Compound Nucleus Theory Research Articles

Evidence of compound nucleus theory in the population of incompletely fused composite system $$^{160}$$Dy*

Evidence of compound nucleus theory in the population of incompletely fused composite system $$^{160}$$Dy*

Investigating the influence of input angular momentum on independence hypothesis in heavy-ion induced fusion reactions

The experimental verification of compound nucleus theory has successfully been performed for light ion induced reactions using proton and α-particle beams on different targets. However, such studies using the heavy ion beams are scarce due to the complex nature of heavy ion interaction process. The present work is an attempt to validate the Bohr's independent hypothesis using heavy ion beam of 18O beam on 159Tb targets and 12C on 165Ho targets, forming the same compound nucleus 177Ta. A channel wise analysis of cross section data for evaporation residues produced in 18O+159Tb and 12C+165Ho systems has been performed within the framework of statistical model code PACE4 and found to reasonably agree with the experimental data. Further, a comparison of reaction cross section data for the same evaporation residues produced in the two different systems has been found to follow Bohr's compound nucleus hypothesis at relatively higher excitation energies. However, at relatively lower excitation energies, a significant deviation in the measured cross section data of the same residues in the above mentioned systems have been observed and is attributed to the discrepancies in angular momentum values. Such discrepancies are well explained on the basis of input angular momentum involved in the reactions.

Cross section measurements of the 7 8Se(p,7)7 9Br and 8 0Se(p,7)8 1Br reactions

In beam cross section measurements of the 78Se(p,7)79Br and 80Se(p,7)81Br reactions have been carried out at Ep=1.4-3.5 MeV, by using high efficiency HPGe detectors with BGO shields for Compton background suppression. A preliminary analysis yielded total cross sections ranging from 10 μb to 3 mb. By means of the statistical compound nucleus theory of Hauser-Feshbach cross sections have also been calculated. A comparison between experimental data and theoretical predictions is presented.

Statistical model calculations of the 7Li +11 Β reaction

The 7Li + 11 Β reaction has been studied in the energy range from a little below to about three times the Coulomb barrier by measuring the cross section of the 7- ray transitions in the residual nuclei produced. Statistical compound nucleus calculations have been performed in order to interpret the experimental data as well as to extract cross sections of the individual exit channels. The statistical compound nucleus theory can reproduce rather well the absolute j - ray and the various reaction channel excitation functions.

Cross section measurements of the93Nb(p,γ)94Moreaction atEp=1.4–4.9MeVrelevant to the nucleosyntheticpprocess

In-beam cross section measurements of the Nb-93(p,gamma)Mo-94 reaction have been carried out at E-p = 1.4-4.9 MeV, by using high efficiency high-purity Ge detectors, partly with BGO shields for Compton background suppression. From the resulting cross sections, which lie in the 0.5-300 mub range, astrophysical S factors as well as reaction rates have been obtained. By means of the statistical compound nucleus theory of Hauser and Feshbach, cross sections and reactions rates have also been calculated. A good agreement between the experimental data and the theoretical predictions has been found.

Computation of activities induced by 14 MeV neutrons for the elemental analysis of human tissues, skin and tooth enamel

For planning experiments for neutron activation analysis investigations at 14 MeV, suitable induced beta activities in Bq/g/neutron flux have been computed via appropriate reactions for the estimation of 19F, 23Na, 24Mg, 31P, 32S, 35,37Cl, 39K, 40Ca, 55Mn, 56Fe, 66Zn, 63,65Cu, 107,109Ag and 208Pb. The computational work for (n,p); (n,α); (n,n′) and (n,2n) reactions induced with 14 MeV neutrons are based on the pre-equilibrium emission mechanism and also the compound nucleus theory with otpical model potential and pairing energy corrections. The cross-sections obtained by pre-equilibrium computer codes are reasonable and have been used in the present computations.

Cross-sections of a few (n,α) and (n, p) reactions induced at 14.7 MeV neutrons

Cross-sections of the nuclear reactions27Al(n, p)27Mg,30Si(n, α)27Mg,52Cr(n, p)52V,53Cr(n, p)53V,54Cr(n, p)54V,54Cr(n, α)51Ti and120Sn(n, α)117Cd at 14.7 Mev neutrons were measured using56Fe(n, p)56Mn and27Al(n, α)24Na as monitor reactions. For comparison, theoretical values of the cross-section for these reactions were also obtained through different approaches of compound nucleus theory and computer code Alice. Accuracies achieved in the present measured values of the cross-sections are better than those available in literature.

Resonances in27Al+α Reaction atEα=3.4-6.4 MeV

The gamma-radiation following the reactions 27 Al(α, y) 31 P, 27 Al(α, py) 30 Si, 27 Al(α, α'y) 27 Al and 27 Al(α, ny) 30 P have been measured. Excitations functions were obtained at 90°in the energy range E α =3.4-6.4 MeV for selected of y-ray energies with a high resolution HpGe detector and a large volume Nal(TI) scintillator. In all, about 300 resonances were observed and the corresponding excitation energies (E x =12−15 MeV) of the compound system 31 P were determined. The obtained level density in this region was compared with the calculation of a statistical compound nucleus theory

The compound nucleus at high excitation energy

Heavy ion reactions produce compound nuclei with high excitation energies and large angular momentum. Under these conditions many of the concepts used in compound nucleus theory lose their validity. Energy levels become broad and overlap and the level density is not properley defined. The life time of a compound nucleus becomes very short and it may not reach equilibrium before it decays. Ways of thinking about the compound nucleus under these conditions are discussed in this lecture.

