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Marco Tardocchi 26.09.2010 Xth International school of neutron scattering F. P. Ricci 1 Detectors for neutron scattering M. Tardocchi

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Presentation on theme: "Marco Tardocchi 26.09.2010 Xth International school of neutron scattering F. P. Ricci 1 Detectors for neutron scattering M. Tardocchi"— Presentation transcript:

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2 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 1 Detectors for neutron scattering M. Tardocchi Istituto di Fisica del Plasma, EURATOM-ENEA-CNR Association, Milan, Italy Xth International school of neutron scattering Francesco Paolo Ricci

3 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 2 Nomenclature CategoryEnergy [meV] Temperature [K] [Å] Ultra-cold< 0.1< 1< 30 Cold0.1 – 101 – – 3 Thermal10– – – 1 Epithermal> 500> 6000> 0.4 Fast >  10 5 > 10 6 >0.03

4 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 3 Neutron detection What does it mean detecting a neutron ? – Need to produce some sort of measurable quantitative (countable) electrical signal – It is not possible to detect directly slow neutrons (they carrry to little energy). It can be done with fast neutrons Neutrons are non ionizing particles. They interact via nuclear force. Nuclear reactions needed to convert neutrons in charged secondary particles (n,  ), (n, p), (n, fission), (n,  Cross sections  N·  tot  scatt +  rad capt + … ; neutron flux  (n·s -1 ·cm -2 ) Typical charged particle detectors can be used: – Gaseous proportional counters & ionization chambers – Scintillation detectors – Semiconductors detectors – (n,  used in the Neutron Resonant Capture detector

5 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 4 1 Elastic collision(rest) mass and T kin are conserved; M 1 =M 2 ; M 3 =M 4 2 Anelastic collision * mass is conserved, T kin is conserved 3 Nuclear reactions mass and T kin are not conserved Q= ( M 1 +M 2 ) – (M 3 +M 4 ) (2) Q-value defintion Condensed matter scientist use the term anelastic to mean reaction of type 1 when E n initial≠ E n final (exchange of and ) Schematics of nuclear reactions Energy conservation M 1 +M 2 +T 1 = M 3 +M 4 +T 3 +T 4 (1)

6 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 5 Schematics of nuclear reactions Energy conservation M 1 +M 2 +T 1 = M 3 +M 4 +T 3 +T 4 (1) M 1 = M 3, M 2 = M 4 and Q =0 Elastic reactions M 1 = M 3, M 2 = M 4 and Q≠0 Anelastic reactions Q<0 Endhotermic Mass is created from kin. energy Q>0 Esothermic Mass is trasnformed in kinetic energy M 1 ≠ M 3 or M 2 ≠ M 4 and Q≠0 Nuclear reactions eq1 +2(T 3 + T 4 ) – T 1 = Q

7 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 6 Some nuclear reactions for neutron detection n + 3 He  3 H + 1 H MeV n + 6 Li  4 He + 3 H MeV n + 10 B  7 Li* + 4 He  7 Li + 4 He MeV  +2.3 MeV(93%)  7 Li + 4 He +2.8 MeV( 7%) n Gd  Gd*   -ray spectrum  conversion electron spectrum n Gd  Gd*   -ray spectrum  conversion electron spectrum n U  fission fragments + ~160 MeV n Pu  fission fragments + ~160 MeV

8 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 7 Ideal dector: High detection efficiency (cross section) Large Q values Stop reaction products Immune to bakground (often  rays) E kinetics of the products=Q + E n =Q Products emitted back-to-back (P init ~0) … Detectors for slow neutrons

9 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 8 Reactions for slow neutron detection n + 10 B (a.i20%)  7 Li* +  7 Li +  MeV  MeV (93%) 3840 barns  7 Li + 4 He MeV ( 7%) n + 3 He  3 H + 1 H MeV (expensive) 5330 barns n + 6 Li (a.i. 7%)  4 He + 3 H MeV (resonance at 100keV) 940 barns

10 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 9 9 Gas Detectors Ionization tracks in proportional counter gas Electrons drift toward the central anode wire. When they get close, they accelerate sufficiently between collisions with gas atoms to ionize the next atom. A Townsend avalanche occurs in which the number of electrons (and ions) increases the number many-fold, about x10 3. Separation of these charges puts a charge on the detector, which is a low-capacitance capacitor, causing a pulse in the voltage that can be amplified and registered electronically.

