Physics 736. Experimental Methods in Nuclear-, Particle-, and Astrophysics

Transcription

1 Physics 736 Experimental Methods in Nuclear-, Particle-, and Astrophysics - Ionization & Semiconductor Detectors - Karsten Heeger heeger@wisc.edu

2 Homework #6 Is due on Friday March 22 at 4.30pm

3 Make-up Lecture Friday March 22 at 4.40pm

4 Review of Last Lecture? Q: What determines the energy resolution in ionization detectors? Karsten Heeger, Univ. of Wisconsin Physics 736, Spring 2011

5 Review of Last Lecture? Q: What are the physics/detector characteristics that characterize ionization detectors? Karsten Heeger, Univ. of Wisconsin Physics 736, Spring 2011

6 Review of Last Lecture? Q: What are the physics/detector characteristics that characterize ionization detectors? diffusion drift velocity mobility energy resolution multiplication, gain Karsten Heeger, Univ. of Wisconsin Physics 736, Spring 2011

7 Ionization Detectors Avalanche formation Positive I ion drill I Id Electron 1 drift Anode Wire Q: why is avalanche drop shaped? Karsten Heeger, Univ. of Wisconsin Physics 736, Spring 2011

8 Ionization Detectors Avalanche formation Positive I ion drill I Id Electron 1 drift Anode Wire electrons are more mobile than ions Karsten Heeger, Univ. of Wisconsin Physics 736, Spring 2011

9 Review of Last Lecture What is a Townsend coefficient?

10 Review of Last Lecture What is a Townsend coefficient? Threshold for gas multiplicalion Eleclnc field strength

11 Ionization Detectors Operating Regions of Ionization Detectors trcoarbimtioa 1 bdcr coircfon f.gao C linit 4 d proportbmll' 5! a o t E lo' o o o, 3 to' z lonholio 2?roporfioncl 3 ; chorb.r Goutl'.? : i-r-i I I -l II Nr 7 II o rorlkl I Oirbrgr 6 rgfco I p F ttd n Vottoge, rcltr Karsten Heeger, Univ. of Wisconsin Physics 736, Spring 2011

12 Ionization Detectors Operating Regions of Ionization Detectors trcoarbimtioa bdcr coircfon f.gao C linit d proportbmll'! a o t E lo' o o o, 3 to' z lonholio?roporfioncl ; chorb.r Goutl'.? : i-r-i I I -l II Nr 7 II o rorlkl I Oirbrgr rgfco I p F ttd n Vottoge, rcltr Karsten Heeger, Univ. of Wisconsin Physics 736, Spring 2011

13 Ionization Detectors Proportional Counter Karsten Heeger, Univ. of Wisconsin Physics 736, Spring 2011

14 Homework #6 - Key Concepts TPC drift, diffusion, ionization, scintillation. electron-ion recombination

15 TPC

16 Homework #6 Q: What difference does it make whether you drift ions or electrons? - in terms of diffusion? - in terms of signal detection?

17 Homework #6 Q: What difference does it make whether you drift ions or electrons? - in terms of diffusion? diffusion can be much smaller for ions - in terms of signal detection? positively charged ions cannot induce avalanches

18 Homework #6 Q: What are the forms of energy transfer to Xenon atoms?

19 Homework #6 Q: What are the forms of energy transfer to Xenon atoms?

20 Homework #6 Q: What about Xenon and Fano factor?

21 Semiconductor Detectors

22 Review of Semiconductor Detectors What distinguishes a semiconductor from an insulator or conductor?

23 Review of Semiconductor Detectors What distinguishes a semiconductor from an insulator or conductor? What is the typical energy gap of a semiconductor?

24 Semiconductor Detectors Energy Band Structure En =6.eV Conduction band Energy 9ap valence band electrons Valence band Insutator Semiconductor Metat

25 Semiconductor Detectors Energy Band Structure En =6.eV Conduction band Energy 9ap valence band electrons Valence band Insutator Semiconductor Metat

26 Semiconductor Detectors Energy Band Structure

27 Semiconductor Detectors Covalent Bonding of Silicon T=0K T=300K (a) Valence electrons Semiconductor atom Free elcctron (b) Hole +o -i i. J I- *rt#'. o Fb. f0.2. Covalcnt bonding of silicon: (r) at 0 K, all clectrons participate in bonding, (b) at higher temperatur6 some bonds are broken by thcrmal encrgy leaving a hole in the valence band

