Cross sections for proton induced reactions on 41K and for the reaction 62Ni(α, p)65Cu

Excitation functions have been measured for ⁶²Ni(α, p)⁶⁵Cu in the energy range 6.5–9.0 MeV, for ⁴¹K(p, α)³⁸Ar in the range 0.8–2.6 MeV, for ⁴¹K(p, γ)⁴²Ca, ⁴¹K(p, αγ)³⁸Ar, ⁴¹K(p, nγ)⁴¹Ca, and ⁴¹K(p, p'γ)⁴¹ in the range 0.6–4.0 MeV, and for ⁴¹K(p, n)⁴¹Ca from threshold to 3.0 MeV. Cross sections have been extracted from the data and these are compared with statistical-model calculations based on global optical model parameters. Alternative parameter sets have been tried for the ⁶²Ni(α, p)⁶⁵Cu data and published data for ⁶²Ni(α, γ)⁶⁶Zn and ⁶²Ni(α, n)⁶⁵Zn, and both these and the global parameters have been used in statistical-model calculations of ⁶⁵Cu(p, γ)⁶⁶Zn, ⁶⁵Cu(p, n)⁶⁵Zn and ⁶⁵Cu(p, α)⁶²Ni cross sections, which are compared with published data for these reactions. Both the global and the alternative parameters lead to very good agreement with experiment for all six reactions. Alternative parameters have been tried for the ⁴¹K + p reactions also. The global parameters lead to agreement to within a factor of 2 and the alternative parameters lead to agreement to within a factor of 1.3. The ⁴¹K + p alternative parameters are used in calculations of ⁴¹Ca(n, γ)⁴²Ca, ⁴¹Ca(n, p)⁴¹K and ⁴¹Ca(n, α)³⁸Ar cross sections, and these and the experimental ⁴¹K + p data are used in calculations of thermonuclear reaction rates under stellar conditions for the ⁴¹Ca + n and ⁴¹K + p reactions.     

The influence of the spin-orbital bond on direct photonuclear reactions (γ, n) and (γ, p)

The Courant model for direct photonuclear reactions is modified by using the wave functions of a shell model with spin-orbital bond. It is shown that the introduction of spin-orbital interaction does not influence the cross-section. The changes caused by the spin-orbital bond are apparent only on the angular distribution, which has the Courant forma+bsin² , but with a different value ofb/a, i.e. the anisotropy coefficient. New selection lawsj j, j j±1 are found. The introduction of spin-orbital interaction permits the negative value of the anisotropy coefficient, found in some experimental papers, to be explained in a natural way.

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- - (, n) (, )

: - . , . , - , , a+bsin² , , b/a, . . . j j, j j±1. - , .

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Excerpt from diploma work done at Faculty of Technical and Nuclear Physics in Prague.

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In conclusion the author thanks lecturer J. Kvasnica for the choice of subject and valuable remarks.     

Excitation functions of 40Ar(p,p′γ)40Ar and 40Ar(p,γ)41K reactions

The excitation functions of ⁴⁰Ar(p,p′γ)⁴⁰Ar and ⁴⁰Ar(p,γ)⁴¹K reactions are measured in the E _p = 1.0–3.0 eV range of accelerated protons. The excitation function in the E _p > 2.6 MeV range of accelerated protons is measured for the first time. The strengths of all (more than 200) measured resonance states are calculated.     

Relaxation of the analyzing power of the (p, τX) and (p, αX) reactions in the continuum

The observed continuous decrease of the analyzing power for the reactions ($\text{p}$, τX) and ($\text{p}$, αX) on ⁹⁰Zr and ²⁰⁹Bi at E_p = 72 MeV as a function of the excitation energy of the final nucleus is described by a phenomenological relaxation process.     

Studies of the gamma-strength function and low energy levels in 65Ga using the (p, γ) average resonance method

The ⁶⁴Zn(p, γ)⁶⁵Ga reaction has been studied in the proton energy ranges E_p = 2.0–2.9 and 3.3–4.3 MeV. Using a three-crystal pair spectrometer, gamma-ray spectra of primary transitions were measured throughout this proton energy interval in steps of about 20 keV. An average gamma ray spectrum for each energy region was formed by adding all the relevant individual spectra after adjustment due to the change of the proton energy. In the excitation energy range 0.0–3.7 MeV 50 levels, of which 20 are new, were observed. The gamma strength function was deduced from the average intensities of the primary gamma-rays. The absolute value of the strength function was found to be 5–10 times smaller than that expected from the extrapolation of the lorentzian shape of the El giant resonance.     

