Delayed Coincidence Technique Research Articles

Isomeric state in the odd-odd 68Ga nucleus

The half life of the 7− isomeric state of the odd-odd 68Ga nucleus was measured using a particle-γ delayed coincidence technique. The 68Ga nuclei were produced using the fusion-evaporation reaction 55Mn(16O,2pn)68Ga at 55 MeV incident beam energy. The beam was produced by the 8 MV Pelletron accelerator of the Nuclear Physics Open Laboratory of the University of São Paulo. The half life was measured using the Isomeric State Measurement System (SISMEI). The obtained value was 60.83(25) ns, compatible with previous measurements. The 68Ga excited states were well described with the Large Scale Shell Model using the JUN45 residual interaction.

Measurement of the {}^{212}{mathrm{Po}}, ^{214}hbox {{Po}} and ^{212}hbox {{Pb}} half-life time with Timepix3

The half-life times of the relatively short-lived alpha -decaying isotopes ^{212}hbox {{Po}} and ^{214}hbox {{Po}} were measured with a hybrid pixel detector of Timepix3 technology. Radon daughter products were collected at the backside of a 1 mm thick silicon sensor so that subsequent decays inject the polonium isotopes of interest shallowly into the backside of the sensor. The detector’s high spatial and time resolution allow for particle identification and application of the delayed coincidence technique with low systematic uncertainty even at high rates. We find t_{1/2}^{^{212}{hbox {Po}}} = ( 295.02 pm 0.18{_{mathrm{stat.}}} pm 0.17_{mathrm{syst.}} ),hbox {ns} and t_{1/2}^{{}^{214}mathrm{Po}} = ( 163.64 pm 0.038{_{mathrm{stat.}}} pm 0.093_{mathrm{syst.}} ),upmu hbox {s}. Studying the decay of the accumulated radon daughter products after removing the detector from the ^{220}hbox {{Rn}} field, the half-life time of the beta -decay of ^{212}hbox {{Pb}} was measured to be t_{1/2}^{^{212}{mathrm{Pb}}} = ( 10.620 pm 0.011_{mathrm{stat.}} pm 0.014_{mathrm{syst.}} ),hbox {h}. The results are discussed in the context of previous works.

Novel technique for simultaneous detecting three naturally occurring radon isotopes (222Rn, 220Rn and 219Rn)

Radon inspection is becoming increasingly prevalent due to its negative effects on human health. After cigarette smoking, radon is the second leading cause of lung cancer due to its internal dosage through respiration. In this study, we employed a novel liquid scintillation technique to simultaneously detect three naturally occurring radon isotopes (222Rn, 220Rn and 219Rn). The detection method utilises the delayed coincidence technique and the pulse shape discrimination implemented by digital charge comparison. Furthermore, a Monte Carlo simulation was performed to obtain the gamma response functions of the detector using standard 22Na, 60Co and 137Cs gamma sources. Additionally, the detector resolution and energy calibration parameters were determined by comparing the measured and simulated light output distributions. For the measurement, radon gas from the atmosphere was infused into 700 mL of Ultima Gold AB for 48 h. We determined that the minimum detectable activities of 222Rn (238U decay chain), 220Rn (232 Th day chain) and 219Rn (235U decay chain) were 1.7, 1.0 and 1.2 mBq/l, respectively. The proposed novel technique offers a potential application for detecting all three naturally occurring radon isotopes in water samples.

Study of ultraviolet-visible fluorescence emission following resonant Auger decay of the 2p-1nl core-excited states of argon atoms

We have studied the excitation and relaxation of Ar+ ions populated in resonant Auger decay from the Ar 2p−1nl core-excited states by using ultraviolet-visible fluorescence spectroscopy and photon-photon delayed coincidence technique. Fluorescence emission yields were measured in the photon energy range of 240-–255 eV for the 3s23p4(1D)5s(2D) → 3s23p4(1D)4p(2F) (393 nm) and 3s23p4(1D)4d(2F) → 3s23p4(1D)4p(2F) (335 nm) transitions as well as for the 380–500 nm wideband emission. Delayed coincidence photon decay curves for the cascade transitions of the 335/459 nm and 393/459 nm lines were measured at the four most intense Ar 2p core excitations and the coincidence yields for both studied cascade channels were obtained at these Ar 2p excitations.

