Angular Correlation Studies Research Articles

Angular Correlation Studies of Electric Field Gradients in Dilute Silver Alloys

Angular Correlation Studies of Electric Field Gradients in Dilute Silver Alloys

Angular correlation studies of nuclear polarization following inelastic scattering of alpha particles from C 12 and Mg 24

Alpha-gamma angular correlations have been measured at 73 scattering angles in the reaction plane for the reaction C 12(α, α′γ 4.43) and at 40 scattering angles for the reaction Mg 24 (α, α′γ 1.37). The correlation functions were determined at each alpha-particle scattering angle by measuring the coincidence gamma-ray yield for at least 11 different gamma-ray detection angles. All of the particles in both reactions except the excited nuclei and the gamma rays are spinless, greatly simplifying interpretation of the correlation data. These data have been analysed in terms of the polarization of the excited nucleus, and show the presence of curious and distinctive behaviour in the functional dependence of the polarization parameters on scattering angle for both reactions studied. These results are compared with the predictions of reaction theories and show strong disagreement with semi-classical, plane-wave, and adiabatic theory predictions, while giving at least qualitative agreement with DWBA calculations. Predictions of compound nucleus theory are investigated, and the relevance of this type of measurement to the investigation of reaction mechanisms and their interference effects is discussed.

Coulomb Excitation ofCu63andCu65

Properties of levels Coulomb excited in ${\mathrm{Cu}}^{63}$ and ${\mathrm{Cu}}^{65}$ with 4- to 8-MeV alpha particles have been investigated. The $B(E2)'\mathrm{s}$ for excitation determined from the yields of gamma rays observed in singles and coincidence spectra for the (668\ifmmode\pm\else\textpm\fi{}4)-, (961\ifmmode\pm\else\textpm\fi{}6)-, and (1323\ifmmode\pm\else\textpm\fi{}16)-keV levels in ${\mathrm{Cu}}^{63}$ are, respectively, (1.16\ifmmode\pm\else\textpm\fi{}0.12), (3.49\ifmmode\pm\else\textpm\fi{}0.34), and $(4.0\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}50}{e}^{2}$ ${\mathrm{cm}}^{4}$; for the (771\ifmmode\pm\else\textpm\fi{}7)-, (1115\ifmmode\pm\else\textpm\fi{}11)-, and (1474\ifmmode\pm\else\textpm\fi{}19)-keV levels in ${\mathrm{Cu}}^{65}$, they are (1.02\ifmmode\pm\else\textpm\fi{}0.11), (3.45\ifmmode\pm\else\textpm\fi{}0.38), and $(4.3\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}50}{e}^{2}$ ${\mathrm{cm}}^{4}$. These results give $B(E2)'\mathrm{s}$ for decay which are 13 to 16 times the single-particle $B(E2)$. This similarity of $B(E2)'\mathrm{s}$ was predicted by de Shalit for levels which result from the coupling of the odd particle to the first excited state of the even-even core. From angular correlation studies the 961- and 1115-keV levels have been assigned spin $\frac{5}{2}$ and the 1323-keV level spin $\frac{7}{2}$. Mixing ratios obtained from these measurements along with the $B(E2)'\mathrm{s}$ establish values of 0.09 and 0.4 ${(\frac{e\ensuremath{\hbar}}{2} \mathrm{Mc})}^{2}$ for the $B(M1)'\mathrm{s}$ of the 961- and 1115-keV transitions.

Energy levels of the Si 28 nucleus

Angular correlation studies of (p, α), (p, α, γ) and (p, γ, γ) on Al 27 have established the spin and parity for ten levels in the Si 28 nucleus corresponding to resonance proton capture at E p=0.992 MeV (3 +), 1.025 MeV (3 +), 1.184 MeV (2 +), 1.198 MeV (3 +), 1.212 MeV (3 −), 1.261 MeV (3 −), 1.316 MeV (3 − or 4 +), 1.355 MeV (3 −), 1.514 MeV (2 −) and 1.589 MeV (3 −) . One of the doublet levels at 6.88 MeV is found to have spin and parity 2 −. The partial widths, strengths of radiative transitions and the reduced transition strengths for the γ-rays leading to the first excited state are estimated in order to test the validity of the isobaric spin selection rule.

