Dynamics of incomplete fusion in reactions induced by heavy ions Manoj Kumar Sharma Department of Physics Aligarh Muslim University Aligarh HQP_2008_Dubna

1.Introduction 2.Scientific Motivation 3.Experimental details 4.Analysis of the data 5.Conclusions HQP_2008_Dubna

a + X  Y + b A nuclear reaction takes place, when an incident ion of sufficient energy (above the Coulomb barrier) interacts with a target nucleus. Where, a-projectile, X-target Y-residual nucleus, b-emitted particle  Incident ion Target nucleus Residual nucleus Ejectile + Introduction HQP_2008_Dubna

Grazing collision Incomplete fusion and deep inelastic collision Elastic scattering Direct reactions Peripheral collision Complete fusion Distant collision b b  Impact parameter A pictorial representation of heavy ion reactions Rutherford Scattering HQP_2008_Dubna

In heavy ion reactions, at moderate excitation energies, the dominant processes are; Complete Fusion (CF) Incomplete Fusion (ICF) Pre-equilibrium (PE) emission HQP_2008_Dubna

Complete Fusion (CF) Projectile is completely fused with the target nucleus, leading to the formation of an excited composite system that may decay by the emission of n, p,  etc., after attaining statistical equilibrium. 65 Tb Ta O 16 + Ta 174 Hf 174 Lu 171 n p  Target Composite system Projectile HQP_2008_Dubna

Incomplete Fusion (ICF) Only a part of the projectile fuses with the target nucleus and the rest of it is going into the beam direction with almost the same velocity as that of incident ion beam. 65 Tb Lu Lu 170 Yb 170 Er 167 n p  Target Composite system Residues Projectile   6 C O= 12 C+  HQP_2008_Dubna

Some of the important features of ICF……  Higher measured cross-sections than predicted by statistical models, M. K. Sharma et. at., Phys. Rev. C70 (2004) HQP_2008_Dubna

 Fractional momentum transfer, in which the residue formed as a result of ICF of projectile travels to a lower range in a given medium. Incomplete Momentum Transfer M. K. Sharma et. at., Phys. Rev. C70, (2004) HQP_2008_Dubna

ICF reactions have attracted attention……..  The threshold for ICF is not well established.  Early studies show occurrence of ICF at higher energies above 10 MeV/nucleon  Recent experimental studies have shown that ICF starts competing with CF even at energies around 5-7 MeV/nucleon i.e, just above the Coulomb barrier. HQP_2008_Dubna

Why? Relative contributions of CF and ICF are not well known. The dynamics of ICF is not well understood at energies around 5-7 MeV/A. Energy dependence of CF and ICF contributions is not well understood. No satisfactory theory for ICF is available. Limited studies are available at <10 MeV/A. HQP_2008_Dubna

In order to answer some of these, measurements of…….. Excitation functions covering a large range of energy, Recoil range distributions at several energies, Angular distributions of the residues, Spin distribution of the residues HQP_2008_Dubna

 12 C+ 27 Al  39 K, Coulomb barrier  24 MeV  Beam energy (  42 to 82 MeV)  16 O+ 27 Al  43 Sc, Coulomb barrier  27 MeV  Beam energy (  55 to 95 MeV)  14 N+ 128 Te  142 Pr, Coulomb barrier  58 MeV  Beam energy (  64 to 90 MeV)  16 O+ 130 Te  146 Nd, Coulomb barrier  53 MeV  Beam energy (  42 to 82 MeV)  16 O+ 103 Rh  119 I, Coulomb barrier  48 MeV  Beam energy (  48 to 90 MeV)  16 O+ 159 Tb  175 Ta, Coulomb barrier  66 MeV  Beam energy (  70 to 95 MeV)  16 O+ 169 Tm  185 Ir, Coulomb barrier  68 MeV  Beam energy (  70 to 95 MeV) In the present work, Excitation functions (EFs) for the following systems have been studied; HQP_2008_Dubna

