Double-sided Si Strip Detector Research Articles

βand isomeric decay ofV64

Background: Collectivity has been inferred in $^{64}\mathrm{Cr}$ based on measurements of the excitation energy of the first excited ${2}^{+}$ state and $B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}{0}_{1}^{+})$ value. However, the energy of the ${2}_{1}^{+}$ state in $^{64}\mathrm{Cr}$ is not precisely known.Purpose: The objective was to precisely determine the energy of the ${2}_{1}^{+}\ensuremath{\rightarrow}{0}_{1}^{+}$ transition in $^{64}\mathrm{Cr}$ following the $\ensuremath{\beta}$ decay of $^{64}\mathrm{V}$.Method: $^{64}\mathrm{V}$ ions were produced by projectile fragmentation at the National Superconducting Cyclotron Laboratory and stopped in a double-sided Si strip detector. $^{64}\mathrm{V}$ isomeric and $\ensuremath{\beta}$-delayed $\ensuremath{\gamma}$ rays were detected in an ancillary array of high-purity Ge detectors in order to determine the energies of excited states in $^{64}\mathrm{V}$ and $^{64}\mathrm{Cr}$.Results: The first excited ${2}^{+}$ state in $^{64}\mathrm{Cr}$ was populated following the $\ensuremath{\beta}$ decay of $^{64}\mathrm{V}$, and an energy of 430(2) keV was determined. Additionally, an isomeric state in $^{64}\mathrm{V}$ with an energy of 81.0(7) keV and a half-life less than 1 $\ensuremath{\mu}$s was discovered.Conclusion: The excitation energy of the ${2}_{1}^{+}$ state in $^{64}\mathrm{Cr}$ has been precisely determined and an isomeric state is identified in $^{64}\mathrm{V}$ for the first time.

Spectra distortion by the interstrip gap in spectroscopic silicon strip detectors

The NUSTAR experiments to be carried out as the part of the FAIR program (Facility for Antiproton and Ion Research) now under development in GSI, Germany, require unique spectrometers for heavy ions, for an energy range between a hundred keV up to hundreds of MeV. These spectrometers are constructed on the basis of silicon double sided detectors capable of providing simultaneously the energy spectrum of the particles and the position of hit points. The double sided Si strip detectors for high resolution ion spectroscopy and tracking were developed by the PTI-RIMST consortium. Reduced sized detectors were studied with alpha-particles from a 238Pu source to define the spectral response of their p+ side. The energy resolution was measured and found to be the highest, 9.6 keV, in the p+ strips area. The energy spectrum for the particles hit at the interstrip gap was shown to be much broader and have a maximum at the low energy edges. In this study the alpha-particle spectra were measured on the p+ side of strip detector and their shape was found to depend on the p+ strip structure and potential distribution under the strip and in the interstrip gap, where the surface is passivated by SiO2 layer. Therefore, the 2D potential distribution in the interstrip gap was simulated and interpreted through the effective entrance window for alpha-particles. The calculated spectrum of a detector from alpha-particle source has a shape specific to the experimental detector spectral response, i.e., the peak at low energies. These findings are to be taken into account in the analysis of short range particle spectra and may well contribute to further development of spectroscopic single sided and double sided Si strip detectors to be used in investigations in nuclear physics.

Fine-Pitch Semiconductor Detector for the FOXSI Mission

The Focusing Optics X-ray Solar Imager (FOXSI) is a NASA sounding rocket mission which will study particle acceleration and coronal heating on the Sun through high sensitivity observations in the hard X-ray energy band (5-15 keV). Combining high-resolution focusing X-ray optics and fine-pitch imaging sensors, FOXSI will achieve superior sensitivity; two orders of magnitude better than that of the RHESSI satellite. As the focal plane detector, a Double-sided Si Strip Detector (DSSD) with a front-end ASIC (Application Specific Integrated Circuit) will fulfill the scientific requirements of spatial and energy resolution, low energy threshold and time resolution. We have designed and fabricated a DSSD with a thickness of 500 {\mu}m and a dimension of 9.6 mm x 9.6 mm, containing 128 strips with a pitch of 75 {\mu}m, which corresponds to 8 arcsec at the focal length of 2 m. We also developed a low-noise ASIC specified to FOXSI. The detector was successfully operated in the laboratory at a temperature of -20 C and with an applied bias voltage of 300 V, and the energy resolution of 430 eV at a 14 keV line was achieved. We also demonstrated fine-pitch imaging successfully by obtaining a shadow image, hence the implementation of scientific requirements was confirmed.