11 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 10 Ionization Mode Electrons drift to anode, producing a charge pulse with no gas multiplication. Typically employed in low-efficiency beam-monitor detectors. Proportional Mode: electron collisions ionize gas atoms producing even more electrons. Gas amplification increases the collected charge proportional to the initial charge produced. Gas gains of up to a few thousand are possible, above which proportionalityis lost. 10 Gas Detectors – operational modes

12 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 11 Gas Detectors Proportional counters (PCs) come in a variety of different forms. Simple detector Linear position-sensitive detector (LPSD): The anode is resistive, read out from both ends—the chargedistributes between the ends according to the position of the neutron capture event in the tube. Usually cylindrical. 2-D position-sensitive detector (MWPC). Many parallel resistive wires extend across a large thick area of fill gas. Each wire operates either as in LPSD or without position. information as in a simple PC. or Two mutually perpendicular arrays of anode wires. Each is read separately as an LPSD to give two coordinates for the neutron capture event. MWPCs usually have a planar configuration.

13 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 12 Gas proportional counter ~25,000 ions and electrons produced per neutron

14 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 13 BF 3 detector response function For large BF 3 detectors the secondaries are completely absorbe In small BF 3 wall effect is present Range in BF 3 

15 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 14 Pulse Height Discrimination Can set discriminator levels to reject undesired events (fast neutrons, gammas, electronic noise). Pulse-height discrimination can make a large improvement in background. Discrimination capabilities are an important criterion in the choice of detectors ( 3 He gas detectors are very good).

16 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 15 Reuter-Stokes LPSD

17 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 16 MAPS LPSD Detector Bank (at ISIS)

18 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 17 Multi-Wire Proportional Counter Array of discrete detectors. Remove walls to get multi-wire counter.

19 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 18 MWPC Segment the cathode to get x-y position

20 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 19 Brookhaven MWPCs

21 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 20 Efficiency of Detectors Full expression: eff  = 1 - exp(-N· sigma · d). Approximate expression for low efficiency: eff = N  · sigma ·  d. Here: sigma = absorption cross-section (function of wavelength) N = number density of absorber d = thickness N = 2.7 x cm -3 per atm for a gas at 300 K. Detectors rarely register all the incident neutrons. The ratio of the number registered to the number incident is the efficiency. For 1-cm thick 3 He at 1 atm and 1.8-Å neutrons,  = For a real 3d detector geometry Monte Carlo codes are needed in order to calculated the detector efficiency,

22 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 21 Spatial Resolution of Proportional Counters Spatial resolution (how well the detector tells the location of an event) is always limited by the charged-particle range and by the range of neutrons in the fill gas, which depend on the pressure and composition of the fill gas. And by the geometry: Simple PCs:  z ~ diameter; 6 mm - 50 mm. LPSDs:  z ~ diameter,  y ~ diameter ; 6 mm - 50 mm. MWPC:  z and  y ~ wire spacing; 1 mm - 10 mm.

23 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 22 Fission Counters With large thickness of fissile material deposition (UO 2) the fission fragments may lose a significant fraction of their energy in the material itself thus releasing less energy into the detector Ionization chamber coated in its inner surface with fissile deposit. One of the the two fission fragment can be detected. Very large Q value ( MeV)

24 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 23 The fission reaction

25 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 24 Fission cross sections Thermal neutron region Fast neutron region U235 Pu Energy (ev) Energy (ev) 10 8 U238 U235 Pu239 Np237

26 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 25 Scintillation Detectors

27 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 26 Some Common Scintillators for Neutron Detectors Intrinsic scintillators contain small concentrations of ions (“wave shifters”) that shift the wavelength of the originally emitted light to the longer wavelength region easily sensed by photomultipliers. ZnS(Ag) is the brightest scintillator known, an intrinsic scintillator that is mixed heterogeneously with converter material, usually Li 6 F in the “Stedman” recipe, to form scintillating composites. These are only semitransparent. But it is somewhat slow, decaying with ~ 10 µsec halftime. GS-20 (glass,Ce 3+ ) is mixed with a high concentration of Li 2 O in the melt to form a material transparent to light. Li 6 Gd(BO 3 ) 3 (Ce 3+ ) (including 158 Gd and 160 Gd, 6 Li,and 11 B), and 6 LiF(Eu) are intrinsic scintillators that contain high proportions of converter material and are typically transparent. An efficient gamma ray detector with little sensitivity to neutrons, used in conjunction with neutron capture gamma-ray converters, is YAP (yttrium aluminum perovskite, YAl 2 O 3 (Ce 3+ )).

