Focal Plane Detector System Research Articles

Scanning-assisted focal plane-detection system for a sector-field mass spectrometer - Part-I: Simulation and data processing

In this paper, a novel detection system, the Scanning-Assisted Focal Plane-Detection System (SAFPDS), is proposed as a focal plane detector for sector-field mass spectrometers. The principle of SAFPDS is to decouple the spatial resolution and local count rate of the microchannel plate (MCP) focal plane-detection system in order to enhance the local count rate and dynamic range limited by the MCP. This decoupling is achieved by deflecting ions along the vertical direction of the focal plane detector using an ion deflector during acquisition. Simulations of the SAFPDS are reported for optimal geometrical design, operation, and performance. Additionally, a dedicated novel data processing protocol for deriving a representative mass spectrum from the 3D-recorded data obtained with SAFPDS is developed in combination with the SAFPDS hardware. Our study shows that this protocol effectively enhances the spectrometer's Figure of Merit (FOM), defined as the integral of the mass resolution (m/Δm) over the relevant mass range, by a factor of 2.4. Furthermore, the evaluation of the spectrometer equipped with SAFPDS highlights its capability to enhance the local count rate and dynamic range of sector field mass spectrometers with an MCP-based detector by at least one order of magnitude. Importantly, this enhancement is achieved with a deterioration in mass resolving power that remains below 30%, which we consider acceptable given the significant improvements in local count rate and dynamic range.

Segmented silicon-based solid-state detector with thin dead layer for superheavy element research

Silicon-based solid-state detectors (SSDs) are crucial for investigating the properties of superheavy elements (SHEs), since they measure the energy of SHEs and charged particles that are emitted as successive decay events of the SHEs. We have developed a segmented SSD for SHE studies using the new gas-filled recoil ion separators (GARIS-II and GARIS-III) at RIKEN. It is based on a back-illuminated Si PIN photodiode in which the irradiation is through the N+ layer. The detector is introduced as a side one for the GARIS focal plane detection system. To investigate the characteristics of the SSD, 241Am α particles were irradiated by automatically moving and rotating the α source for each segmented portion of the SSD. A Monte Carlo simulation was also performed to estimate the dead layer thickness of the segmented SSD.

High-resolution (p,t) study of low-spin states in Pu240 : Octupole excitations, α clustering, and other structure features

A high-resolution $(p,t)$ experiment at $E_{p}$= 24 MeV was performed to populate low-spin states in the actinide nucleus ${}^{240}$Pu. The Q3D magnetic spectrograph of the Maier-Leibnitz Laboratory (MLL) in Munich (Germany) was used to identify the ejected tritons via $dE/E$ particle identification with its focal-plane detection system. Angular distributions were measured at nine different Q3D angles to assign spin and parity to the excited states based on a comparison with coupled-channels DWBA calculations. In total, 209 states have been excited in $^{240}$Pu up to an excitation energy of 3 MeV. Many previously known states have also been observed and their spin-parity assignments were confirmed. However, many of the populated states have been seen for the first time. The low-spin one-octupole phonon excitations, i.e. $K^{\pi} = 0^-,1^-,2^-,3^-$, could be observed and a new candidate for the $K = 3$ projection is proposed. Furthermore, the double-octupole or $\alpha$-cluster structure of the $0^+_2$ state in $^{240}$Pu has been studied in more detail. It is shown that the $0^+_2$ state in $^{230}$Th has a distinctly different structure. In addition, strongly excited $1^-$ states have been observed at 1.5\,MeV and 1.8\,MeV in $^{240}$Pu. The present study suggests that similar states might be observed in $^{230}$Th. At least two different and distinct structures for $J^{\pi} = 0^+$ states are present in the actinides. These are pairing states and states with enhanced octupole correlations. We have shown that it is crucial to consider negative-parity single-particle states being admixed to some $K^{\pi} = 0^+_2$ rotational bands to understand the $\alpha$-decay hindrance factors and enhanced $E1$-decay rates. Based on our analysis, we have identified the double-octupole or $\alpha$-cluster $K^{\pi} = 0^+$ candidates from $^{224}$Ra to $^{240}$Pu.

