen@tue.nl, A.P.J.v.Deursen@tue.nl Workshop on Streamers, Sprites, Leaders, Lightning: from micro- to macroscales Lorentz Center, Leiden, The Netherlands October 8-12, 27

2 Outline 1. Introduction 2. Experimental setup 4. Conclusions 5. Recommendations and outlook 2

3 1. Introduction These phenomena are not well understood, especially the acceleration of electrons to produce high-energetic radiation. 3

4 1. Introduction Main objective: Investigate the high-energy production related to lightning - study on long laboratory produced sparks - conditions for gamma production - energies produced - underlying mechanisms 4

5 2. Experimental setup 12 stage 2MV Marx generator.7 m spark 5

6 2. Experimental setup Floor plan 6

7 2. Experimental setup LaBr 3 scintillator with PMT 31 ns decay time (1/e).5 mm Al cover +.5 mm Al cabinet window 1/e cutoff at 17 kev Dig. oscilloscope for HV and PMT signal + laptop storage. 8 bit, max 2 Gs/s Calibration by 662 kev from 137 Cs. 7

8 NaI(Tl) response on 137 Cs source Photo / Compton = 1 / 2.55 Background low 25 Background 137Cs source Counts/sec Compton Photo 7.8 % FWHM Peak voltage 'PW4119' 8

9 NaI(Tl) detector response Example of γ-pulse (Inverted) _18 9 kv 566 kev leader formation discharge MV (b), MeV (r) Time [µsec.] 9

10 V surge 1MV NaI(Tl) detector response 14626_18 space limitations In 1% of surges γ s seen about 75% V max Very occasionally after V max γ s related to leader formation burst of γ s up to or exceeding ev max detected MV (b), MeV (r) Time [µsec.] 1

11 NaI(Tl) detector response 9526_3.2 Occasionally very energetic ones, exceeding ev max MV (b), MeV (r) _ kv Overloaded > 114 kev MV (b), MeV (r) kev -875 kv Time [µsec.] Less detection with Negative discharges for NaI(Tl) Time [µsec.] 11

12 LaBr 3 (Ce) response on 137 Cs source Photo / Compton = 1 / 2.5 Background low 7 Backround 137Cs source 6 5 Photo Counts/sec % FWHM Compton Peak voltage 'Brilliance 38' 12

13 LaBr3(Ce) detector response Example of γ-pulse (inverted) with LaBr3 detector (7 cm gap) MV (b), 1 ka (g), ka (r) and MeV (k) 26327_7 84 kv kev kev ka leader formation discharge Time [µsec.] 13

14 LaBr3(Ce) detector response; Al-electrodes Very often multiple intense γ-bursts detected (inverted)! 28926_ kev 877 kev 8 kv MV (b), MeV (r&k) kev Time [µsec.] 14

15 LaBr3(Ce) detector response; Pb-electrodes With lead electrodes gamma energy seems to increase and γ s occurred more frequently 28926_ MeV 2.5 MV (b), MeV (r&k) MeV 1.5 MeV.5 23 kev 195 kev 218 kev Time [µsec.] 15

16 LaBr3(Ce) detector response More intense γ s with Negative discharges! Tek.txt.2 MV (b), 5kA (g), 2MeV (k) and 2MeV (r) MeV 4.4 MeV 11.2 MeV -9 kv 5 ka 24.2 Mev Time [µsec.] 16

17 LaBr3(Ce) detector response Fitting of detector s signal using 137 Cs-pulse Tek.txt.2 MV (b), ka (g), 2MeV (k) and 2MeV (r) Energies [MeV] :.4694, 1.11, 3.282, 21.97, , , , , , Time [µsec.]

18 LaBr3(Ce) detector response; Negative discharges Histogram of 42 negative discharges, V breakd -9 kv 42 Neg_discharges (Al electrodes) bursts during 38 surges 1 Counts/surge Energy/pulse [kev] 18

19 LaBr3(Ce) detector response; Negative discharges Histogram of 44 negative discharges, V breakd -9 kv With 22 mm Al-absorber; 1/e cutoff 1 kev.8 44 Neg_discharges (Al electrodes).7.6 Counts/surge bursts during 22 surges Energy/pulse [kev] 19

20 LaBr3(Ce) detector response; Negative discharges Histogram of negative discharges without and with 22 mm Al-absorber; 1/e cutoff 1 kev Neg_surges (Al electrodes) 228 bursts during 38 surges 1 Counts/surge bursts during 22 surges Energy/pulse [kev] 2

21 LaBr3(Ce) detector response; with and without absorber Histogram of negative discharges without and with 1.5 mm Pb-absorber (1/e cutoff 1.4 MeV) 3 Neg_dis charges (A l electrodes) + 1.5mm Pb abs orber (1/e c utoff = 1.4M ev) bursts during 3 surges 1.5 Counts/surge bursts during 24 surges Energy/pulse [k ev] 21

22 BaF2 detector response Fast γ-pulse 4427_8 MV (b), 1 ka (g), ka (r) and 1 MeV (k) kv 5.55 ka Time [µsec.] 22

23 BaF2 & LaBr3 detector response BaF2 vs. LaBr3 γ-detection 4427_28 MV (b), 1 ka (g), 1 MeV (r), a.u. (k) ka MeV -915 kv Time [µsec.] 23

24 Localization measurement with Pb tube Localization (LaBr3) - Positive discharge: Only γ-detection at anode! - Negative discharge: γ-detection at anode and cathode as well as in air! 24

25 Multi-angle measurement (2x LaBr3) Floor plan 2 1/e =17 kev (cut-off energy) 1/e =94 kev (cut-off energy) 25

26 Multi-angle measurement (2x LaBr3) Indication for pile-up 13427_1.2 MV (b), 1 ka (g), ka (r) and 1 MeV (k) kev 18 kev 24 kev 5.36 ka -.8 > 6.9 MeV -885 kv Time [µsec.] 26

27 Measurement on a wire-plate corona reactor X-ray registered in wire-plate corona reactor. No total breakdown needed! 2 1 C1Cspiek2666.trc signal measured signal filtered Positive supply voltage: 65kV pulse + 2kV DC offset 15/25ns rise/fall time Energy [kev] keV Time [µsec.] 27

28 Gurevich & Zybin: Run-away electrons? Runaway region > 2keV for high in the atmosphere Experiments (at STP): In spite of an absorber with 1/e cutoff energy of 1.4 MeV high-energetic pulses are still detectable! 28

29 4. Conclusions TU/e More intense γ-burst with negative discharges (LaBr3) γ s likely originate near the anode at streamer formation. Positive discharge only γ-detection near anode. Negative discharge γ-detection near electrodes as well as in air. No total breakdown needed for γ-production. Cosmic radiation as cause less probable because. low background count rate timing with the surge 29

30 5. Recommendations and outlook Investigation of difference in γ-production for positive and negative surges need for fast current measurement! Role of humidity should be investigated more. Better conditioning Marx generator voltage waveform needed. Direct detection of fast particles. Variable gas conditions. Modeling work is needed. 3