Search for a 2-quasiparticle high-Kisomer inRf256

The energies of 2-quasiparticle (2-qp) states in heavy shell-stabilized nuclei provide information on the single-particle states that are responsible for the stability of superheavy nuclei. We have calculated the energies of 2-qp states in Rf256, which suggest that a long-lived, low-energy 8− isomer should exist. A search was conducted for this isomer through a calorimetric conversion electron signal, sandwiched in time between implantation of a Rf256 nucleus and its fission decay, all within the same pixel of a double-sided Si strip detector. A 17(5)-μs isomer was identified. However, its low population, ~5(2)% that of the ground state instead of the expected ~30%, suggests that it is more likely a 4-qp isomer. Possible reasons for the absence of an electromagnetic signature of a 2-qp isomer decay are discussed. These include the favored possibility that the isomer decays by fission, with a half-life indistinguishably close to that of the ground state. Another possibility, that there is no 2-qp isomer at all, would imply an abrupt termination of axially symmetric deformed shapes at Z=104, which describes nuclei with Z=92–103 very well.Received 25 February 2011DOI:https://doi.org/10.1103/PhysRevC.83.064311©2011 American Physical Society

Energy-sensitive imaging detector applied to the dissociative recombination ofD2H+

We report on an energy-sensitive imaging detector for studying the fragmentation of polyatomic molecules in the dissociative recombination of fast molecular ions with electrons. The system is based on a large area (10 cm x 10 cm) position-sensitive, double-sided Si-strip detector with 128 horizontal and 128 vertical strips, whose pulse height information is read out individually. The setup allows to uniquely identify fragment masses and is thus capable of measuring branching ratios between different fragmentation channels, kinetic energy releases, as well as breakup geometries, as a function of the relative ion-electron energy. The properties of the detection system, which has been installed at the TSR storage ring facility of the Max-Planck Institute for Nuclear Physics in Heidelberg, is illustrated by an investigation of the dissociative recombination of the deuterated triatomic hydrogen cation D2H+. A huge isotope effect is observed when comparing the relative branching ratio between the D2+H and the HD+D channel; the ratio 2B(D2+H)/B(HD+D), which is measured to be 1.27 +/- 0.05 at relative electron-ion energies around 0 eV, is found to increase to 3.7 +/- 0.5 at ~5 eV.

Experimental Results of the Gamma-Ray Imaging Capability With a Si/CdTe Semiconductor Compton Camera

A semiconductor Compton camera that combines silicon (Si) and cadmium telluride (CdTe) detectors was developed, and its imaging capability was examined with various kinds of gamma-ray targets such as a point source, arranged point sources and an extended source. The camera consists of one double-sided Si strip detector and four layers of CdTe pad detectors, and was designed to minimize the distance between a scatterer and the target. This is because the spatial resolution with Compton imaging improves as the target approaches the scatterer. This new camera realizes a minimum distance of 25 mm. By placing the target at a distance of 30 mm from the detector, resolving power better than 3 mm was demonstrated experimentally for a 364 keV (131I) gamma-ray. Positional determination with accuracy of 1 mm was also demonstrated. As a deconvolution method, we selected the iteration algorithm (called List-Mode Expectation-Maximizing Maximum Likelihood), and applied it to several kinds of experimental data. The Compton back projection images of the arranged point sources and an extended object were successfully deconvolved.

Development of semiconductor imaging detectors for a Si/CdTe Compton camera

Si and CdTe semiconductor imaging detectors have been developed for use in a Si/CdTe Compton camera. Based on a previous study using the first prototype of a Si/CdTe Compton camera, new detector modules have been designed to upgrade the performance of the Compton camera. As the scatter detector of the Compton camera, a stack of double-sided Si strip detector (DSSD) modules, which has four layers with a stack pitch of 2 mm, was constructed. By using the stack DSSDs, an energy resolution of 1.5 keV (FWHM) was achieved. For the absorber detector, the CdTe pixel detector modules were built and a CdTe pixel detector stack using these modules was also constructed. A high energy resolution ( Δ E / E ∼ 1 % ) was achieved. The improvement of the detection efficiency by stacking the modules has been confirmed by tests of the CdTe stack. Additionally, a large area CdTe imager is introduced as one application of the CdTe pixel detector module.

The MEGA Project for Medium Energy Gamma-ray Astronomy

The Medium Energy Gamma-ray Astronomy (MEGA) telescope concept will soon be proposed as a MIDEX mission. This mission would enable a sensitive all-sky survey of the medium-energy gamma-ray sky (0.4–50 MeV) and bridge the huge sensitivity gap between the COMPTEL and OSSE experiments on the Compton Gamma Ray Observatory and the visionary Advanced Compton Telescope (ACT) mission. The scientific goals include compiling a much larger catalog of sources in this energy range, performing far deeper searches for supernovae, better measuring the galactic continuum and line emissions, and identifying the components of the cosmic diffuse gamma-ray emission. MEGA records and images gamma rays by completely tracking Compton and pair creation events in a stack of double-sided Si strip detectors surrounded by a pixellated CsI calorimeter. A prototype instrument has been developed and calibrated in the laboratory and at a gamma-ray beam facility. We present calibration results from the prototype and describe the proposed satellite mission.