Single-particle strength in neutron-richCu69from theZn70(d,He3)Cu69proton pick-up reaction

We have performed the $^{70}\mathrm{Zn}(d,^{3}\mathrm{He})^{69}\mathrm{Cu}$ proton pick-up reaction in direct kinematics using a deuteron beam at 27 MeV. The outgoing $^{3}\mathrm{He}$ particles were detected at the focal-plane detection system of an Enge split-pole spectrometer. The excitation-energy spectrum was reconstructed up to 7 MeV and spectroscopic factors were obtained after analysis of the angular distributions in the finite-range distorted-wave Born approximation. The results show three new angular distributions for which the $\ensuremath{\pi}{f}_{7/2}$ strength was measured and a lower limit of the centroid is established. State-of-the-art shell-model calculations are performed and predict a $\ensuremath{\pi}{f}_{7/2}$ strength that lies too high in energy in comparison to our experimental results.

<x content-type="symbol">α</x> decay studies of the neutron-deficient uranium isotopes <sup>215<x content-type="symbol">-</x>217</sup>U

The α -decay study is an important tool for obtaining information on the nuclear structure of heavy neutron-deficient nuclei. For the N =126 and 124 isotones with even proton number, an intruder state ( π h 9/2 π f 7/2)8+ based on the attractive interaction of f 7/2 protons and f 5/2 neutrons was observed, which increases the binding energy of this configuration with increasing proton number. Additionally, taking into account the octupole correlations, a large-scale shell model calculations predict that the ( π h 9/2 π f 7/2)8+ state lies close or below the ( π h 9 / 2 2 ) 6+ state in the 216Th and 218U. To extend the systematic of the I π =8+ isomeric state in N =124 isotones and search for the most neutron-deficient uranium isotopes, an experiment for the α -decay studies of 215 - 217U was performed at the gas-filled recoil separator SHANS at the Heavy Ion Research Facility in Lanzhou (HIRFL). Heavy ion induced fusion evaporation reactions of the 180W(40Ar, x n)220 - x U ( x =3 - 5) were used to synthesize these neutron-deficient uranium isotopes. The 40Ar beam was delivered by the sector focusing cyclotron of the HIRFL. The evaporation residues recoiled from the thin target were separated in-flight from the primary beam particles by the gas-filled recoil separator SHANS. After passing through two multi-wire proportional counters, the residues were planted into a focal plane detection system. Based on the energy-position-time correlation measurement, the isotopes 215 - 217U were identified. At a beam energy of 187.2 MeV, two α -decaying states were observed in 216U with E α =8.384(30) MeV, T 1/2=

Experiment for synthesis of neutron-deficient protactinium isotopes

The complete fusion reaction 40Ca+175Lu was studied at a beam energy of 5.1 MeV u−1. Evaporation residues recoiled from the target were separated from the primary beam by the gas-filled recoil separator SHANS and then implanted into the focal plane detection system. Based on the energy-position-time correlation measurement, neutron-deficient nuclei 208–213Ac, 212Pa and 211Th produced in this reaction were identified. Previously reported decay properties of the ground state in 212Pa were confirmed and improved values of ms and MeV for the half-life and α-particle energy of 212Pa were obtained. No correlated decay chain arising from 211Pa was observed and an upper limit for the cross section of 211Pa was estimated.

The investigation of properties of short-lived SF isotopes (Z > 100) at the focal plane of VASSILISSA separator

For experiments aimed at the study of spontaneous fission of transfermium nuclei improvements in the focal plane detector system of recoil separator VASSILISSA have been made. A neutron detector consisting of 54 3He-filled counters has been mounted around the focal-plane detector chamber. The reaction 48Ca +206Pb = 2n +252No is used for tuning the separator settings and calibrating the detector system with the spontaneous fission of the 252No. The average neutron number per 252No spontaneous fission event is as large as ¯ν = 4.06 ± 0.12. The short-lived heavy isotopes 244,246Fm, produced in the complete fusion reactions 40Ar +206,208Pb, are investigated. The average number of neutrons per spontaneous fission of 244,246Fm from the experimental data were ( ¯ν = 3.3 ± 0.3) and ( ¯ν = 3.55 ± 0.50), respectively. Both values are determined for the first time

In-beam spectroscopy with intense ion beams: Evidence for a rotational structure in246Fm

The rotational structure of ${}^{246}$Fm has been investigated using in-beam $\ensuremath{\gamma}$-ray spectroscopic techniques. The experiment was performed using the JUROGAMII germanium detector array coupled to the gas-filled recoil ion transport unit (RITU) and the gamma recoil electron alpha tagging (GREAT) focal plane detection system. Nuclei of ${}^{246}$Fm were produced using a 186 MeV beam of ${}^{40}$Ar impinging on a ${}^{208}$Pb target. The JUROGAMII array was fully instrumented with Tracking Numerical Treatment 2 Dubna (TNT2D) digital acquisition cards. The use of digital electronics and a rotating target allowed for unprecedented beam intensities of up to 71 particle-nanoamperes for prompt $\ensuremath{\gamma}$-ray spectroscopy at a level of approximately 11 nb. With all these major experimental advances a rotational band is observed in ${}^{246}$Fm.

