Singles Spectra Research Articles

Shape coexistence in 66Se

The nuclear structure of 66Se, nucleus beyond the N=Z line on the proton-rich side of the valley of stability, was investigated by the neutron knock-out reaction 67Se(12C,X)66Se using a 12C target. The analysis of the singles spectrum of the γ-rays emitted during the de-excitation of the populated low-lying excited states revealed two previously detected (927(4) keV, 1460(32) keV) and three new (744(6) keV, 1210(17) keV, 1661(23) keV) transitions. The 744-keV, the 1210-keV, and the 1460-keV transitions were found to be in coincidence with the one at 927 keV. The spectrum coincident with the 927-keV transition showed a further possible transition at 299(35) keV, which was obscured by significant atomic background in the singles spectrum. This transition might correspond to a peak previously reported at 273(5) keV that could not be assigned to 66Se unambiguously. Based on a comparison of the experimental data to theoretical calculations, four new excited states are proposed which suggest that 66Se exhibits shape coexistence.

Real-Time Gain Control of PET Detectors and Evaluation With Challenging Radionuclides.

Accurate gain control of PET detectors is a prerequisite for quantitative accuracy. A shift in the 511 keV peak position can lead to errors in scatter correction, degrading quantitation. The PET detectors in a PET/MR scanner are subject to thermal transients due to eddy currents induced during gradient-intensive MRI sequences. Since the gain of silicon photomultiplier-based detectors changes with temperature, good gain control is particularly challenging. In this paper we describe a method that utilizes information from the entire singles spectrum to create a real-time gain control method that maintains gain of PET detectors stable within approximately ±0.5% (±2.5 keV) with varying levels of scatter and in the presence of significant thermal transients. We describe the methods used to combine information about multiple peaks and how this algorithm is implemented in a way that permits real-time processing on a field-programmable gate array. Simulations demonstrate rapid response time and stability. A method ("virtual scatter filter") is also described that extracts unscattered photopeak events from phantom data and demonstrates the accuracy of the photopeak for various radionuclides that emit energies in addition to the pure 511 keV annihilation peak. Radionuclides 52 Mn, 55 Co, 64 Cu, 89 Zr, 90 Y, and 124 I are included in the study for their various forms of spectral contamination.

Uncertainties on gamma-ray energies and intensities measured in the decay of 83Sr

We analyze once again the [Formula: see text] singles spectra and [Formula: see text]-[Formula: see text]-[Formula: see text] coincidence spectra following the [Formula: see text]EC decay of 83Sr. Multipeaks are carefully separated and many [Formula: see text] transition cascades are clearly obtained in the work. As a complement to our previous work, the uncertainties on [Formula: see text]-rays energies, [Formula: see text]-rays intensities and deduced level energies in the [Formula: see text]EC decay of 83Sr are given now.

Simulating γ–γ coincidences of β-delayed γ-rays from fission product nuclei

Analyzing radiation from material that has undergone neutron induced fission is important for fields such as nuclear forensics, reactor physics, and nonproliferation monitoring. The γ-ray spectroscopy of fission products is a major part of the characterization of a material׳s fissile inventory and the energy of incident neutrons inducing fission.Cumulative yields and γ-ray intensities from nuclear databases are inputs into a GEANT4 simulation to create expected γ-ray spectra from irradiated 235U. The simulations include not only isotropically emitted γ-rays but also γ–γ cascades from certain fission products, emitted with their appropriate angular correlations. Here γ singles spectra as well as γ–γ coincidence spectra are simulated in detectors at both 90° and 180° pairings.The ability of these GEANT4 Monte Carlo simulations to duplicate experimental data is explored in this work. These simulations demonstrate potential in exploiting angular correlations of γ–γ cascades in fission product decays to determine isotopic content. Analyzing experimental and simulated γ–γ coincidence spectra as opposed to singles spectra should improve the ability to identify fission product nuclei since such spectra are cleaner and contain more resolved peaks when compared to γ singles spectra.

A capture-gated neutron spectrometer for characterization of neutron sources and their shields

A portable capture-gated neutron spectrometer was designed and built. The spectrometer consists of a boron-loaded scintillator. Data acquisition is performed in list-mode. 252Cf and AmBe sources and various neutron and gamma shields were used to characterize the response of the device. It is shown that both the unfolded capture-gated neutron spectrum and the singles spectrum up to 5MeV should be utilized. Source identification is then possible and important information is revealed regarding the surroundings of the source. The detector׳s discrimination of neutrons from photons is relatively good; specifically, one out of 105 photons is misclassified as a neutron and, more importantly, this misclassification rate can be calculated precisely for different measurement environments and can be taken into account in setting alarm limits for neutron detection. The source and source shield identification capabilities of the detector make it an interesting asset for security applications.

