Magnetic Lens Spectrometer Research Articles

80mBr/80Br – A New Electron-Gamma PAC Probe

Conversion electron-gamma PAC measurements of the 49–37 keV cascade in 80Br through the intermediate 2− state with T1/2=7.4 ns were performed with a system of two magnetic lens spectrometers and two BaF2 scintillation detectors. The parent 80mBr activity with a halflife of 4.4 hrs was implanted into Ni, Zn and graphite at the ISOLDE separator at CERN. The observed interaction frequency in the nickel matrix is in good agreement with the known value of the hyperfine field for Br in Ni and the magnetic moment of the 2− state. From the measured quadrupole interaction in Zn and graphite the electric field gradients at Br were obtained.

Proton-neutron multiplet states in112Sb

Excited states of {sup 112}Sb were investigated through the {sup 112}Sn(p,n{gamma}){sup 112}Sb reaction. {gamma}-ray, {gamma}{gamma}-coincidence, and internal conversion electron spectra were measured with Ge(HP) {gamma} and superconducting magnetic lens plus Si(Li) electron spectrometers at 8.5, 8.9, 9.1, and 9.3 MeV bombarding proton energies. A significantly extended level scheme was constructed. Spins and parities have been assigned to the levels from Hauser-Feshbach analysis of reaction cross sections, internal conversion coefficients, angular distribution of the {gamma} rays, and decay properties of the states. The low lying states were assigned to proton-neutron multiplets on the basis of their decay properties. The energy splitting of these multiplets have been calculated using the parabolic rule. {copyright} {ital 1997} {ital The American Physical Society}

Structure of 72As nucleus

Abstract γ-ray, internal conversion electron and γγ-coincidence spectra of the 72Ge(p,nγ) 72As reaction were measured with Ge(HP) γ and superconducting magnetic lens plus Si(Li) electron spectrometers at eight bombarding proton energies between 5.75 and 6.51 MeV. Energies and relative intensities of 123 (among them 58 new) 72As γ-rays, as well as 51 (including 38 new) internal conversion coefficients have been determined. A more complete level scheme, γ-ray branching ratios, level spin and parity values have been deduced. The energy spectra and electromagnetic properties were calculated using the interacting boson-fermion-fermion model. The calculations reasonably well describe the level spectra and electromagnetic properties of 72As nucleus.

Low-lying states in the doubly odd nucleus 132Pr from beta decay of 132Nd

Abstract The low-lying level scheme of the odd-odd nucleus 132Pr has been investigated for the first time. The radioactive nuclei were produced by bombarding 96Mo targets with a 225 MeV 40Ca beam. Levels in 132Pr have been populated from the 132Nd β-decay. A new value of its half-life has been measured: T 1 2 = 88 ± 7 s . The activities produced in the reaction have been transported with a He-jet device and γγt, Xγt, e−γt coincidence measurements performed. Internal conversion coefficients have been measured with a magnetic lens spectrometer. The experimental level scheme of 132Pr is compared to theoretical calculations performed with the interacting boson-fermion-fermion model (IBFFM).

Level scheme of 116Sb from (p,n gamma ) reaction.

The \ensuremath{\gamma}-ray and internal conversion electron spectra of the $^{116}\mathrm{Sn}$(p,n\ensuremath{\gamma}${)}^{116}$Sb reaction have been measured at ${\mathit{E}}_{\mathit{p}}$=6.3, 6.7, and 7.2 MeV bombarding energies with Ge(HP), Ge(HP,LEPS) \ensuremath{\gamma} and superconducting magnetic lens plus Si(Li) electron spectrometers. The energies and relative intensities of 90 $^{116}\mathrm{Sb}$ \ensuremath{\gamma} rays, as well as internal conversion coefficients of 21 $^{116}\mathrm{Sb}$ transitions have been determined. Angular distribution data have been obtained for 37 \ensuremath{\gamma} rays. A more complete level scheme of $^{116}\mathrm{Sb}$ has been deduced, which contains 38 levels below 1500 keV excitation energy. Multipolarities of transitions and \ensuremath{\gamma}-ray branching ratios have been deduced. Calculated Hauser-Feshbach (p,n) cross sections have been compared with experimental values. Level spins and parities have been determined on the basis of the Hauser-Feshbach analysis, internal conversion coefficients, and \ensuremath{\gamma}-ray angular distribution data. The energies of several $^{116}\mathrm{Sb}$ proton-neutron multiplets have been calculated using the parabolic rule. Members of different multiplets have been identified.