28 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 27 Some Common Scintillators for Neutron Detectors Li glass (Ce)1.75x % 395 nm ~7,000 LiI (Eu)1.83x % 470 ~51,000 ZnS (Ag) - LiF1.18x % 450 ~160,000 Material Density of 6 Li atoms (cm -3) Scintillation efficiency Photon wavelength (nm) Photons per neutron Li 6 Gd(BO 3 ) 3 (Ce), YAP ~18,000 per MeV gamma 3.3x10 22 ~40,000 ~

29 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 28 GEM Detector Module (at ISIS)

30 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 29 Hamamatsu Multicathode Photomultiplier Compact photomultipliers are essential components of scintillation area detectors. The figure shows a recently developed multicathode photomultiplier, Hamamatsu model 8500.

31 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 30 Principle of Crossed-Fiber Position-Sensitive Scintillation Detector Outputs to multi-anode photomultiplier tube Outputs to coincidence-encoded single-anode photomultiplier tubes 1-mm-square wavelength- -shifting fibers Scintillator screen

32 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 31 Neutron Beam Coincidence tube 2-D tube Scintillator Screen Clear Fiber Wavelength-shifting fiber Aluminum wire 16-element WAND Prototype Schematic and Results

33 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 32 Crossed-Fiber Scintillation Detector Design Parameters (ORNL I&C) Size: 25-cm x 25-cm. Thickness: 2-mm. Number of fibers: 48 for each axis. Multi-anode photomultiplier tube: Phillips XP1704. Coincidence tube: Hamamastu Resolution: < 5 mm. Shaping time: 300 nsec. Counting-rate capability: ~ 1 MHz. Time-of-flight resolution: 1  sec.

34 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 33 SNS 2-D Scintillation Detector Module Shows scintillator plate with all fibers installed and connected to multi-anode photomultiplier mount.

35 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 34 Normalized scattering from 1-cm-high germanium crystal. E n ~ eV. Detector 50 cm from crystal. Neutron Scattering from Germanium Crystal Using Crossed-Fiber Detector

36 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 35 The scintillator screen for this 2-D detector consists of a mixture of 6 LiF and silver-activated ZnS powder in an optical grade epoxy binder. Neutrons incident on the screen react with the 6 Li to produce a triton and an alpha particle. These charged particles passing through the ZnS(Ag) cause it to emit light at a wavelength of approximately 450 nm. The 450- nm photons are absorbed in the wavelength-shifting fibers where they convert to 520-nm photons, some of which travel toward the ends of the fibers guided by critical internal reflection. The optimum mass ratio of 6 LiF:ZnS(Ag) is about 1:3. The screen is made by mixing the powders with uncured epoxy and pouring the mix into a mold. The powder settles to the bottom of the mold before the binder cures. The clear epoxy above the settled powder mix is machined away. The mixture of 40 mg/cm 2 of 6 LiF and 120 mg/cm 2 of ZnS(Ag) used in this screen provides a measured neutron conversion efficiency of over 90% for 1.8 Å neutrons. Neutron Detector Screen Design

37 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 36 Spatial Resolution of Area Scintillation Detectors /arb The spatial resolution accomplishable in SDs is typically better than in gas detectors. The range of neutrons is less. The range of ionizing particles is less in solid materials than in gases. However, the localization of the light source (an optical process) imposes the limit on position resolution. This in turn depends statistically on the number of photons produced in the scintillator (more is better, of course).

