Alpha-induced Reactions Research Articles

Alpha-induced reactions on natural erbium

Stacks of natural erbium were bombared with α-particles with energie of 85 MeV. Cumulative cross sections for the productions of different nuclei were measured using γ-ray spectroscopy. The data are compared with the theoretical predictions provided by the equilibrium and preequilibrium reaction model.

Alpha-induced reactions in iridium.

The excitation function of (\ensuremath{\alpha},xn) reactions on $^{191}\mathrm{Ir}$ (abundance 37.3%) and on $^{193}\mathrm{Ir}$ (abundance 62.7%) has been measured for the 17--55 MeV alpha-particle bombarding energy range. The stacked foil activation technique and \ensuremath{\gamma}-ray spectroscopy were used to determine the cross sections. The experimental data were compared with calculated values obtained by means of a geometry-dependent hybrid model. The initial exciton number ${\mathit{n}}_{0}$=4 with n=2, p=2, and h=0 gives the best agreements with the presently measured results. To calculate the excitation function theoretically a computer code was used. This set of excitation functions provides a data basis for probing the validity of combined equilibrium and preequilibrium reaction models in a considerable energy range.

Pre-equilibrium emission effects in the measured isomeric yield ratios in alpha-induced reactions on 197Au.

Excitation functions of isomeric yields have been measured for $^{198}\mathrm{Tl}$, $^{197}\mathrm{Hg}$, $^{198}\mathrm{Au}$, and $^{196}\mathrm{Au}$ produced by \ensuremath{\alpha}${+}^{197}$Au reactions in the 35--50 MeV energy range. The isomeric yield ratios are analyzed in terms of pre-equilibrium and evaporation emissions. Single as well as two-nucleon pre-equilibrium emissions are taken into account. Various combinations of pre-equilibrium and equilibrium emissions together with different sequences in which the ejectiles may be emitted are explicitly considered to evaluate the average spin distribution of the final nucleus. The choice of the spin cutoff parameter and the effect of forward-angle emissions of pre-equilibrium particles have been investigated. The isomeric yield ratios are found to depend sensitively on the pre-equilibrium angular distribution and on the spin cutoff parameter for equilibrium emissions. Inadequate description of the reaction mechanism leads to incorrect predictions of excitation functions as well as isomeric yield ratios.

Heavy fragment emission in alpha-induced reactions on aluminum at 60 MeV

The production of intermediate-mass fragments ranging from Z=3 to 8 emitted in the reaction of 60 MeV alpha on an aluminum target has been experimentally studied. The energy spectra of the emitted fragments in the angular range of 20\ifmmode^\circ\else\textdegree\fi{}--130\ifmmode^\circ\else\textdegree\fi{} have been measured and the total production cross sections of each fragment have been estimated from the data. The double-differential cross-section data have been compared with the predictions made using (a) a phenomenological moving source model and (b) a binary fragmentation model. The absolute total emission cross sections for various fragments have been calculated assuming the statistical decay of a fully equilibrated compound nucleus and have been compared with the corresponding experimental estimates. It is found that the exit-channel deformation plays a significant role in the estimation of the Coulomb barrier of the separating nuclei. A theoretical procedure for the estimation of the exit-channel Coulomb barrier for the deformed system has been incorporated in the present calculation.

Exciton model analysis of alpha-induced reactions on manganese

Excitation functions for the reactions55Mn(α, n)58Co,55Mn(α, 2n)57Co,55Mn(α,3n)56Co,55Mn(α,4n)55Co,55Mn(α, nα)54Mn+55Mn(α, 3n2p)54Mn,55Mn(α,3nα)52Mn have been measured in the energy range ≈(10÷60) MeV using stacked foil technique. Irradiations have been performed for two separate stacks with the alpha-particle beams of (59.96±0.54) MeV and (29.93±0.54) MeV, respectively. Ge(Li) gamma-ray spectroscopy has been used for analysis of irradiated samples. Excitation functions have also been calculated theoretically using two different computer codes,viz. ALICE/LIVERMORE-82 and ACT. Calculations using code ACT with the inclusion of pre-compound contribution based on exciton model agree well with the measured excitation functions, particularly in the high-energy region. Analysis of the data has indicated the preference for first chance neutron emission and interesting trend in pre-equilibrium fraction with energy has been observed.

Alpha-induced reactions on fissile nuclei at energies to 50 MeV.

