Triton Pick-up Research Articles

Angular correlations in the 27Al(p, α1γ)24Mg reaction at E p = 7.4 MeV

The results from measuring the 27Al(p, α)24Mg reaction’s differential cross sections at E p = 7.4MeV with the formation of the final nucleus in the ground and first excited (2+, 1.369 MeV) states are presented. The differential cross sections are obtained in the 25°–160° (lab) range of α-particle emission angles. Double-differential cross sections for the 27Al(p, α1γ)24Mg reaction are measured at the same proton energy for several α-particle angles in the forward hemisphere. All even components of the density matrix spin tensors of the 24Mg nucleus in the 2+ (1.369 MeV) state are reconstructed and its orientation characteristics are determined. The experimental results are compared with calculations for the triton pickup mechanism using coupled channels, and in the the statistical limit of the compound nucleus model.

States in 10Be populated in 6,7Li(7Li,3,4He)10Be* reactions at 30 and 52 MeV

In this contribution, an analysis of an experiment with the 30 and 52 MeV 7Li beam and the 7LiF and 6LiF targets is given, emphasizing population of cluster states by triton transfer to 7Li. Results concerning both reactions are given and discussed. Aside from the dominant α + d structure in 6Li, a rather large overlap with 3He+t cluster configuration populates cluster states in 10Be by triton pick-up. A comparision with t pick-up from 7Li, resulting with detected α instead of 3He, with a considerably higher Q-value is given.A special attention was paid to analysing and compensating non-uniformity of thicknes of standard 50 μm thin silicon detectors used in the measurement. Rather than measuring their thickness independantly, a method was derived to calculate and compensate the thickness variation directly from the measured data.

The 58Ni(p, α) reaction mechanism through a study of the analyzing power

Analyzing powers of the 58Ni(p, α) reaction at E p = 22 and 72 MeV have been calculated for transitions to the ground state of 55Co and to excited states in the continuum. DWBA calculations have been performed with both the α knock-out and triton pick-up models. The analyzing power at 72 MeV in the continuum was calculated with the statistical multistep direct theory. It is found that while the g.s. transition is dominated by the triton pick-up process, the analyzing power in the continuum can only be reproduced by an α knock-out mechanism. Some general considerations on the interplay between these two mechanisms and on the consistency with results obtained in the past with semiclassical preequilibrium models are made.

Emission of preformed alpha particles through a collective process in 150Sm(p, alpha ).

Analysis of the /sup 150/Sm(p,..cap alpha..) reaction with the triton pickup and ..cap alpha.. knockout models fails to give the magnitude of the measured cross section. We show that a calculation based on a collective form factor successfully gives both the angular distribution and the absolute magnitude of the cross section. Some insight into the collective process is provided by the recent extension of the interacting boson model to alpha clustering in deformed nuclei.

Parameter dependence in pick-up calculations of (p,α) reactions to highly excited continuum states

The multi-step reaction theory of Tamura and Udagawa (1977), which views (p, alpha ) reactions in terms of triton pick-up, is studied numerically, but in more detail with allowance made for improvements in the basic theory. Reactions induced on A approximately 90 nuclei by 40-70 MeV protons are considered. Either the predicted absolute magnitude or the energy and angular dependence of the calculated cross sections change considerably when the alpha -particle optical-model parameters and the geometrical factors of the bound triton well are varied. Calculations based on the knock-on mechanism and the parameters suggested by Gadioli et al. (1980) are found to reproduce the experimental data satisfactorily. It is suggested that this last approach may allow a more reliable a priori prediction of the energy and angular distribution of the alpha particles emitted.

Pickup mechanism in (p, α) pre-equilibrium reactions

The contribution of the one-step triton pickup to the continuous spectra of (p, α) reactions is analyzed in terms of the DWBA theory. The formalism is succesfully applied to 93Nb(p, α) 90Zr and 118Sn(p, α) 115In reactions at two incident proton energies.