Sensitive neutron detection method using delayed coincidence transitions in existing iodine-containing detectors

This work explains a new, highly sensitive method for the detection of neutrons, which uses the T1/2=845ns delay in the decay of 128I at the 137.8keV energy level, resulting from the capture of thermal neutrons by iodine nuclei in NaI and CsI scintillation detectors. The use of delayed coincidence techniques with a several μs delay time window for delayed events allows for the highly effective discrimination of neutron events from any existing background signals. A comparison of ambient neutron measurements between those identified through the suggested method from a cylindrical, ø63mm×63mm NaI(Tl) scintillator and those from a low-background proportional 3He counter experimentally demonstrates the efficacy of this neutron detection method. For an isotropic, 4π, thermal neutron flux of 1ncm−2s−1, the absolute sensitivity of the NaI detector was found to be 6.5±1countss−1 with an accidental coincidence background of 0.8eventsday−1 for any delay time window of Δt=1μs. The proposed method can provide low-background experiments, using NaI or CsI, with measurements of the rate and stability of incoming neutron flux to a greater accuracy than 10−8ncm−2s−1.

Lifetime measurement of the first excited state in S37

Lifetime of the $3/{2}^{\ensuremath{-}}$ first excited state in $^{37}\mathrm{S}$ populated by the ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{37}\mathrm{P}$ has been measured using $\ensuremath{\beta}\ensuremath{-}\ensuremath{\gamma}$ delayed coincidence technique. The $B(E2;7/{2}^{\ensuremath{-}}\ensuremath{\rightarrow}3/{2}^{\ensuremath{-}})$ value in $^{37}\mathrm{S}$ deduced from the lifetime comes close to the $B(E2;{0}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})$ value in weakly deformed $^{38}\mathrm{S}$ but deviates significantly from that in spherical $^{36}\mathrm{S}$. This manifests that $^{37}\mathrm{S}$ is a weakly deformed rather than spherical nucleus.

Shell-model states with seniorityν=3, 5, and 7 in odd-Aneutron-rich Sn isotopes

Excited states with seniority $\ensuremath{\nu}=3$, 5, and 7 have been investigated in odd neutron-rich $^{119,121,123,125}\text{Sn}$ isotopes produced by fusion-fission of 6.9-MeV/$A\phantom{\rule{4pt}{0ex}}^{48}\text{Ca}$ beams with $^{208}\text{Pb}$ and $^{238}\text{U}$ targets and by fission of a $^{238}\text{U}$ target bombarded with 6.7-MeV/$A\phantom{\rule{4pt}{0ex}}^{64}\text{Ni}$ beams. Level schemes have been established up to high spin and excitation energies in excess of 6 MeV, based on multifold gamma-ray coincidence relationships measured with the Gammasphere array. In the analysis, the presence of isomers was exploited to identify gamma rays and propose transition placements using prompt and delayed coincidence techniques. Gamma decays of the known $27/{2}^{\ensuremath{-}}$ isomers were expanded by identifying new deexcitation paths feeding $23/{2}^{+}$ long-lived states and $21/{2}^{+}$ levels. Competing branches in the decay of $23/{2}^{\ensuremath{-}}$ states toward two $19/{2}^{\ensuremath{-}}$ levels were delineated as well. In $^{119}\text{Sn}$, a new $23/{2}^{+}$ isomer was identified, while a similar $23/{2}^{+}$ long-lived state, proposed earlier in $^{121}\text{Sn}$, has now been confirmed. In both cases, isomeric half-lives were determined with good precision. In the range of $\ensuremath{\nu}=3$ excitations, the observed transitions linking the various states enabled one to propose with confidence spin-parity assignments for all the observed states. Above the $27/{2}^{\ensuremath{-}}$ isomers, an elaborate structure of negative-parity levels was established reaching the ($39/{2}^{\ensuremath{-}}$), $\ensuremath{\nu}=7$ states, with tentative spin-parity assignments based on the observed deexcitation paths as well as on general yrast population arguments. In all the isotopes under investigation, strongly populated sequences of positive-parity ($35/{2}^{+}$), ($31/{2}^{+}$), and ($27/{2}^{+}$) states were established, feeding the $23/{2}^{+}$ isomers via cascades of three transitions. In the $^{121,123}\text{Sn}$ isotopes, these sequences also enabled the delineation of higher-lying levels, up to ($43/{2}^{+}$) states. In $^{123}\text{Sn}$, a short half-life was determined for the ($35/{2}^{+}$) state. Shell-model calculations were carried out for all the odd Sn isotopes, from $^{129}\text{Sn}$ down to $^{119}\text{Sn}$, and the results were found to reproduce the experimental level energies rather well. Nevertheless, some systematic deviations between calculated and experimental energies, especially for positive-parity states, point to the need to improve some of the two-body interactions used in calculations. The computed wave-function amplitudes provide for a fairly transparent interpretation of the observed level structures. The systematics of level energies over the broad $A$ = 117--129 range of Sn isotopes displays a smooth decrease with mass $A$, and the observed regularity confirms most of the proposed spin-parity assignments. The systematics of the $B(E2)$ reduced transition probabilities extracted for the $23/{2}^{+}$ and $19/{2}^{+}$ isomers is discussed with an emphasis on the close similarity of the observed $A$ dependence with that of the $E2$ transition rates established for other $\ensuremath{\nu}=2$, 3, and 4 isomers in the Sn isotopic chain.