An existing model of alpha-particle-induced reactions has been extended to include fission competition. Forty-six excitation functions from nine target nuclei at incident energies to 50 MeV have been calculated and compared to experimental data taken from the literature of the last 35 years. In particular, it is shown that specific modes of interaction of the alpha particle are responsible for the features of individual excitation functions. A simple fission barrier characterized only by its height is shown to suffice in reproducing the fission-evaporation competition.

Measurement and analysis of the excitation function for alpha-induced reactions on Ga and Sb isotopes.

Excitation functions for the reactions $^{69}\mathrm{Ga}$(\ensuremath{\alpha},xn${)}^{73\mathrm{\ensuremath{-}}x}$As, $^{69}\mathrm{Ga}$(\ensuremath{\alpha},p3n${)}^{69}$Ge, $^{69}\mathrm{Ga}$(\ensuremath{\alpha},2p4n${)}^{67}$Ga, $^{71}\mathrm{Ga}$(\ensuremath{\alpha},xn${)}^{75\mathrm{\ensuremath{-}}x}$As, $^{121}\mathrm{Sb}$(\ensuremath{\alpha},xn${)}^{125\mathrm{\ensuremath{-}}x}$I, $^{121}\mathrm{Sb}$(\ensuremath{\alpha},p3n${)}^{121}$Te, and $^{123}\mathrm{Sb}$(\ensuremath{\alpha},xn${)}^{127\mathrm{\ensuremath{-}}x}$I were obtained from the measurements of the residual activity of stacked foils from threshold to 65 MeV. The excitation functions for the production of $^{74}\mathrm{As}$, $^{72}\mathrm{As}$, $^{71}\mathrm{As}$, $^{69}\mathrm{Ge}$, and $^{67}\mathrm{Ga}$ from \ensuremath{\alpha}-induced reactions on Ga and $^{126}\mathrm{I}$, $^{124}\mathrm{I}$, $^{123}\mathrm{I}$, $^{121}\mathrm{I}$, and $^{121}\mathrm{Te}$ from \ensuremath{\alpha}-induced reactions on Sb are presented.The experimental data are compared with calculations considering equilibrium as well as preequilibrium reaction mechanisms according to the hybrid model of Blann. The high-energy part of the excitation functions are dominated by the preequilibrium reaction mechanism. Calculations were done using the a priori calculational method of Blann. From the reactions $^{71}\mathrm{Ga}$(\ensuremath{\alpha},3n${)}^{72}$As and $^{123}\mathrm{Sb}$(\ensuremath{\alpha},3n${)}^{124}$I, an initial exciton number ${n}_{0}$=4 (${n}_{n}$=2, ${n}_{p}$=2, ${n}_{h}$=0) with the mean-free-path multiplier parameter k set to 2 has been deduced for both the targets. However, there are a few exceptions. The theory overestimates the cross section for the $^{69}\mathrm{Ga}$(\ensuremath{\alpha},2p4n${)}^{67}$Ga reaction whereas it underestimates the cross section for the $^{121}\mathrm{Sb}$(\ensuremath{\alpha},p3n${)}^{121}$Te reaction and the high-energy tail of $^{121}\mathrm{Sb}$(\ensuremath{\alpha},2n${)}^{123}$I excitation function. For the (\ensuremath{\alpha},2p4n) reactions on Ga the discrepancy between theory and experiment may be attributed partly to a breakup of the \ensuremath{\alpha} particle and partly to much more complex reaction mechanisms, whereas for the $^{121}\mathrm{Sb}$(\ensuremath{\alpha},p3n${)}^{121}$Te reaction two different reaction mechanisms may be attributed.The large discrepancy between theory and experiment for the reaction $^{121}\mathrm{Sb}$(\ensuremath{\alpha},2n${)}^{123}$I at the high-energy tail of the excitation function may be attributed to emission of more than one preequilibrium nucleon which the theory cannot account for at present. Barring these reactions we have found that the overall agreement between theory and experiment is reasonably good, taking the limitations of the theory into account.

Intermediate structure in 12C+16O system through alpha-induced reactions on 24Mg in the energy range E alpha =26-37 MeV.

