Neutron Pickup Research Articles

Neutron hole states inPb207,206,205isotopes via the (He3,α) reaction at 100 MeV

Neutron hole states were investigated in the $^{207,206,205}\mathrm{Pb}$ isotopes up to 25 MeV excitation energy using the ($^{3}\mathrm{He}$,$\ensuremath{\alpha}$) reaction at 100 MeV incident energy with 100 keV energy resolution. Above the well-matched low-lying levels corresponding to high angular momentum transfers, new peaks are identified. In addition, three gross structures, riding on a continuous background, are observed in each of the three isotopes, with some fine structures showing up to 10 MeV excitation energy. For $^{207}\mathrm{Pb}$, angular distributions have been obtained for the low-lying levels as well as for the deeply bound hole states. The data have been analyzed with distorted-wave Born-approximation calculations and spectroscopic factors extracted. It has been found that the low-lying levels do not exhaust the $1i\frac{13}{2}$ and $1h\frac{9}{2}$ neutron hole strengths. Corrections for exact finite-range effects, form factor shapes, and indirect pickup contributions have been calculated, and modify significantly the $2f\frac{7}{2}$ spectroscopic measured strength but not the $1i\frac{13}{2}$ and the $1h\frac{9}{2}$ ones. Most of the $1i\frac{13}{2}$ and $1h\frac{9}{2}$ missing strengths are found in the "bump" located at about 5 MeV excitation energy. The highly fragmented bump observed at about 8 MeV excitation energy is shown to arise from $1h\frac{11}{2}$ neutron pickup exhausting 45% of the sum-rule limit. Finally, the very smooth structure extending to 21 MeV excitation energy is tentatively attributed to $1g\frac{7}{2}+1g\frac{9}{2}$ neutron holes with 80% of the total strength. In $^{207}\mathrm{Pb}$, the four first isobaric analog states are observed as narrow structures around 20 MeV excitation energy.NUCLEAR REACTIONS $^{208,207,206}\mathrm{Pb}$ ($^{3}\mathrm{He}$, $\ensuremath{\alpha}$), $E=101.75$ MeV; measured $\ensuremath{\sigma}({E}_{\ensuremath{\alpha}}, \ensuremath{\theta})$, $^{207,206,205}\mathrm{Pb}$ deduced levels, $\mathrm{Ex}$, $l$, $J$, $\ensuremath{\pi}$, ${C}^{2}S$; $^{207,206,205}\mathrm{Pb}$ inner shell spectroscopic factors: enriched targets, magnetic spectrometer.

Theoretical rotational signatures for neutron pickup reactions to [formula omitted] bands

It is shown with the particle-rotor model that non-yrast low-spin states, which are structurally related to the rotation-aligned ( i 13 2 ) 2 band causing backbending at higher spins, can be populated selectively by means of l=6 neutron pickup from an odd-neutron target with an appropriate ground-state configuration.

Li7andC13(p,d)reactions atTp=800MeV

Cross sections for the /sup 7/Li( p,d)/sup 6/Li and /sup 13/C( p,d)/sup 12/C reactions have been measured at a bombarding energy of 800 MeV. Exact finite range distorted-wave Born-approximation calculations are compared to cross sections for known levels excited by 1p neutron pickup and are found to give reasonable agreement in most cases. However, the large strength for the excitation of the 2.184 MeV /sup 6/Li 3/sup +/ level is not reproduced by the calculation. Levels in /sup 12/C are strongly excited at 800 MeV which are not appreciably populated in lower energy ( p,d) studies.

Neutron pickup fromNe22

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Neutron orbit sizes in the isotopes of tin

Root-mean-square radii of 3 s 1 2 , 2 d 3 2 , 1 g 7 2 and 1 h 11 2 neutron orbits in the isotopes of tin with A = 113, 115, 117, 118, 119 and 120 have been determined from a DWBA analysis of cross section data from the sub-Coulomb (t, d) reaction. The differential cross sections for the (t, d) reaction were measured at lab angles in the range from 120° to 160° for triton energies in the range from 4.25 MeV to 5.75 MeV. Spectroscopic factors of the populated states were obtained from a sum rule analysis of published neutron stripping and pickup reactions on the isotopes of tin. The measured rms orbit radii were used in a calculation of the rms radii of the neutron excess in the even tin isotopes, and the resulting values were compared with those extracted from an analysis of Coulomb displacement energies. The behaviour of neutron orbit size and parameters of the neutron bound state potential within the isotopic sequence of final nuclei is discussed. The systematics of matter, charge and neutron radii are discussed.

