The Fifth Conference “ Nuclear Science and Its Application”, 14-17 October 2008
DOUBLE-DIFFERENTIAL AND INTEGRAL CROSS-SECTIONS OF
REACTION (P,XP) ON LED ISOTOPES 2‘«°7 Pb AT Ep=30MEV
A. DUISEBAEV. B. DUISEBAEV, T. ZHOLDYBAEV, K. ISMAILOV, B. SADYKOV
Institute o f Nuclear Physics, Almaty, Kazakhstan
Double-differential and integral cross-sections of reactions 204 207 Pb (p,xp) at Ep=30MeV have been measured. The analysis of experimental results in exciton model has been made.
The inclusive spectra of protons in reactions 204,207Pb(p, px) at Ep=30 MeV in angular range 15-135° with the step 15° have been measured on isochronous cyclotron U-150M of Institute of Nuclear Physics NNC RK. In these experiments the self-supporting isotopic enriched foils of isotopes 204 Pb with thickness 2.42 mg/cm2 (enriched 51%) and 207Pb 3.58 rng/cm2 (enriched 78.8%) have been used.
The registration and identification of reaction products have been performed by system multi-dimensional programmed analysis based on (AE-E) - method, spectrometric rules ORTEC and PC. Two-detector telescope consisted of silicon surface-barrier ORTEC detector (thickness 100 micron) and a scintillation detector with a full absorption Csl (Tl). The solid angle subtended by a telescope of detectors was equal to 0=2.59* 10'5sr.
Section II. Basic Problems O f Nuclear Physics 31
The Fifth Conterence “ Nuclear Science and Its Application”, 14-17 October 2008
The energy calibration o f a spectrometer has been carried out on kinematics of levels of residual nuclei in the reaction 12C(p,x) and with use of recoil protons emitted from polyethylene target. The systematic errors in cross-sections are errors in determination thickness o f targets, calibration of current bean integrator and solid angle of spectrometer. The beam energy of accelerated particles was measured with accuracy 1%. The registration angle was fixed accurate within 0.5°. The total systematic error of measured cross-sections was not more than 15%.
The processing of obtained experimental data has been done. Double differential and differential cross-sections of reactions (p,xp) in angle region 15-135° with the step 15° for nuclei 204’207Pb have been calculated.
The integral cross-sections o f reactions on figure were obtained by integration o f double differential cross-sections on angle.
The analysis of experimental data was performed on the base o f exciton model [1] o f pre equilibrium decay of nuclei by code PRECO-D2 [2]. It was assumed that evolution o f the system goes through consecution of tangle configurations and at each phase the emission o f particles is possible. The states o f intermediate system are divided on two classes: bound and unbound. This allows calculate integral cross-sections statistical multi-step direct (MSD) and multi-step compound (MSC) processes in exciton model. Contributions of additional MSC components that are not considering in Griffin model were determined semi-empirically with taking into account reactions of direct nucleon transfer and direct knock-out processes [3]. Evaporation from equilibrium compound nucleus is included in total cross-section of MSC process.
The contributions of all processes in formation of integral cross-sections of reactions 204> 207Pb(p, px) calculated by code PRECO-D2 are shown in figure. It follows from comparison of experimental and theoretically calculated integral spectra that main contribution has MSD mechanism. Contribution of single-step mechanism of proton knock-out in reaction (p, xp) is negligible.
It should be noted that because of high atomic number of target nuclei 204,207Pb cross sections of proton emission from equilibrium state are small. Coulomb barrier for this reactions is Bcou)omb=l 1.9 MeV. Also one can see that evaporation (low-energy) part of cross-section is underestimated in frame of used exciton model version. It can be explained that this approach gives only pre-equilibrium part of MSC process without considering emission from complex equilibrium configuration of compound system.
Results o f reaction analysis m - 207Pb (p, xp) by code PRECO-D2. Points - experiment, 1 - single-step process of proton knock-out, 2 - MSD component, 3 - MSC component, 4 - equilibrium emission, 5 - total integral cross-section
The Fifth Conference “ Nuclear Science and Its Application”, 14-17 October 2008 References
1. J. J.Griffin, Phys. Rev. Lett. 17(1966) 478.
2. C.Kalbach, “PRECO-D2: Program for Calculating Pre-equilibrium and Direct Reaction Double Differential Cross Sections,” LA-10248-MS (February 1985).
3. C.Kalbach, Phys. Rev. C 23 (1981) 124; Phys. Rev. C 24 (1981) 819
Section II. Basic Problems O f Nuclear Physics 33