The excitation functions have been measured in the energy range ${E}_{\ensuremath{\alpha}}$=26--37 MeV for the reaction $^{24}\mathrm{Mg}$${(}^{4}$He${,}^{12}$C${)}^{16}$O at ${\ensuremath{\theta}}_{\mathrm{lab}=30}$\ifmmode^\circ\else\textdegree\fi{}, 40\ifmmode^\circ\else\textdegree\fi{}, and 50\ifmmode^\circ\else\textdegree\fi{} and for $^{24}\mathrm{Mg}$${(}^{4}$He${,}^{4}$He'${)}^{24}$Mg at ${\ensuremath{\theta}}_{\mathrm{lab}=152}$\ifmmode^\circ\else\textdegree\fi{}--160\ifmmode^\circ\else\textdegree\fi{}. Prominent structures are observed in the excitation functions. The cross sections are compared with the Hauser-Feshbach statistical-model calculations. Probability distributions of the deviations from the average are calculated for all the excitation functions and compared with the statistical-model expectations for the fluctuations. The coherence width is estimated to be 176--214 keV from the observed number of maxima in the excitation functions and it is in agreement with the expected value for the excitation region of 32--42 MeV in the compound nucleus. Cross-channel correlations have been calculated between the $^{12}\mathrm{C}$ channel and alpha elastic and inelastic scattering channels. At ${E}_{\ensuremath{\alpha}}$=27.8 and 28.6 MeV where large cross-channel correlations have been observed, angular distributions of $^{12}\mathrm{C}$ have been measured and found to follow the pattern [${P}_{11}$(cos\ensuremath{\theta}${)]}^{2}$. These results show that the excitation functions are all generally in agreement with the fluctuations expected from the statistical model. However, at ${E}_{\ensuremath{\alpha}}$=27.8 and 28.6 MeV where large cross-channel correlations are observed, though there is a small chance of less than 6\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ for these to be due to statistical fluctuations, the possibility that these structures at these two energies are nonstatistical in origin cannot also be ruled out.

Measurement and analysis of excitation functions for alpha-induced reactions in copper

Excitation functions for the production of68Ga,67Ga,66Ga,65Ga +65Zn and61Cu fromα-induced reactions in natural copper have been measured in the energy range ≈ 10–40 MeV using the stacked foil technique. A stack of nine copper foils was irradiated by a 40 MeVα-beam. Theγ-rays emitted from the irradiated samples were recorded. Excitation functions have also been calculated theoretically using a statistical model with and without the inclusion of pre-equilibrium emission of particles. Pre-equilibrium component simulated by exciton model shows that the inclusion of pre-equilibrium emission gives better agreement between experimental and theoretical excitation functions. Pre-equilibrium fraction depends on the incident energy and the target mass number.

Alpha-induced reactions on gold

The excitation functions of the 197Au(( alpha ,n), ( alpha ,2n), ( alpha ,3n), (d,2pn), ( alpha , alpha n) and ( alpha , alpha 3n)) reactions were measured up to 75 MeV. The experimental data were compared with the calculated values obtained by means of a hybrid model (ALICE/85/300) using the initial exciton number n0=4(4p0h) and the level density parameters a=A/8. A general agreement was found for all except the ( alpha , alpha n) and ( alpha , alpha 3n) reactions, where the disagreement was by about two orders of magnitude.

Measurement and analysis of alpha-induced reactions on Ta, Ag and Co

Excitation functions for the reaction181Ta (α,xn)185−x Re,107,109Ag (α, ypxn) and59Co (α, ypxn) were obtained from measurements of residual activity of stacked foils from threshold to 60 MeV. The excitation functions for the production of181Re,182Re,183Re,184Re,105Ag,111In,54Mn,56Co,58Co, and60Co, are being presented. The experimental data are compared with calculations considering equilibrium as well as pre-equilibrium reactions according to the hybrid model of Blann. High energy part of the excitation functions is dominated by the pre-equilibrium reaction mechanism. Calculations were done using a priori calculational method of Overlaid Alice Code of Blann. Most of the excitation functions in the energy range mentioned above could be very well fitted with the hybrid model calculation for exciton numbern=4 withn p=2 andn n=2. The overall agreement with theory is good. Certain discrepancies, however, indicate the necessity to revise the hybrid model with respect to emission of complex particles.

