Page 45 - Modern physical chemistry

34 Structure in Molecules and Atoms

FIGURE 2.6 Beam particle just grazing a
target nucleus.

TABLE 2.2 Nuclear Radii from Neutron Cross Sections*

Cross Neutron Nuclear Parameter
Section cr, Energy, Radius R A , Ro,
Element barns MeV jermis jermis
Be 0.65 14 2.4 1.17
B 1.16 14 3.4 1.54
C 1.29 25 3.8 1.65
0 1.60 25 4.3 1.71
Mg 1.83 14 4.5 1.57
AI 1.92 14 4.6 1.52
AI 1.85 25 4.6 1.52
S 1.58 14 4.1 1.30
Cl 1.88 25 4.7 1.44
Fe 2.75 14 5.6 1.46
Cu 2.50 25 5.5 1.38
Zn 3.03 14 5.9 1.48
Se 3.03 14 6.3 1.46
Ag 3.82 14 6.8 1.44
Ag 3.70 25 6.9 1.46
Cd 4.25 14 7.2 1.48
Sn 4.52 14 7.4 1.52
Sb 4.35 14 7.3 1.46
Au 4.68 14 7.5 1.33
Hg 5.64 14 8.3 1.42
Hg 5.25 25 8.4 1.44
Pb 5.05 14 7.8 1.32
Bi 5.17 14 7.9 1.34
*H. Feshbach and V. F. Weisskopf, Phys. Rev. 76, 1550-1560 (1949)

constant, with the value
F4J = 1.4 fm. [2.42]

Similar experiments have been performed with protons. After correcting for the scat-
tering caused by electric interaction, one obtains similar results.
The radius RA within which the charge seems to be distributed uniformly can be deter-
mined. One may use electrons having such a high kinetic energy (200 to 500 Me V) that
each follows a nearly classical (nonquantal) trajectory. The nuclear radius Rb of the elec-