The 12C(9Be,n)20Ne reaction

A study of the ¹²C(⁹Be, n)²⁰Ne reaction has been carried out at bombarding energies of 16 and 24 MeV. The spectra at both incident energies are dominated by a consistent set of levels between an excitation energy of 7.3 ± 0.4 and 15.7 ± 0.3 MeV. The rotational band based on the K^π = 0₃⁺ state appears to be strongly populated. Based on this selectivity, additional evidence is provided in favor of identification of the 8⁺ state at 15.9 MeV with this 0₃⁺ band. Angular distributions measured at the higher bombarding energy are compared with statistical compound-nuclear calculations. It appears that a non-statistical mechanism is responsible for the reaction's selective population of states with 8p-4h configuration. Such a mechanism, involving the preferential breakup of the ⁹Be into ⁸Be plus a neutron, is discussed.     

A generalized r-matrix interpretation of the 89Y + n total cross section at low incident energies

The resonance structure observed in the ⁸⁹Y(n, n)⁸⁹Y total cross-section measurements in the range of 0.9 to 1.2 MeV neutron energy is investigated using a comprehensive theory of nuclear reactions. A shell-model calculation which formed the initial stage of this study predicts satisfactorily the energies of the negative-parity states that contribute to the observed anomalies. The neutron decay widths for these resonances are evaluated using the model wave functions. The general trends in the energy dependence of the total cross section are satisfactorily reproduced by the theory. The factors that could contribute to the discrepancies between theory and experiment are discussed. The theoretical estimates of the damping widths for the two 1^? anomalies that occur in this region were within 20 to 25% of the experimental values and support the view that these are intermediate-type resonances. Their configurational structure as predicted by the model calculation suggests that they are the parent states of the T_> components of the giant dipole resonance near 21.0 MeV in ⁹⁰Zr. The distribution of E1 widths calculated for a proposed 1^? → 2⁺ (at 0.78 MeV) transition in ⁹⁰Y indicates that an anomaly corresponding to these 1^? states can also be expected in the (n, γ) reaction.     

The reaction 14C(3He,n)16O and the coexistence model of 16O

The reaction ¹⁴C(³He, n)¹⁶O has been measured at a ³He bombarding energy of 25.4 MeV. The zero-degree differential cross section for the excitation of the three low lying 0⁺T = 0 states, at energies 0.0, 6.05 and 12.05 MeV are, respectively, 1.33 ± 0.10, 0.49 ± 0.10, and 0.50 ± 0.10 mb/sr These measured cross sections are in rough agreement with single-step zero-range DWBA calculations using an empirically determined ¹⁴C ground state wave function and in which the Brown and Green coexistence-model wave functions are used to describe the ¹⁶O 0⁺ states. The angular distribution of the transition to the ground state is measured between 0° and 32°.     

Investigation of 89Y and 87Rb by (p,p′) reactions

The (p, p′) reaction on ⁸⁹Y at incident energies of 20.51 MeV and 14.33 MeV and on ⁸⁷Rb at 20.89 MeV has been studied. In ⁸⁹Y 28 levels with E_ex between 2 and 4.2 MeV and 79 levels with E_ex between 4.2 and 6 MeV have been identified. In ⁸⁷Rb 45 levels with E_ex up to 4.2 MeV have been found. Transferred orbital angular momenta and deformation parameters have been deduced from a macroscopic DWBA analysis of the differential cross sections. The experimental results are not consistent with the interpretation of states in ⁸⁹Y and ⁸⁷Rb as resulting from the weak-coupling of a proton or proton-hole to excited states of the ⁸⁸Sr core. Simple shell model arguments are able to yield at least a qualitative agreement with the level scheme as found for ⁸⁹Y.     