Discrepancy between proton- and alpha-induced cluster knockout reactions onO16

Cross sections for ($p, \mathrm{pd}$) and ($p, \mathrm{pt}$) reactions at 101.3 MeV and ($\ensuremath{\alpha}, \ensuremath{\alpha}d$), ($\ensuremath{\alpha}, \ensuremath{\alpha}t$), and ($\ensuremath{\alpha}, \ensuremath{\alpha}^{3}\mathrm{He}$) reactions at 139.2 MeV have been measured for an $^{16}\mathrm{O}$ target. Distorted wave impulse approximation analyses of the data yield spectroscopic factors for the proton induced reactions which are comparable to shell model estimates. However, the alpha induced reactions yield values up to two orders of magnitude larger. The relationship of these results to similar results for alpha knockout reactions is discussed.NUCLEAR REACTIONS $^{16}\mathrm{O}(p, pd)$, ($p, \mathrm{pt}$), $E=101.3$ MeV, ($\ensuremath{\alpha}, \ensuremath{\alpha}d$), ($\ensuremath{\alpha}, \ensuremath{\alpha}t$), ($\ensuremath{\alpha}, \ensuremath{\alpha}^{3}\mathrm{He}$), $E=139.2$ MeV; measured $\ensuremath{\sigma}({E}_{1}, {E}_{2}, {\ensuremath{\theta}}_{1}, {\ensuremath{\theta}}_{2})$; DWIA analysis, deduced spectroscopic factors.

Alpha-induced reactions on cobalt

Alpha-induced reactions on the target element cobalt were investigated in the energy region from 25 to 172.5 MeV using the stacked foil technique. Twenty excitation functions were measured for the production of 61Cu, 57Ni, 60m+gCo, 58m+gCo, 57Co, 56Co, 55Co, 59Fe, 52Fe, 56Mn, 54Mn, 52m+gMn, 51Cr, 48V, 47Sc, 46m+gSc, 44mSc, 44gSc, 43K and 42K. Only for 61Cu, 58Co, 57Co and 56Mn were cross sections available earlier, which, however, were limited to α-energies ≦ 41 MeV. The experimental data are compared with calculations considering equilibrium as well as preequilibrium reactions according to the hybrid model of Blann. The excitation functions of half the product nuclides are dominated by preequilibrium effects over wide energy ranges. From the reaction 59Co(α, 2n) 61Cu an initial exciton number between n 0 = 4 (2 n-2 p-0h) and n 0 = 5 (2n-3p-0h) or (3n-2p-0h) is deduced. However, the theoretical analysis reveals several severe shortcomings, e.g. the underestimation of the excitation functions for 60m+gCo, 58m+gCo and 59Fe for up to 2 orders of magnitude. For 60m+gCo the discrepancy between theory and experiment can be attributed to break-up reactions of the α-particle, whereas for the two other product nuclides even more complex reaction mechanisms have to be assumed. Moreover, the strong contributions of preequilibrium emission of α-particles observed for ( α,2p xn) and (α, 4p xn), which are not accounted for by the program OVERLAID ALICE, indicate that the initial reaction phase for α-induced reactions is more differentiated than is supposed by the present form of the hybrid model.

Nuclear fragment production from 720-MeV alpha-induced reactions

Heavy-fragment (Z > 2) energy spectra from 720-MeV ..cap alpha..-induced nuclear reactions on Al, Ag, and Ta have been measured at 30/sup 0/, 60/sup 0/, 90/sup 0/, and 120/sup 0/. The angular distributions are not well reproduced by thermodynamic evaporation models with either one or two emitting sources. The anisotropy of the low-Z fragments is, however, better described by three sources whose evenly spaced velocities and temperatures indicate that the three sources may represent a discrete approximation to an actual continuum of sources. The observed anisotropy may also be a manifestation of large contributions to the forward-angle cross sections from pre-equilibrium fragment emission. Extension of this analysis to our hydrogen- and helium-isotope data indicates that the light fragments continue the trends exhibited by the heavy-fragment data. A comparison with data from proton-induced reactions indicates that the anisotropy observed may be a manifestation of higher energy and momentum deposition in the target nucleus by ..cap alpha..-particles than by protons.

Low-energy nucleosynthesis of lithium, beryllium, and boron

Results for detailed calculations of lithium, beryllium, and boron production by spallation reactions at low energies are reported. Proton and alpha-induced reactions, destruction, and deceleration effects are included. The abundances and isotopic ratios for particle spectra analogous to those observed in solar flares (power law in kinetic energy) agree with the solar-system values. It is suggested that stellar flares, low-energy cosmic rays, or both are the main contributors to the nucleosynthesis of these elements.

