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Isospin effect in the projectile fragmentation of calcium isotopes and a possible experimental observable? Chun-Wang Ma Department of Physics, Henan Normal University Email: [email protected] Outlook: 1. Backgrounds 2. The SAA Model 3. PF of calcium isotopes 4. Results and Discussion 5. Conclusions 1. Backgrounds Projectile fragmentation is one of the basic experimental method in RIB era. NSCL experiment: 40,48Ca+9Be/181Ta, 58,64Ni+9Be/181Ta, 86Kr+9Be New generation or updated RIB facilities expand the nuclear chart to more neutron-rich and protonrich sides. Increasing interests in EOS of asymmetric nuclear matter: n-rich nuclei Hotter in the research of ISOSPIN physics. Neutron density distribution of neutron-rich nucleus hard to be extracted or measured. Neutron skin thickness important in nuclear phys. etc. 1. backgrounds– neutron skin thickness and EOS 1. Backgrounds Neutron density distribution or neutron skin thickness of asymmetric nuclear matter: not easy to know but important in nuclear physics. Isospin phenomena are strongly related to the different proton and neutron density distribution of asymmetric nucleus. Can the isospin phenomena be used to extract neutron density distribution of neutron skin thickness directly? The observable! D.Q.Fang, et al., PhysRevC61(2000)044610;Ma Chun-Wang, et al., Chin.Phys.B,17(2008)1216; Ma Chun-Wang, et al., Phys.Rev.C79(2009)034606,Chin. Phys. B18(11)(2009), to be published Chin. Phys. B 17(04)(2008)1674 1. Backgrounds Isospin dependence of PF 140A MeV 40,48Ca/ 58,64Ni+9Be Isospin effect in fragments production and it’s decrease Obvious in the productions of peripheral reactions. (big difference of proton and neutron density distribution in the surface of nucleus) Decrease and disappear in the productions of central collisions. (similar proton and neutron density distributions in the core of nucleus) Ma Chun-Wang, et al., Chin. Phys. B18(11)(2009), to be published 1. Backgrounds How do the peak position of the fragments distributions change in the PF of a series of isotopes? If there are some parameters or observables that are related to neutron skin thickness? Find the correlation between neutron skin thickness and some observables. 2. The statistical abrasion-ablation (SAA) model Brohm & Schmidt, Fang, Zhong, etc, Simple and useful; 2-steps reactions: Collisions—participant and spectator De-excitation Refs:NPA569(1994)821, PRC61(2000)044610, CPC 27(2003)39, EPJA10(2001)381,PRC79(2009)034606 2. The statistical abrasion-ablation (SAA) model The colliding nuclei: parallel tubes. Isotope production De-excitation transmission probabilities for neutrons (protons) at b: Key for frag production the average absorbed mass in an infinitesimal tubes at b Density distributions: Fermi-type Y.Eisenberg, PhysRev 52(1954)1378 3. PF of odd 36-52Ca isotopes Fragments productions of 80A MeV 36-52Ca+12C reactions Plateau and its drop Disappearance of the isospin effect: the overlap of the fragment cross section distributions 4. Results and discussion Fit these isotopic distributions by Gaussian function Peak positions Widths Good linear correlation: pk Vs. Zfrag Fit the linear correlations between pk position and Zfrag Slope (b) Intercept (a) 4. Results and discussion correlations between slope b and binding energy, b and Nproj y 0.0205x 2.3833 adj.R square: 0.8299 y 1.4037exp( x / 14.6169) 2.44485 2 0.1441 4. Results and discussion Correlation between b and Sn-Sp: y 0.1016x 2.1536 adj.R square: 0.96431 4. Results and discussion Correlation between b and neutron skin thickness Good linear correlation: y bx a b : 2.1639(0.0017) a : 1.5179(0.0483) AR square: 0.99194 4. Results and discussion 5. Conclusion The cross sections of fragments produced in 80 A MeV even 36-52Ca PF on 12C were calculated by the SAA model. The fragments isotopic cross section distributions were fitted by Gaussian function, peak positions were obtained. The Apk have good linear correlation to the Zfrag. The linear correlation were fitted and slopes b were obtained. The correlation between b and Nproj., Sn, Sn-Sp, δnp were analyzed. Good linear correlation between b and δnp are found. Still a question: b possible to serve as an observable for neutron skin thickness?