The (n, 2n) cross sections of 85Rb, 87Rb and 144Sm

The (n, 2n) cross sections at neutron energies between 14.9 and 17.0 MeV have been measured for ⁸⁵Rb, ⁸⁷Rb and ¹⁴⁴Sm by the mixed-powder method and γ-ray detection by a Ge(Li) spectrometer. Using the ²⁷Al(n, α)²⁴Na reaction for monitoring, the measured cross sections were (in mb): ${}^{85}\text{Rb}\text{(}\text{n}\text{, 2}\text{n}\text{)}{}^{\mathrm{<mtext>84(</mtext><mtext>m+g</mtext><mtext>)</mtext>}}\text{Rb}\text{, 1125±141, 1177±148}\text{and}\text{1235±162}\text{at}\text{15.0±0.4}\text{MeV}\text{, 16.2±0.7}\text{MeV and}\text{17.0±0.9}\text{MeV, respectively}\text{;}{}^{85}\text{Rb}\text{(}\text{n}\text{, 2}\text{n}\text{)}{}^{\mathrm{<mtext>84</mtext><mtext>m</mtext>}}\text{Rb}\text{, 662±83, 688±87}\text{and}\text{765±99}\text{at}\text{15.0±0.4}\text{MeV}\text{, 16.2±0.7}\text{MeV and}\text{17.0±0.9}\text{MeV}\text{,}\text{respectively}\text{;}{}^{87}\text{Rb}\text{(}\text{n}\text{, 2}\text{n}\text{)}{}^{\mathrm{<mtext>86(</mtext><mtext>m+g</mtext><mtext>)</mtext>}}\text{Rb}\text{, 1336±168}\text{and}\text{1301±162}\text{at}\text{15.0±0.4}\text{MeV and}\text{16.2±0.7}\text{MeV respectively}\text{;}{}^{144}\text{Sm}\text{(}\text{n}\text{, 2}\text{n}\text{)}{}^{\mathrm{<mtext>143(</mtext><mtext>m+g</mtext><mtext>)</mtext>}}\text{Sm}\text{, 1202±130, 1300±141, 1516±179}\text{and}\text{1514±179}\text{at}\text{14.9±0.3}\text{MeV}\text{, 15.5±0.3}\text{MeV}\text{, 16.4±0.5}\text{MeV and}\text{16.7±0.2}\text{MeV, respectively}$. The measured values are compared with the statistical model calculations of Pearlstein.     

13.5—14·6 MeV能区中子引起的89Y39（n，2n）88Y39反应截面的测量

用^93Nb（n,2n）^92mNb和^90Zr（n,2n）^89m＋gZr截面比法测定中子能量,以^93Nb（n,2n）^92mNb反应截面作中子注量标准,用活化法测量了13．5-14．6MeV中子引起的^89Y（n,2n）^88Y的反应截面值。由（13．5±0．3）,（14.1±0．2）,（14.6±0．3）MeV中子引起的^89Y（n,2n）^88Y反应截面值分别为（759±42）,（835±42）和（958±53）mb。Cross section for （n, 2n） reaction on Yttrium have been measured at energy of 14 MeV neutrons from H（d, n）He by using activation technique. The ^93Nb（n, 2n）^92mNb reaction was used to monitor the neutron fluence, HPGe detector was used to detect the γ-rays. The cross section of ^89Y （n, 2n）^88Y reaction are 759 ± 42, 835 ±42, 958 ±53 mb for neutron energy 13.5 ±0.3, 14.1±0.2, 14.6 ±0.3 MeV, respectively.     

An accurate measurement of the 7Li(d,p)8Li excitation function from Ed = 0.6 MeV to 2.0 MeV

The excitation function for the ⁷Li(d, p)⁸Li reaction was determined at incident deuteron energies ranging from 0.613 to 1.948 MeV by measuring delayed α-particles. This excitation function revealed resonances at 0.773 ± 0.010 MeV and 1.025 ± 0.010 MeV with cross sections of 181 ± 8 mb and 168 ± 7 mb, respectively. No resonance was observed in the region of 1.4 MeV.     

Neutron total,scattering and inelastic Gamma-ray cross sections of yttrium at few MeV energies

Neutron total, scattering and (n; n′,γ) cross sections of elemental yttrium (⁸⁹Y) were measured in the few-MeV region. The neutron total-cross-section measurements were made with broad resolutions from ≈0.5 to 4.2MeV in steps of ?0.1 MeV. Neutron elastic- and inelastic-scattering cross sections were measured from ≈1.5 to 4.0 MeV, at incident-neutron energy intervals of ≈50keV and at ten or more scattering angles distributed between 20 and 160 degrees using neutron detection. Inelastic-scattering cross sections were also determined using the (n; n′,γ) reaction at incident energies from 1.6 to 3.8 MeV at intervals of 0.1 MeV. Gamma-rays and/or inelastically-scattered neutrons were observed corresponding to the excitation of levels at: 909.0±0.5, 1,507.4 ±0.3, 1,744.5±0.3, 2,222.6±0.5, 2,530±0.8, 2,566.4±1.0, 2,622.5±1.0, 2,871.9 ±1.5, 2,880.6±2.0, 3,067.0±2.0, 3,107.0±2.0, 3,140.0±2.0, 3,410.0±2.0, 3,450.0±2.0, 3,504.0 ±1.5, 3,514.0±2.0, 3,556.0±2.0, 3,619.0±3.0, 3,629.0±3.0 and 3,715.0±3.0 keV. The experimental results are discussed in terms of the spherical-optical-statistical, coupledchannels, and core-coupling models, and in the context of previously reported excitedlevel structure.     