A study of the gamma radiation produced in the alpha-particle bombardment of O 16

The excitation function for gamma radiation from the reaction O 16(α, γ)Ne 20 has been studied for laboratory alpha-particle energies E α from 4.8 to 9.9 MeV. Resonances were observed at E α = 5.374, 5.94, 6.61, 6.930, 7.94, 8.17, 8.54 and 9.40 MeV, corresponding to Ne 20 states at excitation energies E x of 9.029, 9.48, 10.02, 10.270, 11.08, 11.27, 11.56, and 12.25 MeV. Gamma-ray angular distribution measurements establish spins and parities of 4 + and 2 + for the 9.029 and 10.270 MeV states, respectively, and indicate that the 11.08 MeV state is probably 4 +. The 2 + assignment for the 10.270 MeV state is supported by the results of triple angular-correlation studies of the gamma-ray cascade through the 1.63 MeV state. Decay schemes have been investigated and estimates made of radiative widths and total widths. It is concluded that the 10.270 MeV state is the first T = 1 state of Ne 20 on the basis of measurements of its excitation energy, spin and parity, total width, and M1 radiative width. The excitation function for 6.13 MeV gamma rays from the reaction O 16(α,α′γ)O 16 has been studied for E α from 8.9 to 9.9 MeV; the data clearly show a resonance at E α = 9.57 MeV corresponding to a state at 12.39 MeV in Ne 20, and there is some evidence for a weaker resonance at E α = 1.25 MeV corresponding to E x = 12.13 MeV.

Gamma transitions in the decay of V 52

A fast-slow coincidence set-up with a time resolution of 3 ns (at 1 MeV) has been constructed using a time to pulse-height converter as the fast coincidence unit. This instrumentation, which is transistorized throughout, has been used in the search for weak gamma transitions following the decay of V 52 (3.8 min). Three new transitions of 1.21 MeV (0.29±0.06%), 1.53 MeV (0.53±0.04%) and 1.73 MeV (<0.05%) have been found. A gamma-gamma angular correlation study on the 1.43 MeV-1.53 MeV cascade is consistent with a 2 +(E2+M1)2 +(E2)0 + cascade with a large M1 component (>90%).

Spin-Parity Determination of theΞπResonance (1. 530 GeV)

The XI pi resonance at 1.530 Bev, which was produced by meson (K/sup -/) reactions in a hydrogen bubble chamber at 1.801.95 Bev/c, was investigated. A complete angular correlation study of the decay sequence XI /sup *o/ yields XI /sup -/ + pi /sup +/, XI /su p -/ yields LAMBDA + pi /sup -/ is reported. lt is concluded that the simplest spin-parity assignment of the resonance is (3/2)/sup +/. (C.E.S.)

Decay ofSm156

The radiations following the decay of 9.4 surface proces 0.2 h Sm/sup 156/ were studied using techniques of scintillation spectrometry and 4 ceramic materia beta counting. The isotope was produced by fissioning natural uranium in a high neutron flux and except for Sm/sup 153/, was separated from other fission products by radiochemical techniques. The following gamma-ray energies were observed in the decay of Sm/sup 156/: 38, x rays ( ontrol migra- 20%), The 87-kev gamma transition was found to be coincident with both the 165 and 203-kev gamma transitions. Its Kshell conversion coefficient is 0.35 surface proces 0.02. Angular correlation studies indicated the 87-203 kev gamma anisotropy to be about -0.25 and the 87-165 kev gamma anisotropy to be 0 < A < 0.1. Fermi plots of the beta spectra coincident with the 165 and 203-kev gamma rays produced identical end points of 430 surface proces 10 kev. Another beta group, 45% in abundance, had an end point of 715 surface proces 15 kev and presumably goes to the ground state of Eu/sup 156/. (auth)

Decay of Cd115(2.3d)

The decay of Cd115 (2.3d) has been studied by scintillation beta and gamma spectroscopy. The K-internal conversion coefficients of the 35 and 335 keV gamma transitions in the de-excitation of In115 have been measured to be 7.6±0.8 and 0.84±0.09, respectively. The β-γ coincidences showed that the 590 and 860 keV beta branchings may be of an allowed and ΔI = 2 unique forbidden types, respectively. From the angular correlation studies of the 35–492 keV and 230–262 keV cascades, 5−2, 3−2and1−2or3−2 may be assigned to the 597, 827 and 862 keV levels, respectively.