Energy Dependence ofHe4(p, d)He3

The cross section of $^{4}\mathrm{He}(p, d)^{3}\mathrm{He}$ at $\ensuremath{\theta}=22.5\ifmmode^\circ\else\textdegree\fi{}$ has been measured between ${T}_{p}=200 \mathrm{and} 500$ MeV, which together with previous data provides the first excitation function for the ($p, d$) reaction up to ${T}_{p}=700 \mathrm{MeV} \mathrm{and} 0.7 \mathrm{GeV}/c$ momentum transfer. The energy variation is found mainly to reflect a strong dependence upon momentum transfer. Using known nuclear wave functions we examine the contributions from ordinary neutron pickup and certain multinucleon reaction mechanisms.

Inner hole states inPb207via thePb208(He3, α)Pb207reaction at 70 MeV

The $^{208}\mathrm{Pb}(^{3}\mathrm{He}, \ensuremath{\alpha})^{207}\mathrm{Pb}$ reaction at 70 MeV incident energy was used to populate hole states up to 28 MeV excitation energy in $^{207}\mathrm{Pb}$. A split-pole spectrometer was used for particle analysis and detection. For the excitation energy range between 0 to 4.5 MeV, about eleven well resolved states are excited. These levels contain the main part of the spectroscopic strengths of the $3{p}_{\frac{1}{2}}$, $2{f}_{\frac{5}{2}}$, $3{p}_{\frac{3}{2}}$, $2{f}_{\frac{7}{2}}$, $1{i}_{\frac{13}{2}}$, and $1{h}_{\frac{9}{2}}$ neutron subshells. Three additional regions of enhanced cross sections, centered at 5.5, 8.5, and 14 MeV excitation energy in $^{207}\mathrm{Pb}$, are also observed. The 65 keV energy resolution of the present study revealed fine structure in the peak previously observed around 8.5 MeV in $^{207}\mathrm{Pb}$. About fifteen levels or groups of levels are populated between 4.5 and 10.5 MeV, and angular distributions have been extracted for each individual peak as well as for the gross structures. A distorted-wave Born-approximation analysis of the data was carried out and shows that the missing $l=3 \mathrm{and} 5$ strengths in $^{207}\mathrm{Pb}$ are located in some strong peaks at 5.13, 5.62, and 6.37 MeV. Thus the full sum rule is obtained for the neutron subshells between $N=126$ and $N=82$. The highly fragmented peak located at 8.5 MeV excitation energy is shown to arise from $1{h}_{\frac{11}{2}}$ neutron pickup. Finally, the large structure, 5 MeV wide and centered around 14 MeV, observed for the first time in this work is tentatively interpreted as arising from neutron pickup from the $1{g}_{\frac{9}{2}}$ inner shell. The ${T}_{&gt;}$ components of the deeply-bound state are also observed between 20 to 24 MeV in $^{207}\mathrm{Pb}$ and therefore from the sum-rule analysis, centroid energies and total strengths for each inner subshell are deduced.NUCLEAR REACTION $^{208}\mathrm{Pb}(^{3}\mathrm{He}, \ensuremath{\alpha})$, $E=70$ MeV; measured $\ensuremath{\sigma}(E, \ensuremath{\theta})$. $^{207}\mathrm{Pb}$ deduced levels, ${E}_{x}$, $l$, ($J$), $\ensuremath{\pi}$, ${C}^{2}S$; inner shell spectroscopic factors; enriched target, magnetic spectrometer.

Observation of theT>=452Components of Deep Hole States inPb207via the (He3,α) Reaction at 70 MeV

A number of narrow lines are observed around 20 MeV excitation energy in $^{207}\mathrm{Pb}$ in the study of $^{208}\mathrm{Pb}$($^{3}\mathrm{He}$,$\ensuremath{\alpha}$) at 70 MeV. Their excitation energies and relative spacing suggest that these peaks arise from the neutron pickup from the inner filled sdhg shell between magic numbers 82 and 50 with isospin number $T=\frac{45}{2}$. In addition, distorted-wave Born-approximation (DWBA) calculations of the angular distributions agree in shape with the data. The solution of the Lane coupled-channels equations leads to a DWBA cross section in reasonable agreement with experiment.

The 85Rb(p, d) 84Rb reaction

The spectrum seen in single neutron pickup leading to the doubly odd nucleus 84Rb is remarkably clean, with only five levels populated by l = 4 and six by l = 1 transitions. A simple 2 J+1 weighting for the l = 4 data, combined with previous information on 84Rb, allowed the J π = 2 −–7 − states of the ( v g 9 2 −3⊗ π f 5 2 −3 ) multiplet to be identified. These data are used to determine the two-hole π f 5 2 −1-v g 9 2 − interaction matrix elements.

