Investigation of neutron-induced background was carried out by studying interactions of cosmic-ray neutrons with an HPGe detector inside its shield placed on a ground floor of a 3-storey building. ...The study was conducted experimentally and by Monte Carlo simulations using GEANT4 simulation tool. Detailed analysis of measured background γ-ray spectra showed that many γ-lines visible in the spectra were induced by neutrons. The majority of detected γ-rays originated in germanium, copper, lead and tin. Iron and aluminium components were less important background sources. Inelastic scattering and neutron capture were the most often occurring processes of neutron interactions with the detector and its shielding. The contamination by natural radionuclides, specifically of 40K, 214Pb, 214Bi and 208Tl, was also present in the background spectra. Nevertheless, approximately 35% of 208Tl peak at the energy of 2614.51 keV was produced by inelastic scattering of neutrons on 208Pb nuclei. The experimental background was compared with GEANT4 simulations, which were carried out without and with the shielding layer of the building. The final integral counting rates for measured spectrum in the energy range from 50 keV to 2875 keV was 1.26 ± 0.07 s−1 and for simulated one 1.25 ± 0.13 s−1, indicating a good agreement with the experiment.
•Study of cosmic ray interactions with an HPGe detector was carried out.•Many γ-lines visible in the spectra were induced by neutrons.•Inelastic scattering and neutron capture were the most often occurring processes.•GEANT4 simulations were in a very satisfactory agreement with the experiment.•Inelastic neutron scattering on 208Pb nuclei contributes by 35% to the 2614.51 keV peak.
The article provides an overview of the different components of programmes for the evaluation of the environmental impact of accelerator facilities. The starting point is the knowledge of radiation ...and radionuclides that may be encountered in the environment of accelerators. The second step is an efficient environmental monitoring programme suitable for the given source term. The results of the monitoring programme provide an input for models calculating the maximum effective dose received by members of the public, so expressing the dosimetric impact of the facility.
As the levels of radionuclides observed at present in the environment are very low, high sensitive analytical systems are required for carrying out environmental investigations. We review recent ...progress which has been done in low-level counting techniques in both radiometrics and mass spectrometry sectors, with emphasis on underground laboratories, Monte Carlo (GEANT) simulation of background of HPGe detectors operating in various configurations, secondary ionisation mass spectrometry, and accelerator mass spectrometry. Applications of radiometrics and mass spectrometry techniques in radioecology and climate change studies are presented and discussed as well. The review should help readers in better orientation on recent developments in the field of low-level counting and spectrometry, and to advice on construction principles of underground laboratories, as well as on criteria how to choose low or high energy mass spectrometers for environmental investigations.
Water released into the environment from CERN's accelerator installations may contain both long-lived (
7Be,
22Na) and short-lived (
11C,
13N,
24Na) gamma radioactivity. Each potential release point ...is equipped with an on-line monitor for short-lived radionuclides, which consists of a scintillation probe immersed in a tank filled with monitored water. Whilst calibration standards are available for long-lived radioactivity, computer simulations are the only feasible way to determine the monitor efficiency for the short-lived radionuclides. The paper describes computer simulations using the Monte Carlo code GEANT 3.21. An excellent agreement between measured and computed efficiencies was obtained for the long-lived radionuclides, validating the computer model. A calibration method is proposed for light positron emitters, which combines an experimental calibration for
7Be and correction factors obtained in the simulations.
The radionuclide levels observed at present in the marine environment are very low, therefore high sensitive spectrometric systems are required for carrying out oceanographic investigations. The ...present-state-of-the-art carefully designed low-level HPGe γ-spectrometers, which do not operate underground, have a dominating background component induced by cosmic rays, mostly by cosmic muons. High energy cosmic rays can initiate a large number of physical processes leading to background induction. Analytic solutions for describing these processes are not available and therefore, a Monte Carlo simulation is necessary. The development of a simulation code for background induction is useful for the optimisation of a counting system in respect to its background characteristics. It enables to assert the background before the system is built and also to perform systematic investigation of the influence of various parameters on the background of the detector. The GEANT code has been selected from the codes systems facilitating the simulation of the passage of particles through matter, as it best meets the requirements for simulations with high-energy muons. The obtained results show that the background depends most significantly on the thickness, the size and lining of the shield. Lead shielding of 15 cm thick has been found to be the optimum shielding for most applications. It is not advisable to build an unnecessarily large shield. A shield with removable lining would be the best as the lining can be removed from applications where the lead X-rays are not a disturbing influence.
A computer simulation of the cosmic-muon background induction in a HPGe γ-spectrometer using GEANT3.15 is described. Relative contributions of muon interaction mechanisms in parts of a detector ...shield were investigated. The direct muon ionisation in the Ge-diode, production of δ-electrons, direct e
−e
+-pair production, muon decay and muon bremsstrahlung contribute to the induced lower-energy background by 2.5%, 81.2%, 10.0%, 4.0% and 2.3%, respectively. For muons with momenta below ≈0.7 GeV/
c the muon decay is the most contributing mechanism. The contribution of the δ-electron production reaches a maximum at 1.7 GeV/
c and extends to the highest momenta. Above ≈70 GeV/
c the direct e
−e
+-pair production dominates. About 97% of muon primary interaction vertices are situated in shield materials. An inner shield layer that is 4.7 cm thick contains 90% of all the vertices. A 3 mm thick CdCu shield lining accounts for 15% of all events. The simulated spectrum agrees well with an experimental one. Limitations of the standard GEANT for simulating the background induction by cosmic rays are discussed as well.
Computer simulations using GEANT 3.21 with shields of various parameters are performed to investigate how shield parameters can influence the cosmic-muon induced background of a typical low-level ...HPGe γ-spectrometric system. It was found that the background increases with increasing inner shield dimensions to reach a saturated value for very large dimensions when the composition of the shield (bulk material, thickness, lining and proportion between height and width) is not changed. The background for a large shield is almost twice that for a tight one. The background does not depend significantly on the position of the detector inside a shield and on the shape (cylinder or rectangular) provided the inner dimensions are the same. There is a strong dependence on bulk material and lining. Backgrounds are lower below ≈500 keV but higher above ≈500 keV and in the 511 keV annihilation peak for higher-
Z materials. Several types of lining are simulated and compared. Best results are obtained for a lead shield lined with 2 mm of tin.
The DELPHI very forward tracker for LEP200 Andreazza, A; Aubret, C; Baubillier, M ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,
12/1995, Letnik:
367, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
The design of a new silicon tracker detector for the forward region in the DELPHI experiment is presented. It consists of two layers of macropixel and two layers of ministrip detectors in both the ...forward directions. The motivations and the requirements for this detector will be shown together with test beam results.
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