Kamal K. Seth

Spectroscopy of even tin isotopes by inelastic scattering of 24.5 MeV protons

Elastic and inelastic scattering of 24.5 MeV protons by even isotopes of tin, 116, 118, 120Sn and 122, 124Sn, has been studied with an energy resolution better than 20 keV. Approximately 30 levels in each isotope have been resolved up to an excitation energy of 4 MeV. Elastic scattering angular distributions have been analysed to yield optical-model parameters and the inelastic scattering angular distributions have been analysed in the distorted wave Born approximation (DWBA) using collective form factors to determine l and βl corresponding to a large number of the transitions observed. The systematics of the states of each Jπ are discussed and the results are compared to recent theoretical calculations.

s- AND p-WAVE NEUTRON SPECTROSCOPY. PART VII. WIDTHS OF NEUTRON RESONANCES

Abstract Neutron reduced widths Γn0 and Γn1 are reported for about 200 resonances observed in neutron total cross sections of Ca40, 44, Ti48, Cr50, 52, 54, Fe54, 56, Ni58, 60, Sr88, Y89, Sn124, Te130, Ba136, 138, and Pb206, 207, 208, in the energy region 1 to 200 kev. Average parameters Γ n 0 , Γ n 0 D , and Γ n (1) D have been derived and the Wigner distribution for local spacings and the Porter-Thomas distribution for reduced widths are verified for the resonances in the even-even nuclei Ca40, Fe56, Ni58, and Ni60. A simple method of area analysis which is less tedious and time consuming than the method reported before in Part III is also described.

NEUTRON CAPTURE CROSS SECTIONS IN THE Kev REGION. PART II. SPIN-ORBIT COUPLING AND THE OPTICAL MODEL

Abstract An intensive study of average neutron capture cross sections of nuclei with 75 ≦ A ≦ 130 has been carried out in the neutron energy region 3 to 200 kev, using the activation method. Assuming s-wave parameters within the limits of error specified by low-energy total cross sections determinations, the data has been analyzed for corresponding p-wave parameters: the neutron strength function Γ n (1) D and the γ-ray strength function Γ γ D 0 . It is found that the s- and p-wave γ-ray strength functions are the same within the rather large limits of experimental error for the odd A targets: Rh103, Ag107, Ag109, In115, I127, and As75. The even-even isotopes of Pd, and Mo are more complicated in this respect. The p-wave neutron strength functions Γ n (1) D derived from the analysis of these capture cross sections are found to be in agreement with Γ n (1) D as obtained from the analysis of neutron total cross sections. These strength functions exhibit a broad, double-peaked, distribution around A = 100 instead of the single peak predicted by the simple optical model. It is shown that the experimental results may be explained by the addition of a small spin-orbit part to the optical potential. The parameters of the square well optical potential V ± = V 0 [1 + iξ + δ 2 {−1 ± (2l + 1)}] which are found to fit the p-wave strength functions best are V0 = 41 Mev, ξ = 0.02, δ = 0.085, and R = 1.45 A 1 3 fermis.

Elastic scattering of 0.8-GeV protons from C12, Ni58, and Pb208

Differential cross sections for elastic scattering of 0.8-GeV protons from /sup 12/C, /sup 58/Ni, and /sup 208/Pb have been measured. Preliminary analysis of the data in terms of the Kerman-McManus-Thaler formalism with spin-dependent nucleon-nucleon amplitudes shows sensitivity to details of proton and neutron matter distributions.

s- and p-wave neutron spectroscopy: Part III. Area analysis of neutron resonances☆

Abstract In the commonly used methods of area analysis of neutron resonances observed in transmission experiments the interference between resonance and potential scettering is either neglected or taken into account only approximately. A method of analysis is developed here which takes into account such interference accurately. It is shown that the importance of the interference effect in obtaining Γ or gΓn is determined not only by the size of the potential phase shift, but also by the sample thickness. Results of calculations are presented and it is shown that the errors inherent in the conventional methods of analysis due to the neglect of interference effect can become abnormally large in certain cases. Such cases are usual in the kev region of neutron energy and not uncommon in the ev region. In the kev region of neutron energy certain cases also occur in which the conventional area is close to zero and leads to very inaccurate determination of widths. For such cases a new method of area analysis is proposed. Some applications of the new analysis techniques for analhsis of individual resonances are presented.

