Application of CLTDs* for the investigation of Z-yield distributions - PowerPoint PPT Presentation

Application of CLTDs* for the investigation of Z-yield distributions of fission fragments NUSTAR Annual Meeting 2018, GSI (Germany) 26 th Feb – 2 nd Mar 2018 Talk by: Santwana Dubey (PhD) PhD Supervisor – Prof. Dr. Peter Egelhof Institute of Physics, Johannes Gutenberg University Mainz GSI Helmholtz Center for Heavy Ion Research Darmstadt *CLTDs – Calorimetric Low Temperature Detectors

Motivation motivation for studying fission fragment yields:  Various nuclear energy applications  better understanding of the nuclear fission process  data relevant for reactor physics Application of CLTDs for fission studies! Thermal neutron induced fission reactions neutrons neutron target nucleus fission fragments

Outline  Calorimetric Low Temperature Detectors: • Concept • Advantages • Design  Nuclear Charge Distribution Measurements: • Experimental Set-up • Preliminary results:  First time direct Z-yield determination for heavy fragment masses - Using passive absorber method  Proton odd-even effect in masses approaching symmetric fission for 239 Pu & 241 Pu - - Important for nuclear model description near scission  Precise 92 Rb & 96 Y yields for 235 U, 239 Pu, 241 Pu (n th , f) - - Important for reactor antineutrino anomaly studies 3

CLTDs: Introduction Calorimetric Detector → detec�on of heat Idea: detection of particle energy independent of ionization processes ° particle thermometer phonons Interaction of ions with matter: Potential Advantages: • Primary: • energy resolution Ioniza�on → ioniza�on detectors • energy linearity • Secondary: • detection threshold thermaliza�on → calorimetric detectors (conversion of energy to heat • variety of detector materials  detection of thermal phonons) 4

CLTDs: Advantages Si Detector CLTDs  E(FWHM)=  E(FWHM) = Counts/bin Counts/bin 1k 300 2808 keV 91 keV Energy Resolution ( 238 U @ 20.7MeV) 0 0 15 20 25 15 20 25 Energy [MeV] Energy [MeV] Pulse height [ADC channels] Pulse height [ADC channels] 4 He 13 C 6k 2k 13 C Pulse Height 197 Au 197 Au 238 U Defect 238 U ( 13 C, 197 Au, 238 U ) 3k 1k C, Au, U 0 0 0 30 60 0 10 20 Energy [MeV] Energy [MeV] Losses at energy conversion: More complete energy detection Due to dead layer, →Be�er resolu�on and linearity charge recombination Plots from: Kraft-Bermuth et al., Rev. Sci. Instrum. 80, 103304 (2009) 5

CLTDs: Detection Principle Absorber thermal signal: Incident particle temperature Thermometer with energy E T  T +  T t 1 t 2 ΔT time Heat sink 1 – 10  s Rise-Time Absorber: 100  s – 10 ms Decay-Time (C/k) Particle energy is converted into heat, E  ΔT  c m  High sensitivity for small specific heat c and small mass  c ̴ (T 3 /Ɵ D 3 ) from Debye law (for insulators, superconductors)  Operation at Low Temperatures 6

CLTDs: Detection Principle Absorber 150 normal state Incident particle Thermometer with energy E 100 T  T +  T R [k  ] operation temperature 50 transition region: super- dR/dT  const conducting 0 Heat sink 1.60 1.62 1.64 1.66 T [K] Thermometer: Transition Edge sensors are used. • Resistance (superconductor) biased with constant current. • ∆T→∆R(T)→∆V voltage signal is detected. Detector temperature stabilized in phase transition region  high dR/dT. • 7

CLTDs: Current Detector Design Sapphire Sapphire Thermometer 3 x 3 x 0.43 mm 3 Transition Edge Sensor absorber absorber Incident particle 10 nm thick meander shaped Al-layer Heater strip T  T +  T 25μm Au/Cr strip R (T) Operational Temperature: 1.5 – 1.6 K T ~ 1 K Heat sink Active area: 15×15mm 2 (25 pixels) S. Kraft-Bermuth et al., Rev. Sci. Instrum. 80 , 2009 A.Echler et al., J. Low Temp. Phys. 167 , 2012, 8

CLTDs: Current Detector Design windowless 4 He bath cryostat Sapphire Sapphire Thermometer absorber absorber Incident particle T  T +  T Operational Temperature: 1.5 – 1.6 K T ~ 1 K Heat sink 9

Z- distributions of fission fragments (n th ,f) light fragment group Methods for Z- separation: K.H. Schmidt et al.  Radio chemistry   -spectroscopy  restricted to particular nuclides  Passive-absorber method symmetry U. Quade et al., Nucl. Phys. A487 (1988) 1 region best Z-resolution with: • Parylene C absorbers • ionization chamber  restricted to light fragment group heavy fragment group absorber  E(Z) A = const E(Z) = E 0 -  E(Z) E 0 (Z)= const energy fission fragments detector Z 2 Z 1 energy residual energy 10

