Alpha-Particle Reaction Cross Sections at 40 MeV

Abstract

We have measured the nonelastic cross section O-R for 40-MeV alpha particle for 19 target elements ranging in atomic weight A between 9 and 232. The results have been compared with the predictions of the optical model ai. The ratio 0-/2/07 deviates from unity in a systematic fashion being less than 1 for the lightest elements and greater than 1 for the heaviest. Superimposed on this trend, O-R/O-I dips by 18% for elements where the nuclear charge is near 28. A similar effect had been noted earlier in proton-reaction cross-section data but not in deuteron-reaction cross-section data. W E have measured the reaction cross section v R for 40-MeV alpha particles, and we compare it with the prediction ai of the optical-model potential for alpha particles. 1,2 The ratio (TR/<TI plotted against A 2,z (A, the atomic number) deviates from unity in a systematic fashion. A straight line with a slope of S.5X10 -3 fits the data in Fig. 1. Superimposed on this trend, CTR/<JI dips by 18% near A = 28 protons as was also noted in the 10-MeV proton measurements. 3 The experimental apparatus used in the reaction cross-section measurements (see Fig. 2) has been described in detail elsewhere 4 and will not be discussed here except where parameters of the experiment have been altered because of the change in the projectile. A beam particle is denned by a coincidence event between counters 1, 2, 3, and 4 of the kind 12 3 4, where a bar denotes a counter in anticoincidence. In what follows we understand that the intensity Jo represents the frequency of events of this kind, i.e., 7o= 12 3 4. In the attenuation technique utilized here the quantity IQ-I is measured by placing counter 5 (see Fig. 2) in anticoincidence, i.e., Io-I-12 3 4 5.Absorption of the alpha particles occurs more frequently in the degrader (see Fig. 2), since it is several times as thick as the targets. This contribution had to be subtracted. This is done by removing the target and placing a "dummy" target in the beam ahead of the scattering foil of such a thickness that the beam energy incident on the degrader foil is the same, and the numbers of io(= 1 2 3 4) and io-i(-12 3 4 5) events are measured.Since elastic and inelastic scattering cannot, in general, be neglected, counter 5 must subtend an angle 6 large enough so that the elastic scattering Jd 6 *(rei(0)dtt outside the angle 0 5 [where <r e i(6) is the differential elastic-scattering cross section^, is not so large that the uncertainty in this quantity limits the accuracy of the measurement. Of course, 6 5 is made as small as is possible to reduce the inelastic contribution *=o Jo ai(d)dtt, 1 G.where <ri(6) is the differential inelastic cross section for the excitation of the ith level of the target element, and the sum extends from the ground state up to the Nth state. Higher lying states are excluded by the energy resolution afforded by the degrader. By oo (0) we mean the compound elastic differential cross section.When a " target-in" measurement (Jo, Io-I) and a "dummy-in" measurement (io, io-i) are made, th...

Reaction cross sections for 75–190 MeV alpha particles on targets fromC12toAuce1, Carlson2, Cox3 et al. 1994Phys. Rev. C

“…(6) for our data at 103.2 MeV. The AT dependence at the other energies is rather similar as shown in Fig.…”

“…As mentioned above, experimental results for the reaction cross sections for alpha particles for several nuclei are Eoecgy cocleoc (MeV) O'R = 7r(R~AT, + 1.12A~~) , (6) where AT and A are the mass numbers of the target and the incident alpha particle, respectively. They found that this parametrization, with R~--1.30, was more successful than sophisticated expressions with Coulomb and other corrections.…”

“…There are, however, very few results for reaction cross sections for alpha particles. Measurements on several nuclei have been made at Berkeley [6] at 40 MeV and at Kiev at 96 -100 MeV [7 -11]. Beside these measurements the reaction cross section for C was measured at 380 and 620 MeV at Berkeley [12).…”

Modeling astatine production in liquid lead-bismuth spallation targets

“…4, in which the model is compared to the few available experimental data [25][26][27] and to the predictions of the original version. This success may seem surprising since INC models are not supposed to be used to describe reactions below ∼ 150 MeV and even less fusion reactions.…”

Astatine production in a lead-bismuth target bombarded by a proton beam: a detailed study using INCL4.6-Abla07

“…With these modifications, the model is able to predict rather well the helium-induced total reaction cross-sections as can be seen in Figure 2 in which the model is compared to the few available experimental data [7,8] and to the predictions of the original version. …”