Nuclear structure studies of 125Te with (n,γ), (d,p) and (3He,α) reactions

Levels in ¹²⁵Te were investigated in the range up to 3.3 MeV excitation energy by the (n,γ), (d,p) and (³He,α) reactions. Over 160 levels and about 360 γ-transitions were established, most for the first time. The states below 2.3 MeV with the most complete spectroscopic information were interpreted in terms of the interacting boson-fermion model (IBFM). Unitary treatment of both positive- and negative-parity states is achieved with the same model parameter close to the intermediate case between O(6) and U(5) limits. Excitation energies, electromagnetic transition rates, γ-branchings and spectroscopic factors are discussed in connection with the possible structures. A family of low-spin negative-parity states has been identified and understood by the IBFM proving their antialigned origin.     

Spectroscopy of 88Sr with the 87Sr(n, γ) and 87Sr(d,p) reactions

The γ-ray spectrum emitted after thermal neutron capture in ⁸⁷Sr was studied at the ILL high flux reactor with pair- and intrinsic Ge-spectrometers. 661 transitions were assigned to the reaction ⁸⁷Sr(n, γ)⁸⁸Sr and 205 of them were placed into a ⁸⁸Sr level scheme of 47 levels. This represents 88% of the observed intensity. The level energies were determined with a precision of better than 20 ppm; the neutron binding energy was determined as 11 112.69 (22) keV. To aid the analysis high resolution particle spectra of the reaction ⁸⁷Sr(d, p)⁸⁸Sr were measured at 20 MeV deuteron energy with the Munich Q3D spectrometer. 85 states were observed with this reaction. The data helped to establish newly found levels and to differentiate between primary and secondary transitions in the (n, γ) data. The observed level densities and primary transition strengths are compared with statistical model predictions and non-statistical effects are discussed.     

Correlations and the cross section of exclusive (e,e′p) reactions for 16O

The reduced cross section for exclusive (e, e′p) reactions has been studied in DWIA for the example of the nucleus ¹⁶O using a spectral function containing effects of correlations. The spectral function is evaluated directly for the finite nucleus starting from a realistic nucleon-nucleon interaction within the framework of the Green's function approach. The emphasis is focused on the correlations induced by excitation modes at low energies described within a model-space of shell-model configurations including states up to the sdg shell. Cross sections for the p-wave quasi-hole transitions at low missing energies are presented and compared with the most recent experimental data. In the case of the so-called perpendicular kinematics the reduced cross section derived in DWIA shows an enhancement at high missing momenta as compared to the PWIA result. Furthermore the cross sections for the s- and d-wave quasi-hole transitions are presented and compared to available data at low missing momenta. Also in these cases, which cannot be described in a model without correlations, a good agreement with the experiment is obtained.     

The 39(α, p)42Ca cross section and thermonuclear reaction rate

Excitation functions have been measured for the reaction ³⁹K(α, p)⁴²Ca over the energy range 4.5–9.0 MeV. Cross sections have been extracted from the data for individual proton groups and for aggregates of proton groups. These are compared with statistical-model calculations based on global optical model parameters. The overall agreement is good to within a factor of 1.5. The data and the statistical-model results are used in calculations of thermonuclear reaction rates for temperatures of astrophysical interest.     

Level structure of 87Sr from the 86Sr(n, γ) and 86Sr(d,p) reactions

The γ-ray spectrum emitted after thermal neutron capture in ⁸⁶Sr was studied at the ILL high flux reactor with pair- and intrinsic Ge spectrometers. 759 transitions were assigned to the reaction ⁸⁶Sr(n, γ)⁸⁷Sr and 385 of them were placed into a ⁸⁷Sr level scheme of 80 levels. This represents 90% of the observed intensity. The level energies were determined with a precision of better than 20 ppm; the neutron binding energy was determined to be 8428.16 (17)keV. In a second set of experiments high resolution particle spectra of the reactions ⁸⁶Sr(d, p)⁸⁷Sr and ⁸⁸Sr(d, t)⁸⁷Si were recorded at 20 MeV deuteron energy with the München Q3D spectrometer. These data were used to establish newly found levels and to differentiate between primary and secondary transitions in the (n, γ) data. The observed level densities and primary transition strengths are compared with statistical models.     

Direct measurement of the resonance strengths and branching ratios of low-energy(p, γ) reactions on Mg isotopes

Proton capture reactions on Mg isotopes are significant in the Mg-Al cycle in stellar H-burning.In particular,the resonance strengths and branching ratios of low-energy resonances in Mg(p,y)26 A1 reactions determine the production of ~(26)Al,which is one of the most important long-lived radioactive nuclei in nuclear astrophysics.In this article,we report our first experiment using the intense proton beam of approximately 2 mA provided by the JUNA accelerator ground laboratory and a new technique that can minimize the composition change of targets under intense beam irradiation.The resonance strengths and branching ratios of E=214,304,and 326 keV resonances in the reactions of ~(24)Mg(p,γ)~(26)Al,~(25)Mg(p,γ)~(26)Al,and ~(26)Mg(p,γ)~(27)Al,respectively,were measured with high accuracy.The success of this experiment provides a good calibration for the nuclear astrophysical experiment at the Jinping underground laboratory.     