27 Al( 12 C,  n) 34 Cl, 27 Al( 12 C,2  3p) 28 Mg, 27 Al( 12 C,3  2pn) 24 Na, 27 Al( 16 O,2  n) 34 Cl, 27 Al( 16 O,3  3p) 28 Mg, 27 Al( 16 O,3  3pn) 27 Mg, 27 Al( 16 O,4  2pn) 24 Na, 27 Al( 16 O,4  3p) 24 Ne, 128 Te( 16 O,4n) 138 Pr, 128 Te( 16 O,5n) 137 Pr, 128 Te( 16 O,p4n) 137 Ce, 128 Te( 16 O,  5n) 133 La, 128 Te( 16 O,  6n) 132 La, 128 Te( 16 O,  2pn) 135 La, 128 Te( 16 O, 2  2pn) 131 I, 128 Te( 16 O, 3  ) 130 I, 103 Rh( 16 O,pn) 117 Te, 103 Rh( 16 O,p2n) 116 Te, 103 Rh( 16 O,p3n) 115 Te, 103 Rh( 16 O,p4n) 114 Te, 103 Rh( 16 O,2n) 117 Sb, 103 Rh( 16 O,2pn) 116 Sb, 103 Rh( 16 O,2p2n) 115 Sb, 103 Rh( 16 O,  p4n) 110 Sn, 103 Rh( 16 O,2  ) 111 In, 103 Rh( 16 O,2  n) 110 In, 103 Rh( 16 O,2  2n) 109 In, 103 Rh( 16 O,2  3n) 108 In, 103 Rh( 16 O,3  n) 106 Ag, 103 Rh( 16 O,3  3n) 104 Ag, 103 Rh( 16 O,3  4n) 103 Ag, 159 Tb( 16 O,3n) 172 Ta, 159 Tb( 16 O,4n) 171 Ta, 159 Tb( 16 O,5n) 170 Ta, 159 Tb( 16 O,p3n) 171 Lu, 159 Tb( 16 O,p4n) 170 Lu, 159 Tb( 16 O,  ) 172 Hf, 159 Tb( 16 O,  n) 170 Hf, 159 Tb( 16 O,  2n) 169 Hf, 159 Tb( 16 O,  3n) 168 Hf, 159 Tb( 16 O,  4n) 167 Hf, 159 Tb( 16 O,  p3n) 167 Lu, 159 Tb( 16 O,2  n) 166 Tm, 159 Tb( 16 O,2  2n) 165 Tm, 169 Tm( 16 O,3n) 182 Ir, 169 Tm( 16 O,4n) 181 Ir, 169 Tm( 16 O,p2n) 182 Os, 169 Tm( 16 O,p3n) 181 Os, 169 Tm( 16 O,  ) 181 Re, 169 Tm( 16 O,  2n) 179 Re, 169 Tm( 16 O,  3n) 178 Re, 169 Tm( 16 O,  4n) 177 Re, 169 Tm( 16 O,  p3n) 177 W, 169 Tm( 16 O,  2pn) 178 Ta, 169 Tm( 16 O,  3pn) 177 Hf 169 Tm( 16 O,2  p3n) 172 Hf, 169 Tm( 16 O,3  n) 172 Lu HQP_2008_Dubna

The experiments have been carried out using the Pelletron accelerator facility of the Inter University Accelerator Facilities (IUAC) (Formerly known as NSC), New Delhi, INDIA. Samples preparation: 27 Al (Rolling Method) 103 Rh (Rolling Method) 128,130 Te (Vacuum evaporation) 159 Tb (Rolling Method) 169 Tm (Vacuum evaporation) Methodology adopted HQP_2008_Dubna

Thickness measurements The thickness of each target was determined by the  -transmission method. 27 Al  2.00 mg/cm Rh  1.80 mg/cm Te (66%)  0.90 mg/cm Te (68%)  1.00 mg/cm Tb  1.80 mg/cm Tm  0.50 mg/cm 2 HQP_2008_Dubna