Theory of vibrational, rotational, and phonon inelastic collisions of a triatomic molecule by a crystal surface. II. Approximate methods and applications to resonance and adsorption.

Realistic theoretical approximation schemes for the calculation of phonon and vibrational-rotational (triatomic) molecule--crystal-surface inelastic scattering were derived from the formulation in the preceding paper. These schemes can be adopted to a flexible input potential and are at the same time capable of yielding effective ab initio computation. An iterative coupled-integral-equation method thus obtained is much more tractable than its counterpart of the coupled differential equation when phonons in the solid and vibrations and rotations of the molecular projectile are taken into account. This approach is further useful for the triatomic projectile case where multiphonon transitions become more probable compared to the light atom and/or diatom projectile, since it yields calculational procedures of DWBA of any higher orders as a byproduct. A rotationally impulsive integral-equation scheme appropriate for the triatomic molecular projectile (and basically applicable to the polyatomic case) with simplification of the rotational states of the molecule in the calculational procedures is also derived from this method.For the purpose of studying direct (nonresonant) inelastic scattering of the simultaneous diffraction, phonon, and vibrational-rotational transitions, angular, velocity, and vibrational-rotational state distribution of the scattered molecule, a coupled-diffractive-channel transition-matrix (CDCTM) method and a coupled-molecular-state transition-matrix (CMSTM) method with an exponential unitarization scheme are obtained. The former may be used when the corrugation of the molecule--crystal-surface interaction potential is significant as in nonmetallic crystals and the latter could be used when the dependence on the internal coordinates of the molecule or the anisotropy is considerably large in the interaction potential. As an application of the present scattering formulation, a bound-state resonance scattering method for a (triatomic) molecule-surface system is presented within the framework of a Feshbach-type internal excitation approach. Our emphasis here is on a systematic and unified treatment of the mediations of the diffraction, phonon, and vibration-rotation in selective adsorption and desorption, which are analogous to compound nucleus theory in nuclear reaction studies.The present method describes such trapping-desorption processes for inelastic (indirect) resonance scattering. Our method is adoptable again to arbitrary input potentials, and even with inclusion of phonons and vibrations and rotations, it yields efficient ab initio calculational procedures from which the resonance energies, the energy shift, width function, line shapes, and the intensities of the simultaneous diffraction, phonon, and vibrational-rotational transitions can be obtained. Among other effective calculational schemes, we discuss a method where the bound-state resonance scattering amplitude is computed from our explicit expressions with simplified wave functions. They are obtained as products of the spatial wave function generated from the elastic diffraction potential and vibrational-rotational and phonon states. The nonresonant potential scattering amplitude is obtained within open channels from, e.g., a coupled-diffractive-channel transition-matrix approach. Finally, a method of obtaining the quantal trapping or physisorption probabilities of the molecule, which deals with a half-collision process, is presented as another application of our scattering formulation.

Recent Developments in Compound-Nucleus Theory

The evaporation model interpretation of compound-nucleus reactions is reviewed. Among the topics considered are pole parametrization, the K-matrix, cross sections, and intermediate structure. (AIP)

Identification of a 3+ state in16O and evidence for a (1f 7/2 1p 1 2/?1 ) component in its wave function

Excitation functions and angular distributions for the elastic scattering of protons on15N and the reactions15N(p, α 0)12C and15N(p,α 1)12C* were measured in the proton energy range of 2.50−5.14 MeV (E x (16O)=14.47−16.94 MeV). Besides known resonances two new ones were found at 16.46 and 16.82MeV. For the latterJ ⋆=3+ is assigned using the compound nucleus theory. The wave function of this state contains a (1f 7/2 1p 1 2/−1 )3-particle-hole-component. Earlier spin parity assignments of other resonances are discussed.

Energy levels of80,82Br from (p, n?) reactions

The levels of odd-odd80, 82Br nuclei have been investigated via80, 82Se(p, nγ)80, 82Br reactions. Excitation functions and angular distributions were analysed with the Hauser-Feshbach compound nucleus theory. 27 and 29 levels have been identified. The transitions connecting the first 1+ and 2−levels have been studied by the delayed coincidence method and their half-lives are 7.8±0.5 ns and 7.2±0.8 ns for80Br and82Br respectively. The experimental results are discussed in the framework of thej- j coupling.

55Mn(n, n'γ) cross-section studies for En = 1.0–3.6 MeV

Absolute 55Mn(n, n′γ) γ-ray production cross sections have been measured for 19 transitions from levels up to and including the 2429 keV state in 55Mn over the energy range E n = 1.0–3.6 MeV. Angular distributions were also measured for 6 of the transitions. Branching ratios were extracted and total inelastic neutron cross sections were inferred for these 55Mn excited states. The measured and inferred cross sections are compared with calculated cross sections using the statistical compound nucleus theory.

