Balaram Dey Variable Energy Cyclotron Centre 1/AF Bidhan Nagar, - PowerPoint PPT Presentation

Giant Dipole Resonance with at very low temperatures and the critical behavior Balaram Dey Variable Energy Cyclotron Centre 1/AF Bidhan Nagar, Kolkata-700064, INDIA Supervisor : Prof Sudhee Ranjan Banerjee COMEX5-2015 16 -09-2015

Giant Resonance : Collective modes of vibration of nucleus Giant Dipole Resonance E Γ 2 2     GDR F E    ( Ε Ε ) E Γ 2 2 2 2 2   GDR GDR 0.25 GDR Strength Fn (a.u.) 0.20 E GDR 0.15  GDR 0.10 0.05 0.00 0 5 10 15 20 25 30 E  (MeV) Centroid Energy : Inversely proportional to the linear dimension of the nucleus. Strength Function: Gives an idea about the nuclear shape degrees of freedom. Resonance Width : Related to the damping mechanism of the collective motion.

Evolution of GDR width as a function of temperature Experimental observation Mostly investigated Nucleus  120 Sn Experimental systematic shows  GDR width increases monotonically with temperatures (typically 6- 10 MeV for change in ‘T’ of 1.5 -2.5 MeV) GDR Width (MeV) (b) 120 Sn PLB 709 (2012) 9 10 5 J = 15 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 Temperature (MeV) Why GDR width increases with increase in temperature ??? Thermal Shape Fluctuation Model : ( ∆β vs T)

5 GDR Width (MeV) (b) 120 Sn GDR width (MeV) 10 TSFM J = 15 5 2 3 1 0 Temperature (MeV) !! At low temperatures (T<1.5 MeV), the picture is not clear !! Critical Temperature Fluctuation Model : Including an important physics point GDR vibration itself produce a quadrupole moment causing the nuclear shape to fluctuate even at T = 0 MeV ( GDR vibration induced intrinsic fluctuation) : β GDR 5 GDR Width (MeV) Critical behavior : GDR width (MeV) (b) 120 Sn 10  At low T : β GDR > ∆β  β GDR  Independent of T  ∆β  Increases with temperature J = 15 5  Competition between β GDR and ∆β CTFM 3 2 0 1 The effect of thermal fluctuation on GDR width will appear only when it becomes greater than the intrinsic fluctuation . Temperature (MeV)

My WORK:  Study of GDR width at very low temperatures (T < 1.5 MeV).  Verify the critical behavior : The number of GDR width measurements at low T < 1 MeV are inadequate to conclude that GDR width remains same at below the critical point.  Mass dependence of the critical behavior. We probed A=100 mass region at very low temperature (T ~ 0.8 to 1.5 MeV ) to understand exact nature of the damping mechanism inside the nucleus.

Experimental Details LAMBDA Projectile : 4 He Target : 93 Nb E lab : 28, 35, 42, 50 MeV 4 He + 93 Nb  97 Tc * Liquid Scintillator Multiplicity Filter E* : 29.3, 36.0, 43.0, 50.4 MeV J = 10 – 20 h High energy gamma photons are the main tools to study GDR characteristics  Need a detector system with high detection efficiency and very good time resolution.

Experimental Setup Electronics Setup

Schematic Electronics Circuit Diagram for LAMBDA and Multiplicity 5 m E long (1/10) F.A (Attenuator) QDC 1 ARRAY DELAY 100 ns F.A 2 s 20 ns CFD 1 5 m QDC 2 E short (9/10) F.A CFD 2 CFD 3 QDC 3 GDG Long gate 2 s LED 1 FAN IN (Logic) 20 ns LED 2 40 QDC 4 ns LED 3 DISC DISC CFD 4 OR Short gate AND 1  50 ns MULT DISC FAN IN TOP 70 (Logic) ns 5 m CFD 5 OR FAN IN  (Logic) 100 ns DISC FAN IN CFD 6 CFD 7 OR (Logic)  150 ns BOTT MULT DISC TDC 1 5 m 70 GDG OR ns AND 2 20 ns  FAN IN (Linear) TDC 2 100 ns FOLD gic) (Lo FA IN N VETO

Schematic Electronics Circuit Diagram for BC501A

TOF Spectrum PSD spectrum 1200 Time-of-flight spectrum 1000 800 Prompt  - cut Counts 600 400 200 500 1000 1500 2000 2500 3000 3500 Channel Number cluster summing Cosmic rejection

Extraction of GDR parameters Experimental data compared with a 10 5 theoretical model (CASCADE) to extract the GDR parameter 10 4 Yield /(0.5 MeV) 10 3 !! The following steps are essential !! 10 2  Detector Response Function 10 1  Measuring angular momentum distribution 10 0  Measuring Nuclear Level Density 5 10 15 20 25 E  (MeV) parameter

(1) Detector simulation studies using GEANT4 Detector response function must be folded with CASCADE calculation. Only after that it can be compared with experimental spectrum NIM A 582 (2007) 603