The 75Se(n, γ)76Se reaction and the low-lying level structure of 76Se

The ⁷⁵Se(n, γ)⁷⁶Se reaction was studied through consecutive neutron capture with the use of pair and curved crystal spectrometers. The high-resolution data have allowed construction of a very well established level scheme including many new levels above ～ 2.8 MeV excitation energy. The resulting neutron binding energy, 11154.0 ± 0.3 keV, is lower than the value given in the mass table. The ⁷⁵Se(n, γ) cross section was determined to be 330 ± 100 b. The level scheme and branching ratios were compared with results from calculations in the framework of the interacting boson model.     

Two-nucleon pick-up from spin-12 targets (II). 89Y

The angular distributions for the ⁸⁹Y(p, t), (p, τ), and (d, α) reactions are compared to DWBA predictions and to the data for the ⁹⁰Zr(p, t) and (d, α) reactions. Several new spins are assigned to levels of ⁸⁷Y. A weak coupling model is tested by the comparison between the reactions on ⁸⁹Y and ⁹⁰Zr, and found to fail. The (d, α) reaction is found to populate strongly levels at excitation energies of 2.70 MeV and 3.07 MeV in ⁸⁷Sr, corresponding roughly in Q-value and strength to states formed in ths ⁸⁸Sr(d, α)⁸⁶Rb reaction.     

Radiative capture of fast neutrons by 89Y and 140Ce

The γ-ray spectra from the reactions ⁸⁹Y(n, γ)⁹⁰Y and ¹⁴⁰Ce(n, γ)¹⁴¹Ce have been measured in the neutron energy range of 6.2–15.6 MeV. The pulse-height spectra were recorded with NaI(Tl) spectrometers and time-of-flight techniques were used to improve signal-to-background ratio. Capture cross sections were determined for γ-ray transitions to the two $\text{2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ levels at 0 and 203 keV of ⁹⁰Y and to the $\text{2}\text{f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ ground state of ¹⁴¹Ce as well as integrated cross sections to bound states in these nuclei. The observed γ-ray spectra and partial radiative capture cross sections were compared with predictions of the direct-semidirect capture theory. The resonance behaviour with neutron energy of both the ground-state and integrated partial capture cross sections shows the validity of the semidirect model for ⁸⁹Y and ¹⁴⁰Ce in the region of neutron energy encompassing the giant-dipole resonance. The observed symmetry of the cross sections about the peak of the resonance argues strongly for the complex form of the particle-vibration coupling interaction. A detailed comparison of the predictions of the DSD model using the complex coupling interaction shows that the capture cross sections are relatively insensitive to the real part of the interaction.     

Étude des niveaux du noyau 27Al par la réaction 26Mg(d,n)27Al

The ²⁶Mg(d, n)²⁷Al reaction has been studied at 6 and 8 MeV deuteron bombarding energies using the time-of-flight technique for neutron detection. The good neutron energy resolution of the present work permitted the determination of the excitation energy of 70 states populated by the reaction. Angular distributions of neutrons leading to 50 levels in ²⁷Al were measured between 0° and 100°. The experimental cross sections were analysed in the framework of the DWBA and Hauser-Feshbach theories to deduce l_p values and transition strengths. New spin and parity assignments were obtained for 11 levels. The agreement between the DWBA predictions and some of the measured angular distributions was improved by modifying the optical-model radii in both incoming and outgoing channels. The experimental results are compared with the corresponding data from previous studies and with Nilsson-model and recent shell-model calculations.     

Spin distribution factors for formation of metastable states of 90Y and 91Y through (n,p) reactions over neutron energies 5–15 MeV

The variations in the isomer ratio with the spin distribution factor were studied to obtain the cross-sections for formation of metastable states of ⁹⁰Y and ⁹¹Y nuclei formed respectively through ⁹⁰Zr(n,p)⁹¹Y^m and ⁹¹Zr(n,p)⁹¹Y^m reactions over the neutron energy range 5 to 15 MeV. The theoretical values of the cross-sections could be obtained very close to the respective literature experimental values by varying the spin distribution factor from 1.5 to 2.75. The limiting value of the cross-section was derived from the maximum value of the isomer ratio at that neutron energy, and for this the spin distribution factor was found to vary from 2 to 3.5 over the neutron energies 5 to 15 MeV. Using enriched zirconium targets, cross-sections for formation of ⁹⁰Y^m and ⁹¹Y^m nuclei at 14.8 MeV neutron energy were also measured in the laboratory; the values obtained are 17 ± 2 mb and 22 ± 2 mb respectively for ⁹⁰Y^m and ⁹¹Y^m. Both these values are close to the corresponding limiting cross-sections at 14 MeV neutron energy.     