Incident beam Al-Catcher foil/ Energy degreder Target A typical stack arrangement for the measurement of EFs HQP_2008_Dubna

Irradiation The irradiations were carried out in the General Purpose Scattering Chamber (GPSC) having in-vacuum transfer facility. A typical experimental set up for the measurement of EFs Incident beam Target Catcher Faraday cup HQP_2008_Dubna

General Purpose Scattering Chamber ITF HQP_2008_Dubna

Inside view of GPSC Lower arm Upper arm HQP_2008_Dubna

 The delay time between stop the irradiation and beginning of the counting may be minimized.  Target may be replaced without disturbing the vacuum inside the chamber. Invacuum Transfer Facility Pirani gauge Valve-I Valve-II Port for rotary pump HQP_2008_Dubna

INCIDENT BEAMINCIDENT BEAM Post Irradiation Analysis The samples were taken out from the scattering chamber and activities induced in the samples were analyzed using HPGe detector. The detector was pre-calibrated using various standard sources i.e., 22 Na, 60 Co, 133 Ba, 137 Cs, 152 Eu etc., HQP_2008_Dubna

A typical geometry dependent efficiency curves for various source detector distances as a function of  - ray energy is shown. M. K. Sharma et. al., Nucl. Phys. A 776, 2006 (84) HQP_2008_Dubna

The observed  -rays spectrum for 16 O+ 27 Al and 16 O+ 159 Tb systems M. K. Sharma et al., Phys. Rev. C 70 (2004) M. K. Sharma et. al., Phys. Rev. C 75 (2007) HQP_2008_Dubna

M. K. Sharma et al., Nucl. Phys. A776 (2006)84 The observed  -rays spectrum for 16 O+ 159 Tb system at 95 MeV HQP_2008_Dubna

The intensity of these  -rays are used to measure the reaction cross-section using following formulation. where, A is the total observed counts during the accumulation time t 3 of the induced activity of decay constant, N o the number of target nuclei irradiated for time t 1 with a particle beam of flux , t 2 the time lapse between the stop of irradiation and the start of counting,  the branching ratio of the characteristic  -ray and G  the geometry dependent efficiency of the detector. The factor [1-exp ( t 1 )] takes care of the decay of evaporation residue during the irradiation and is typically known as the saturation correction. HQP_2008_Dubna

Analysis of the excitation functions has been done using three different computer codes, CASCADEPACE2ALICE-91 Compound nucleus Compound nucleus as well as PE emission Hauser-Feshbach Theory Monte Carlo Simulations Weisskopf-Ewing model for CN calculations, Hybrid model for PE-emission. None of these codes take in account ICF contribution Analysis HQP_2008_Dubna

M. K. Sharma et al., Phys. Rev. C 70 (2004) Experimentally measured and theoretically calculated EFs HQP_2008_Dubna

The residues 171 Hf which may be formed via the reaction 159 Tb( 16 O,p3n) and may also be formed by the  + decay of higher charge isobar precursor 171 Ta produced via the reaction 159 Tb( 16 O,4n). As such, the measured activity of residues 171 Hf has contribution from precursor decay also O 159 Tb 175 Ta 171 Ta 171 Hf ++ 4n p3n M. K. Sharma et. al., Nucl. Phys. A 776 (2006) 86 HQP_2008_Dubna

Experimentally measured and theoretically calculated EFs HQP_2008_Dubna

Experimentally measured and theoretically calculated EFs M. K. Sharma et. al., Nucl. Phys. A 776 (2006)83 HQP_2008_Dubna

Experimentally measured and theoretically calculated EFs At higher energies, the calculation of EFs done with code ALICE-91 gives significant contribution from PE-emission also. M. K. Sharma et. al., Nucl. Phys. A 776 (2006) 83 HQP_2008_Dubna