Experimental study of theNi66(d,p) Ni67one-neutron transfer reaction

The quasi-SU(3) sequence of the positive parity νg9/2,d5/2,s1/2 orbitals above the N=40 shell gap are assumed to induce strong quadrupole collectivity in the neutron-rich Fe (Z=26) and Cr (Z=24) isotopes below the nickel region. In this paper the position and strength of these single-particle orbitals are characterized in the neighborhood of Ni68 (Z=28,N=40) through the Ni66(d,p)Ni67 one-neutron transfer reaction at 2.95 MeV/nucleon in inverse kinematics, performed at the REX-ISOLDE facility in CERN. A combination of the Miniball γ-array and T-REX particle-detection setup was used and a delayed coincidence technique was employed to investigate the 13.3-μs isomer at 1007 keV in Ni67. Excited states up to an excitation energy of 5.8 MeV have been populated. Feeding of the νg9/2 (1007 keV) and νd5/2 (2207 keV and 3277 keV) positive-parity neutron states and negative parity (νpf) states have been observed at low excitation energy. The extracted relative spectroscopic factors, based on a distorted-wave Born approximation analysis, show that the νd5/2 single-particle strength is mostly split over these two excited states. The results are also compared to the distribution of the proton single-particle strength in the Zr90 region (Z=40,N=50).6 MoreReceived 25 February 2015Revised 28 April 2015DOI:https://doi.org/10.1103/PhysRevC.91.054321This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical Society

Lifetime measurements of even and odd states in neutral terbium (Tb I)

Radiative lifetimes of 7 odd and 11 even parity states of Tb I (Z = 65) have been measured by the time resolved laser induced fluorescence method (TR-LIF). Experimental data for 9 out of the 18 states are obtained for the first time. The radiative lifetimes presented in this study are in good agreement with previous TR-LIF experimental results but systematically shorter than those obtained by the delayed coincidence technique.

Sub-nanosecond nuclear half-life and time-of-flight measurements with CeBr3

CeBr3 is a new fast scintillator with timing and energy resolution similar to LaBr3:Ce. The excellent timing resolution, measured here to be 93ps at 511keV for 1cm3 crystals, naturally lends itself to direct electronic measurements of excited nuclear state lifetimes in the nanosecond and sub-nanosecond range. To demonstrate this, half-lives of a 1.40ns isomer in 152Sm and 537 ps isomer in 177Hf were directly measured using the delayed coincidence technique. With its fast timing, high light output and high efficiency, the possibility of CeBr3 as a time-of-flight PET detector was also explored through γ-ray time-of-flight measurements.

A spectrometer for lifetime determination by β–γ–γ delayed coincidence technique at KUR-ISOL

Abstract A new spectrometer for measuring nuclear level lifetimes has been installed at the on-line isotope separator of the Kyoto University Reactor. The spectrometer consists of a LaBr 3 (Ce), Ge and a thin plastic scintillation detector, and the lifetimes are determined using a β – γ – γ delayed coincidence technique. In this study, the LaBr 3 detector was used to obtain time spectra, whereas the Ge detector was used to select a desired γ branch. The energy dependence of the time resolutions was measured down to a photon energy of 100 keV. The lifetimes measured for the excited levels in 93 Sr and 148 Ce agree well with their evaluated values. The lifetime of 8.5(5) ns was obtained for the first time for the 98.2 keV level in 148 Pr.

Determination of the Lamb-Mössbauer factor by the delayed coincidence technique

A method for determining the Lamb-Mossbauer factor by means of the delayed coincidence technique is proposed. The effective thickness of a series of K4Fe(CN)6 · 3H2O samples was measured and recoilless fraction f = 0.339 ± 0.004 was determined.