αdecay of97249Bk and levels in95245Am

$\ensuremath{\alpha}$ decay of ${}^{249}$Bk has been investigated by measuring its $\ensuremath{\alpha}$ and $\ensuremath{\gamma}$-ray spectra, both in singles and in coincidence modes. The $\ensuremath{\alpha}$ spectrum of a freshly purified ${}^{249}$Bk sample was measured with a high-resolution, double-focusing magnetic spectrometer. $\ensuremath{\gamma}$ singles, $\ensuremath{\gamma}$-$\ensuremath{\gamma}$ coincidence, and $\ensuremath{\gamma}$-$\ensuremath{\alpha}$ coincidence spectra were also recorded. The absolute intensity of the 327.45-keV $\ensuremath{\gamma}$ ray has been determined to be ($1.44\ifmmode\pm\else\textpm\fi{}0.08)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$% per ${}^{249}$Bk decay. Assignments of previously known single-particle states were confirmed. A new rotational band was identified in the $\ensuremath{\alpha}$ singles spectrum and Am K x rays have been observed in its decay. This single-particle state, with an energy of 154 keV, has been assigned to the 3/2${}^{\ensuremath{-}}$[521] Nilsson state. This is the lowest excitation energy for this orbital in any Am nucleus. More precise energies and intensities of the ${}^{249}$Bk $\ensuremath{\alpha}$ groups and $\ensuremath{\gamma}$-ray transitions are provided.

AutoCal: a method for automatic energy calibration of β–γ systems based on a 137Cs spectrum

A method was developed and implemented that calculates energy versus channel calibrations. This method utilizes a 137Cs spectrum acquired in β–γ coincidence. Both the γ singles and the β–γ coincident spectrum are utilized. The γ singles spectrum is utilized to calculate the γ detector energy versus resolution function. The Compton line in the β–γ coincidence is then used to calculate the β detector energy versus resolution function. Currently a linear regression (y = mx + b) is utilized to fit the data. However, higher order polynomials may easily be implemented if desired.

Thermal Neutron Capture onto the Stable Tungsten Isotopes

Thermal neutron-capture measurements of the stable tungsten isotopes have been carried out using the guided thermal-neutron beam at the Budapest Reactor. Prompt singles spectra were collected and analyzed using the HYPERMET -ray analysis soft- ware package for the compound tungsten systems 183 W, 184 W, and 187 W, prepared from isotopically-enriched samples of 182 W, 183 W, and 186 W, respectively. These new data pro- vide both confirmation and new insights into the decay schemes and structure of the tung- sten isotopes reported in the Evaluated Gamma-ray Activation File based upon previ- ous elemental analysis. The experimental data have also been compared to Monte Carlo simulations of -ray emission following the thermal neutron-capture process using the statistical-decay code DICEBOX. Together, the experimental cross sections and modeled- feeding contribution from the quasi continuum, have been used to determine the total radiative thermal neutron-capture cross sections for the tungsten isotopes and provide im- proved decay-scheme information for the structural- and neutron-data libraries.

