Efficient Reduction of Piled-Up Events in Gamma-Ray Spectrometry at High Count Rates

Petrovič, T.; Vencelj, M.; Lipoglavšek, M.; Novak, Roman; Savran, D.

doi:10.1109/tns.2014.2298552

Cited by 12 publications

(9 citation statements)

References 28 publications

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“…First, a condition was applied on the central-contact energy obtained by the moving window deconvolution algorithm built in the AGATA electronics [18]. This energy had to be the same as the energy derived from the pulse-shape-analysis (PSA) traces recorded over 1-μs length, which was equivalent to a pile-up rejection [34]. Second, the option assured that the interaction positions obtained with the PSA grid-search algorithm [35] were given by the simulated AGATA Detector Library [36] (ADL) without any smearing of the positions.…”

Section: Fragment Identificationmentioning

confidence: 99%

Lifetime measurement of neutron-rich even-even molybdenum isotopes

Ralet¹,

Piétri²,

Rodríguez³

et al. 2017

Phys. Rev. C

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Background: In the neutron-rich A ≈ 100 mass region, rapid shape changes as a function of nucleon number as well as coexistence of prolate, oblate, and triaxial shapes are predicted by various theoretical models. Lifetime measurements of excited levels in the molybdenum isotopes allow the determination of transitional quadrupole moments, which in turn provides structural information regarding the predicted shape change. Purpose: The present paper reports on the experimental setup, the method that allowed one to measure the lifetimes of excited states in even-even molybdenum isotopes from mass A = 100 up to mass A = 108, and the results that were obtained. Method:The isotopes of interest were populated by secondary knock-out reaction of neutron-rich nuclei separated and identified by the GSI fragment separator at relativistic beam energies and detected by the sensitive PreSPEC-AGATA experimental setup. The latter included the Lund-York-Cologne calorimeter for identification, tracking, and velocity measurement of ejectiles, and AGATA, an array of position sensitive segmented HPGe detectors, used to determine the interaction positions of the γ ray enabling a precise Doppler correction. The lifetimes were determined with a relativistic version of the Doppler-shift-attenuation method using the systematic shift of the energy after Doppler correction of a γ -ray transition with a known energy. This relativistic Doppler-shiftattenuation method allowed the determination of mean lifetimes from 2 to 250 ps. Results: Even-even molybdenum isotopes from mass A = 100 to A = 108 were studied. The decays of the low-lying states in the ground-state band were observed. In particular, two mean lifetimes were measured for the first time: τ = 29.7 Conclusions:The reduced transition strengths B(E2), calculated from lifetimes measured in this experiment, compared to beyond-mean-field calculations, indicate a gradual shape transition in the chain of molybdenum isotopes when going from A = 100 to A = 108 with a maximum reached at N = 64. The transition probabilities decrease for 108 Mo which may be related to its well-pronounced triaxial shape indicated by the calculations.

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Section: Fragment Identificationmentioning

confidence: 99%

Lifetime measurement of neutron-rich even-even molybdenum isotopes

Ralet¹,

Piétri²,

Rodríguez³

et al. 2017

Phys. Rev. C

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“…We employ a variable length filter where the longest filter that can be evaluated between the previous and next events is used to evaluate the current event. Our method, developed independently, is similar to that presented in [14]. The resulting energy spectrum for the Cs-137 source is shown in Figure 3.…”

