1. Surface Characterization of 14 N Implanted Targets Abhijit Bisoi Saha Institute of Nuclear Physics 1/AF Bidhannagar, Kolkata-64

2. Introduction In experimental Nuclear Physics, target is one of the essential ingredients for any type of measurements. a) Solid target. 1. Evaporated target 2. Sputtered target 3. Targets prepared by rolling from a pellet 4. Implanted Target. b) Gas target. In Nuclear Astrophysics, in most cases implanted targets are used because of its stability and purity (isotopically enrich ). 14 N(p,γ) 15 O reaction is hampered by 15 N(p,αγ) 12 C background reaction with 15 N impurity in the target. The 14 N implanted targets have a 15 N depletion of about two order of magnitude.

3. Target preparation Simulation: Implanted energy and backing have been selected by the simulation code TRIM. Experiment: Place Specification (Instrument) *Isotope separator SINP, Kolkata E max = 200 keV I beam ~ μA for Ar *ECR source TIFR, Mumbai E max = 400 keV I beam ~ 40 μA for 14 N (Target-I) ECR source TIFR, Mumbai E max = 400 keV I beam ~ 40 μA for 14 N (Target=II) Ion beam 14 N +14 N 3+ Beam energy50 keV75 keV BackingTantalum (Ta) Backing thickness0.3 mm Implanted dose10 17 atoms/ cm 2 2.2*10 16 atoms/cm 2 10 18 atoms/cm 2 Beam spot diameter2 mm 2.54 cm Implantation time 2 hour 1.5 hour60 hour *No special treatment of the foil was undertaken to reduce contaminants in the foil.

4. Scanning Electron Microscope (SEM) Measurement In order to investigate the effect of implantation on the surface of the target, a pure Ta sheet and an irradiated Ta sheet were characterized by SEM measurement. SEM Measurement: Target surface After implantation Before implantation

5. X-ray photoelectron spectroscopy (XPS) Measurement XPS spectrum (1486.6 eV (Al K α ) X- ray)for 14 N implanted target. The peak corresponding to nitrogen is shown in the inset. ElementRelative % present in the sample O N C Ta Na F 37.2 5.94 42.4 3.7 6.84 5.97 ElementRelative % present in the sample O N C Ta Ti Ag Cu 21.4 12.4 21.5 33.9 7.4 1.3 2.0 Target-II Target-I

6. Conclusion  No Fluorine & Sodium peaks observed in Target-II.  Reduced Oxygen & Carbon contamination in Target -II.  Additional efforts have to be taken to remove all contaminants from the target.  Effort has to be made to extract quantitative estimation of 15 N impurity present in these targets. Future plan:  Investigation of nitrogen distribution in the bulk of the material by using Rutherford Back Scattering (RBS) Spectroscopy or 278 keV 14 N(p,γ) 15 O Resonance reaction.

7. Acknowledgement: References: [1] C. Rolfs and W S Rodney, Cauldrons in the Cosmos (University of Chicago Press) 1988. [2] S. Suethe et. al, Nucl. Instr. and Meth. A 260, 33 (1987). [3] H.Y. Lee et. al, Nucl. Instr. andMeth. B 267, 3539 (2009). [4] J. Cruz et. al, Nucl. Instr. and Meth. B 267, 478 (2009). [5] T.A.D. Brown et. al, Nucl. Instr. and Meth. B 267, 3302 (2009). [6] James F. Ziegler,http://www.srim.org [7] http://www.srdata.nist.gov/xps The authors acknowledge Prof. M. Mukherjee, Prof. K.S.R. Menon, A. K. M. Maidul Islam, Souvik Banerjee and Jayanta Das for their sincere help and cooperation for XPS, SEM and EDX measurements and data analysis.

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