Coulomb Excitation Process in the Lighter Odd-Mass Nuclei

Excitation of Nuclei by Charged Particles

“…Insufficiently thin targets are revealed by their steeper excitation functions ; the ultimate test of a thin target is to observe no further change in shape of the excitation curve upon using a thinner target, i.e., one yielding less radiation. The modifications introduced into the si�ple, semi-classical expression by the WKB approximation (5 1) were definitely needed to improve the agreement with the observed shapes of the excitation functions (58). However, no evidence for the type of behavior illustrated in Figure 2 for low values of '17. was found within the accuracy of these experiments.…”

“…Unfortunately there exists no case of a pure M1 transition which does not admit of E2 excitation alsoY How· ever, in two cases of very small E2 admixture (La l 39 and Pr141) no evidence of any Coulomb excitation was found in spite of conditions comparing favor ably as to excitation energy with neighboring nuclei (98). In addition, sev eral cases with measurable E2 components but predominant Ml matrix elements show that Ml Coulomb excitation is unimportant (58). This merely bears out what is expected theoretically in view of the depressing influence of the retardation factor vic for (relatively) slow particles and magnetic transitions on the one hand, and what is known empirically for the size of the quantity B (Ml) on the other hand (8).…”

“…For radiation (a), it has been shown that the higher Coulomb barrier for higher Zl projectiles insures an adequate range of bombarding energies in which Coulomb excitation is predominant, even for rather low Z% targets (58,105), so that meaningful transition probabilities can be extracted from the measured cross section values. Bremsstrahlung (b) is a component which must always be subtracted when using protons (60,93) ; heavier particles generally contribute negligible quantities of bremsstrahlung (55,130) Finally, the characteristic K and L x-rays emitted under bombardment must always be reckoned with.…”

“…A thick-target curve (see Targets above) covering a more than 20,OOO-fold yield increase and showing excellent agreement with E2 theory is shown in Figure 8 for RU10 4 which has the lowest excited s.tate and largest transition probability of any even-even nucleus below A = 145. This sort of agreement can usually be taken as confirmation of the E2 character of the excitation process, although sometimes the distinction be tween the shapes of El and E2 excitation is small over limited ranges of bombarding energy (58,90). To sum up, then, the experimentally observed excitation curves confirm the theoretically predicted dependence upon � to within the experimental error (about 3 to 5 per cent) over a considerable range of tlE (50 kev to 850 kev), Z2 (9 to 94), and E (1 Mev to 7 Mev).…”

“…Excitation junctions.-The first experimental checks of semi-classical Coulomb excitation theory, bearing on the correct �-dependellce of the func tion jE2m revealed satisfactory agreement for thick targets (6,77,86,87) ; for a number of the stronger transitions in lighter nuclei it was possible to obtain excitation curves with thin targets (58). One of these curves for Na23 is illustrated in Figure 7.…”