A scatter-corrected list-mode reconstruction and a practical scatter/random approximation technique for dynamic PET imaging**This work was supported by the Canadian Institute of Health Research, a TRIUMF Life Science Grant, the Natural Sciences and Engineering Research Council of Canada UFA (V Sossi) and the Michael Smith Foundation for Health Research Scholarship (V Sossi).

We describe an ordinary Poisson list-mode expectation maximization (OP-LMEM) algorithm with a sinogram-based scatter correction method based on the single scatter simulation (SSS) technique and a random correction method based on the variance-reduced delayed-coincidence technique. We also describe a practical approximate scatter and random-estimation approach for dynamic PET studies based on a time-averaged scatter and random estimate followed by scaling according to the global numbers of true coincidences and randoms for each temporal frame. The quantitative accuracy achieved using OP-LMEM was compared to that obtained using the histogram-mode 3D ordinary Poisson ordered subset expectation maximization (3D-OP) algorithm with similar scatter and random correction methods, and they showed excellent agreement. The accuracy of the approximated scatter and random estimates was tested by comparing time activity curves (TACs) as well as the spatial scatter distribution from dynamic non-human primate studies obtained from the conventional (frame-based) approach and those obtained from the approximate approach. An excellent agreement was found, and the time required for the calculation of scatter and random estimates in the dynamic studies became much less dependent on the number of frames (we achieved a nearly four times faster performance on the scatter and random estimates by applying the proposed method). The precision of the scatter fraction was also demonstrated for the conventional and the approximate approach using phantom studies.

Levels in 127La fed by the 127Ce beta-decay

The low-lying levels in 127La have been studied through the β-decay of 127Ce ( T1/2 = 29s) produced by bombarding a natMo target with a 185-MeV 35Cl beam. Reaction products were on-line mass-separated, and γ-ray singles and γ-γ coincidence measurements were performed. Conversion electrons were also measured and multipolarities of transitions have been derived. The half-life of the 210.9-keV level was determined to be (1.9±0.3)ns by the β-γ delayed coincidence technique. The level scheme obtained has been compared with calculations based on the Nilsson model.

Electron spectroscopy of Na-like autoionizing metastable ions

Ejected electrons from the decay of metastable ${2p}^{5}3s3p{}^{4}{D}_{7/2}$ autoionizing states of Na-like ${\mathrm{Ar}}^{7+}, {\mathrm{Cl}}^{6+},$ and ${\mathrm{S}}^{5+}$ have been detected using an ion-beam delayed-coincidence technique. The previously calculated and measured ${\mathrm{Ar}}^{7+}$ Auger line at $114.10\ifmmode\pm\else\textpm\fi{}0.33 \mathrm{eV}$ was used to calibrate a high-efficiency two-stage parallel-plate electron spectrometer. The energies of the corresponding Auger lines from decay of metastable ${\mathrm{Cl}}^{6+}$ and ${\mathrm{S}}^{5+}$ were subsequently determined to be $102.0\ifmmode\pm\else\textpm\fi{}1.2 \mathrm{eV}$ and $86.6\ifmmode\pm\else\textpm\fi{}1.0 \mathrm{eV},$ respectively. The results are consistent with published data for other members of the Na isoelectronic sequence, and they together exhibit a quadratic scaling with ionic charge q over the range $4l~ql~15.$

Half-life and internal conversion electron measurements in low-lying levels of ^{125,127}Ba

Decay spectroscopy using on-line mass separators has the advantage of allowing the study of level properties in the low energy region, including band head information, since g transitions between low-spin states can be measured more intensively under lower background conditions than can those with in-beam spectroscopy measurements. Neutron-deficient nuclides of 125,127 Ba have been studied by means of in-beam spectroscopy, and the level structures for high-spin states were successfully interpreted within the framework of the IBFM model @1‐5#. Decay studies of these nuclides have rarely been reported. Therefore, the last evaluations in Refs. @6, 7# were mainly based on in-beam studies. In 1991, the possibility of static octupole deformation, similar to that of the A5145 and 225 regions proposed, was proposed for the A5130 region by Cottle @8#. The presence of static octupole deformation is represented by parity doublets, which have equal spins and opposite parity levels of rotational bands with alternating bands. The E1 transitions between parity doublets are characterized by a two to four orders of magnitude enhancement compared to those of more normal cases. The 127‐130 Ba isotopes were successively studied by in-beam conversion electron measurements to investigate for parity doublets, and no evidence of them was observed @9,10#. These studies, however, focused only on the conversion electron measurements; the transition probabilities were not measured. It is necessary to measure not only the conversion electrons, but also the half-lives of the excited states in order to explain this feature. The aim of this investigation was to study the level properties of 125,127 Ba in the low energy region, focusing on a search for E1 transitions, and to study their properties by measuring the half-lives of low-lying excited states. The half-lives and conversion electrons were measured for the first time through the decays of 125,127 La, by means of a delayed coincidence technique and a cooled Si~Li! detector, respectively. The expected enhanced E1 transitions were not observed. Level properties based on the Nilsson model are proposed.