Feasibility study of a double-lens internal-pair spectrometer for multipolarity analysis

A combination of semicircular Si(Li) detectors with two magnetic-lens spectrometers is shown to offer a possibility to construct an effective spectroscopic instrument for multipolarity determinations. The proposed method is based on the fact that the angular correlation between the electron-positron pair is sensitive to multipolarity, even at high transition energies. Response characteristics and multipole discrimination power are given for different conversion-electron or internal-pair spectrometers. The results show that for multipolarity analysis of high-energy nuclear transitions internal-pair spectrometry with a double lens spectrometer may be a superior method in the low- and intermediate- Z region. Optimum multipole discrimination effects are obtained using two detectors on the spectrometer axis placed at 180° relative to the target. The calculations are based on the zero-order Born approximation (ZBA) and are sufficiently accurate for at least E > 1.5 MeV and Z < 50.

A servo system for reducing stray AC magnetic fields in an iron-free environment

Slow disturbances are compensated at the site of an iron-free magnetic lens spectrometer (Jennings 1972) by a servo system driven by a fluxgate magnetometer at a site remote from the spectrometer. To avoid the presence of ferromagnetic material near the spectrometer, a pickup coil 0.20 m in diameter and of approximately 6000 turns (DC resistance 600 Omega : inductance 10 H) is placed near to the spectrometer and detects the disturbances in the vertical magnetic field.

Determination of half-live, endpoint energy and shape factor in the decay of 27Si and 24Na with an on-line beta spectrometer

A magnetic lens spectrometer of Siegbahn-Sla¨tis type has been installed at the Dynamitron-Tandem accelerator at Bochum such that measurements of continuous beta spectra even for short half-lives can be performed as well as the determination of discrete conversion lines in the multi-sweep mode. Electrons and positrons can be focussed up to an energy of 10.7 MeV with transmission up to about 8% or a resolution of about 1% depending on the width of entrance and central baffle inside the spectrometer. The system was tested by determination of the half-life of 27Si, and the endpoint energy as well as the shape of the allowed spectrum of 24Na. The quantities amount to t 1/2=(4.206±0.008)s, W 0=(1.390±0.001) MeV and a=(−1.10±0.21) %/m 0c 2, respectively.

Multipole mixing ratios of electromagnetic transitions in 152Gd

Using γ-γ(θ), γ(θ) (nuclear orientation) and e k-γ(θ) directional correlation techniques, we have determined the multipole character of some transitions connecting the quadrupole and octupole quasi-vibrational bands to the ground state quasi-rotational band in 152Gd following the decay of 152Tb. For the γ-γ directional correlation measurements a high-energy resolution system employing a Ge(Li) and a NaI(Tl) detector was used while for the e k-γ correlation we used a NaI(Tl) and magnetic lens spectrometer system. The nuclear orientation measurements were carried out at low temperatures obtained with a 3He- 4He dilution refrigerator. The results show that the 2 + → 2 + transition between the β-vibrational and the ground state bands contains ≈ 10% Ml admixture, δ = − 3.05 ± 0.14, and a large E0 contribution while the similar transition from the γ-vibrational band has δ = 4.3 ± 0.7. These results are compared with Kumar's predictions for similar transitions in 152Sm. Three other mixing ratios were also determined.

Further Investigation of Penetration Effects inCs133

The internal-conversion coefficient of the 223-keV transition was determined, from precise $\ensuremath{\gamma}$-ray and conversion intensities, as ${\ensuremath{\alpha}}_{K}(223)=0.082\ifmmode\pm\else\textpm\fi{}0.004$. $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ directional correlations of the ${\ensuremath{\gamma}}_{223}\ensuremath{-}{\ensuremath{\gamma}}_{80+81}$ and ${\ensuremath{\gamma}}_{276}\ensuremath{-}{\ensuremath{\gamma}}_{80+81}$ cascades were measured using a 33-${\mathrm{cm}}^{3}$ Ge(Li) detector and a 2 \ifmmode\times\else\texttimes\fi{} 2-in. NaI(Tl) detector. The ${A}_{22}$ coefficients are ${A}_{22}({\ensuremath{\gamma}}_{276}\ensuremath{-}{\ensuremath{\gamma}}_{80+81})=+0.100\ifmmode\pm\else\textpm\fi{}0.004$ and ${A}_{22}({\ensuremath{\gamma}}_{223}\ensuremath{-}{\ensuremath{\gamma}}_{80+81})=\ensuremath{-}0.030\ifmmode\pm\else\textpm\fi{}0.004$, which are consistent with $\ensuremath{\delta}(223)=\ensuremath{-}0.108\ifmmode\pm\else\textpm\fi{}0.014$. These values of ${\ensuremath{\alpha}}_{K}$ and $\ensuremath{\delta}$ imply $\ensuremath{\lambda}(223)={2}_{\ensuremath{-}3}^{+4}$, consistent with a normal conversion process for this transition. In addition, the relative correlations of the ${K}_{276}\ensuremath{-}{\ensuremath{\gamma}}_{161}$ and ${K}_{276}\ensuremath{-}{\ensuremath{\gamma}}_{80+81}$ cascades were measured using a magnetic-lens spectrometer and 2 \ifmmode\times\else\texttimes\fi{} 2-in. NaI(Tl) detector. The ratio of these ${A}_{22}$ coefficients allows cancellation of electron scattering factors, spectrometer geometry factors, and correlation attenuation factors. The results imply $\ensuremath{\delta}(161)=+{0.59}_{\ensuremath{-}0.16}^{+0.18}$, which supports the existence of large penetration effects in the 161-keV transition.