On 1f2p-shell Nuclei. Structures of 55Mn, 55Fe and 57Fe with Emphasis on High-spin States

The structures of 55Mn, 55Fe and 57Fe have been investigated by coincidence, yield, angular distribution, and linear polarization measurements of gamma-ray decay from alpha-induced reactions on 52Cr and 54Cr at Eα = 14.2 MeV. Several high-spin states are assigned: In 55Mn 984 keV 9/2-, 1 291 keV 11/2- (both confirmed) and 2 309 keV 13/2-; in 55Fe 931 keV 5/2-, 1 316 keV 7/2-, 1 408 keV 7/2-, 2 211 keV 9/2- 2 300 keV 9/2-, 2 539 keV 11/2- (all six confirmed) and 2 814 keV 13/2(-), 2 982 keV 11/2(-), 3 071 keV 11/2-, 3 419 keV 15/2(-) and 3 456 keV (tentative 13/2-); in 57Fe 316 keV 3/2-, 706 keV 5/2- (both confirmed) and 1 007 keV 7/2-, 1 197 keV 9/2-, 1 357 keV 3/2(-), 1 989 keV 9/2(-), 2 355 keV 11/2-, 2 455 keV 9/2-, 2 879 keV 13/2-, 3 135 keV 15/2(-), 3 268 keV 13/2(-) and 4 429 keV, 4 524 keV (spins undetermined).

Excitation functions for alpha-induced reactions on gold

Synopsis The excitation functions of 197 Au ( α, xn ) reactions have been measured by a stacked foil method. For 52 MeV alpha particles x can be as high as 5. The sum of the cross-sections of the competing ( α, xn ) reactions is within the errors equal to the reaction cross-section as has been calculated by Huizenga and Igo for 195 Pt .

Protons from Alpha-Induced Reactions

The results of proton energy spectra measured at several angles from 30.5-Mev alpha particle induced reactions on ${\mathrm{Al}}^{27}$, ${\mathrm{V}}^{51}$, ${\mathrm{Co}}^{59}$, ${\mathrm{As}}^{75}$, ${\mathrm{Nb}}^{93}$, ${\mathrm{Rh}}^{103}$, ${\mathrm{In}}^{115}$, and ${\mathrm{Ta}}^{181}$ were analyzed using the statistical model. The analysis yielded the differential cross section $\frac{{d}^{2}\ensuremath{\sigma}}{d\ensuremath{\Omega}\mathrm{dE}}$ and the relative level density $\ensuremath{\omega}(E)$ of the residual nucleus as a function of proton and excitation energy of the residual nucleus. The nuclear temperature $\frac{1}{T}\ensuremath{\equiv}\frac{d(\mathrm{ln}\ensuremath{\omega})}{\mathrm{dE}}$ and the level density parameter $a$ of $\ensuremath{\omega}=C\mathrm{exp}[{(\mathrm{aE})}^{\frac{1}{2}}]$ were obtained. The energy and angular dependence of the spectra are adequately described by the statistical model at back angles, with the indication of the presence of a direct-reaction mechanism contribution at forward angles, which extends to high excitation energies.

Excitation Functions for Inelastic Scattering Reactions of Cadmium-111 and Indium-115

Excitation functions have been measured for the formation of ${\mathrm{Cd}}^{111m}$ and ${\mathrm{In}}^{115m}$ in the bombardment of ${\mathrm{Cd}}^{111}$ and ${\mathrm{In}}^{115}$, respectively, with 6-10 Mev protons, 10-20 Mev deuterons, and 15-40 Mev alpha particles. The excitation function for the ${\mathrm{In}}^{115}(\ensuremath{\alpha}, \ensuremath{\alpha}n){\mathrm{In}}^{114m}$ reaction has also been obtained. All the excitation functions increase monotonically with energy. The cross sections for the formation of ${\mathrm{In}}^{115m}$ at the highest bombarding energies are 1.5 mb, 42 mb, and 5.2 mb, for the proton-, deuteron-, and alpha-induced reactions, respectively. The corresponding cross sections for the formation of ${\mathrm{Cd}}^{111m}$ are 2-3 times larger. The results have been compared with the predictions of the statistical theory. The only definite conclusion can be drawn in the case of the ($\ensuremath{\alpha}, \ensuremath{\alpha}\ensuremath{\gamma}$) reaction where it is shown that an evaporation mechanism cannot account for the measured cross sections at bombarding energies above 25 Mev. The contribution of Coulomb excitation to the observed yields has been calculated. It is found that this process contributes substantially to the ($\ensuremath{\alpha}, \ensuremath{\alpha}\ensuremath{\gamma}$) and ($p, p\ensuremath{\gamma}$) reactions, particularly at low bombarding energies.

Erratum: “Excitation Functions for Alpha-Induced Reactions on Manganese-55”

Erratum: “Excitation Functions for Alpha-Induced Reactions on Manganese-55”