Neutron emission from the reaction 232Th(n, xn′f)

The energy distributions of neutrons accompanying the fission of ²³²Th are measured by the time-of-flight technique at the bombarding-neutron energies of E _n=14.6 and 17.7 MeV. The data obtained in this way are compared with the results of previous investigations. An excess of soft neutrons that was observed in the experimental spectra of neutrons from ²³⁸U fission at E _n=13.2, 14.7, 16.0, and 17.7 MeV in relation to the results of the calculations based on the model of two sources is also present in the spectra for ²³²Th. The discrepancy between the results of the calculations and experimental data disappears as soon as one assumes the presence of a third source that is related to neutron emission from nonaccelerated fragments.     

Structure in the subthreshold 232Th(n,f) cross section

The fission cross section of ²³²Th has been measured over the neutron energy range 0.1 MeV to 30 MeV at the Livermore 100 MeV electron linac. The observed structure in the cross section between 0.7 MeV and 1.4 MeV, attributed to vibrational states in the second well of the double-humped fission barrier, is clearly correlated with the angular anisotropy of fission fragments measured by others.     

Thermonuclear reaction rates from (p,n) reactions

Thermonuclear reaction rates for the temperature range 1≤T ₉≤5 have been extracted from experimentally measured (p, n) cross sections for⁴⁵Sc⁵⁰Ti,⁵¹V,⁵⁴Cr,⁵⁵Mn and⁵⁹Co nuclides below 5 MeV bombarding energy. These reaction rates are important in the build-up of medium and heavy nuclides in the stellar evolution process and nucleosynthesis. To enhance the usefulness of these reaction rates in astrophysical calculations, they have been fitted to an analytic function of temperature, valid throughout the temperature range considered here.     

Calculation of prompt fission neutron spectrum for 233U（n,f）reaction by the semi-empirical method~

The prompt fission neutron spectra for the neutron-induced fission of ²³³U for low energy neutrons (below 6 MeV) are calculated using nuclear evaporation theory with a semi-empirical method, in which the partition of the total excitation energy between the fission fragments for the n_th+²³³U fission reactions is determined by the available experimental and evaluation data. The calculated prompt fission neutron spectra agree well with the experimental data. The proportions of high-energy neutrons of prompt fission neutron spectrum versus incident neutron energies are investigated with the theoretical spectra, and the results are consistent with the systematics. The semi-empirical method could be a useful tool for the prompt evaluation of fission neutron spectra.     

Low-energy excited states in 128I produced by the (p,n) reaction

Gamma spectra produced in the ¹²⁸Te(p, n)¹²⁸I reaction were taken as a function of proton bombarding energy E_p = 2.8 MeV to 5.0 MeV. A level scheme composed of 41 excited states was constructed on the basis of singles γ-spectra and extensive γ-γ coincidence measurements. The coincidence measurements were carried out utilizing a three-parameter Ge(Li)-Ge(Li)-timing system. Upper limits were placed on the lifetime of six levels. The modes of de-excitation of many levels as deduced in the present investigation are significantly different from the results obtained in the (n, γ) reaction. Angular distribution measurements combined with the results from the coincidence counting rates and the population strength of the states by primary transitions in the (n, γ) reaction enabled some spin and parity assignments and tentative assignments for many other levels. The ground state and nine positive-parity states were described in terms of admixed twoquasiparticle multiplets.     

Parity-violating asymmetry in the reactions 6Li(n,\alpha) 3H and 10B(n,\alpha)^{7}Li* \rightarrow 7Li + \gamma

We present two experiments measuring the parity-violating asymmetry (P-odd) of tritons emission in the reaction ⁶Li(n,??)³H and ??-quanta emission in the reaction ¹⁰B(n,??)⁷Li* ?? ⁷Li + ?? with polarized cold neutrons, aiming at estimation of the weak meson-nucleon coupling constants. These experiments started in the PNPI, Gatchina and continued in the ILL, Grenoble. We describe an integral method to measure P-odd asymmetry and the two experiments. The results of our measurements are: $\alpha{}_{P-odd}^{6Li}=(-8.8\pm2.1)\cdot10^{-8}$ and $\alpha{}_{P-odd}^{10B}=(0.8\pm3.9)\cdot10^{-8}$ .     

Prompt neutron and gamma-ray yields in fission induced in Pu by resonance neutrons: Existence of the (n, γf) reaction

Fluctuations of the fission neutron multiplicity and prompt γ-ray energy have been measured for resonance neutron induced fission of ²³⁹Pu below 110 eV. An observed anticorrelation between fluctuations of these two parameters is attributed to the role of the (n, γf) reaction.     

A study of the Li(p,n)Be reaction by the neutron threshold technique

The reaction ⁶Li(p,n)⁶Be has been studied by slow-neutron detection, with particular attention to the ⁶Be ground state threshold. The detector response was calculated by a Monte Carlo technique and verified with a measurement of the ⁷Li(,n)¹⁰B threshold. An analysis of the shape of the ⁶Be threshold indicated that both s- and p-wave neutrons contribute significantly to the reaction. The results depend on what mode of decay is assumed for the ground state of ⁶Be. If a two-stage process is assumed, with either an alpha particle and an unbound diproton or ⁵Li and a proton as intermediate state, the width is found to be 95±28 keV and the Q-value obtained for the ⁶Li(p,n)⁶Be reaction is −5074±13 keV. It was not possible to detertmine which process is predominant. No higher thresholds in the slow neutron yield up to 4 MeV of excitation in ⁶Be were observed. The data above the ground state threshold are consistent with a broad excited state of ⁶Be or with the occurrence of other neutron-producing reactions.     