Experimentally measured and theoretically calculated EFs HQP_2008_Dubna

Experimentally measured and theoretically calculated EFs HQP_2008_Dubna

Experimentally measured and theoretically calculated EFs M. K. Sharma et. al., Nucl. Phys. A 776 (2006)83 HQP_2008_Dubna

Experimentally measured EFs M. K. Sharma et. al., Nucl. Phys. A 776 (2006)83 Phys. Rev C 77 (2008) HQP_2008_Dubna

 From the analysis of the excitation functions, enhancement of the cross-sections in comparison to theoretical calculations done using statistical model codes, may be attributed to ICF processes.  Following reactions have been found to have significant contribution from ICF 27 Al( 16 O,2  n) 34 Cl, 27 Al( 16 O,3  3p) 28 Mg, 27 Al( 16 O,3  3pn) 27 Mg, 27 Al( 16 O,4  2pn) 24 Na, 27 Al( 16 O,4  3p) 24 Ne, 128 Te( 16 O,  5n) 133 La, 128 Te( 16 O,  6n) 132 La, 128 Te( 16 O,  2pn) 135 La, 128 Te( 16 O, 2  2pn) 131 I, 128 Te( 16 O, 3  ) 130 I, 103 Rh( 16 O,2p2n) 115 Sb, 103 Rh( 16 O,  p4n) 110 Sn, 103 Rh( 16 O,2  ) 111 In, 103 Rh( 16 O,2  n) 110 In, 103 Rh( 16 O,2  2n) 109 In, 103 Rh( 16 O,2  3n) 108 In, 103 Rh( 16 O,3  n) 106 Ag, 103 Rh( 16 O,3  3n) 104 Ag, 103 Rh( 16 O,3  4n) 103 Ag, 159 Tb( 16 O,  ) 172 Hf, 159 Tb( 16 O,  n) 170 Hf, 159 Tb( 16 O,  2n) 169 Hf, 159 Tb( 16 O,  3n) 168 Hf, 159 Tb( 16 O,  4n) 167 Hf, 159 Tb( 16 O,  p3n) 167 Lu, 159 Tb( 16 O,2  n) 166 Tm, 159 Tb( 16 O,2  2n) 165 Tm, 169 Tm( 16 O,  ) 181 Re, 169 Tm( 16 O,  2n) 179 Re, 169 Tm( 16 O,  3n) 178 Re, 169 Tm( 16 O,  4n) 177 Re, 169 Tm( 16 O,  p3n) 177 W, 169 Tm( 16 O,  2pn) 178 Ta, 169 Tm( 16 O,  3pn) 177 Hf 169 Tm( 16 O,2  p3n) 172 Hf, 169 Tm( 16 O,3  n) 172 Lu HQP_2008_Dubna

F ICF increases with increase in beam energy The Contribution of ICF has been deduced by subtracting the cross-section of CF from total cross-sections. Phys. Rev C 77 (2008) HQP_2008_Dubna

Mass asymmetry dependence of ICF fraction ICF is observed in competition with CF in energy range presently studied. In present systems ICF is found to increase with beam energy. S CF is found to be large in more mass asymmetric systems as compared to mass symmetric system. It may however, be pointed out that the results shown here may not be conclusive and more experimental data for a large number of systems may be required to get detailed information about the suppression of CF over ICF. HQP_2008_Dubna

Recoil Range Distributions The measurement of RRD is based on the linear momentum transfer of the projectile to the target nucleus. In CF reactions, the linear momentum is completely transferred to the target nucleus, thus the residues formed by CF may be trapped at a larger distance in the stopping medium. While in case of ICF reactions, partial transfer of projectile momentum takes place thus the residues may be trapped at a shorter distance in the stopping medium. HQP_2008_Dubna

Thin Al -catcher foils Experimental Set-up for Recoil Range Distribution measurements Target foil Incident Beam Recoiling Nucleus HQP_2008_Dubna