Triton pick-up in the (p,α) reaction on208Pb at 20 MeV

The 208Pb(p, alpha )205Tl reaction to four low-lying excited states of the residual nucleus was measured in order to study the reaction mechanism. The shapes of the angular distributions and the relative transition strengths can be explained by means of the triton pick-up mechanism, calculated using the semimicroscopic model of (p, alpha ) reactions.

(p,α) reaction onNb93andY89

The ($p,\ensuremath{\alpha}$) reaction has been studied at 15.2 MeV on $^{93}\mathrm{Nb}$ and $^{89}\mathrm{Y}$ and analyzed using distorted-wave Born-approximation and cluster form factors. The reaction is a direct triton pickup and compound nucleus effects are negligible. In the first case the transferred neutrons are the two extra core neutrons and the reaction behaves like a proton pickup. Positive parity states of $^{90}\mathrm{Zr}$ are populated by the transfer of ${g}_{\frac{9}{2}}$ protons with strengths in good agreement with a simple model; new levels are excited corresponding to ${p}_{\frac{3}{2}}$ and ${f}_{\frac{5}{2}}$ proton holes. In the second case the neutrons are removed from the filled $N=50$ shell; states corresponding to proton and neutron configurations in $^{86}\mathrm{Sr}$ are excited with comparable strengths and it is difficult to get unambiguous spectroscopic information.NUCLEAR REACTIONS $^{93}\mathrm{Nb}(p,\ensuremath{\alpha})$, $^{89}\mathrm{Y}(p,\ensuremath{\alpha})$, ${E}_{p}=15.2$ MeV; measured $\ensuremath{\sigma}({E}_{\ensuremath{\alpha}},\ensuremath{\theta})$, $\ensuremath{\theta}=10\ensuremath{-}160\ifmmode^\circ\else\textdegree\fi{}$, $^{90}\mathrm{Zr}$ levels up to 5.1 MeV, $^{86}\mathrm{Sr}$ levels up to 3 MeV. Reaction mechanism. DWBA analysis.

Selectivity in the 11B( 3He, 6Li) 8Be reaction

The 11B( 3He, 6Li) 8Be reaction was studied at 26 MeV incident energy. Angular distributions and excitation functions were measured. The unobserved 1 +, T = 0, 18.15 MeV state is at least one order of magnitude less populated than the 1 +, T = 1, 17.64 MeV state. This selectivity between the two 1 + states suggests that one configuration only of the three transferred nucleons is involved in the ( 3He, 6Li) reaction. An analysis performed under the assumption of triton pick-up is shown to predict the occurrence of such selectivities although it cannot account for the one observed using current shell-model wave functions.

The ( 3He, 6Li) reaction on 9Be as a direct reaction

The 9Be( 3He, 6Li) 6Li reaction ( Q = −1.90 MeV) has been measured for the energy range from 6.0 to 9.25 MeV. Sharply forward peaked angular distributions at 7.0 and 9.0 MeV and yield curves, smoothly varying with energy, suggest that the reaction is predominantly direct. Zero-range DWBA calculations, antisymmetrized to account for the identical particles in the exit channel, were made for the differential cross section assuming a triton pick-up process. Distorted waves were generated from optical potentials deduced from elastic scattering measurements appropriate to the entrance and exit channels. Spectroscopic factors (core plus tritoncluster parentage) extracted from the distorted-wave analyses, as well as from previous analyses of ( 3He, 6Li) reactions on 11B and 19F, compare favourably with theoretical calculations. The ( 3He, 6Li) reaction promises to be a useful probe of triton clustering in nuclei.