Z- distributions of fission fragments (n th ,f) light fragment group Methods for Z- separation: K.H. Schmidt et al.  Radio chemistry   -spectroscopy  restricted to particular nuclides  Passive-absorber method symmetry U. Quade et al., Nucl. Phys. A487 (1988) 1 region best Z-resolution with: • Parylene C absorbers • ionization chamber  restricted to light fragment group heavy fragment group Preliminary results from CLTDs using SiN absorber foils: SiN foils:  First time possible to measure in the heavy mass • Homogeneity region. • High thermal stability  New measurements in the light mass region • Extreme hardness approaching symmetric fission for 239 P(n th ,f) and • Chemical inertness 241 Pu(n th ,f).  Precise yield determination of 92 Rb, 96 Y. 11

Investigation of Z- distributions of fission fragments (n th ,f) Experimental Set-up LOHENGRIN mass separator High flux neutron source Electrostatic deflector Target Dipole magnet cryostat Filters a specific A, E and Q but not Z. CLTD array SiN absorber foil stacks 10×16mm Manipulator for changing foil stacks 12

Z-Resolution: Optimum thickness of SiN residual energy spectra Systematic studies: A = 89, E= 94MeV Z-Resolution vs SiN foil 1  m 4  m 300 36 Kr 200 thickness 200 35 Br 100 100 37 Rb 0 0 21000 22000 12000 300 5  m 6µm 400 36 Kr 36 Kr 300 200 counts 50 200 35 Br 35 Br 100 100 37 Rb 37 Rb 40 0 0  10000 11000 7000 8000 300 7µm 8  m 30 36 Kr 36 Kr 100 200 A=96, Z=40 A=89, Z=35 35 Br 20 100 35 Br 37 Rb 37 Rb 0 1 2 3 4 5 6 7 8 9 0 0 foil thickness [µm] 5000 6000 3000 4000 Residual energy (a.u.) 13

Procedure for determining Z-yields  fit of spectrum 241 Pu 150 13k 43 Tc Z=39 A=108 - relative Z-Yield peak position Z=41 Counts/bin 100 44 Ru - line shape from Tandem Z=43 42 Mo 241 Pu 50 12k experiment (for heavy masses) 45 Rh E=100MeV  Z-Identification 0 30 35 90 100 110 mass  take into account Residual Energy (MeV) 15 A = 92 - energy dependence A = 92 0.15 E = 94MeV Q=20 isotopic yield [a.u.] isotopic yield [a.u.] - electronic charge state 10 0.10 Sr Rb Sr dependence (ns-isomers) Kr Rb 5 0.05 Kr  absolute normalization 0 0.00 - target burnup 15 20 25 30 80 90 100 110 Energy (MeV) ionic charge state, Q 100 Burn-up Exponential fit for Z-Yield of one mass: Burn-up 75  upto 300 spectra to be analyzed 235 U 50 0 5 10 15 14 Time (Days)

Resolution Quality of Z-Separation Light mass region A=89 Mass 7  m SiN foils E in =94MeV 80 90 100 110 120 130 235U(nth,f) 60 36 Kr 35 Br 37 Rb Symmetry region 40 A=108 6  m SiN foils 43 Tc Ein=100MeV Z/  Z counts 241 Pu(n th ,f) 44 Ru 42 Mo 20 CLTD + SiN (ILL 2016, E = 94-100 MeV & 80 MeV for Z=52) 45 Rh CLTD + SiN (MLL 2016, E/A = 80/127 MeV/u) Heavy mass region ---------------------------------------------------------------------------------- A. Djebara et al. Nuclear Physics A496 (1989) 346 IC + Parylene C (Djebara et al., E = 101-106 MeV) A=130 U. Quade et al., Nucl. Phys. A487 (1988) 1 IC + Parylene C (Quade, E = 98 MeV) 6  m SiN foils 0 E in =88MeV 32 36 40 44 48 52 51 Sb 239 Pu(n th ,f) Nuclear Charge Z 50 Sn CLTD+SiN: good resolution & linearity →Possibility to measure in symmetry & heavy 52 Te Residual energy (a.u.) mass region 15

Heavy mass analysis First direct Z-yield measurements in Heavy mass region:  Standard method for unresolved peaks: Constrained fits with - good statistics (≈10000 counts) - good knowledge of response function  With same set-up, measurements at similar mass and energy at MLL tandem tandem accelerator, allow to estimate the response function for the residual energy spectra.  Stable fits for measured distributions. 600 A = 129 A = 130 A = 128 E = 88MeV E = 88MeV 400 E = 88MeV 800 6 SiN foils 6 SiN foils 6 SiN foils Z=50 Z=50 400 Z=51 Counts Counts Counts Z=50 200 400 200 Z=51 Z=49 Z=49 Z=51 Z=52 0 0 0 5000 5500 5000 5500 5000 5500 Residual Energy (a.u.) Residual Energy (a.u.) Residual Energy (a.u.) Preliminary Results 16

Heavy masses Z-yields Analysis width asymmetry 150 asymmetric parameter width parameter 100 125 100 50 75 0 128 130 132 134 136 138 128 130 132 134 136 138 Mass Mass separation Z-Identification d1 52 Z=49 4750 51 50 d2 400 Peak Position (a.u.) 53 separation 54 4500 55 200 xc1 xc2 4250 xc3 0 128 130 132 134 136 138 128 130 132 134 136 138 Mass Mass 17