Lifetimes of some excited states in 182W

Abstract The lifetimes of five excited states in 182W have been measured using a magnetic double lens spectrometer coupled to a pulse-height converter and a fast-slow coincidence system. The half-lives of the 100 keV, 1289 keV, 1374 keV, 1488 keV and the 1553 keV levels were found to be 1.48 ± 0.03 ns, 1.06 ± 0.02 ns, 1.70 ± 0.05 ns, ≦ 1.70 ns and 1.35 ± 0.04 ns, respectively. Some nuclear parameters are deduced and discussed.

Monopole mixing ratio of the 793 keV 2 + → 2 + transition in 184W

The amplitude mixing ratios of the E2 to M1 and E0 to E2 components of the 2 +(793 keV) 2 + transition in 184W were obtained from γγ, and gamma-conversion electron angular correlation measurements. The γγ measurements used a Ge(Li) detector in some cases; the eγ correlations were performed using a magnetic lens spectrometer. The results obtained are δ(E2:M1) = + 18.7 +4.6 −3.1 + 0.38 ≧ q( E0: E2) ≧ − 0.28 for + 53 ≧ λ ≧ − 113 . Agreement with Kumar's theoretical values for δ and q is contradictory: the former favours a 2″ assignment, the latter a 2prime; assignment to the 904 keV level.

Note on the β-circularly polarized γ-angular correlations in the decays of 46Sc and 58Co

The β-γ circular polarization correlations of the (357 keV, 4 + → 4 +, β −) − (1.121 + 0.889 MeV, γ) cascade in 46Sc and the (475 keV, 2 + → 2 +, β +) − (0.810 MeV, γ) in 58Co have been measured by using the standard forward scattering technique for the detection of circular polarization of γ-rays. The energy selection of the β-rays was performed with a magnetic lens spectrometer. The measured asymmetry coefficients, Fermi to Gamow-Teller matrix element ratios, values of the Fermi matrix elements, isospin impurity coefficients and the effective Coulomb matrix elements are as follows: A =M F/M GT |M F| × 10 3 |α| × 10 3 |〈H C〉|keV 46Sc 0.06±0.03 0.03±0.04 1.9±2.5 0.95±1.25 6.7±10 58Co 0.18±0.04 0.02±0.05 0.7±1.8 0.3 ±0.7 1.8± 4.7

Beta-gamma circular polarization correlation in the decay of 48V

The β-γ circular polarization correlation of the (698 KeV, 4 +→4 +, β +)−(1.31+0.99 MeV, γ) cascade in 48V has been measured using the standard forward Compton scattering technique for the detection of the circular polarization of the gamma rays. The energy selection of the β-rays was performed with an anthracene crystal in one experiment and with a magnetic lens spectrometer in a second one. The use of the latter instrument has the following advantages: no scattering of electrons in air, negligible gamma-gamma coincidence background, improved energy selection of the beta rays and elimination of interfering 511 keV annihilation radiation in the β-detector in case of positon emitters. The measured asymmetry coefficient is A = 0.002±0.0035 for the first experiment and A = −0.005±0.031 for the second. The average value A = −0.002±0.024 gives for the isospin impurity coefficient and the effective Coulomb matrix element (4.0±1.1)×10 −3and 28±8 keV, respectively.