Nuclear data for A = 206 isobars

Abstract Nuclear data relating to nuclear isobars with A = 206 are presented. When new data with better accuracy are available, older data are often not quoted but only referred to. Similarly, only the latest data from an author are quoted when the measurement has been reported several times. From the cumulative data presented, conclusions about level energies, spins and parities are derived. Decay schemes, γ -ray properties and other properties of nuclear levels are also presented, whenever pertinent data are available. The schematic relation of isobars of A = 206 is presented in Drawing 1 as a summary of the entire chain. Since very good theoretical calculations are now available for two-hole states in A = 206 nuclei, these theoretical results are presented in Drawing 2 together with the adopted level schemes for 206 Tl (1 proton — 1 neutron hole) and 206 Pb (2 neutron holes). For 206 Hg no experimental data are available. For Z ⩾ 83 no results of theoretical calculations are presented. The only available calculation for 206 Bi is suspect because of problems revealed in a similar calculation for 208 Bi. A number of serious gaps in the available data are exposed, and attention is drawn to the possible experiments. These are:

(p,t) reactions on odd-A nuclei and the weak-coupling core-excitation model

Abstract Excited 7 2 − states to which enhanced L = 0 (p, t) transitions are observed have been identified in 41Ca at 2958 keV and in 57Co at 2611 keV. A comparison of these (p, t) transitions with those to the 0+ states in 40Ca at 3353 keV and in 58Ni at 2940 keV leads to the conclusion that these states are obtained by weak-coupling of a f 7 2 particle and hole, respectively, to the excited 0+ states of the doubly even cores. It is suggested that these cases are examples of a rather general weak-coupling phenomenon.

ISOVECTOR PROPERTIES OF COLLECTIVE STATES AND THE IBA-2 MODEL

Abstract The IBA-2 model of nuclear structure makes explicit predictions of isovector properties of collective states which have never before been tested. We have made the first measurements of separate neutron ( M n ) and photon ( M p ) matrix elements for the first 2 + and 3 − states in 104, 106, 108, 110 Pd by means of inelastic scattering of 180 MeV π + and π − . It is found that the IBA-2 model with core polarization can explain the trend of the data for M p and M n / M p , but only if its parameters are empirically adjusted.

Neutron strength functions and average total cross sections II. The behavior of the average cross sections and the S-wave scattering lengths

Abstract Average neutron total cross sections have been measured in the keV region for natural samples of KCl, Sc, V, Mn, Co, Cu, Zn, As, Se, RbBr, CsI, Ce, Nd, Gd, Tb, Dy, Ho, and Hg, and for the separated isotopes 144,146,148Nd and 149,152Sm. The measurements were combined with those made earlier here (TUNL) and elsewhere to give total data set which is comprised of the total corss sections for most of the natural elements and many separated isotopes. The cross sections were averaged over hundreds of keV and compared to various optical model calculations. The data are in fair agreement with spherical optical model calculations below A = 140 and in poor agreement for heavier nuclei. The calculations using deformed potentials agree much better with the data, especially above A = 140. The s-, p-, and d-wave strength functions, the s-(or R′) and p-wave phase shifts were extracted from the average cross sections of the nuclei mentioned above by the Duke average cross section method, but in this paper only and R′ are discussed (see Part III for strength functions). The values of R′, supplemented by those from other measurements, made both here and elsewhere, were compared to available optical model calculations which use deformed optical potentials. The calculations agree fairly well with the data. Measurements of R′ indicate that it rises much more rapidly at A = 140 than would be predicted by the spherical optical model and confirm the rapid rise predicted by the deformed model. Similarly, a rise in R′ is evident around mass number A = 50, however, enough experimental points are not available for a detailed comparison with theory.

Neutron strength functions and average total cross sections I. A new method

Abstract Neutron total cross sections of In, Sb, I, Re, and Hg have been measured in the energy region from 30 to 650 keV using a number of different sample thicknesses. A technique is developed for the analysis of the multiple-thickness transmission data to uniquely determine s- , p- , and d -wave strength functions and potential scattering phase shifts. The method exploits the differences in the behavior of the areas under transmission dips of s - and p -wave resonances as a function of sample thickness, and is shown to be well-suited for the keV region of neutron energies.