Electron-gamma angular correlation studies with the radiations from the de-excitation of Pt192

Abstract e −γ angular correlation studies have been made between the 308, 296 and 316 KeV radiations of the triple cascade of Pt192. The measurements are in agreement with 2-2 1 2 and ≈ 7% M1/E2 mixtures for the 296 and 308 keV transitions respectively and an E0/E2 K-electrton mixture of 9±4% for the 296 keV transition. The phase, in all cases, is negative.

Neutron-gamma angular correlation studies from the reaction Be 9(d, nγ)B 10

A study has been made of the Be 9(d, nγ)B 10 reactions. Two neutron groups were observed in coincidence with γ-rays and these have been shown to correspond to the levels in B 10 at 3.58 and 5.16 MeV excitation. Angular correlation measurements made at deuteron energies of 2.65, 3.3 and 4.4 MeV show that these levels are of even parity. While a spin of 1 cannot be excluded for the 5.16 MeV level, the evidence favours a spin of 2, supporting the belief that this is the second lowest T = 1 state in B 10.

The Argonne 60-in. scattering chamber

The 60-in. scattering chamber used with the external beam of the Argonne 60-in. cyclotron is described. The scattering chamber permits operation over an angular range from 4° to 176° with an accuracy of ±3 min of arc. The geometrical factors involved in the measurement of cross sections are known to ± 0.1% or better. The angular positions of the detectors, the target changer, and an absorber foil system in front of the detection units are operated by remote control so as to permit continuous operation of the cyclotron when these parameters are varied. It is possible to operate several detectors simultaneously; and in order to permit angular correlation studies, the angular position of one detector can be varied by remote control with respect to the other detector units.

An integral-bias summing spectrometer for gamma-gamma coincidence and angular correlation studies

A new type of scintillation coincidence spectrometer is designed which sums pulses from scintillation events occurring simultaneously in two NaI(TI) crystals, integral-bias discriminator outputs being used in coincidence or in anticoincidence with sum-pulses, to select wanted coincidences. This “sum-peak spectrometer” has a better efficiency and resolution than an ordinary coincidence spectrometer, from which it can be obtained by an easy modification to give additional information on coincidence relations of gamma-rays. As no pulse-height selector windows are involved, the performance of the spectrometer is insensitive to minor electronic drifts, which also makes this system especially useful in angular correlation studies. Here in some cases it permits a simultaneous measurement of several angular correlation functions. It also offers the possibility of using a known gamma cascade as an internal monitor, as demonstrated in this paper, which reduces uncertainties due to geometrical and other effects.

Angular correlation studies of the 326, 405 and 630 keV Al 27(p,γ) resonances

The Al 27(p,γ)Si 28 reaction at the 326, 405 and 630 keV resonances has been investigated. The gamma ray spectra were studied with large NaI scintillators and a three crystal scintillation pair spectrometer, while decay schemes and relative intensities were determined by coincidence techniques. Angular correlation studies, (p,γ) and (p,γ,γ), have established the spin and parity of the first two excited states in Si 28, 1.78 and 4.62 MeV, as 2 + and 4 +, respectively, and of the proton capture states: 11.90 MeV, 4-; 11.98 MeV, 4-; and 12.20 MeV, 3-. A weak cascade branch, observed at the 405 keV resonance, proceeds through the 8.59 and 1.78 MeV levels. Correlation studies on this cascade are in agreement with a spin and parity assignment of 3+ for the 8.59 MeV level.