Lifetime measurements and total relaxation cross-sections of some rovibrational levels of the B0 u+ state of Te 2 using laser spectroscopy

The fluorescence lifetime of some rovibrational levels of the B0 u + state of Te 2 has been measured using a delayed coincidence technique. By irradiation of a natural sample with selected multimode lines of a pulsed Ar ion laser, different isotopomer molecules of Te 2 were excited. Zero-pressure radiative fluorescence lifetimes and total relaxation cross-sections were obtained. Coincidences and discrepancies with other reported values are discussed.

Determination of the lifetime of the 4p 1 P 0 state of calcium by electron photon coincidence

The electron-photon delayed coincidence technique has been used to measure precisely the lifetime for the 4p1P0 state in calcium. The lifetime of this state was obtained by measuring the time correlation spectrum between the inelastically scattered electrons and the corresponding de-excitation photons. By using the least-squares fitting program to fit Gale's equation to the data points, a value of (4.15±0.17) ns was obtained. The result was compared to some of the earlier experimental measurements.

The GREAT triggerless total data readout method

Recoil decay tagging (RDT) is a very powerful method for the spectroscopy of exotic nuclei. RDT is a delayed coincidence technique between detectors usually at the target position and at the focal plane of a spectrometer. Such measurements are often limited by dead time. This paper describes a novel triggerless data acquisition method, which is being developed for the Gamma Recoil Electron Alpha Tagging (GREAT) spectrometer, that overcomes this limitation by virtually eliminating dead time. Our solution is a total data readout (TDR) method where all channels run independently and are associated in software to reconstruct events. The TDR method allows all the data from both target position and focal plane to be collected with practically no dead-time losses. Each data word is associated with a timestamp generated from a global 100-MHz clock. Events are then reconstructed in real time in the event builder using temporal and spatial associations defined by the physics of the experiment.

Corrections for the effects of accidental coincidences, Compton scatter, and object size in positron emission mammography (PEM) imaging

Positron emission mammography (PEM) has begun to show promise as an effective method for the detection of breast lesions. Due to its utilization of tumor-avid radiopharmaceuticals labeled with positron-emitting radionuclides, this technique may be especially useful in imaging of women with radiodense or fibrocystic breasts. While the use of these radiotracers affords PEM unique capabilities, it also introduces some limitations. Specifically, acceptance of accidental and Compton-scattered coincidence events can decrease lesion detectability. The authors studied the effect of accidental coincidence events on PEM images produced by the presence of /sup 18/F-Fluorodeoxyglucose in the organs of a subject using an anthropomorphic phantom. A delayed-coincidence technique was tested as a method for correcting PEM images for the occurrence of accidental events. Also, a Compton scatter correction algorithm designed specifically for PEM was developed and tested using a compressed breast phantom. Finally, the effect of object size on image counts and a correction for this effect were explored. The imager used in this study consisted of two PEM detector heads mounted 20 cm apart on a Lorad biopsy apparatus. The results demonstrated that a majority of the accidental coincidence events (/spl sim/80%) detected by this system were produced by radiotracer uptake in the adipose and muscle tissue of the torso. The presence of accidental coincidence events was shown to reduce lesion detectability. Much of this effect was eliminated by correction of the images utilizing estimates of accidental-coincidence contamination acquired with delayed coincidence circuitry built into the PEM system. The Compton scatter fraction for this system was /spl sim/14%. Utilization of a new scatter correction algorithm reduced the scatter fraction to /spl sim/1.5%. Finally, reduction of count recovery due to object size was measured and a correction to the data applied. Application of correction techniques for accidental coincidences, Compton scatter, and count loss due to image size increased target-to-background contrast ratios to approximately the maximum level theoretically achievable with this PEM system.