Coincidence Measurement of 189W Decay Gamma Rays

To our knowledge, the earliest work concerning W decay was done by Flegenheimer et al. in 1963. They determined the half-life of W to be 11min. A maximum energy of around 1.4MeV for W was obtained. In 1965, Kauranen and Ihochi studied W through the Os(n, ) W reaction. Its half-life was determined to be 11:5 0:3min. An end-point energy of 2:5 0:2MeV for the -spectrum of W was obtained. Its ten rays with energies of 94, 130, 178, 222, 258, 360, 417, 550, 855, and 955 keV were found. A cascade of two rays at 222 and 258 keV was observed. In ref. 3, Mirzadeh et al. investigated W decay via the Os(n, ) W reaction. Through the measurement of singles spectra, they observed two rays with energies of 260.4 and 421.7 keV from W decay and got their relative intensities. In 1997, Yang et al. made a singles -ray spectrum measurement by using an HPGe detector. Twenty two rays which can be assigned to the decay of W were found. Eighteen of these rays were observed for the first time. Subsequently in 2003, Wu and Niu gave a sample decay scheme (Fig. 1) including two rays of W at 222.0 and 260.4 keV based on the -ray data of Yang et al. and the reaction data of Hirning et al. But until now, no precise coincidence measurement for W rays was made. The present work is to check the coincidence relations inferred from previous work. The measurement of rays from W decay was taken with X– and – coincidence methods in our experiments. The (n, ) and (n, ) reactions were proved to be efficient ways for producing W in previous work. So in this work, we selected the Os(n, ) W reaction to produce W. The present experiments were performed using 14MeV neutrons from the 600-kV Cockcroft–Walton accelerator at the Institute of Modern Physics, Chinese Academy of Sciences. 14MeV neutrons were produced by the reaction of TiT targets with deuterons. W activities were produced using irradiation of isotopically enriched Os metallic powder of 100mg/cm with 14MeV neutrons. Osmium targets each were irradiated for 30min to fit the 10.7min half-life of W. And then they were transported into a lead-shielded room by an improved rabbit system. The measurement started 20 s after the end of irradiation with a planar HPGe detector (for X-ray and low energy -ray measurement) and a clover detector which consists of four coaxial N-type Germanium detectors. The former has an energy resolution of 0.6 keV for the 122 keV line of Co, an active diameter of 32mm, and a sensitive depth of 10mm; each of the latter has a 25% efficiency and an energy resolution of 2.1 keV for the 1332 keV line of Co. The two detectors were placed face to face on both sides of the source in the lead-shielded room. The measurement lasted 30min to fit the half-life of W. The count rate of single detector was about 100/s in the experiment. The coincidence window width of 100 ns was chosen. Thus the infection of the chance coincidence was not significant. The procedure mentioned above was repeated many times to improve the counting statistics. (X)-ray singles events and three parameter coincidence (X)– –t were recorded with a Multi-Parameter Data Acquisition System, where t was the time of each event after the beginning of a counting period. During the irradiation, several radioactive isotopes of Os, Re, and W were produced by (n,2n), (n, ), (n,p) and (n, ) reactions, respectively. It was not possible to observe rays from W decay through singles spectra because of the lower W yield and the large backgrounds from other nuclides produced in the experiments. The X– coincidence measurement was made so as to obtain rays from W decay. A part of the -ray spectrum in coincidence with 61.1 keV Re K 1 and 59.7 keV Re K 2 X rays is presented in Fig. 2.

Energy levels ofCf251populated in the α decay of100255Fm and EC decay of99251Es

Gamma-ray singles spectra of extremely pure (chemically and isotopically) samples of $^{255}\mathrm{Fm}$, with strengths of $~1$ mCi, have been measured with a high-resolution 2-cm${}^{2}\ifmmode\times\else\texttimes\fi{}$10-mm germanium LEPS detector and with a 25% Ge spectrometer. Gamma rays with intensities as low as $1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$% per $^{255}\mathrm{Fm}$ \ensuremath{\alpha} decay have been identified. The electron spectrum of a mass-separated $^{251}\mathrm{Es}$ source was measured with a cooled Si(Li) electron spectrometer. The spectrum provided the conversion coefficients of low-energy transitions in $^{251}\mathrm{Cf}$ and thereby their multipolarities. The present measurements confirm the previous assignments of single-particle states in $^{251}\mathrm{Cf}$. These include $1/{2}^{+}$[620], 0.0 keV; $7/{2}^{+}$[613], 106.30 keV; $3/{2}^{+}$[622], 177.59 keV; $11/{2}^{\ensuremath{-}}$[725], 370.47 keV; $9/{2}^{\ensuremath{-}}$[734], 433.91 keV; $5/{2}^{+}$[622], 543.98 keV; $1/{2}^{\ensuremath{-}}$[750], 632.0 keV; $9/{2}^{+}$[615], 683 keV; and $9/{2}^{+}$[604], 974.0 keV. A vibrational band was identified in previous studies at 981.4 keV and given an assignment of ${7/{2}^{+}[613]\ensuremath{\bigotimes}{2}^{\ensuremath{-}}}3/{2}^{\ensuremath{-}}$. Three new vibrational bands are identified in the present work at 942.5, 1086.5, and 1250.0 keV with tentative assignments ${7/{2}^{+}[613]\ensuremath{\bigotimes}{1}^{\ensuremath{-}}}5/{2}^{\ensuremath{-}},{7/{2}^{+}[613]\ensuremath{\bigotimes}{1}^{\ensuremath{-}}}9/{2}^{\ensuremath{-}}$, and ${7/{2}^{+}[613]\ensuremath{\bigotimes}{0}^{+}}7/{2}^{+}$, respectively. A level was identified at 1185.5 keV with spin of 5/2 or 7/2 but it was not given any configuration assignment. Another level was identified at 1077.5 keV and given a spin of 9/2. Again, no configuration could be assigned to this level.