Some recent intermediate-and high-energy proton-nucleus research

A review of several new or very active areas of research in the field of intermediate-and high-energy proton-nucleus research is presented. Theoretical advances used in treating the data are described. The areas covered include: $p$---$^{4}\mathrm{He}$ elastic scattering and polarization; elastic and inelastic scattering, $A\ensuremath{\ge}4$; the neutron pickup reaction; and particle production and elastic scattering near 180\ifmmode^\circ\else\textdegree\fi{}.

Neutron pickup from 194Pt, 196Pt and 198Pt

The (p, d) reaction at 27 MeV has been studied on three doubly even Pt targets. Many new states are noted below an excitation of about 1.4 MeV. Comparison to DWBA calculations allows l-assignments and the extraction of spectroscopic factors for most of these. A striking difference is noted between the first levels of 193Pt and 195Pt and those for 197Pt, where five states are strongly excited below an excitation of 130 keV. The systematic behavior of the first 9 2 + and 13 2 + states is compared to that predicted in the Coriolis decoupling model.

Neutron pickup on 93Nb

The reaction 93Nb( 3He, α) 92Nb has been investigated with a 19.5 MeV 3He beam. Fortyfive levels of 92Nb were identified up to 4.36 MeV excitation energy. Angular distributions were measured and compared with DWBA calculations. A previously unreported set of states arising from l n = 4 pickup was observed in the excitation energy range 2.75–3.75 MeV. Fourteen additional lower levels in 92Nb were identified to proceed with l = 4 and l = 2 + 4 neutron pickup, of which eleven were unassigned previously. The sextuplet of levels of the 92Nb ground-state configuration [π(1g 9 2 )v(2d 5 2 )] j π = 2 + → 7 + have angular distributions characteristic of l = 2 neutron pickup. Extracted spectroscopic factors are compared with previous neutron pickup results. The sum-rule analysis shows that most of the g 9 2 . pickup strength has been observed in the present experiment and its centroid energy is at 3.11 MeV excitation.

Single-neutron transfer toSi29,Ca41,49, andFe55states induced by the (O18,O17(g.s.)) and (O18,O17(0.87 MeV))

Differential cross sections for the (/sup 18/O,/sup 17/O) reaction on targets of /sup 28/Si, /sup 40/ /sup 48/Ca, and /sup 54/Fe have been measured at E (/sup 18/O) = 50 MeV. The /sup 17/O nuclei were detected in both the ground state (5/2/sup +/) and the first excited state (0.87 MeV,1/2/sup +/). The data were analyzed using full-recoil finite-range distorted-wave Born-approximation calculations. Spectroscopic factors were, with one exception, in good agreement with the products of spectroscopic factors obtained from light ion reactions. In particular, the ratio of spectroscopic factors for neutron pickup from /sup 18/O, S (/sup 18/O ..-->.. /sup 17/O(0.87 MeV))/S (/sup 18/O ..-->.. /sup 17/O(g.s.)), was found to be independent of the target. Thus these data are consistent with a one-step direct reaction interpretation of the transfer. However, some problems remain in connection with understanding the location of the grazing angle peaks in the angular distributions.

Deeply bound hole states and isobaric analog states observed by neutron pickup reactions on even tin isotopes

Deeply bound hole states in the odd tin isotopes 115, 117, 119, 123Sn were investigated by using 81 MeV ( 3He, α) and 52 MeV (p, d) reactions. Excitation of low-spin states was largely suppressed in ( 3He, α) reactions due to the angular-momentum mismatch so that the excitation energies and widths of the 1 g 9 2 states have been clearly determined. DWBA analyses showed that the deeply bound hole states have spectroscopic factors less than 20% of the sum-rule limit. Isobaric analog states 1 g 9 2 , 2 p 3 2 and 2 p 1 2 corresponding to the ground and two lowest excited states of In isotopes were investigated in 115, 117, 119, 121, 123Sn isotopes. Coulomb displacement energies were deduced. DWBA analyses of these states were used to check the calculations for the deeply bound states. The spectroscopic factors of the analog states are in good agreement with the sum-rule prediction.