Research on the prompt neutron multiplicity of fission fragments for 235U(n,f)

According to some experimental and evaluated data, the total excitation energy partitioning way between both of the fission fragments was given with a semi-empirical method. With the calculated energy partitioning way, the prompt neutron multiplicity as a function of fragment mass, (-v)(A), for neutron-induced fission of 235U at En=0.0253 eV, 3 MeV, and 5 MeV was calculated. The results are checked with the total average prompt neutron multiplicities (-v) and compared with the experimental and evaluated data.     

The effect of gamma de-excitation competition on the (α, n) and (α, 2n) reactions on gold and antimony

Absolute cross sections for P¹⁹⁷Au(α, n)²⁰⁰Tl ¹⁹⁷Au(α, 2n)¹⁹⁹Tl, ¹²¹Sb(α, n)¹²⁴I and ¹²¹Sb(α, 2n)¹²³I are measured in the energy range from threshold to 27 Me V.The experimental results are interpreted in terms of evaporation statistical theory, including gamma de-excitation. The values of the level density parameters and of the average γ-ray strength for the compound systems are extracted.     

The d(e,e′p)n reaction and the neutron electric form factor

The cross section for the d(e, e′p)n reaction is calculated for quasi-free kinematics in the impulse approximation including the final state interaction and the pair current contributions. Its dependence on the recoil momentum agrees quite well with recent Saclay data up to p = 350 MeV/c. We also show a measurement of the cross section for quasi-elastic scattering in which one detects low energy protons may provide information on G_Eⁿ.     

Observation of the ABC effect in the reaction n+p → d+(mm)0 with A 1.88 GeV/c neutron beam

A significant production of the ABC effect is observed in the free nucleon reaction n+p → d+(mm)°, using a 1.88 GeV/c neutron beam. The complete deuterón momentum spectra produced in this inclusive experiment are measured at 0°, 4.5°, 7.5° and 10.5° (lab). The double differential cross sections $\text{d}{}^2\text{σ/}\text{d}\text{Ω}\text{d}\text{p}$, are compared with the predictions of two exchange models.     

Cross-section measurement for the ~(93)Nb(n,2n)~(92g)Nb reaction at the neutron energy of 14.6 MeV by the AMS method

The cross-section for the~(93)Nb(n,2n)~(92g)Nb reaction has been measured at the neutron energy of 14.6 Me V using neutron activation and accelerator mass spectrometry(AMS)determination of the long-lived product nuclide~(92g)Nb.The neutron energy was generated from the D+T neutron source at the China Institute of Atomic Energy(CIAE).The neutron flux was monitored by measuring the activity of~(92m)Nb produced in the competing reaction channel of~(93)Nb(n,2n)~(92m)Nb.At the neutron energy of 14.6 MeV,the~(93)Nb(n,2n)~(92g)Nb reaction cross-section of(736±220)mb was obtained for the first time.     

High spin level structure in127Ba produced by the118Sn(12C, 3n) reaction

High-spin states in¹²⁷Ba have been produced by the reaction¹²⁸Sn(¹²C,3n)¹²⁷Ba and studied by in-beamγ-ray spectroscopic techniques. The odd-parity states form a level system based upon a 9/2^? state and generated by an odd neutron in theh _11/2 shell coupled to a triaxial core. Theg _7/2 shell is responsible for theΔ I=1, even-parity band.     

On the mechanism of the reactions24,25,26Mg(n,α)21,22,23Ne at neutron energies near 14 MeV

Differential cross sections of the reactions²⁴Mg(n,α)²¹Ne,²⁵Mg(n,α)²²Ne, and²⁶Mg(n,α)²³Ne have been measured at neutron energies of 13.19,13.93 and 14.33 MeV, at 13.93 and 14.33 MeV, and at 13.47 and 13.93 MeV, respectively. In forward direction, differential excitation functions of those reactions have been measured at energies between 12.67 and 16.05 MeV. The results are analysed in terms of direct-reaction and compound-nucleus theories.     

The study of the (α, α′ f) reaction at 120 MeV on 232Th and 238U: (II). Fission barrier properties deduced from fission probabilities and angular distributions

The fission probabilities and angular distributions of the fission fragments for the (α, α'f) reaction on ²³²Th and ²³⁸U at a bombarding energy of 120 MeV have been measured from about 4 to 14 MeV excitation energy. Evidence for sub-barrier resonances has been found, the negativeparity ones occurring at the same excitation energy where photofission resonances have been observed. The data are analyzed with the two-humped barrier model. For ²³⁸U the data are reasonably well fitted with barriers similar to those known from the literature. For ²³²Th though, the outer barrier parameters are quite different: the height E_B = 6.6 MeV and the width (khω)_B = 1.2 MeV. Also for ²³²Th, introducing an additional mass symmetric and axially asymmetric outer barrier, as was previously found necessary for ²³⁸U, does not result in a good fit to the data at higher excitation energies.