Recent results from a Si/CdTe semiconductor Compton telescope

We are developing a Compton telescope based on high-resolution Si and CdTe detectors for astrophysical observations in sub-MeV/MeV gamma-ray region. Recently, we constructed a prototype Compton telescope which consists of six layers of double-sided Si strip detectors (DSSDs) and CdTe pixel detectors to demonstrate the basic performance of this new technology. By irradiating the detector with gamma rays from radio isotope sources, we have succeeded in Compton reconstruction of images and spectra. The obtained angular resolution is 3.9°(FWHM) at 511 keV, and the energy resolution is 14 keV (FWHM) at the same energy. In addition to the conventional Compton reconstruction, i.e., drawing cones in the sky, we also demonstrated a full reconstruction by tracking Compton recoil electrons using the signals detected in successive Si layers. By irradiating 137Cs source, we successfully obtained an image and a spectrum of 662 keV line emission with this method. As a next step, development of larger DSSDs with a size of 4 cm × 4 cm is under way to improve the effective area of the Compton telescope. We are also developing a new low-noise analog ASIC to handle the increasing number of channels. Initial results from these two new technologies are presented in this paper as well.

α decay ofTe105

The α decay of the neutron-deficient nuclide Te105 was observed. The Cr50(Ni58,3n) reaction was used to produce Te105 nuclei. The Te105 residues were selected with the Argonne Fragment Mass Analyzer and implanted into a double-sided Si strip detector where their subsequent α decay was detected. An α-decay Q value of Qα=4900(50) keV and a half life of T1/2=0.70(-0.17+0.25)μs were measured for Te105 and a reduced α-decay width of Wα=3.3(-1.7+2.1) was deduced. The decay properties of Te105 are compared with those of heavier Te isotopes and theoretical predictions. © 2006 The American Physical Society.

Reinvestigation of direct proton decay ofSb105

Proton radioactivity from $^{105}\mathrm{Sb}$ has been reinvestigated at the GSI on-line mass separator. The nucleus was produced in the reaction $^{50}\mathrm{Cr}$($^{58}\mathrm{Ni}$,$1p2n$), and collected with a tape transport system. A double-sided Si strip detector was used for proton spectroscopy. The direct proton decay of $^{105}\mathrm{Sb}$ reported in an earlier experiment at Berkeley was not observed. The present data imply an upper limit $~{10}^{\ensuremath{-}3}$ for the ground-state proton decay branching ratio for proton energies higher than 430 keV.

β-Decay Studies Close to the N=82 r-process Path

New half-lives for neutron-rich ruthenium, rhodium and palladium isotopes close to the r-process path along the N=82 closed shell have been measured at the National Superconducting Cyclotron Laboratory at Michigan State University. The studied isotopes are close to the critical A=118-126 mass region in the astrophysical r-process, where incorrect nuclear structure development towards the shell closure may have the most pronounced effect on the abundances of elements produced. Neutron-rich nuclei were produced by fragmentation of a 120-MeV per nucleon 136 Xe beam on Be and were separated by the A1900 fragment separator. The nuclei of interest were implanted into a double-sided Si strip detector at the center of the MSU β counting system. Charge states and fully- stripped isotopes were distinguished by a measurement of the total kinetic energy of each implant. Our measured half-lives will provide first clues on whether our understanding of nuclear structure evolution in this mass region is correct.

A Si/CdTe semiconductor Compton camera

We are developing a Compton camera based on Si and CdTe semiconductor imaging devices with high energy resolution. In this paper, results from the most recent prototype are reported. The Compton camera consists of six layered double-sided Si Strip detectors and CdTe pixel detectors, which are read out with low noise analog ASICs, VA32TAs. We obtained Compton reconstructed images and spectra of line gamma-rays from 122 keV to 662 keV. The energy resolution is 9.1 keV and 14 keV at 356 keV and 511 keV, respectively.

A prototype Si/CdTe Compton camera and the polarization measurement

A Compton camera is the most promising approach for gamma-ray detection in the energy region from several hundred kiloelectronvolts to megaelectronvolts, especially for application in high energy astrophysics. In order to obtain good angular resolution, semiconductor detectors such as silicon, germanium and cadmium telluride(CdTe) have several advantages over scintillation detectors, which have been used so far. Based on the recent advances of high resolution CdTe and silicon imaging detectors, we are working on a Si/CdTe Compton camera. We have developed 64-pixel CdTe detectors with a pixel size of 2 mm /spl times/ 2 mm and double- sided Si strip detectors(DSSDs) with a position resolution of 800 /spl mu/m. As a prototype Si/CdTe Compton camera, we use a DSSD as a scatterer and two CdTe pixel detectors as an absorber. In order to verify its performance, we irradiate the camera with 100% linearly polarized 170 keV /spl gamma/-rays and demonstrate the system works properly as a Compton camera. The resolution of the reconstructed scattering angle is 22/spl deg/(full-width at half-maximum). Measurement of polarization is also reported. The polarimetric modulation factor is obtained to be 43%, which is consistent with the prediction of Monte Carlo simulations.