Section: The Uhrge Detector Systemmentioning

confidence: 99%

Spent Nuclear Fuel Measurements

Fast¹,

Chenault²,

Glasgow³

et al. 2014

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An unsolved longstanding challenge to expand the Safeguards regime is to assay spent nuclear fuel (SNF) for its plutonium content. Regardless of the process used to assay the fissile content, there must be a gamma-ray measurement to determine the plutonium mass. Fissile material isotopic measurements in the presence of the intense gamma-ray background from 137 Cs and other fission products are difficult. Plutonium-mass measurements using high-resolution passive gamma-ray spectroscopy are practically impossible due to the ~10 7 higher activity of isotopes such as 137 Cs. Assay using measurements of gamma rays with energies above 3 MeV that are emitted from the short-lived decay products of neutron irradiated SNF is more promising but still requires gamma-ray spectroscopy at rates on the order of 1 million counts per second (Mcps) or higher in the gamma-ray spectrometers due to the passive gamma ray background. PNNL has developed new digital filtering and analysis techniques to produce an ultra high-rate gammaray spectrometer that can operate at these count rates. A standard coaxial ~40% efficient high-purity germanium (HPGe) crystal has made passive gamma-ray measurements of SNF at a throughput of about 400 kcps at an input rate of 1.3 Mcps. Optimized filtering algorithms have been developed to preserve the spectroscopic capability of the system even in the very short processing times between events at these high rates. This Ultra-High Rate HPGe (UHRGe) spectroscopy system also operates at real time using a field-programmable gate array to perform spectral operations. The system operation was demonstrated in a measurement with an aged SNF rod segment in a hot cell at PNNL's Radiochemical Processing Laboratory. This piece of fuel originates from the Quad Cities reactor complex, has a well-known burnup and adjacent sections have been destructively assayed using radiochemical techniques. The UHRGe system was calibrated using known sources and the direct measurements of the SNF matched the predicted rates from the known mass and isotopic composition. This test confirms the promise of the UHRGe system's approach for high-rate gamma-ray spectroscopy of SNF.

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“…However, as a result of pile-up rejection, information on the energy distribution using these methods would be lost. [17][18][19] In the case of the LINAC pulse structure, all the energy is deposited in the detector; therefore, if the number of events is known, it is potentially possible to correct for the effect of the pile-up.…”

Section: Introductionmentioning

confidence: 99%

Determination of the photon spectrum of a therapeutic linear accelerator near the maze entrance: Comparison of Monte Carlo modeling and measurements using scintillation detectors corrected for pulse pile‐up

2020

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The determination of x-ray spectra near the maze entrance of linear accelerator (LINAC) rooms is challenging due to the pulsed nature of the LINAC source. Mathematical methods to account for pulse pileup have been examined. These methods utilize the highly periodic pulsing structure of the LINAC, differing from the effects of high-intensity radioactive sources. Methods: Sodium iodide (NaI) and plastic scintillation detectors were used to determine the energy spectra at different points near the maze entrance of a medical LINAC. Monte Carlo calculations of the energy distribution of scattered photons were used to simulate the energy spectrum at the maze entrance. The proposed algorithm uses the Monte Carlo code, FLUKA, to calculate a response function for both detectors. To determine the effects of the pileup in the spectra, the Poisson distribution was used, employing the average number of photons per pulse (l) interacting with the detector. The quantity, l, was obtained from the ratio of the number of events detected to the number of pulses delivered. The energy spectra at various distances from the maze entrance were measured using NaI and plastic scintillation detectors. From these measurements, the values of µ were calculated, and the pileup probability was determined. The FLUKA Monte Carlo code was used to calculate the spectrum at the maze entrance and the response matrices of the NaI and plastic scintillation detectors. The algorithm based on the Poisson distribution was applied to calculate the spectrum. Results: The agreement between the calculated and measured spectra was within the first standard deviation of the variance expected in µ. This agreement confirms that photons at the maze entrance have energies between 30 and 240 keV for a maze with three turns, with an average energy of around 85 keV. After pileup correction, the range of the pulse height distribution with the plastic scintillation detector, which has a low atomic number, was decreased (0 to 140 keV). In contrast, the range of the pulse height distribution with the NaI scintillation detector was closer to the photon spectrum (0 to 240 keV). Conclusions: The corrected spectrum demonstrates that using a FLUKA Monte Carlo code and an algorithm based on the Poisson distribution are effective methods in removing the distortion due to the pileup in LINAC spectra when measuring with NaI and plastic scintillation detectors. The agreement between the corrected and measured spectra indicates that Monte Carlo modeling can accurately determine the spectrum of a LINAC machine at the maze entrance.

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Efficient Reduction of Piled-Up Events in Gamma-Ray Spectrometry at High Count Rates

Cited by 12 publications

References 28 publications

Lifetime measurement of neutron-rich even-even molybdenum isotopes

Lifetime measurement of neutron-rich even-even molybdenum isotopes

Spent Nuclear Fuel Measurements

Determination of the photon spectrum of a therapeutic linear accelerator near the maze entrance: Comparison of Monte Carlo modeling and measurements using scintillation detectors corrected for pulse pile‐up

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