The reaction19F(n,?)16N atE n =13.9 MeV and 15.6 MeV

Differential cross sections of the reaction19F(n, α)16N have been measured atEn = 13.9 MeVd and 15.6 MeV. The results can be interpreted in terms of compound nucleus theory. Statistical model calculations were undertaken to clear up the different reaction behaviour of the reactions19F(n, α)16N and19F(p, α)16O at bombarding energies near 14 MeV.

Energy Spectra of Secondary Neutrons from the 238U(n, 2n) and (n, 3n) Reactions

A consistent compound nucleus theory of (n,2n) and (n,3n) neutron emission was applied to $sup 238$U to obtain the energy spectra of the second and third secondary neutrons. The evaluation was based on inelastic level excitation and evaporation data for $sup 238$U, $sup 237$U, and $sup 236$U. The $sup 238$U and $sup 236$U data were retrieved from ENDF/B-IV files; the $sup 237$U data were evaluated in the Soreq Nuclear Research Center using experimental information and statistical reaction theory codes. At reaction energies E$sub 0$ just above the (n,2n) threshold energy B$sub 2$, the energy E of the second inelastic neutron has a spectrum of (E$sub 0$ - B$sub 2$ - E); above the (n,3n) threshold, B$sub 3$, the third neutron energy has a spectrum of (E$sub 0$ - B$sub 2$ - E)$sup 3$. At energies E$sub 0$, high above the thresholds, the second and third neutron spectra approach the evaporation form. A secondary neutron spectrum for any given reaction energy E$sub 0$ is approximated by a composite form for which the temperatures and blending coefficients were evaluated for several energies in the range from threshold up to 15 MeV. 6 figures, 3 tables. (auth)

Cross sections for the (n, n') and (n, 2n) reactions on 113In and 204Pb

The cross sections for the (n, n') m and (n, 2n) reactions on the target nuclei 113In and 204Pb were measured by the activation method in the neutron energy range 13 to 18 MeV. The results were compared with the predictions of compound nucleus theory. The angular momentum effects and the γ-decay of unbound states were taken into account.

Excitation Functions for Helion-Induced Reactions in Iron

Target foil stacks of iron were bombarded with beams of helions at incident energies \ensuremath{\le} 70 MeV. $\ensuremath{\gamma}$ spectra of individual foils were measured and analyzed to obtain excitation functions for production of $^{56,\phantom{\rule{0ex}{0ex}}57}\mathrm{Ni}$, $^{55,56,57,58}\mathrm{Co}$, $^{52,54,56}\mathrm{Mn}$, and $^{51}\mathrm{Cr}$; for $^{53}\mathrm{Fe}$ and $^{52}\mathrm{Mn}$, data were obtained for both ground and isomeric states. The yields of $^{56}\mathrm{Co}$ and $^{57}\mathrm{Co}$ are much larger than those of the respective Ni isobars. Recoil measurements (to determine momentum transfer to the target nucleus) were made at ${E}_{h}=41 \mathrm{and} 51$ MeV. These data show $^{57}\mathrm{Co}$ to result principally from direct reactions. There is also evidence of a large contribution by direct reactions to the $^{56}\mathrm{Co}$ yield. The excitation-function data are compared with predictions of compound-nucleus evaporation theory; these indicate compound-nucleus reactions to be the dominant contributor to the yields of $^{51}\mathrm{Cr}$, $^{52,\phantom{\rule{0ex}{0ex}}54}\mathrm{Mn}$, $^{52,\phantom{\rule{0ex}{0ex}}53}\mathrm{Fe}$, $^{55}\mathrm{Co}$, and $^{56,\phantom{\rule{0ex}{0ex}}57}\mathrm{Ni}$.

The [formula omitted] reaction: Angular correlations and the 14.8 MeV level in 16O

Angular correlations in the reaction 12 C(α,α 1γ 4.43) 12 C have been studied for incident energies of 10.2, 10.3 and 10.5 MeV. The data were compared to a single-level compound-nucleus theory. The data substantiate the recent assignment of J π = 6 + to the 14.8 MeV level in 16O.

Gamma-rays from Neutron-induced Reactions in Nitrogen

The gamma-ray production cross sections of nitrogen have been measured at three different incident neutron energies, 4.2, 5.9 and 6.9 MeV. The gamma-ray spectrometer was a Ge(Li)-detector. Time-of-flight techniques were employed to suppress the background caused by neutron interactions in the Ge(Li)-detector. The efficiency of the gamma-ray spectrometer was measured with calibrated gamma-ray sources and (p,γ)-reactions. The primary neutron flux was measured with a proton-recoil telescope. Differential gamma-ray production cross sections at 55° are given. The angular distributions of the gamma-rays were measured at En = 6.9 MeV between 40° and 140°. The results were compared with calculated distributions obtained with a statistical compound-nucleus theory. The life-times of the six lowest excited states in 14N could be estimated from the observed Doppler shifts in the angular distribution measurement.