The branching ratio [formula omitted] of the 4.033 MeV state in 19Ne

The 15O(α,γ) 19Ne reaction is an important pathway from the hot CNO cycle to the rp process that leads to the synthesis of heavier nuclei. At lower temperatures, the reaction rate is dominated by the transition to the 4.033 MeV 3/2 + state in 19Ne, the first level above the 15O(α,γ) threshold at 3.534 MeV. We have performed an indirect measurement of the ratio Λ α Λ γ by populating the 3/2 + state via the 3He( 20Ne,α) 19Ne reaction in inverse kinematics. The α particles were detected in a double-sided Si strip detector telescope while the heavy reaction products, 19Ne and 15O, were identified in the focal plane of a magnetic spectrograph. For the 4.033 MeV state in 19Ne an upper limit Λ α Λ γ of ≤ 7×10 −4 has been obtained.

Correlated emission of three α-particles in the β-decay of 12N

The β-decay of 12N is used to populate α-emitting excited states in 12C. The α-particles from the break-up of both the 10.3 MeV and 12.71 MeV states were measured in coincidence with an efficient detector setup consisting of two double-sided Si strip detectors. The break-up of the 12.71 MeV 1+ state is an interesting testing ground for the different descriptions of multi-particle break-up, whereas the properties of the 10.3 MeV state, which under some astrophysical conditions is relevant for the production of 12C in stars, are poorly known. First results from the analysis of the data is presented and compared with Monte Carlo simulations.

Time measurement considerations for a double-sided Si strip detector

Timing with the MUST double-sided XY Si microstrip detectors is presented in this paper. This detector measures the energy d E, the arrival time T and the positions X and Y of light charged particles depositing 0.5–30 MeV. Eight MUST double-sided Si strip detectors of this type are currently in use in the GANIL heavy-ion accelerator, France.

Observation of the exotic nucleus145Tmvia its direct proton decay

Proton emission from ${}^{145}\mathrm{Tm}$ was observed for the first time via the ${}^{92}\mathrm{Mo}{(}^{58}\mathrm{Ni},p4n)$ reaction, using the Holifield Radioactive Ion Beam Facility Recoil Mass Spectrometer in conjunction with a double-sided Si strip detector at the focal plane. The measured energy of the emitted proton is 1.728(10) MeV and its half-life is 3.5(10) \ensuremath{\mu}s, the shortest ever observed for ground-state proton radioactivity. When compared to the calculated WKB half-life for an $l=5$ transfer, the spectroscopic factor is 0.51(16), which is consistent with the value of 0.64 calculated via the BCS approximation for a spherical nucleus. Also, the half-life of ${}^{113}\mathrm{Cs}$ was determined with a greater precision than previously available to be 16.7(7) \ensuremath{\mu}sec.

The α -decay properties of 186Bi

The α decay of 186Bi was investigated via the 97Mo(92Mo, p2n) reaction and the use of a fragment mass analyzer with a double-sided Si strip detector. In contrast to an earlier work wherein only one α transition was reported, we observed two transitions arising from two isomers in 186Bi with energies and half-lives of: 7158(20) keV, T1/2 = 15.0(17) ms; and 7261(20) keV, T1/2 = 9.8(13) ms.

α-decay properties of190Po and the identification of191Po

The $\ensuremath{\alpha}$-decay properties of ${}^{190}$Po were investigated through the use of a fragment mass analyzer in conjunction with a double-sided Si strip detector. The isotope was produced via the ${}^{96}\mathrm{Mo}{(}^{96}\mathrm{Mo},2n)$ reaction, and its $\ensuremath{\alpha}$-decay energy and ${T}_{1/2}$ were measured as 7529(10) keV and ${2.4}_{\ensuremath{-}0.3}^{+0.4}$ ms, respectively. The resulting reduced width is nearly identical to that of the ${}^{192,194}\mathrm{Po}$ isotopes. This is believed to result from significant mixing between the ground state $\ensuremath{\pi}(2p)$ and the low-lying ${0}^{+}\ensuremath{\pi}(4p\ensuremath{-}2h)$ intruder state in the Po parent. The result provides further evidence for shape coexistence in the light Po isotopes. In addition, ${}^{191}\mathrm{Po}$ was unambiguously identified, and the ${}^{186}\mathrm{Pb}$ $\ensuremath{\alpha}$-decay branch was determined experimentally for the first time.