38 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 37 Semiconductors detectors 6 Li

39 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 38 Coating with Neutron Absorber-Surface- Barrier Detectors Layer ( 6 Li or 10 B) must be thin (a few microns) for charged particles to reach the detector. – Detection efficiency is low. Most of the deposited energy doesn’t reach detector. – Poor pulse-height discrimination

40 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 39 Semiconductor Detectors ~1.5  10 6 holes and electrons produced per neutron (large number comapre to scintilator and gas detectors) The detector acts as a capacitor. The ionization partially discharges the capacitor and can be detected directly without further amplification. – However, standard device semiconductors do not contain enough neutron-absorbing nuclei to give reasonable neutron detection efficiency. Options: i) Put neutron absorber on surface of semiconductor? These exist and are called surface barrier detectors. ii) Develop, for example, boron phosphide semiconductor devices? This is a challenge for future development.

41 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 40 Epithermal neutrons from spallation sources For moderatoirs at ISIS H K (two types) H 2 20 K CH K

42 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 41 The Time of flight technique  t = 3-5  s  F = 20 ms p Proton detectorSpllation target Flight path t 1 = L/V 1 t 2 = L/V 2 1 start and e multi-stop fro mthe detector in one frame of 20 ms LLD tempo V

43 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 42 Time of flight neutron spectroscopy in inverted geometry moderator sample resonant foil  L0L0 L1L1 E 0, v 0 E 1, v 1

44 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 43 Total Cross Section of Tantalum Tantalum is essentially monoisotopic 181 Ta and is used as a neutron converter sensitive to energies near 4.28 eV Energy (meV)

45 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 44 Neutron detection techniques for epithermal neutrons RD (resonance detector) FD (filter detector) n n’ n  X Neutron Detector (Lithium glass scintillator) Gamma Detector (YAP scintillator)

46 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 45 FDT RDT TOF spectra for FD (neutron detector) and RD (  detector) Pb sample U foil

47 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 46 Resonance Detector principles Two step process i) Neutron absorption and conversion trough (n,  ) reaction ii) Detection of the emitted prompt gammas RD properties -The absorbing resonance fixes the final neutron energy -Neutron conversion controls mainly the energy resolution (  E/E) -Ability to detect gammas controls the signal to background ratio (S/B) Advantages over Li-glass detectors no principle need for background subtraction no 1/v decrease of the detection efficiency: i) detection efficiency not dependent on the neutron energy ii) high efficiency for epithermal neutrons ( eV)

48 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 47 Choice of the resonant element Neutron absorbing resonance E 0 neutron resonance energy  0 peak cross section (at E=E 0 )  (FWHM) intrinsic resonance width Criteria for resonant elements  Resonance energy: E 0 = eV  Isolated resonance (to avoid overlapping with other resonances)  High cross section (high conversion efficiency)   0 = b

49 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 48  Narrow resonance (low  E/E)   ~ 100 meV   ~ 100 meV (Thermal Doppler broadening)  Foil thickness Compromise between neutron absorption probability, P(E n ), and  E/E  N d  0 =1  High yield of low energy gammas ( keV)  choice of suitable detector Other desiderable features: high isotopic abundance, exist as metallic or oxide, low gamma self-absorption

50 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 49 Best Isotopes Gamma yield (absolute) exists for thermal neutron capture, but incomplete database for resonant neutron capture 139 La keV 9 % 238 U keV 32 % 288 keV 9 % 48 keV 13 % 60 keV 12 % 150 Sm keV30 %134 keV 94 %105 keV 9 % 4060 keV 7 %168 keV 8 %

51 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 50 Suitable isotopes for eV neutron energy selection

52 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 51 Energy and relative intensities of  -rays

53 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 52 Suitable  detectors for the RDS Scintillators 1) NaI(Tl): good efficiency and energy resolution for MeV gamam ray. High sensitiviy to neutron backgorund (need of shielding). 2) YAP: good efficieny and moderate energy resolution. Low sensitivity to neutron backgoround Solid Sate 1) HpGe: excellente energy resoltuion, adequate efficienct. Radiation damange. Need to operate at cold temperature (77k) 2) Silicum: good for x-ray and low energy  ray. Requires some cooling. Radiation damage 3) CdZnTe (CZT): Good efficiency and high energy resolution. Operate at room temperare. small areas.

54 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 53 YAP detector 6mm thick Biparametric acquisition >40keV >600keV S/B Intensity fom

55 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 54 Fast neutrons detection ·Spherical dosimeters Scintillators 3 He proportional counters Proton Recoil Telescope Activation threshold targets Bonner Sphere TFBC Diamond detectors

56 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 55 Fast neutron flux on VESUVIO (at ISIS) Measured with activation targets Enormous energy range MeV!