Investigation into the neutron multiplicity of spontaneously fissioning short-lived heavy nuclei at the VASSILISSA separator

For experiments aimed at the study of the spontaneous fission of transfermium nuclei, improvements in the focal-plane detector system of the VASSILISSA recoil separator have been made. A neutron detector consisting of 54 3He-filled counters has been mounted around the focal-plane detector chamber. A description of the detection system and the results of experiments aimed at investigating the neutron multiplicity of neutron-deficient isotopes of 252No and 244,246Fm are presented.

Characterization of the Flip Capacitor Filter for the XFEL-DSSC Project

The European X-ray Free Electron Laser (XFEL) under construction in Hamburg (Germany) will be able to deliver high intensity X-ray pulses of few tens of femto seconds of duration, at 5 MHz pulse repetition rate. Thanks to its characteristics, this instrument will open up new research opportunities for experiments in femto chemistry, structural biology and material research. A high speed focal plane detector system has been presented, based on a novel non-linear DEPFET as a detector. DEPFETs have been chosen since they can provide excellent energy resolution and high speed readout, a fundamental property to cope with the very demanding pulse time structure of XFEL. Full parallel readout is required, with every channel comprising analog filtering, data conversion and memory storage. In this paper we show results for the first prototype of the analog front end that implements the current readout of the DEPFET pixel. The circuit is based on the Flip Capacitor Filter technique, here briefly presented, and has been designed in 130 nm 1.2 V CMOS technology from IBM. Careful characterization of the individual circuit alone and also connected to a single pixel linear detector has been carried out and the measured performance is summarized.

Hybrid recoil mass analyzer at IUAC — First results using gas-filled mode and future plans

Hybrid recoil mass analyzer (HYRA) is a unique, dual-mode spectrometer designed to carry out nuclear reaction and structure studies in heavy and medium-mass nuclei using gas-filled and vacuum modes, respectively and has the potential to address newer domains in nuclear physics accessible using high energy, heavy-ion beams from superconducting LINAC accelerator (being commissioned) and ECR-based high current injector system (planned) at IUAC. The first stage of HYRA is operational and initial experiments have been carried out using gas-filled mode for the detection of heavy evaporation residues and heavy quasielastic recoils in the direction of primary beam. Excellent primary beam rejection and transmission efficiency (comparable with other gas-filled separators) have been achieved using a smaller focal plane detection system. There are plans to couple HYRA to other detector arrays such as Indian national gamma array (INGA) and 4π spin spectrometer for ER tagged spectroscopic/spin distribution studies and for focal plane decay measurements.

Neutron multiplicity at spontaneous fission of 246Fm

The neutron-deficient isotope 246Fm , produced in the complete fusion reaction 40Ar$ + $208Pb , was investigated. The main goal of the experiment was to determine the neutron multiplicity at spontaneous fission of this isotope. For experiments aimed at the study of spontaneous fission of transfermium nuclei improvements in the focal plane detector system of recoil separator VASSILISSA have been made. A neutron detector consisting of 54 3He -filled counters has been mounted around the focal-plane detector chamber. From the experimental data the average number of neutrons per spontaneous fission of 246Fm was determined ( $ \bar{{\nu}}$ = 3.55±0.5) .

A new focal-plane detector system for low fusion-evaporation cross section measurements

A new focal-plane detector system has been designed and constructed for measuring very small heavy-ion induced fusion-evaporation cross sections with the Fragment Mass Analyzer (FMA) at Argonne National Laboratory. The system has been tested and successfully used in a fusion-evaporation excitation function measurement for 64 Ni + 100 Mo down to the 5 nb level. The design and performance of the detector system are described in detail with some examples from the latest data. Besides excellent tracking capabilities for each event measured in the detector, suppression of scattered beam background of the order of 4 × 10 - 17 has been demonstrated.

The focal plane detector of the magnetic spectrometer PRISMA

The characteristics and performance of the focal plane detector system developed for the magnetic spectrometer PRISMA are presented. It is composed of a multi-wire parallel plate avalanche counter (providing X, Y and timing signals) followed by a multi-parametric transverse field ionization chamber array (providing multiple Δ E signals). The detector array has been built to match the very large acceptance of PRISMA and provides optimal performance in the complete identification (nuclear charge, energy and mass) of nuclei produced in heavy-ion binary reactions.