Note on the energy dependence of the beta-gamma directional correlation in the decay of 154Eu

The 1855 keV-123 keV β-γ directional correlation in the decay of 154Eu has been measured as a function of beta energy. A magnetic-lens spectrometer was used as the beta-energy analyser. The attenuation of the directional correlation was carefully studied. The maximum measured value of A 2 corrected for attenuation is −0.31 at 1638 keV and decreases rapidly with decreasing energy.

Decay dependent background signals in a magnetic electron spectrometer

Scattering of the radiation emitted in a radioactive decay at the constructional components of a magnetic spectrometer will give rise to a background which usually is not eliminated by coincidence techniques. The background spectrum depends upon the features of the decay under investigation, the instrumental settings and the design parameters of the spectrometer. We investigated origin and intensity of various types of background signals observed in a magnetic lens spectrometer. Quantitative representative results are given which can provide an order of magnitude estimate for the background intensity to be expected in a certain decay. Significant background intensities are caused by γ-radiation as well as by electrons emitted in the decay. It was found that scattered conversion electrons can give rise to sharp structures in the apparent electron spectrum, which are comparable to or even narrower than the instrumental resolution. It is shown by which counter measures the various types of backgrounds can be minimized.

On the decay of 106In

The half-life for decay of 106In has been measured to be 5.3±0.1 min. A magnetic lens spectrometer was used to investigate the positon spectrum of this isotope. Two positon components were found whose transition energies are 4.89±0.03 and 2.7±0.1 MeV. Seven gamma rays involved in the decay of 106In have been resolved at energies of 0.53, 0.63, 0.86, 0.99, 1.66, 1.88 and 2.2 MeV. Beta-gamma coincidence measurements indicate the highest energy positon component to be coincident with only the 0.63 MeV gamma ray. In addition, the 2.7 MeV positon transition is coincident with gamma rays at 0.63, 0.86, 0.99, 1.66 and 1.88 MeV. The gamma rays at 0.63, 0.86 and 0.99 MeV were measured to be in coincidence. A search was made for the presence of an isometric state in the decay of 106In with a half-life in the range from 0.5 sec to several hours. The investigation produced no evidence for the existence of such a state.

Relative measurements of longitudinal electron polarization in the β-decay of P 32, In 114, Pr 142, Ho 166 and Re 188

Relative measurements of the electron longitudinal polarization in the β-decay of P 32, In 114, Pr 142, Ho 166 and Re 188 were made at E β ≈ 1250 keV by measuring bremsstrahlung of circular polarization (β-electrons stopped in a lead target). The circular polarization of the bremsstrahlung γ-quanta of In 114, Pr 142, Ho 166 and Re 188 β-electrons was compared with that of P 32 β-electrons. The electron energy was fixed with a magnetic lens spectrometer. The following values were obtained for the longitudinal polarization P 1 relative to P P 32 : P In 114 / P P 32 = 0.960±0.015, P Pr 142 / P P 32 = 0.934±0.015, P Ho 166 / P P 32 = 0.942±0.015, P Re 188 / P P 32 = 1.005±0.016.

A magnetic lens spectrometer for electron-gamma and electron-electron directional correlation measurements

A magnetic lens spectrometer has been adapted for electron-gamma and electron-electron directional correlation measurements. One electron channel has magnetic momentum selection provided by a medium short magnetic lens spectrometer. The lens spectrometer is iron-free with the exception of two steel end plates which decouple the already weak magnetic field in the lens from the electron detector and from the movable gamma or electron detector. The source sits outside the magnetic field and is accessable through 180° to a movable detector. Directional correlations of electrons with gamma-rays or electrons have been carried out by using a NaI(Tl) detector or an anthracene scintillation detector, respectively. A special source holder was designed for the electron-electron work. Electron energies down to 20 keV have been measured in the lens. A proportional counter may be used to lower energies. The maximum lens energy is ≈ 5 MeV. The spectrometer mean emission angle was chosen to be 13.5°. The resolution can then be varied from 1 to 5 per cent with a corresponding transmission of 0.4 to 1.5 per cent.

Computation of beta-ray line shape and luminosity in spheroidal field and other magnetic lens spectrometers

The use of convolution integrals in the computation of β-ray line shapes is discussed. Line shapes are found by numerical integration for the case of a lens spectrometer in which the only aberrations present are those due to aperture and to size of source. From the computed shapes a relation is found between the half width and the relative size of the two aberrations. The relation is used to estimate the dependence of luminosity on resolution in the case of a prolate spheroidal field spectrometer and of a spectrometer which uses a superposition of this field on a uniform field. The performance is compared with that of a uniform field lens spectrometer of similar size. It seems that each type of instrument may be better than the others in an appropriate range of aperture and of size of source.