GEANT4-based calibration of an organic liquid scintillator Mauritzson, N.; Fissum, K.G.; Perrey, H. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
01/2022, Letnik:
1023
Journal Article
Recenzirano
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A light-yield calibration of an NE 213A organic liquid scintillator detector has been performed using both monoenergetic and polyenergetic gamma-ray sources. Scintillation light was detected in a ...photomultiplier tube, and the corresponding pulses were subjected to waveform digitization on an event-by-event basis. The resulting Compton edges have been analyzed using a GEANT4 simulation of the detector which models both the interactions of the ionizing radiation as well as the transport of scintillation photons. The simulation is calibrated and also compared to well-established prescriptions used to determine the Compton edges, resulting ultimately in light-yield calibration functions. In the process, the simulation-based method produced information on the gain and intrinsic pulse-height resolution of the detector. It also facilitated a previously inaccessible understanding of the systematic uncertainties associated with the calibration of the scintillation-light yield. The simulation-based method was also compared to well-established numerical prescriptions for locating the Compton edges. Ultimately, the simulation predicted as much as 17% lower light-yield calibrations than the prescriptions. These calibrations indicate that approximately 35% of the scintillation light associated with a given gamma-ray reaches the photocathode. It is remarkable how well two 50 year old prescriptions for calibrating scintillation-light yield in organic scintillators have stood the test of time.
The response of a position-sensitive Li-glass scintillator detector being developed for thermal-neutron detection with 6 mm position resolution has been investigated using collimated beams of thermal ...neutrons. The detector was moved perpendicularly through the neutron beams in 0.5 to 1.0 mm horizontal and vertical steps. Scintillation was detected in an 8 × 8 pixel multi-anode photomultiplier tube on an event-by-event basis. In general, several pixels registered large signals at each neutron-beam location. The number of pixels registering signal above a set threshold was investigated, with the maximization of the single-hit efficiency over the largest possible area of the detector as the primary goal. At a threshold of ∼50% of the mean of the full-deposition peak, ∼80% of the events were registered in a single pixel, resulting in an effective position resolution of ∼5 mm in X and Y. Lower thresholds generally resulted in events demonstrating higher pixel multiplicities, but these events could also be localized with ∼5 mm position resolution.
The Applied Nuclear Physics Group at Lund University has constructed a CANS (Compact Accelerator-driven Neutron Source). The CANS is based around a 3 MV, single-ended, Pelletron accelerator, which is ...used to impinge a 2.8 MeV deuterium beam into a beryllium target. The anticipated neutron production will be on the order of 10
10
n/s in 4π sr, with future upgrades expected to increase neutron production to 10
11
n/s. Neutron energy will be up to 9 MeV with peak emission at ∼5 MeV. Shielding and moderation will be provided by a large water tank surrounding the target, with exit ports to allow moderated neutrons to be directed to experiments. The thermal-neutron flux at the exit of the extraction ports is anticipated to be up to 10
6
n/cm
2
/s. The CANS will be used to forward the activities of the group in the area of neutron-activation analysis, in addition to a broader range of neutron related applications.
To ascertain the frequency of treatment-related acute myeloid leukemias and myelodysplastic syndromes (t-AML/t-MDS) in an unselected series, we have identified all adult cases analyzed in our ...department from 1976 to 1993. Further aims were to compare karyotypic features of t-AML/t-MDS with de novo AML/MDS, in our material as well as in 5098 unselected, cyto- genetically abnormal, published cases, and to analyze associations between type of prior therapy and karyotype. Among our 372 AML and 389 MDS, 47 (13%) were t-AML and 62 (16%) were t-MDS. Clonal abnormalities were significantly more common in t-AML and t-MDS than in de novo disease (68% vs 50%, P < 0.05 and 84% vs 45%, P < 0.001, respectively). Among the available 4230 AML and 1629 MDS (the present series and published cases), 14% were t-AML and 15% were t-MDS. In t-AML/t-MDS, the number of anomalies and the ploidy levels differed significantly from de novo cases, with complex and hypodiploid karyotypes being more common in t-AML/t-MDS. In t-AML, unbalanced changes in general, t(1;3), der(1;7), 3p-, -5, 5q-, -7, 7q-, t(9;11), t(11;19), t(11q23), der(12p), -17, der(17p), -18, and -21 were significantly more frequent than in de novo AML. In t-MDS, -5, -7, 7q-, 13q-, der(17p), and -18 were significantly more common. Type of prior treatment correlated significantly with number of anomalies in t-AML and with ploidy levels in t-AML/t-MDS. The frequencies of several aberrations varied with type of therapy, eg, 5q- was more frequent in radiotherapy-associated t-MDS, monosomy 7 was more common in t-AML and t-MDS after treatment with alkylators, and t(11q23) in t-AML was associated with topoisomerase II inhibitors. Abnormalities significantly more common in de novo disease were +8 as a sole anomaly, balanced changes in general, t(8;21), t(9;22), t(15;17), inv(16), and t(21q22) in AML, and -Y, 5q-, and 20q- as sole anomalies and +8 in MDS. The results emphasize the strong association between previous genotoxic exposure and karyotypic features.
Vanadium-based neutron beam monitor Maulerova, V.; Kanaki, K.; Kadletz, P. M. ...