Energy Dependence of the Three-Nucleon Transfer Reactions on Light Nuclei

Excitation functions and angular distributions for ($p,\ensuremath{\alpha}$) reactions on $^{12}\mathrm{C}$, $^{15}\mathrm{N}$, and $^{16}\mathrm{O}$ have been measured from 19- to 45-MeV incident energy. The mean slope of the integrated cross sections for all the above reactions and for ($p,\ensuremath{\alpha}$) reactions on $^{9}\mathrm{Be}$, $^{11}\mathrm{B}$, and $^{19}\mathrm{F}$ is the same, when plotted as a function of the intermediate-system excitation energy, and is of the type ${[{({E}_{p})}_{\mathrm{c}.\mathrm{m}.}+{B}_{p}]}^{\ensuremath{-}3.75}$. For the $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$ targets, the differential and integrated cross sections, which have been measured in energy steps of the order of some hundred keV, show a marked resonant structure with modulations having widths and spacings of the order of 1 MeV. Angular distributions, although presenting a well-developed diffraction pattern especially at forward angles, vary very rapidly with energy, particularly below 30 MeV. The analysis of excitation functions performed with a distorted-wave Born-approximation point triton pickup calculation gives ambiguous results. A statistical Hauser-Feshbach calculation gives too steep a slope which agrees with experimental data only when direct transitions are hindered. The analysis of the excitation functions, performed in the framework of the pre-equilibrium decay model, gives satisfactory results. This could indicate that $\ensuremath{\alpha}$ emission from light nuclei cannot be treated as a simple direct effect.

Study of the 19F( 3He, 6Li) 16O reaction at 11 MeV

Angular distributions of the 19F ( 3He, 6Li) 16O reaction have been measured at 11 MeV for the transitions 6Li g.s. ( 16O g.s), 6Li 3.56 ( 16O g.s.) and 6Li g.s. ( 16O 6.06, 6.14). Zero-range DWBA analysis on the basis of the triton pickup mechanism revealed good fits for the two transitions to 16O g.s. A ratio of 1.6 ± 0.2 is obtained for the spectroscopic factors S ( 6Li g.s¦ 3He, t) and S ( 6Li 3.56¦ 3He, t). Published angular distributions of the reaction 19F(p,α) 16O for E p = 22.8 and 30.5 MeV have been analysed on the basis of the same mechanism using the same triton well geometry as for the ( 3He, 6Li) calculations and yield a spectroscopic factor S ( 19F| 16 O, t) = 0.06 . A rather strong transition 19F ( 3He, 6Li g.s 16 6.06. 6.14 is observed which is not compatible with one-step triton pickup. The corresponding angular distribution shows no pronounced structure.

B11 (α, Li7) Be8 Reaction at 28.4 and 29.0 MeV

Li 7 ions from the B 11 (α, Li 7 )Be 8 reaction were detected with a 50µ thick SSD covered with aluminum absorbers. The analyses suggest that the compound nucleus process is not favorable to the B 11 (α, Li 7 )Be 8 (g.s.) reaction. The angular distributions of Li 7 (0.478 MeV state) can be reproduced by the calculation based on the triton pickup process. The feature of the angular distributions of Li 7 (g.s.) is quite different from that of Li 7 (0.478 MeV state) and is qualitatively explained by the triton pickup process and the Li 7 knockout process interfering with each other.

The 19F( 3He, 6Li) 16O reaction

The 19F( 3He, 6Li) 16O reaction ( Q = 4.092 MeV) has been studied for bombarding energies from 2.0 to 6.0 MeV. Yield curves were measured at 50° and 90° and the angular distribution was measured at 5 MeV. The lack of resonance structure in the yield curves and the diffraction-like nature of the angular distribution suggest that the reaction is predominately a direct process. A zero-range DWBA calculation was carried out for the differential cross section assuming a triton pick-up process. Calculations were also performed for the 11B( 3He, 6Li) 8Be reaction which had been studied previously. From the ratio of the measured to the calculated cross section for the 19F( 3He, 6Li) 16O reaction and the corresponding ratio for the 11B( 3He, 6Li) 8Be reaction, a relative spectroscopic factor (core plus triton-cluster parentage) was obtained.