Excitation of isomeric states in the (γ,n), (n, 2n), and (γ, 2n) reactions on the 113In nucleus

The induced-activity method was used to measure the isomeric ratio of the yields of the (γ, n), (n, 2n), and (γ, 2n) reactions on the ¹¹³In nucleus. The energy dependence of the isomeric ratios of the yields of the photonuclear reactions ¹¹³In(γ, n)^112m,g In and ¹¹³In(γ, 2n)^111m,g In is studied in the energy range of 12–35 MeV.     

Effects of the form factor on exclusive (e, e′p) reactions

For the exclusive (e, e′p) reaction, we discuss the possibility of observing effects due to swollen nucleons in the nuclear medium, such as ⁴⁰Ca and ²⁰⁸Pb, by introducing form factors of the nucleon in the nuclear medium. These form factors include effectively the change of nucleon properties in the nuclear medium. This calculation is performed by using a Dirac-Hartree single particle model for a bound state and a relativistic optical model for a continuum state with inclusion of the electron Coulomb distortion. The effect of the form factor, which increases with higher momentum transfer (q ≥ 400MeV/c) is too small to be discerned from the errors on the available experimental data. But it affects the determination of spectroscopic factors to some extent.     

Microscopic calculation of the 3He(α,γ)7Be and 3H(α,γ)7Li capture cross sections using realistic interactions

The radiative capture cross sections for the 3He(α,γ)7Be and 3H(α,γ)7Li reactions are calculated in the fully microscopic fermionic molecular dynamics approach using a realistic effective interaction that reproduces the nucleon-nucleon scattering data. At large distances bound and scattering states are described by antisymmetrized products of 4He and 3He/3H ground states. At short distances the many-body Hilbert space is extended with additional many-body wave functions needed to represent polarized clusters and shell-model-like configurations. Properties of the bound states are described well, as are the scattering phase shifts. The calculated S factor for the 3He(α,γ)7Be reaction agrees very well with recent experimental data in both absolute normalization and energy dependence. In the case of the 3H(α,γ)7Li reaction the calculated S factor is larger than available experimental data by about 15%.     

Determination of astrophysical ~7Be(p,γ)~8B reaction rates from the ~7Li(d,p)~8Li reaction

The7Be(p,γ)8B reaction plays a central role not only in the evaluation of solar neutrino fluxes but also in the evolution of the first stars.Study of this reaction requires the asymptotic normalization coefficient(ANC) for the virtual decay8 Bg.s.→7Be + p.By using the charge symmetry relation,we obtain this proton ANC with the single neutron ANC of8 Lig.s.→7Li + n,which is determined with the distorted wave Born approximation(DWBA) and adiabatic distorted wave approximation(ADWA) analysis of the7Li(d,p)8Li angular distribution.The astrophysical S-factors and reaction rates of the direct capture process in the7Be(p,γ)8B reaction are further deduced at energies of astrophysical relevance.The astrophysical S-factor at zero energy for direct capture,S17(0),is derived to be(19.9±3.5) e V b in good agreement with the most recent recommended value.The contributions of the1+and 3+resonances to the S-factor and reaction rate are also evaluated.The present result demonstrates that the direct capture dominates the7Be(p,γ)8B reaction in the whole temperature range.This work provides an independent examination to the current results of the7Be(p,γ)8B reaction.     

Cross section of reaction 181Ta(p,nγ)181W and the influence of the spin cut-off parameter on the cross section

In this work, the program Cindy was modified to calculate the formation cross section of each energy level of residual nucleus ¹⁸¹W resulting from the reaction ¹⁸¹Ta(p,nγ)¹⁸¹W. The concerned cross sections calculated at proton energy E_p=4.5-8.5 MeV agreed well with experimental results. The influence of the spin cut-off parameter in the energy level density model on the cross section was studied. The obtained results show that the influence of spin cut-off is obvious for lower energy levels.     

Charge-exchange processes in the quasi-elastic (e,e′p) and (e,e′n) reactions

Calculations of charge-exchange processes in the final state of the quasi-elastic (e, e′N) reaction have been performed employing the Lane formalism. The Lane equations were decoupled by means of a transformation to the isospin representation. It is found that charge exchange has a small effect on the (e, e′p) cross section, but may play an appreciable role in the (e, e′n) reaction.     

Measurement of the exclusive D(p,e+e−)3He and D(p, γ)3He reactions at 98 and 176 MeV

A high resolution magnetic pair spectrometer for medium energy photons has been used for studies of the exclusive (p, e⁺e⁻) and (p, γ) reactions on deuterium at 98 and 176 MeV. The (p, e⁺e⁻) cross sections, obtained at 40° and 80°, are compared with the corresponding data for the (p, γ) reaction measured with the same apparatus. At small virtual photon masses the (p, e⁺e⁻) cross sections show significant enhancement over what is expected from model calculations, a behaviour which has earlier been observed also for the ¹¹B(p, e⁺e⁻)¹²C reaction.