Physical review. Accelerators and beams,
07/2020, Letnik:
23, Številka:
7
Journal Article
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A prototype quasiparasitic thermal neutron beam monitor based on isotropic neutron scattering from a thin natural vanadium foil and standardHe3proportional counters is conceptualized, designed, ...simulated, calibrated, and commissioned. The European Spallation Source designed to deliver the highest integrated neutron flux originating from a pulsed source is currently under construction in Lund, Sweden. The effort to investigate a vanadium-based neutron beam monitor was triggered by a list of requirements for beam monitors permanently placed in the ESS neutron beams in order to provide reliable monitoring at complex beam lines: low attenuation, linear response over a wide range of neutron fluxes, near to constant efficiency for neutron wavelengths in a range of 0.6–10 Å, calibration stability and the possibility to place the system in vacuum are all desirable characteristics. The scattering-based prototype, employing a natural vanadium foil and standardHe3proportional counters, was investigated at the V17 and V20 neutron beam lines of the Helmholtz-Zentrum in Berlin, Germany, in several different geometrical configurations of theHe3proportional counters around the foil. Response linearity is successfully demonstrated for foil thicknesses ranging from 0.04 mm to 3.15 mm. Attenuation lower than 1% for thermal neutrons is demonstrated for the 0.04 mm and 0.125 mm foils. The geometries used for the experiment were simulated allowing for absolute flux calibration and establishing the possible range of efficiencies for various designs of the prototype. The operational flux limits for the beam monitor prototype were established as a dependency of the background radiation and prototype geometry. The herein demonstrated prototype monitors can be employed for neutron intensities ranging from103–1010n/s.
Coincidence and time-of-flight measurement techniques are employed to tag fission neutrons emitted from a 252Cf source sealed on one side with a very thin layer of Au. The source is positioned within ...a gaseous 4He scintillator detector. Together with α particles, both light and heavy fission fragments pass through the thin layer of Au and are detected. The fragments enable the corresponding fission neutrons, which are detected in a NE-213 liquid-scintillator detector, to be tagged. The resulting continuous polychromatic beam of tagged neutrons has an energy dependence that agrees qualitatively with expectations. We anticipate that this technique will provide a cost-effective means for the characterization of neutron-detector efficiency in the energy range 1–6MeV.
•Neutrons emitted from a 252Cf source with a thin window are tagged using the corresponding fission fragments.•The resulting beam of neutrons is continuous and polychromatic.•The energy of each neutron is determined via the time-of-flight technique.•The approach is anticipated to facilitate cost-effective determinations of neutron-detector efficiencies.
Untagged gamma-ray and tagged-neutron yields from 241AmBe and 238PuBe mixed-field sources have been measured. Gamma-ray spectroscopy measurements from 1 to 5MeV were performed in an open environment ...using a CeBr3 detector and the same experimental conditions for both sources. The shapes of the distributions are very similar and agree well with previous data. Tagged-neutron measurements from 2 to 6MeV were performed in a shielded environment using a NE-213 liquid-scintillator detector for the neutrons and a YAP(Ce) detector to tag the 4.44MeVgamma-rays associated with the de-excitation of the first-excited state of 12C. Again, the same experimental conditions were used for both sources. The shapes of these distributions are also very similar and agree well with previous data, each other, and the ISO recommendation. Our 238PuBe source provides approximately 2.6 times more 4.44MeVgamma-rays and 2.4 times more neutrons over the tagged-neutron energy range, the latter in reasonable agreement with the original full-spectrum source-calibration measurements performed at the time of their acquisition.
•Untagged gamma-ray (1–5MeV) and tagged-neutron (2–6MeV) yields from Be compound sources are measured.•Shapes of gamma-ray distributions are similar and agree well with previous data and each other.•Shapes of neutron distributions are similar and agree well with previous data, each other, and the ISO 8529-2 recommendation.
Coincidence and time-of-flight measurement techniques are employed to tag fission neutrons emitted from a
Cf source sealed on one side with a very thin layer of Au. The source is positioned within a ...gaseous
He scintillator detector. Together with α particles, both light and heavy fission fragments pass through the thin layer of Au and are detected. The fragments enable the corresponding fission neutrons, which are detected in a NE-213 liquid-scintillator detector, to be tagged. The resulting continuous polychromatic beam of tagged neutrons has an energy dependence that agrees qualitatively with expectations. We anticipate that this technique will provide a cost-effective means for the characterization of neutron-detector efficiency in the energy range 1-6MeV.
Untagged gamma-ray and tagged-neutron yields from
AmBe and
PuBe mixed-field sources have been measured. Gamma-ray spectroscopy measurements from 1 to 5MeV were performed in an open environment using ...a CeBr
detector and the same experimental conditions for both sources. The shapes of the distributions are very similar and agree well with previous data. Tagged-neutron measurements from 2 to 6MeV were performed in a shielded environment using a NE-213 liquid-scintillator detector for the neutrons and a YAP(Ce) detector to tag the 4.44MeVgamma-rays associated with the de-excitation of the first-excited state of
C. Again, the same experimental conditions were used for both sources. The shapes of these distributions are also very similar and agree well with previous data, each other, and the ISO recommendation. Our
PuBe source provides approximately 2.6 times more 4.44MeVgamma-rays and 2.4 times more neutrons over the tagged-neutron energy range, the latter in reasonable agreement with the original full-spectrum source-calibration measurements performed at the time of their acquisition.
Knowledge of the neutron light-yield response is crucial to the understanding of scintillator-based neutron detectors. In this work, neutrons from 2–6MeV have been used to study the scintillation ...light-yield response of the liquid scintillators NE 213A, EJ 305, EJ 331 and EJ 321P using event-by-event waveform digitization. Energy calibration was performed using a GEANT4 model to locate the edge positions of the Compton distributions produced by gamma-ray sources. The simulated light yield for neutrons from a PuBe source was compared to measured recoil proton distributions, where neutron energy was selected by time-of-flight. This resulted in an energy-dependent Birks parameterization to characterize the non-linear response to the lower energy neutrons. The NE 213A and EJ 305 results agree very well with existing data and are reproduced nicely by the simulation. New results for EJ 331 and EJ 321P, where the simulation also reproduces the data well, are presented.
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