Neutron pickup by alpha particles to unbound states

Two conspicuous peaks are observed in the two-dimensional coincidence spectra of $\ensuremath{\alpha}$ particles and neutrons emitted in bombardments of $^{12}\mathrm{C}$, Rh, $^{208}\mathrm{Pb}$, and U with 90 MeV $\ensuremath{\alpha}$ particles. Through their energy-angle correlation these peaks are identified as arising from the breakup products of $^{5}\mathrm{He}$ (g.s.) formed in the ($\ensuremath{\alpha},^{5}\mathrm{He}(\mathrm{g}.\mathrm{s}.)$) reaction. A somewhat less prominent peaking of events is identified as the signature for the breakup of $^{6}\mathrm{H}\mathrm{e}*$(1.8 MeV) formed by two-neutron pickup. A distorted-wave Born-approximation calculation was carried out for the ($\ensuremath{\alpha},^{5}\mathrm{He}(\mathrm{g}.\mathrm{s}.)$) reaction on $^{208}\mathrm{Pb}$ and was found to fit the measurements. The large differential cross section for the ($\ensuremath{\alpha},^{5}\mathrm{He}(\mathrm{g}.\mathrm{s}.)$) reaction confirms an earlier interpretation of the somewhat square structure observed in the spectra of inelastically scattered $\ensuremath{\alpha}$ particles.NUCLEAR REACTIONS $^{208}\mathrm{Pb}$, Rh, $^{12}\mathrm{C}$, $^{\mathrm{nat}}\mathrm{U}(\ensuremath{\alpha},^{5}\mathrm{He})$ ($\ensuremath{\alpha}$, $^{6}\mathrm{He}$(1.8 MeV)), $E=42,90$ MeV, measured two-dim $\ensuremath{\alpha}\ensuremath{-}n$ coin. Spectra, deduced $\ensuremath{\sigma}(\ensuremath{\theta})$ for $^{208}\mathrm{Pb}(\ensuremath{\alpha},^{5}\mathrm{He})$, compared DWBA.

16, 18O induced transfer reactions on122, 120Sn

The reactions120Sn+72 MeV18O and122Sn+74 MeV16O were investigated with time of-flightΔE-E-telescopes. Data are presented for all quasi-elastic reaction channels. The two neutron stripping and pickup reactions (18O,16O), (18O,20O) and (16O,18O) are analyzed in detail. It is shown that these heavy ion induced two neutron transfer reactions proceed with essentially the same type of selectivity as the corresponding light ion induced reactions. The differential cross sections for transfer reactions leaving the120, 122Sn nuclei in their 2+ first excited states are shown to be influenced by interference effects due to additional inelastic excitations.

Neutron pickup at high energies

Neutron pickup at high energies

Neutron pickup onKr84

The $^{84}\mathrm{Kr}(^{3}\mathrm{He},\ensuremath{\alpha})^{83}\mathrm{Kr}$ reaction has been studied at a bombarding energy of 18 MeV. The isotopically enriched $^{84}\mathrm{Kr}$ target was contained in a gas cell with no entrance window. Excitation energies and angular distributions were obtained for 16 levels up to 2735 keV excitation energy in $_{36}^{83}\mathrm{Kr}_{47}$. A distorted-wave analysis was used to determine $l$ values and spectroscopic strengths. The pickup of neutrons from $1g$, $2p$, and $1f$ orbitals was observed.NUCLEAR REACTIONS $^{84}\mathrm{Kr}(^{3}\mathrm{He},\ensuremath{\alpha})$, $E=18$ MeV; enriched target; measured $\ensuremath{\sigma}({E}_{\ensuremath{\alpha}},\ensuremath{\theta})$; deduced $^{83}\mathrm{Kr}$ levels, $l$, $j$, ${C}^{2}S$.

Excitation of deep lying hole states inC11,O15,Si27, andNi57with the (He3,α) reaction at 216 MeV

The $\ensuremath{\alpha}$ spectra were investigated in the discrete and continuum regions. In addition to the well known low lying levels, peaks and broad structures are observed for each nucleus at higher excitation energies. The bumps location and spreading, and their forward peaked distributions, suggest that they arise from neutron pickup in the deeper shells, i.e., $1s$ for $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$, $1{p}_{\frac{3}{2}}$ for $^{28}\mathrm{Si}$ and $1d+(1p)$ for $^{58}\mathrm{Ni}$.NUCLEAR REACTIONS $^{12}\mathrm{C}$, $^{16}\mathrm{O}$, $^{28}\mathrm{Si}$, $^{58}\mathrm{Ni}(^{3}\mathrm{He}, \ensuremath{\alpha})$, $E=216$ MeV; measured $\ensuremath{\sigma}(E\ensuremath{\alpha}; \ensuremath{\theta})$; high excitation energy observed levels and broad structure in $^{11}\mathrm{C}$, $^{15}\mathrm{O}$, $^{27}\mathrm{Si}$, and $^{57}\mathrm{Ni}$.

Decay of 85Br

Gamma-ray transitions following β− decay of 85Br have been identified through analysis of the γ-ray spectrum of fission product bromine isotopes. Of the forty-four transitions identified, twenty-six have been incorporated in a level scheme which includes the majority of levels observed in the reaction 82Se(α, nγ)85Kr and a number of levels not previously defined. The proposed scheme is compared with 85Kr levels observed in neutron stripping and pickup reactions.