Charged-particle Detector System Research Articles

Isospin and deformation studies in the odd-oddN=ZnucleusCo54

High-spin states in the odd-odd N = Z nucleus Co-54 have been investigated by the fusion-evaporation reaction Si-28(S-32,1 alpha 1p1n)Co-54. Gamma-ray information gathered with the Ge detector array Gammasphere was correlated with evaporated particles detected in the charged particle detector system Microball and a 1 pi neutron detector array. A significantly extended excitation scheme of Co-54 is presented, which includes a candidate for the isospin T = 1, 6(+) state of the 1f(7/2)(-2) multiplet. The results are compared to large-scale shell-model calculations in the fp shell. Effective interactions with and without isospin-breaking terms have been used to probe isospin symmetry and isospin mixing. A quest for deformed high-spin rotational cascades proved negative. This feature is discussed by means of cranking calculations. (Less)

Gamma-ray spectroscopy of the doubly magic nucleus 56Ni

The doubly magic N = Z nucleus 56Ni has been investigated with two fusion-evaporation reactions; 40Ca(28Si, 3α)56Ni at a beam energy of 122MeV and 28Si(32S, 2p2n)56Ni at 130MeV. To detect γ-rays in coincidence with evaporated particles the Ge-detector array Gammasphere was used in conjunction with the charged-particle detector system, Microball and a 1π neutron detector array. Results include a significantly extended level scheme of 56Ni, which is compared to large-scale shell model calculations in the fp shell. The experimental and theoretical results agree to a large extent, with one notable exception; the theoretical model fails to predict the proper sequence of the yrast and yrare 8+ states.

First identification of excited states in the $T_z\! = \!1/2$ nucleus 93 Pd

The first experimental information about excited states in the N = Z + 1 nucleus 93Pd is presented. The experiment was performed using a 205 MeV 58Ni beam from the Vivitron accelerator at IReS, Strasbourg, impinging on a bismuth-backed 40Ca target. Gamma-rays, neutrons and charged particles emitted in the reactions were detected using the Ge detector array Euroball, the Neutron Wall liquid-scintillator array and the Euclides Si charged-particle detector system. The experimental level scheme is compared with the results of new shell model calculations which predict a coupling scheme with aligned neutron-proton pairs to greatly influence the level structure of $N\approx Z$ nuclei at low excitation energies.

“Complete” high-spin structure of57Co

A comprehensive high-spin decay scheme has been deduced for ${}^{57}\mathrm{Co}$ using the Gammasphere Germanium detector array coupled to the $4\ensuremath{\pi}$ charged-particle detector system Microball. Following the fusion-evaporation reaction of ${}^{28}\mathrm{Si}{(}^{36}\mathrm{Ar},1\ensuremath{\alpha}{3p)}^{57}\mathrm{Co}$ at 136 MeV beam energy about 90 excited states have been observed in ${}^{57}\mathrm{Co},$ which are connected by some 230 $\ensuremath{\gamma}\ensuremath{-}\mathrm{r}\mathrm{a}\mathrm{y}$ transitions. The proposed level scheme reaches 16 MeV excitation energy at a spin of $17\ensuremath{\Elzxh}--18\ensuremath{\Elzxh}.$ With its complexity the level scheme of ${}^{57}\mathrm{Co}$ appears to be ``complete'' up to 1 or 2 MeV above the yrast line. This aspect is further investigated through a comparison of the data with spherical shell-model calculations.

SACI—a 4π plastic phoswich array ancillary detector system of a γ-ray spectrometer

A large solid angle low-Z charged particle detector system was built in order to improve the quality of the identification and selection of evaporation channels for in-beam γ-spectroscopy measurements. The array consists of 11 plastic phoswich telescopes closely packed in a 4 π arrangement and to be used as an ancillary system for the Pelletron Laboratory γ-ray spectrometer. The new system was tested in γ- particle and γ–γ- particle coincidence measurements using the 27 Al + 16 O and 100 Mo + 11 B reactions, at 53 and 43 MeV incident beam energies, respectively. The values for the particle detection efficiency and improvement in the peak to background ratios are considered acceptable for the usefulness of the system.

Observation of superdeformed states in 88Mo

High-spin states in Mo-88 were studied using the GAMMASPHERE germanium detector array in conjunction with the MICROBALL CsI(TI) charged-particle detector system. Three gamma-ray cascades with dynamic moments of inertia showing similar characteristics to superdeformed rotational bands observed in the neighbouring A = 80 region have been identified and assigned to the nucleus Mo-88. The quadrupole moment of the strongest band, deduced by the Residual Doppler Shift Method, corresponds to a quadrupole deformation of beta(2) approximate to 0.6. This confirms the superdeformed nature of this band. The experimental data are interpreted in the framework of total routhian surface calculations. All three hands are assigned to two-quasi-particle proton configurations at superdeformed shape.