The [formula omitted] and [formula omitted] reactions near 445 MeV

Ground state group (p, α) angular distributions have been obtained at energies between 30.5 MeV and 45 MeV. It appears that an energy range free from significant resonance effects has been found for the (p, α) reaction. The main process for the 19 F(p, α) 16 O and the 112 C(p, α) 9 B reactions is direct triton pickup, however, the backward angle region is quite different for the two angular distributions and the 12 C(p, α) 9 B reaction probably contains significant heavy particle stripping.

Direct-Interaction (p,α) Reactions inY89andZr90

Alpha-particle energy spectra from ($p,\ensuremath{\alpha}$) reactions in $^{89}\mathrm{Y}$ and $^{90}\mathrm{Zr}$ were obtained at 5-deg intervals between 15 and 90 deg. Bombarding energies of 20.2 and 22.5 MeV were used. Differential cross sections for reactions leading to the ground states and first excited states were determined. Distorted-wave calculations were done for the angular distributions for the reactions leading to each of the ground states and the 0.38-MeV first excited state in $^{87}\mathrm{Y}$. The calculated angular distributions reproduce the general features of the experimental angular distributions. Spectroscopic factors, obtained from normalization of the calculated angular distributions to the experimental data, are consistent with triton pickup as the dominant mechanism for direct-interaction ($p,\ensuremath{\alpha}$) reactions. The normalization factors also indicate the $^{90}\mathrm{Zr}$ ground-state proton configuration to be 70% ${(2{p}_{\frac{1}{2}})}^{2}$ and 30% ${(1{g}_{\frac{9}{2}})}^{2}$.

A study of the Be 9(p, α)Li 6 reaction from 3.5 to 12.5 MeV

Angular distributions and excitation curves for the Be 9(p, α 0)Li 6 and Be 9(p, α 1)Li 6∗ (2.18 MeV) reactions have been measured for proton bombarding energies from 3.50 to 12.50 MeV. Total cross sections, as well as 90° (lab) yields, for α 0 and α 1 are monotonically decreasing functions of energy and the angular distributions show very little change with energy. These data suggest that the reaction is predominantly a direct process over the energy interval studied. No prominent resonance behaviour is observed in the energy interval corresponding to excitation energies in B 10 from 9.3 to 17.8 MeV. In order to perform a consistent distorted-wave Born approximation (DWBA) calculation of the reaction, elastic scattering experiments in the entrance and exit channels were performed. At the same time data were obtained on several other reactions, namely Be 9(p, d)Be 8, Be 9(p, p′)Be 9∗ (2.43 MeV), Li 6(α, α′)Li 6∗ (2.18 MeV) and Li 6(α, d)Be 8. Optical model parameters for the zero-range DWBA calculation of Be 9(p, α)Li 6 were obtained by analysing the elastic scattering data. Results of the calculation based on the triton pick-up process give fairly good agreement with the data for α 0, but not for α 1. These results are compared to plane wave calculations. The possibility of interpreting the data in terms of exchange processes is also discussed, as well as the applicability of the DWBA calculation to this reaction.

Angular Distributions of the Reaction F19(p, α)O16 at 8.0∼14.2 Mev

The alpha particles from the reaction F 19 ( p , α)O 16 resulting in the ground state of O 16 have been measured, making use of a proportional counter method. The excitation curve has been measured at a laboratory angle of 50° from 12.9 to 14.1 Mev. The. curve changes smoothly with incident proton energy. The angular distributions of the alpha particles have been measured at 14.2, 13.5, 13.0, 12.0, 11.0, 10.0, 9.0, and 8.0 Mev, which can be qualitatively explained by the simple triton pickup theory. Although fairly good agreements with the theory can be seen at 14.2, 13.5 and 9.0 Mev, the angular distributions for the other energies deviate from the theory to some extent. The deviation is generally larger for backward angles and especially at 11.0 and 8.0 Mev striking backward peaks are observed. It is considered that for detailed explanation of the results, refinement of the theory or introduction of other processes of the reaction or both are required.