In the present work, following systems have been used to measure RRD of the residues.  16 O Tb  175 Ta (  92 MeV )  16 O Tm  185 Ir (  76, 81 & 87 MeV ) HQP_2008_Dubna

M. K. Sharma et. al., Nucl. Phys. A 776 (2006) 84 Experimental measured Recoil Range Distribution for 16 O MeV HQP_2008_Dubna

M. K. Sharma et. al., Nucl. Phys. A 776 (2006) 84 Experimental measured Recoil Range Distribution HQP_2008_Dubna

Experimental measured Recoil Range Distribution for 16 O MeV HQP_2008_Dubna

The experimentally measured RRD has been fitted with Gaussian peaks. The areas under the two peaks have been computed. The relative contributions of the CF and ICF processes are obtained by dividing the area of the individual peak by the total area. 16 O+ 169 Tm  185 Ir *  181 Re+2p2n (CF  35  5%) 12 C Tm  181 Re * +  +  (ICF  65  5%) M. K. Sharma et. al., Phys. Rev. C 70 (2004) HQP_2008_Dubna

16 O+ 169 Tm  185 Ir *  176 Hf+2  pn CF  25  5% 12 C Tm  181 Re *  176 Hf +  pn ICF of 12 C  45  5% 8 Be Tm  178 Ta*  176 Hf + pn ICF of 8 Be  30  5% Manoj Kumar Sharma et. al., Phys. Rev. C70 (2004) HQP_2008_Dubna

ICF of 8 Be  74  5% ICF of   26  5% M. K. Sharma et. al., Phys. Rev. C70 (2004) HQP_2008_Dubna

ICF of 8 Be  28  5% ICF of   72  5% M. K. Sharma et. al., Phys. Rev. C70 (2004) HQP_2008_Dubna

M. K. Sharma et. al., Nucl. Phys. A 776 (2006) 84 HQP_2008_Dubna

The experimentally measured RRD has been fitted with Gaussian peaks. The areas under the two peaks have been computed. The relative contributions of the CF and ICF processes are obtained by dividing the area of the individual peak by the total area. 30 % CF 70 % ICF M. K. Sharma et. al., Nucl. Phys. A 776 (2006) 84 HQP_2008_Dubna

The experimentally measured RRD 45 % CF 27% ICF 28% ICF M. K. Sharma et. al., Nucl. Phys. A 776 (2006) 84 HQP_2008_Dubna

The experimentally measured RRD 15 % ICF 49 % ICF 36 % ICF M. K. Sharma et. al., Nucl. Phys. A 776 (2006) 84 HQP_2008_Dubna

Angular distribution of residues HQP_2008_Dubna

Stack of annular Al-catchers with concentric holes Experimental set up for the measurement of Angular distribution of residues 169 Tm Target (Thickness   g/cm 2 ) 16 O 7+  6.5cm Aluminium backing (thickness  1.1mg/cm 2 ) 1.8 cm HQP_2008_Dubna

The observed  -rays spectrum for 16 O+ 27 Al system at 85 MeV for angular distribution of residues M. K. Sharma et. al., Phys. Rev. C 75 (2007) HQP_2008_Dubna

Measured angular distribution for reactions 27 Al( 16 O,2  n) 34 Cl M. K. Sharma et. al., Phys. Rev. C 75 (2007) HQP_2008_Dubna

The observed  -rays spectrum for 16 O+ 169 Tm system at 81 MeV for angular distribution of residues HQP_2008_Dubna

Angular distribution of residue 181 Re at 81 MeV HQP_2008_Dubna

Angular distribution of several residues in 16 O+ 169 Tm at 81 MeV HQP_2008_Dubna

The enhancement of experimentally measured cross- sections for alpha emission channels over their theoretical predictions have been attributed to the fact that these residues are not only formed by the complete fusion but also through incomplete fusion. The analysis of RRD and ADs have clearly indicated the significant contribution of ICF. Relative contributions of CF and ICF processes have been separated out. Attempt has been made to separate out energy dependence of CF and ICF. Conclusions HQP_2008_Dubna