Magnetic and quadrupole interactions in Hg 197m. Angular correlations

A series of electron-gamma angular correlation studies of the 165 keV–134 keV cascade in Hg 197m and the 130 keV–279 keV cascade in the decay-product Au 197m are reported. The experiments have been undertaken primarily to settle the much discussed problem of the possible existence of a time dependent coupling between the nucleus and the electron core excited by virtue of a preceding conversion or electron-capture process. For the Au 197m cascade no observable attenuations of the angular correlation pattern were found due to the short lifetime (2.3 × 10 −11s) of the intermediate level. In Hg 197m, where the corresponding lifetime is 1 × 10 −3s, the correlation was found to be attenuated by a static quadrupole interaction for carrier-free sources deposited onto different metal and insulator backings. No measurable attenuation due to an interaction with the electron core was seen for metallic source backings. However, an additional attenuation attributed to the after-effects of the conversion-process was found for sources embedded in insulating environments. The interplay between the two different types of interaction gives a complicated attenuation mechanism, which, however, can be disentangled by means of time-differential angular correlations. A direct proof of the existence of an attenuation-effect due to the excitation of the electron core is furnished by a magnetic decoupling experiment, confirming the results obtained in the correlation experiments.

Neutron-gamma angular correlations studies of the B 11(d, nγ)C 12 reaction

Several (n, γ) angular correlations of the neutron group leading to the 4.43 MeV level in C 12 and the associated γ-rays from the reaction B 11(d, n)C 12 have been measured using time-of-flight techniques. The energies of the incident deuterons were 2.65 MeV and 5.35 MeV, and the angles of the outgoing neutron direction were chosen at intervals of about 20°. The results of these measurements clearly show that the simple theory of Butler stripping is quite inadequate to describe the detailed features of the reaction mechanism but that good qualitative agreement of the results might be obtained with the distorted wave theory. Moreover the (n, γ) angular correlation measurements for backward angles of the neutrons do not show the expected features of the heavy particle stripping mechanism, which has been used by other authors to account for the intensity of neutrons emitted at backward angles.

Angular Correlation Study of theMg24(d, pγ)Mg25Stripping Reaction as a Test of the Distorted-Wave Theory

Angular correlations between protons from the ${\mathrm{Mg}}^{24}(d, p){\mathrm{Mg}}^{25}$ reaction leading to the 3.40-Mev excited state of ${\mathrm{Mg}}^{25}$ and the resulting de-excitation gamma rays were investigated to test the validity of the distorted-wave stripping theory. A natural magnesium target was bombarded by 15-Mev deuterons and proton-gamma coincidences were counted using scintillation detectors in conjunction with conventional fast-slow coincidence circuitry. The correlations were studied at laboratory proton scattering angles of 15\ifmmode^\circ\else\textdegree\fi{} and 45\ifmmode^\circ\else\textdegree\fi{}, each in two mutually perpendicular planes: the reaction plane and the plane perpendicular to it containing the deuteron axis. The angular distribution of protons from this level was also measured and fitted by a Butler stripping curve with ${l}_{n}=1$ and ${r}_{0}=5.0$ fermis.The coordinate system used to describe the correlations is defined with the $z$ axis in the ${\mathrm{k}}_{d}\ifmmode\times\else\texttimes\fi{}{\mathrm{k}}_{p}$ direction and the $x$ axis in the recoil nucleus direction. Correlation functions found by least-squares fits to the experimental data are, for the 15\ifmmode^\circ\else\textdegree\fi{} proton angle, $W({\mathrm{k}}_{d}, {\mathrm{k}}_{p}, \frac{1}{2}\ensuremath{\pi}, \ensuremath{\varphi})=1\ensuremath{-}(0.385\ifmmode\pm\else\textpm\fi{}0.023){cos}^{2}(\ensuremath{\varphi}\ensuremath{-}{\ensuremath{\varphi}}_{0})$, with ${\ensuremath{\varphi}}_{0}=\ensuremath{-}27.7\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}2.9\ifmmode^\circ\else\textdegree\fi{}$, and $W({\mathrm{k}}_{d}, {\mathrm{k}}_{p}, \ensuremath{\theta}, {\ensuremath{\varphi}}_{r})=1+(0.145\ifmmode\pm\else\textpm\fi{}0.029){cos}^{2}\ensuremath{\theta}$, where ${\ensuremath{\varphi}}_{r}$ is the beam direction. The functions found for the 45\ifmmode^\circ\else\textdegree\fi{} proton angle are $W({\mathrm{k}}_{d}, {\mathrm{k}}_{p}, \frac{1}{2}\ensuremath{\pi}, \ensuremath{\varphi})=1\ensuremath{-}(0.366\ifmmode\pm\else\textpm\fi{}0.033){cos}^{2}(\ensuremath{\varphi}\ensuremath{-}{\ensuremath{\varphi}}_{0})$, with ${\ensuremath{\varphi}}_{0}=\ensuremath{-}6.8\ifmmode^\circ\else\textdegree\fi{}\ifmmode\pm\else\textpm\fi{}3.5\ifmmode^\circ\else\textdegree\fi{}$, and $W({\mathrm{k}}_{d}, {\mathrm{k}}_{p}, \ensuremath{\theta}, {\ensuremath{\varphi}}_{r})=1+(0.279\ifmmode\pm\else\textpm\fi{}0.038){cos}^{2}\ensuremath{\theta}$. These observed correlations are in good agreement with the predictions of the distorted wave theory and not with those of the plane wave theory. It is to be noted in particular that the agreement is excellent at 45\ifmmode^\circ\else\textdegree\fi{} indicating that protons scattered at this angle probably arise from the stripping process in spite of the fact that the disagreement between Butler stripping theory and the measured angular distribution is greatest here. This then suggests that protons observed in the entire region beyond the first maximum of a typical angular distribution are due to stripping and might be adequately described by stripping theory if suitably distorted waves are used in the analysis.