Collective excitations and band termination in 85Nb

High-spin states in 85Nb were studied using the Gammasphere Ge detector array and the Microball charged-particle detector system. Three γ-ray cascades with collective rotational characteristics were observed. One of the bands exhibits a forking at the top, most likely reflecting the termination of one branch into a favoured non-collective, near spherical state. The data are interpreted in terms of cranked Strutinsky-type calculations.

Resolution-enhanced spectroscopy of81Y

The fusion-evaporation reaction ${}^{58}\mathrm{Ni}{(}^{32}\mathrm{S},2\ensuremath{\alpha}p)$ has been used to study the neutron-deficient isotope ${}^{81}\mathrm{Y}.$ Multiple particle \ensuremath{\gamma}-ray coincidences have been detected by the GAMMASPHERE array combined with the MICROBALL charged-particle detector system. Gamma-ray spectra with an improved resolution have been achieved from an event-by-event determination of the nucleus recoil momentum, thus allowing a precise Doppler-shift correction. In this way a resolution enhancement by a factor 2 was obtained for a 1 MeV \ensuremath{\gamma} line. During the analysis an ${E}_{\ensuremath{\gamma}}{\ensuremath{-}E}_{\ensuremath{\gamma}}$ matrix as well as an ${E}_{\ensuremath{\gamma}}{\ensuremath{-}E}_{\ensuremath{\gamma}}{\ensuremath{-}E}_{\ensuremath{\gamma}}$ cube have been used to extend the previously known level scheme to higher spin $(I\ensuremath{\approx}\frac{57}{2})$ and excitation energy ${(E}_{x}\ensuremath{\approx}17\mathrm{MeV}).$ More than 100 new \ensuremath{\gamma} rays and 80 new levels have been added to the level scheme and six new bands have been established. The interpretation of these bands in terms of the cranking model and their comparison with similar bands in neighboring nuclei is discussed.

Many-fold coincidence pileup in silicon detectors: Solar X-ray response of charged particle detector systems for space

A technique for computing counting rates of silicon detectors in case of multiple absorption events has been developed. It enables quantitative analysis of the response of solid-state detectors flown in space to solar X-ray events of different intensities and temperatures. The technique is applied to computing the responses of generic types of satellite detectors to solar X-ray emission spectra in the 5 to 40 MK temperature range. Comparison with the data available for the Energetic Particle Experiment (EPE) flown on the IMP 8 satellite confirms that many-fold coincidence of photon absorption pulses can account for the response of solid-state detectors to solar X-rays. With an example of a two-threshold detector, it is shown that silicon detectors can be used to measure both the temperature and the emission measure of solar X-ray flares.

High spin bands in 102Pd

The nucleus 102Pd has been studied using 148 MeV 34S ions impinging on 76Ge. The γ-rays were detected with the Nordball array and the light charged particles with a 4π charged particle detector system. Rotational bands have been extended using γ-ray yields, γγ coincidences and angular correlation information. Calculated spin diabatic surfaces were used for assigning quasiparticle configurations to the bands. The (+,0) high spin band extending to 26+ may be explained by a π(g92)2 ⊗ ν(“g72”)2 quasiparticle configuration. The protons are predicted to align first. The negative parity bands are suggested to be built on ν (“g72”h112) evolving to π(g92)2 ⊗ ν(“g72”h112) at the highest spins.

Highly deformed band in 105Ag.

The isotope $^{105}\mathrm{Ag}$ has been studied using 169.5 MeV $^{37}\mathrm{Cl}$ ions impinging on $^{76}\mathrm{Ge}$. The Nordball Ge array detected the \ensuremath{\gamma} rays and a 4\ensuremath{\pi} charged particle detector system detected emitted light charged particles. A very deformed band has been established using Doppler shift attenuation methods. The analysis is based on the \ensuremath{\gamma}\ensuremath{\gamma} coincidences and the angular dependence of the four rings of Ge detectors in Nordball. The deformation of the band is deduced to be ${\mathrm{\ensuremath{\beta}}}_{2}$=0.${37}_{\mathrm{\ensuremath{-}}0.02}^{+0.03}$.

Identification and Quadrupole-Moment Measurement of a Superdeformed Band in 84Zr.

High-spin states in Zr-84 were studied using the early implementation phase of the Gammasphere array and the ''Microball'' charged-particle detector system. A cascade of nine gamma rays with a dyna ...