Neutron detector at the focal plane of the set up VASSILISSA

For experiments aimed at the study of spontaneous fission of transfermium nuclei improvements in the focal plane detector system of recoil separator VASSILISSA have been made. The neutron detector consisting of 72 3He filled counters has been mounted around the focal plane detector chamber. In the first experiment the multiplicity of prompt neutrons emitted in spontaneous fission of 252No was measured.

In-beam separation and mass determination of superheavy nuclei. Part II

Within the past 15 years, the recoil separator VASSILISSA has been used for the investigations of evaporation residues produced in complete fusion reactions induced by heavy ions. The study of decay properties and formation of cross-sections of the isotopes of elements 110, 112 and 114 was performed using high-intensity 48 Ca beams and 232 Th , 238 U, 242 Pu targets. For further experiments aimed at the synthesis of the superheavy element isotopes ( Z⩾110) with the use of intense 48 Ca extracted beams, improvements in the ion optical system of the separator and the focal plane detector system have been made. The results from the test reactions and new results for the isotope 283112 are presented.

A microchannel plate system for accelerator mass spectrometry measurements

The position-sensitive focal plane detector system for the trace element accelerator mass spectrometer at the US Naval Research Laboratory consists of 12 microchannel plate detector modules. Each module provides a 10×2 cm 2 active area and together they cover 80% of the split-pole spectrograph focal plane. The MCP detects electrons produced when an MeV ion beam passes through a thin carbon foil placed at 45° with respect to the beam. The electric charge is amplified and deposited on a double-delay line anode, with differential timing at the two ends providing horizontal position. Vertical position is evaluated from top-to-bottom charge partitioning. The collected charge is converted to timing signals through specially designed readout electronics based on the MQT300A LeCroy integrated circuit. A 400-μm horizontal resolution was obtained from ion beam generated secondary electrons accelerated to 2.5 keV. A Helmholtz-type coil pair was built for further confining the secondary electrons with a magnetic field.

The upgrade of the kinematic separator VASSILISSA—experimental results and plans

Within the past twelve years, the recoil separator VASSILISSA has been used for the investigations of evaporation residues produced in heavy-ion-induced complete fusion reactions. In the course of the experimental work, fourteen new isotopes have been identified by the parent-daughter correlations in the region of elements with 92≤Z≤94. The study of the decay properties and formation cross sections of the isotopes of elements 110, 112, and 114 was performed using high-intensity 48Ca beams and 232Th, 238U, and 242Pu targets. At the beam energies corresponding to the calculated cross-section maxima of the 3n evaporation channels, the isotopes 277110, 283112, and 287114 were produced and identified. For further experiments aimed at the synthesis of the superheavy element isotopes (Z≥110) with the use of intensive 48Ca extracted beams, improvements in the ion optical system of the separator and the focal plane detector system have been made.

High resolution studies of low lying GT strength using the (d, 2He) reaction and its impact on electron-capture rates in stellar environments

Gamow-Teller transitions in fp-shell nuclei have been studied using the 58Ni( d, 2He) charge exchange reaction at an incident energy of 170 MeV and forward angles. The measurements have been performed at AGOR using the Big-Bite Spectrometer and the EuroSuperNova focal-plane detection system. The unprecedented energy resolution of about 130 keV FWHM for excitations in the residual nucleus 58Co allowed for the first time the extraction of single transitions in the β + direction up to about 4 MeV excitation. The impact on electron-capture rates in astrophysical environments has been evaluated.

Measuring the [formula omitted] reaction with the focal-plane detection system of the BBS magnetic spectrometer at AGOR

At intermediate energies, the ( d, 2 He) charge-exchange reaction can be used to observe Gamow–Teller strength in the β + direction. 2 He denotes the two-proton system being in the singlet 1 S 0 state. In the present experiment the two protons, which in the laboratory frame are emitted into the forward direction, have been momentum analyzed and detected in coincidence by the same spectrometer and detector. Protons from deuteron breakup processes can induce a large accidental coincidence background because of the much larger breakup cross-section as compared to the ( d, 2 He) cross-section. Nevertheless, background-free 2 He spectra with a resolution of 145 keV at an incident energy of 170 MeV are obtained, allowing the identification of many levels with high precision in the residual nuclei. The essential features of the detection system and the data-acquisition and analysis techniques which make our ( d, 2 He) experiments possible are described. Two nuclei, 12C and 24Mg, have been used as a test case.