(2) Mapping of experimental Fold to Angular Momentum space with a very realistic technique 10 4 30 Geant4 Simulation 25 10 3 Counts x 103 20 Counts 10 2 15 10 10 1 5 10 0 0 5 10 15 20 25 30 2 3 4 5 6 7 8 9 Angular Momentum ( ) Fold Very essential  To determine average angular momentum  To determine average rotational energy  To construct initial population matrix for CASCADE calculation Incident distribution :    2 1 M       P M     1 exp M M m  max J =    C NIM A624 (2010) 148

(3) Nuclear level density parameter from neutron evaporation spectrum Crucial input for CASCADE Calculations & important for the proper estimation of nuclear temperature Neutron detector (BC501A) is generally used to measure the neutron energy spectrum by TOF technique

High energy gamma spectra along with CASCADE calculation 10 7 Elab = 28 MeV Elab = 35 MeV 10 6 10 5 F=2 10 4 F=3 10 3 F > 2 F>4 10 2 Yield / 0.5 MeV 10 1 10 0 10 8 Elab = 50 MeV Elab = 42 MeV 10 7 10 6 F=2 F=2 10 5 F=3 F=3 10 4 F>4 F>4 10 3 10 2 10 1 5 10 15 20 25 10 15 20 25 Energy (MeV)

Final GDR spectra along with CASCADE calculation

Results and Discussion 12 First exp data point in A ~ 100 (a) GDR width (MeV) 10 T c = 1.08 MeV 8 TSFM 6 CTFM 4 GDR width (MeV) (b) 10 8 6 PDM 4 0.0 0.5 1.0 1.5 2.0 2.5 Temperature (MeV) GDR induced intrinsic fluctuation could play a decisive role in describing the First experimental data at increase of GDR width as a function of T. below and above the critical temperature Intrinsic fluctuation due to GDR vibration should be incorporated in TSFM (macroscopically) to explain the behavior of GDR width at low T. Balaram Dey et al., Physics Letter B 731 (2014) 92 PDM : PRC 86 (2012) 044333

Summary and conclusion  A systematic study of the Giant Dipole Resonance width at very low temperature (T = 0.8 – 1.5 MeV) in A ~ 100 mass region.  GDR widths have been compared with different theoretical calculations (TSFM, CTFM and PDM).  TSFM fails to explain the experimental data where as CTFM and PDM calculation nicely matches with the experimental data.  GDR induced intrinsic fluctuation plays an important role in describing the evolution GDR width as a function of temperature  First experimental data at below and above the critical temperature.  Microscopic PDM (with pairing fluctuation) also explain the data very well.  It would also be interesting if the pairing fluctuation can be included in the TSFM calculation.

THANKS GDR group at VECC, kolkata, India

1200 500 140 241Am - 9Be Cosmic 22Na 23.1 MeV 120 1000 400 0.511 MeV 4.43 MeV 100 800 300 Counts 80 600 60 200 400 40 1.274 MeV 100 200 20 0 0 0 160 200 240 280 100 120 140 160 180 200 200 400 600 800 1000 0.16  GDR = 0.04 + 4.13/A Channel Number Channel Number Channel Number 40 Ca 0.12  GDR 97 Tc 0.08 28 80 Zr 120 Sn 24 0.04 208 Pb 20 Energy (MeV) 0.00 0.01 0.02 0.03 1/A 16 0.15 12 8  GDR 0.10  4 0.05 0 0.00 100 200 300 400 500 600 700 0.0 0.5 1.0 1.5 2.0 2.5 Channel Number Temperature (MeV)

Detector properties What is the advantage of BaF2 detector over NaI • The time resolution of detector? 35cm BaF2 detector = 960 ps • BaF2 are non -hygroscopic where as NaI is highly 5cm BaF2 detector = 460 ps hygroscopic. • The energy resolution of • NaI detectors cannot be used 35cm BaF2 detector = 16/ √E MeV in modular(array) from since 1.4 thus 20% at 0.662 MeV T c = 0.7 + 37.5/A 63 Cu they have to be T c (MeV) 5cm BaF2 detector = 12% at 0.662 kept inside a air tight 1.2 MeV container. 120 Sn • The intrinsic efficiency of single • Energy resolution is 1.0 comparable. 35cm BaF2 detector = 95 % at 208 Pb 0.662 MeV, 93 % 10 MeV. • BaF2(600 ps) have better 0.8 timing resolution than NaI 5cm BaF2 detector = 80 % at 0.662 (250ns) MeV, 73% at 1 MeV. • Density of BaF2(4.88 g/cc) is • The photopeak efficiency of 0.005 0.010 0.015 greater than NaI(3.67 g/cc) cluster summing technique(3x3) 1/A hence for efficient 35cm BaF2 detector = ~ 50 % from for high energy detection. energy range 10MeV • BaF2 has high Z (56) than • The photopeak efficiency of NaI(53) which is required for cluster summing technique(7x7) high energy gamma 35cm BaF2 detector = ~ 70 % from detection. Also BaF2 has low energy range 10 MeV capture cross section for thermal neutrons due to the neutron magic number