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**Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).**

Nuclear Scattering Elastic or inelastic. Analogous to diffraction. Alternating maxima and minima. First maximum at Minimum not at zero (sharp edge of the nucleus??) Clear for neutrons. Protons? High energy, large angles. Why? Inelastic Excited states, energy, X-section and spin-parity. Accelerator Physics, JU, First Semester, (Saed Dababneh).

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**Reaction Cross Section(s)**

Probability. Projectile a will more probably hit target X if area is larger. Classically: = (Ra + RX)2. Classical = ??? (in b) 1H + 1H, 1H + 238U, 238U + 238U Quantum mechanically: = 2. Coulomb and centrifugal barriers energy dependence of . Nature of force: Strong: 15N(p,)12C = 0.5 b at Ep = 2 MeV. Electromagnetic: 3He(,)7Be = 10-6 b at E = 2 MeV. Weak: p(p,e+)D = b at Ep = 2 MeV. Experimental challenges to measure low X-sections.. HW 14 Accelerator Physics, JU, First Semester, (Saed Dababneh).

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**Reaction Cross Section(s) (Introduction)**

Detector for particle “b” d Ia “b” particles / s , cm2 “X“ target Nuclei / cm2 “a” particles / s Typical nucleus (R=6 fm): geometrical R2 1 b. Typical : <b to >106 b. Accelerator Physics, JU, First Semester, (Saed Dababneh).

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**Reaction Cross Section(s) (Introduction)**

Many different quantities are called “cross section”. Krane Table 11.1 Angular distribution Units … ! Spectroscopic Factor. “Differential” cross section (,) or ( ) or “cross section” …!! Doubly differential t for all “b” particles. Energy state in “Y” Accelerator Physics, JU, First Semester, (Saed Dababneh).

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**Compound Nucleus Reactions**

Direct Time. Energy. CN decays Two-step reaction. CN “forgets” how it was formed. Decay of CN depends on statistical factors that are functions of Ex, J. Low energy projectile, medium or heavy target. EaCM QCN Accelerator Physics, JU, First Semester, (Saed Dababneh).

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**Compound Nucleus Reactions**

Consider p + 63Cu at EpCM= 20 MeV. Calculate EpCM + [m(63Cu) + m(p) – m(64Zn)]c2. Divide by 64 available energy per nucleon << 8 MeV. Multiple collisions “long” time statistical distribution of energy small chance for a nucleon to get enough energy Evaporation. Higher incident energy more particles “evaporate”. See also Fig in Krane. Accelerator Physics, JU, First Semester, (Saed Dababneh).

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**Accelerator Physics, JU, First Semester, 2010-2011 (Saed Dababneh).**

Direct Reactions Random collisions nearly isotropic angular distribution. Direct reaction component strong angular dependence. See also Fig in Krane. Accelerator Physics, JU, First Semester, (Saed Dababneh).

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