List of Publications in International Journals during Influence of incomplete fusion on incomplete fusion; observation of a large incomplete fusion fraction at E  5-7 MeV/nucleon: Pushpendra P. Singh, B. P. Singh, Manoj Kumar Sharma, Unnati, Devendra P. Singh, Rakesh Kumar, K.S. Golda, and R. Prasad, Phys. Rev. C. 77 (2008) Production of fission-like events after complete and in-complete fusion of 16 O projectile with 159 Tb and 169 Tm at E/A~6 MeV: Pushpendra P. Singh, B. P. Singh, Bhavna Sharma, Unnati, Manoj Kumar Sharma, H. D. Bhardwaj, Rakesh Kumar, K. S. Golda and R. Prasad. International Journal of Modern Physics E Vol 17, No. 1 (2000) Reaction mechanism in the 16 O+ 27 Al system: Measurement and analysis of excitation functions and angular distribution: Manoj Kumar Sharma, Unnati, Devendra P. Singh, Pushpendra P. Singh, H. D. Bhardwaj, and R. Prasad: Phys. Rev. C. 75 (2007) A study of pre-equilibrium emission of neutrons in 93 Nb( ,xn) reaction: Manoj Kumar Sharma, H.D. Bhardwaj, Unnati, Pushpendra P. Singh, B.P. Singh and R. Prasad: European Journal of Physics A 31 (2007) Observation of complete and incomplete-fusion components in 159 Tb, 169 Tm( 16 O,x) reactions: Measurement and analysis of forward recoil ranges at E/A  5-6 MeV: Pushpendra P. Singh, Manoj Kumar Sharma, Unnati, Devendra P. Singh, Rakesh Kumar, K.S. Golda, B. P. Singh and R. Prasad, Eur. Phys. J. A 34 (2007) A study of the reaction occurring in 16 O+ 159 Tb system below7 MeV/nucleon energies: Excitation Functions and Recoil Range Distributions: Manoj Kumar Sharma, Unnati, B.P. Singh, H.D. Bhardwaj, Rakesh Kumar, K. S. Golda and R.Prasad: Nuclear Physics A 776 (2006) A study of pre-equilibrium emission in some proton and alpha induced reactions: B.P. Singh, Manoj Kumar Sharma, M. M. Musthafa, H.D. Bhardwaj and R.Prasad, Nuclear Instrument and Methods A 562 (2006) 717. HQP_2008_Dubna

8A study of excitation functions for some residues produced in the system 14 N+ 128 Te in energy range  MeV: Unnati, Manoj Kumar Sharma, B.P. Singh, Sunita Gupta, H.D. Bhardwaj, R.Prasad and A. K. Sinha: International Journal of Modern Physics E 14 (2005) Measurement and analysis of cross-sections for (p,n) reactions in 51 V and 113 In: M.M. Musthafa, Manoj Kumar Sharma, B.P. Singh, and R.Prasad Applied Radiation and Isotopes, 62 (2005) A study of complete and incomplete fusion in 16 O+ 169 Tm system: Excitation Functions and Recoil Range Distributions: Manoj Kumar Sharma, Unnati, B. K. Sharma, B.P. Singh, H. D. Bhardwaj, Rakesh Kumar, K. S. Golda and R.Prasad: Phy. Rev. C. Vo. 70. (2004) HQP_2008_Dubna

List of Collaborators :- 1. Prof. R. Prasad AMU 2. Dr. B. P. Singh AMU 3. Ms. Unnati AMU 4. Mr. Pushpendra P. Singh AMU 5. Mr. Devendra P. Singh AMU 6. Dr. H.D. Bhardwaj Unnao 7. Dr. R. K. Bhaumik IUAC 8. Mr. Rakesh Kumar IUAC 9. Ms. K.S. Golda IUAC HQP_2008_Dubna