28 Semiconductor Detectors Recombination and Trapping Conduction bend Ccntcr Vrlencc band Flg Rccombination and trapping sites in the forbidden energy gap

29 Semiconductor Detectors Recombination and Trapping

30 Semiconductor Detectors Doped Semiconductors n-type semiconductor donor impurities p-type semiconductor acceptor impurities "Excess" electron 0onor impurity "Excess" hote Acceptor impurity (a) Donor impurity level (b) Acceptor impurity level excess of electrons excess of holes

31 Semiconductor Detectors Doped Semiconductors n-type semiconductor donor impurities p-type semiconductor acceptor impurities

32 Semiconductor Detectors pn junction without bias

33 Semiconductor Detectors pn junction without bias

34 Semiconductor Detectors np Junction oa oa oo,, l -l!l lrj I

35 Semiconductor Detectors np junction structure for np junction structure of np junction when current applied When a current is driven through the np junction in the forward direction the electrons drop through the valence band to the empty electron states In a laser this energy drop can either be by the process of spontaneous or stimulated emission of a photon

36 Semiconductor Detectors np junction and diode laser np semiconductor is the laser medium where stimulated emission occurs

37 Semiconductor Detectors np junction and diode laser

38 Semiconductor Detectors reverse bias junction no applied voltage reverse bias enlarges sensitive volume for radiation detection reverse bias holes in the P-type material are pulled away from the junction, causing the width of the depletion zone to increase. 1 Deptetion I l-- Zone.+l with Bias Depletion Zone without Bias lir iit ;rf

39 Semiconductor Detectors junction diode detector Bias Metal contact heavily doped n + layer with almost zero depletion zone => ohmic contact

40 Semiconductor Detectors position sensitive detector uses resistive charge division low-resistive electrode on back charge collected at B will be proportional to energy of particle and resistance of electrode between contact and point of incidence x= L x B/C method of resistive charge division

41 Semiconductor Detectors 2-D position sensitive detector Flg dct tro vid NS

42 Semiconductor Detectors microstrip detector lfm Alminlunr O2pm SIQ p'- lmptrnt.tion (Boiqt) Sl-cry3t.l (n-typc) n'-lmpltntrtion lfm Aluminium (Arrcnk) "bond prd3" ryffile reffino, +- Flg Lay - 36mm+ ls strips (from H

43 Semiconductor Detectors silicon drift chambers created fully depleted waver third n+ contact on edge of waver potential inside waver then parabolic *=\ t I \l )l./l _/l ---/ Electron Potential!: oc, jgo r! O- l : e- created at some point in waver will fall down into potential well then they drift along central valley along longitudinal component of E- field drift time provides spatial information

44 Semiconductor Detectors configurations for Ge detector (0.5 - l.0mm) Lr-contoct (0.5 - t.onm) + \ - I l-l ill Closed- End Ge (Li) Coreless Ge(Li) c P-type IGC (0.5 - l.om) + True- Cooxiol Ge (Li) core Inocttve f,ctrve.e9ron Lr-cmtoct (0.5 lom) + \ FX -----, ron-rmpionlcd or ^T h il ll =JL::.. Hole through Ge(Li) or IGC ll G;-n.o,onrcdor ll I 6/opo6l.d contoct ll---]-.._].- Ge(Li) detectors Ge preferred for gamma detection lon - rmplonted contoct ( 0, 2 7rm ) + Li dilluscd Fig. l0.lt. Coaxial configurations for germanium detectors, Lithium is drifted in from the sides leaving an insensitive core (from PCT detector manual [0.2t1) Closed-End N-type IGC for charged particle detection Si is good too contgt intrinsic Germanium (High Purity Ge detectors)

45 Semiconductor Detectors Ge detector sco soura" Fig Comparison of spectra from source taken with a NaI detector (lop anrue) and a germanium detector o looo.rlt^0", 3ooo 4ooo

46 Semiconductor Detectors Operation of Semiconductor Detectors 1. bias voltage 2. signal amplification 3. temperature effects 4. radiation damage

47 Review of Semiconductor Detectors What is a pn junction and how does it work?

48 Review of Semiconductor Detectors What is a depletion zone?

49 Review of Semiconductor Detectors What is a depletion zone?

50 Karsten Heeger, Univ. of Wisconsin NUSS, July 13, 2009