57 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 56

58 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 57 Principle of operation Escape Capture in the polyethylene Capture in the thermal sensor Thermal neutrons sensor From the measured activity on the sensor after a period of irradiation the neutron flux at the selected energy range is found fast n

59 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 58 Extending measurements above 20 MeV Modified Bonner Spheres by including metal inserts to allow for n(x,n) reactions to occur

60 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 59 Response Functions of Bonner Spheres The very broad response function means that complicated deconvolution codes are needed to infer the incoming neutron spectrum from the mesaurement,

61 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 60 Schematic of a TFBC and the principle of its operation: an incident fission fragment produces an electrical breakdown in the SiO 2 layer. Thin Film Breakdown Counter

62 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 61

63 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 62 Picture of a TFBC array Neutron ToF spectra

64 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 63 Diamond detector grown by Chemical Vapor Deposition sma connector CVD diamondAl contact bonding  15 mm

65 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 64 Diamond Detectors Active medium main characteristics: A = 12 amu  = 3.5 g cm -3 t = up to 150  m S = mm 2 E e-h = 12 eV Y=10 5 (e-h) pairs /MeV Single Crystal Diamond Diamond + Boron Polycrystalline Diamond Al contact n- 12 C neutron cross sections

66 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 65 TOF SPECTRUM FROM DIAMOND 1- ROTAX beam 340 ns 210 ns Ip=1761  Ah

67 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 66 TOF SPECTRUM FROM DIAMOND 2- Moderated beam Ip=3598  Ah

68 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 67 TOF SPECTRA FROM DIAMOND Spectral region below  30 MeV depleted

69 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 68 Modifying the diamond response: 1- with a fissile material Only diamond (25  m) Diamond + nat U sheet 30  m 2- with a Lithium Fluoride sheet (96% enriched 6 Li) : detection extended to thermal neutrons LiF film 4  m thick Diamond Ip= 3958  Ah Ip= 3578  Ah Results from tests on INES beam ISIS-TS1

70 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 69 END

71 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 70 Spherical dosimeters

72 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 71 6 Li-glass scintillators Thermal neutron Fast neutron Solid state detector Scintillatore Li-glass Secindary particles The use of coincidence produces a lowering in the efficiency with increasing neutron energy (E n  Q-value of the reaction)

73 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 72 Some characteristics NE902NE905NE908NE912 D (gr/cm 3 ) n T fusione (°C)1200 max (nm) Light emission (rel.antracene) 22-34%20-30%20%25% Decay time (ns) Arr. 6 Li 95% Activity  min   E/E %15-28 %20-30 %

74 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 73 3 He proportional counters Peak due to (n,p) reactions induced by fast incident neutrons Elastic scettering continuum With a peak at 0.75 E n (cinematica) e Peak at the Q-value dovuto a interazioni di neutroni moderati

75 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 74 Proton Recoil Telescope Coincidence unit n p Hydrogenated radiatior  Detector 1 Detector 2 Efficiency is low: small radiator thickness small detectors for angle determination

76 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 75 Activation threshold technique E (MeV) AA 10 A target of a proper material is irradiated with a neutron beam and after an irradiation time  t is removed from the beam and the induced activity is measured

77 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 76 Some examples Material ReactionAb.Is.(%)H.L EE Treshold (MeV) F 19 F(n,2n) 18 F min Mg 24 Mg(n,p) 24 Na h Al 27 Al(n,  ) 24 Na h Fe 56 Fe(n,p) 56 Mn h Co 59 Co(n,  ) 56 Mn h Ni 58 Ni(n,2n) 57 Ni h Cu 65 Cu(n,2n) 64 Cu min Zn 64 Zn(n,p) 64 Cu h In 115 In(n,n’) 126 In h I 127 I(n,2n) 126 I d

78 Marco Tardocchi Xth International school of neutron scattering F. P. Ricci 77 Micro-Strip Gas Counter Electrodes printed lithographically,producing small features. Implies – High spatial resolution. – High field gradients. – Charge localization. – Fast recovery.


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