Characterization of the first superdeformed band in the A ≈ 80 region

The recently discovered superdeformed band in one of the strontium isotopes has been identified as belonging to 83Sr from a study with the Gammasphere array and the Microball charged-particle detector system. From its decay pattern, a spin of (81 ± 2) 2 h ̵ is deduced for the highest level of this band. Evidence for very fast transition rates and agreement of the characteristics of this band with the theoretical predictions establish the yrast superdeformed nature of this band in 83Sr.

High-spin bands in 105Ag

The nucleus 105Ag has been studied using 162–173 MeV 37Cl ions impinging on 76Ge. The γ-rays were detected with the Nordball array and the light charged particles with a 4π charged-particle detector system. Rotational bands have been established using γ-ray yields, γγ-coincidences and angular-correlation information. Calculations of spin diabatic surfaces are used for assigning quasiparticle configurations to the bands. A high-spin band extending to (67/2) may be explained by five-quasiparticle configurations with moderate deformation or with a highly deformed structure involving πh 11/2 and ν(h 11/2) 2 orbitals.

Collective bands in 106Ag and 107Ag

The nuclei 106Ag and 107Ag have been studied using 80 MeV 17O ions impinging on 94Zr. The γ- rays were detected with the NORDBALL array and light charged particles with a charged-particle detector system. Rotational bands have been established using γ-ray yields, γγ coincidences and angular correlation information. Calculations of spin diabatic surfaces have been done and are used for assigning quasiparticle configurations to the bands. Deformation effects are observed in almost all bands.

Correction of Doppler broadening of γ-ray lines induced by particle emission in heavy-ion induced fusion-evaporation reactions

The effect of the emission of light particles in heavy-ion induced fusion-evaporation reactions on the shape of γ-ray lines measured with Ge detectors has been investigated. A method to correct the position and the width of the γ-ray lines, based on the detection of the evaporated particles, has been developed. The method has been applied to the analysis of the data from a heavy-ion experiment, where a beam of 95 MeV 32S was used to bombard a target of 27Al. The experimental set-up consisted of the NORDBALL γ-ray multi-detector array, combined with a 4π charged particle detector system and a 1π neutron detector assembly. Predictions of a Monte Carlo simulation of the uncorrected and corrected γ-ray lines are presented and compared with the experimental results. The importance of different properties of particle detectors for the correction effectiveness is discussed in view of the simulation results.

Charged particle detector system for Coulomb excitation experiment with NORDBALL

A charged particle detector system for Coulomb excitation experiments with the multi-γ-ray detector system, NORDBALL, has been designed and constructed. The system consists of five position sensitive Si detecors and an annular type Si detector, which are installed in the central space of a BaF 2 inner ball. The experiments have been carried out by using the beams of 32S, 48Ti and 58Ni ions. The combination of the new charged particle detector system and NORDBALL proves to have an excellent performance for heavy-ion-induced Coulomb excitation experiments.

Light meson production and pp-Bremsstrahlung at the COSY time-of-flight spectrometer

Experiments on light meson production and pp-bremsstrahlung as planned for the initial stage at COSY are discussed. Special emphasis will be placed on near-threshold behaviour where due to kinematics all particles are forced into a rather narrow cone around the beam axis. A specially designed charged particle detector system will be used which not only covers the complete forward hemisphere of 2π in the laboratory system but additionally shows maximum resolution in the extreme forward direction with only moderate cuts in the minimally required energy of all ejectiles.

HYSTRIX - A 4π plastic phoswich array providing on-line channel selection for in-beam γ-ray spectroscopy

A modular 4π charged particle detector system HYSTRIX, is described. It has been designed and constructed to provide on-line channel selection for in-beam γ-ray spectroscopy. This spectrometer consists of 12 fast-slow plastic scintillators closely packed in a 4π arrangement. The device is small enough to be enclosed in the NORDBALL and POLYTESSA multi-γ-detector systems. Examples of the performance are given from an experiment in which the HYSTRIX rovided channel selection and the POLYTESSA detected the γ-rays.

Ericius — A plastic phoswich detector array for on-line identification of evaporated protons and α-particles following hi-fusion reactions

In heavy ion fusion reactions many isotopes may be populated in competition, resulting in complex deexcitation γ-ray spectra. Therefore, it is difficult to identify transitions within exotic nuclei, far from the line of β-stability, which are less populated than other isotopes. One solution is tagging of specific reaction channels by identification of evaporated charged particles in coincidence with the emitted γ-radiation. Here a relatively simple charged particle detector system is described. Two innovations are introduced; a new method of signal treatment enabling fast identification of evaporation protons and α-particles, and design of an electronic device, based on analog circuits, making on-line channel selection for in-beam γ-ray spectroscopy feasible.