Conversion-electron study of 0+ excitations in 208Pb

The 208Pb(p,p′e−) reaction has been studied at a proton energy of 17.3 MeV. Singles data show E0 transitions from the 0+2 and 0+3 states at 4868 and 5241 keV, respectively, to the ground state. Proton–electron gated spectra indicate that few electrons from the 0+2 state are in coincidence with backscattered protons, while those from the 0+3 state are somewhat more abundant. From the singles spectra, an upper limit for the E3(0+3 → 3−1)/E0(0+3 → 0+1) branching ratio of less than four has been measured. This observation is in agreement with previous predictions for a two-phonon octupole excitation.

The β-decay of 9Li to the high lying states in 9Be

Mirror β -transitions should have similar strengths as long as binding energy, Coulomb energy and other explicitly breaking effects are small. However, large β -decay asymmetries have been observed in the decay of 9 C [Phys. Rev. C 37 (1988) 766] and the decay of its mirror nucleus 9 Li [Nucl. Phys. A 510 (1990) 189]. These asymmetries could be the indication of structural differences between mirror states. We have focussed on the beta-decays of 9 C and 9 Li to the high lying region (between 11-12 MeV) in the daughter nuclei 9 B and 9 Be. The difficulty in the study of these decays is that they are accompanied by the emission of three particles and one needs to determine the breakup mechanism to extract information about the position, width and feeding of the states. The β -decays of 9 C [Nucl. Phys. A 692 (2001) 427] and 9 Li [Phys. Lett. B. 576 (2003) 22] to the high lying region of the daughter nuclei have been remeasured with setups that allow the study of the complete kinematics of the processes and, hence, the breakup mechanism of the states in the daughter nuclei can be determined. The most recent experiments on 9 C [Nucl. Phys. A 692 (2001) 427, Phys. Rev. C 61 (2000) 064310] gave B GT values of 1.58(16) and 1.20 (15) for the transition 9 C → 9 B (12.2 MeV) whereas the only early determination for 9 Li→ 9 Be (11.81 MeV) [Nucl. Phys. A 510 (1990) 189] gave 5.6 (1.2). The experiments on 9 C employed coincidence detection of charged particles thereby allowing a detailed analysis, whereas the older 9 Li experiment only included singles spectra. The only previous 9 Li experiment where α -particle coincidences were measured [Nucl. Phys. A 366 (1981) 449] did not have sufficient angular resolution and no detailed analysis of the breakup mechanism was performed.

New gamma transitions in 193Ir from the beta decay of 193Os

The population and the mode of decay of the low-lying excited levels of 193Ir have been investigated by single and gg coincidence spectroscopy using 192Os enriched to 99% and several HPGe detectors. From singles spectra analysis the energies of 71 gamma rays have been determined with a better overall precision than previously, 17 of them for the first time. The energies at 1043.244(15) and 1316.628(18)keV , observed for the first time in this work, as well as some preliminary coincidence relationships, suggest that the end point energy Qbmax(»1.14MeV) must be further investigated.

Many-electron effects in the Auger-photoelectron coincidence spectroscopy spectra of the late 3d-transition metals

The valence hole created by the L2–L3 M45 Coster–Kronig (CK) transition may hop away from the ionized atomic site before the L3-hole decays. Then when the third (Auger) electron emitted by the L3-hole decay is measured in coincidence with the photoelectron emitted by the initial L2-level electron ionization, the coincidence spectrum becomes similar or identical to the singles spectrum of the secondary (Auger) electron emitted by the L3-hole decay as if it decayed as an initial single core hole. Thus the coincidence spectrum is essentially governed by the valence-hole dynamics of both the intermediate states and the final states of the L2–L3 (M45) CK-transition preceded Auger transition. In the present paper the Auger-photoelectron coincidence spectroscopy (APECS) spectra of Fe, Co, and Ni metals reported by C.P. Lund et al. (Phys. Rev. B55 (1997) 5455) are analyzed in light of the delocalization and localization of the valence hole(s) created by the CK transition or the CK-transition preceded Auger transition.

Quantitative determination of [formula omitted

Sealed 252Cf sources in the microCurie to milliCurie range are routinely used in industry and research. At present, no reliable analytical method is available for precise determination of the activity. Very strong sources can be analyzed by neutron counting but the error is large. We propose to use γ-ray spectroscopy for such analysis. In particular, high-energy γ rays (above 1MeV) of fission fragments in equilibrium with the source are very convenient because they have little absorption in materials surrounding the source. It is found that the 1435.8-keV γ-ray of 138Cs and the 1596.5-keV γ-ray of 140La are well isolated and sufficiently above the background under these peaks. We have measured the γ/α ratio for the 252Cf with an uncertainty of better than 5%. The experiment involved the preparation of several thin 252Cf sources, alpha pulse height analysis, determination of α decay rate, and the measurement of γ singles spectrum with a well-shielded germanium spectrometer. The measured ratio and the γ-ray spectroscopy of unknown samples can provide the activity of 252Cf in these samples.