Reaction mechanism studies on Si 28(d, p)Si 29 (I) distorted wave effects

A study of the (p, γ) angular correlations involving the 1.28 and 2.03 MeV states in Si 29 populated by the Si 28(d, p)Si 29 reaction has been carried out for deuteron energies in the range from 6 to 9 MeV. In each case measurements were carried out in the (d,p) reaction plane with protons detected on the observed peak of the l n= 2 stripping angular correlation. These data have been analysed within the framework of distorted-wave stripping formalism. The measurements on the 2.03-MeV state alone enable the statistical tensors for the reaction to be determined for each incident deuteron energy. These statistical tensors were then used to compute the angular correlation of the 1.28-MeV radiation, yielding results in good agreement with the experimental measurements and thus supporting the expectation that the matrix elements are essentially independent of the detailed nuclear structure of the final state. The statistical tensors have also been used to predict the general (p, γ) angular correlation function over the sphere as well as the magnitude of the proton polarization for the Si 29∗- proton systems involving both the 1.28 MeV and 2.03 MeV excited states.

Angular correlation studies of the Be 9(α, nγ)C 12 reaction

Several angular distributions and (n, γ) correlations of the neutron group corresponding to the 4.43 MeV level of C 12, produced in the reaction Be 9(α, nγ)C 12, have been measured using time-of-flight techniques. Bombarding energies of 3.35 MeV and 5.10 MeV were used. Results have been analysed in terms of direct interaction mechanisms. The angular distributions show forward peaking and can be fitted reasonably well by Butler's theory assuming contributions from l = 1 and l = 3 but require a rather large value of the radius parameter. Angular correlation measurements have been done in the reaction plane for neutrons emitted at 10°, 20° and 75° to the direction of the incident beam at energies of 3.35 MeV and 5.10 MeV. These have been fitted by a sum of even order Legendre polynomials. The correlations show marked changes both with neutron angle and bombarding energy, but the symmetry axis is in most cases not very far from the direction of momentum transfer. These results would suggest interference either from different reaction mechanisms, different l-values or both.

Decay ofGa66andCu66

The 9.5-hour decay of ${\mathrm{Ga}}^{66}$ and the 5.1-minute decay of ${\mathrm{Cu}}^{66}$ have been studied by a variety of techniques including gamma-ray spectroscopy, internal conversion measurements, and angular correlation studies. All but one of the 18 gamma rays observed have been ordered into a structure of 11 levels and the spins and parities of all but one of these levels have been determined. It is shown that ${\mathrm{Ga}}^{66}$ has spin zero and even parity and that its 4.166-Mev $\ensuremath{\beta}$ spectrum is a pure Fermi transition. The energy of the internal conversion line of the 4.300\ifmmode\pm\else\textpm\fi{}0.005 Mev transition was measured with great care and this line may be useful for spectrometer calibration. The second excited state of ${\mathrm{Zn}}^{66}$, at 1.875 Mev, has 2+ spin and parity. The stopover transition from this state contains at least 10% $M1$ radiation: the stopover to crossover ratio is greater than 100 to 1.