The photoneutron cross section of 45Sc

The photoneutron cross section of ⁴⁵Sc has been measured from threshold to 25 MeV using bremsstrahlung and direct neutron detection. The cross section is found to exhibit a large width of approximately 8 MeV and this is interpreted in terms of the Danos hydrodynamic model for the giant resonance of deformed nuclei. The integrated cross section to 25 MeV is 158 ± 24 MeV mb.     

Study of 20Ne(3He,n)22Mg at 3He energies between 2.6 and 4.0 MeV

The ²⁰Ne(³He, n) reaction leading to the ground state of ²²Mg has been investigated in the ³He⁺ energy range of 2.6 to 4.0 MeV. Angular distributions were determined with a neutron time-of-flight spectrometer at average incident energies (lab) of 3.27, 3.69, and 4.01 MeV between 0° and 120° (lab). Excitation functions for the energy region were measured at 0° and 80° (lab). The observed differential cross sections are explained by coherent contributions from direct interaction and compound-nucleus formation. A spectroscopic factor was extracted for the DWBA calculation from the absolute cross-section measurements and found to be $\text{? = 0.43±0.21}$. Resonances in the compound-nucleus formation were found at 3.00 and 3.33 MeV (c.m.) with widths of 0.28 and 0.21 MeV and spins of $\text{5}\text{2}{}^{\mathrm{+}}\text{and}\text{1}\text{2}{}^{\mathrm{?}}$, respectively.     

THE CROSS SECTION MEASUREMENT FOR THE 107Ag(n,2n)106mAg REACTION

The cross section for 107Ag(n,2n)^106mAg has been measured by using the activation method relative to the cross section of ²⁷Al(n,α)²⁴Na in the neutron energy range of 13.50—14.73MeV.The values of 469±22,480±22,503±24,538±25,555±25,572±26mb were obtained at the 13.50,13.60,13.90,14.10,14.35,and 14.73MeV neutron energy,respectively.The results are compared with the published data.The neutron energies were determined by activity ratios of Nb and Zr foils.     

7Li(p,n)7Be reaction with polarized protons from the threshold to 3.0 MeV

A polarized beam was used to measure angular distributions of the proton analyzing power of the ⁷Li(p,n)⁷Be reaction at 11 energies from 2.05 to 3.00 MeV. The analyzing power is generally large and positive. The analyzing power can be fitted with associated Legendre polynomials. The coefficient of P₁¹ rises rapidly from threshold to a maximum near the 3⁺ state at 2.25 MeV from which it drops to a minimum at 2.42 MeV, whence it gently rises to 3.00 MeV; the coefficient of P₂¹ has small values that increase with energy. The data were measured typically to an accuracy of 0.02 with a target 20 keV thick at 2 MeV bombarding energy. Polarization contour maps are given. Comparison of these analyzing power measurements with previous data for the neutron polarization induced with unpolarized protons shows equality at some energies and slightly higher values at others.     

(γ, γ′) reactions in 89Y, 115In and 197Au at intermediate energies

The yields of isomeric states in ⁸⁹Y, ¹¹⁵In and ¹⁹⁷Au produced by the (γ, γ') reaction have been measured in the energy range 100–800 MeV by the activation method. From the yields the cross sections have been deduced. Large cross sections around the first pion resonance are found. The experimental results are compared to calculations based on the impulse approximation.     

Recoil distance lifetime measurements in 26Mg and 26Al

Levels in ²⁶Mg and ²⁶Al were excited with the ²³Na + α reaction, and the recoil-distance method was used to determine the mean lives of the following levels: ²⁶Mg, 3.59 MeV (9.6 ± 1.2ps) and 3.94 MeV (1.38 ± 0.11 ps); ²⁶Al, 1.76 MeV (6.4 ± 0.4 ps) and 2.072 MeV (1.00 ± 0.10ps). The deduced values are compared to previous measurements by the Doppler-shift attenuation method.     

A study of the 99Tc(p,d)98Tc reaction

The energy levels of ⁹⁸Tc were studied with the ⁹⁹Tc(p, d)⁹⁸Tc reaction at a bombarding energy of 22.9 MeV and 15 keV resolution (FWHM). The Q-value for this reaction was found to be ?6.755 ± 0.009 MeV and the ⁹⁸Tc mass excess was calculated to be ?86.421 ± 0.011 MeV. This reaction provided the excitation energies for 49 neutron hole states below 1.5 MeV excitation. Comparison of experimental angular distributions with DWBA calculations permitted assignment of lf-values and the extraction of spectroscopic factors for 44 of these levels. Extensive configuration mixing is observed except in the low-lying multiplet. Effective proton-particle, neutron-hole interaction matrix elements were obtained from the low-lying positive-parity multiplet of ⁹⁸Tc.