Decay properties of low-lying collective states in 132Ba

The decay properties of low-lying collective states in 132Ba were studied by means of γ spectroscopy following the β-decay of the 2 − ground state ( T 1/2=4.8 h) and a 6 − isomer ( T 1/2=24.3 min) of 132La. The lanthanum nuclei were produced at the Cologne fn tandem accelerator using the reaction 122Sn( 14N, 4n) 132La. The γγ coincidences and singles spectra were measured with the osiris-cube spectrometer. Beside ground and quasi-gamma band many other low-lying states were observed. The γγ angular correlations were analyzed to assign spins to the excited states, and to determine the multipolarities of the depopulating the γ transitions. We also confirmed the expected dominant E2 character of transitions in the quasi-gamma band and from the quasi-gamma to the ground band but with a certain deviation: the decay 6 + 2→6 + 1 shows an unexpected large M1 fraction. Also the decays of the third, fourth and fifth 2 + states are dominated by M1 radiation. A level at 1660 keV could be identified as the 0 + 3 state in 132Ba. The experimental data are compared with calculations using the proton–neutron interacting boson model (IBM-2). Good agreement is reached in the vicinity of the O(6) limit.

Low-spin states of doubly odd 182Au

Low-spin states of 184Au have been studied using the β+/EC decay of 184Hg. γ-ray and conversion-electron singles spectra were recorded with 184Hg mass-separated sources. For γ-γ-t and X-γ-t coincidence measurements, mercury nuclei were produced in the 148Sm + 40Ar reaction and transported by a He-jet system. The electron spectra were recorded from 184Hg sources produced at ISOLDE. A level scheme of 184Au including 48 transitions is proposed. The experimental results are interpreted in the frame of a semi-microscopic axial-rotor-plus-two-quasiparticle model developed in the context of the HF+BCS approximation.

Energy levelsin98251Cf populated in the α decayof100255Fm

Gamma-ray spectra of a 20-h {sup 255}Fm source containing {approx}1 mCi activity were measured with a 25% Ge detector and a low-energy photon spectrometer (LEPS). Gamma lines with intensities as low as 1.0x10{sup -6}% per {sup 255}Fm {alpha} decay were observed. Gamma-gamma coincidence spectra of a {sup 255}Fm sample were measured with the GAMMASPHERE array. A comparison of the {gamma}-ray spectrum gated by the Cf K{sub {alpha}} x-ray peak with the {gamma}-singles spectrum provided spins of the excited states in {sup 251}Cf. The {gamma}-ray data, in conjunction with previously measured {sup 250}Cf(d,p) reaction data, allowed us to characterize several single-particle and vibrational states above the N=152 subshell gap.

Level structure of 123Cs observed from 123Ba decay and described using the IBFM and CQPC models

The decay of 123Ba to 123Cs has been studied with mass-separated sources. Singles spectra of γ-rays, X-rays and conversion electrons as well as γ - γ - t, γ - e − - t, and X - e − - t coincidences were recorded. A level scheme of 123Cs has been constructed including 26 new excited states and 82 transitions. The existence of a I π = 11/2−, T 1/2 = 1.7 s isomer, bandhead of the h 11/2 band, is confirmed. Its excitation energy equals 156.3 keV. A new T 1/2 = 114 ns isomer has been established at 232 keV using the in-beam recoil catcher technique. It is assigned to the I π = 9/2+ bandhead of the gpg 9/2 band. Collective bands based on the 1/2+ ground state and first 3/2+ excited state are proposed. The level structure is described in the frame of the interacting boson-fermion and core-quasiparticle coupling models.

Identification of a New Isotope 186Hf

The new neutron-rich isotope 186Hf has been produced through a multinucleon transfer reaction by irradiation of natural tungsten targets with 60 MeV/u 18O projectiles. The 186Hf activities were separated radiochemically from the tungsten and reaction product mixture. The γ-ray singles spectra were measured with a high resolution HPGe detector. The new isotope 186Hf was identified based on the growth and decay of 737.5 keV γ rays from the β- decay of its daughter 186Ta. Its half-life has been determined to be 2.6 ± 1.2 min.