Response function of a beta detector telescope consisting of HPGe and scintillator

The response function of a beta detector telescope consisting of a 15 mm thick high purity germanium detector stacked with a 1 mm thick plastic scintillation detector has been determined. The telescope covers the energy range from 1 to 14 MeV. Detector response and relative efficiencies were measured at four electron energies between 2.5 and 8.5 MeV. The monoenergetic electrons were obtained using conversion electrons originating from thermal neutron capture in a ¹¹³Cd target.     

New descriptors of radiation quality based on nanodosimetry, a first approach

After a short overview on the latest developments in nanodosimetry, measured frequency distributions of ionisation cluster size caused by 4.6 MeV alpha-particles or low-energy electrons in 'nanometric' volumes of nitrogen are compared with cluster-size distributions for liquid water cylinders that are equal in size to segments of DNA of 10 base-pairs length. Such frequency distributions are, to a greater part, governed by the same basic physical interaction data as those to be expected, if charged particles interact with DNA segments. Quantities derived from ionisation cluster-size distributions should, therefore, behave as a function of radiation quality similarly to the yields of single or double strand breaks in the DNA. To test this assumption, extensive Monte Carlo simulations were performed for electrons in the energy range between 12.5 eV and 100 keV for protons at energies between 0.7 MeV and 250 MeV and for alpha-particles in the energy range between 2 MeV and 100 MeV. The results are then compared with the yields of single- or double-strand breaks in the DNA, taken from the literature.     

Response of NE213 liquid scintillation detectors to high-energy photons (7 MeV < Eγ < 20 MeV)

Two NE213 liquid scintillation detectors of 206 and 412 cm³ in volume were calibrated in high-energy photon fields (E_γ > 7 MeV) at the PTB accelerator facility. The measured pulse height spectra are in excellent agreement with the response functions simulated with the EGS4 Monte Carlo code. The generally assumed linear dependence of the electron light output on the energy deposited does not hold for electron energies above 1.6 MeV. The nonlinear electron light output function was therefore included in the calculation of the response functions. The production of high-energy electrons and positrons in the target assembly and in the air was also taken into consideration.     

Measurement of H'(0.07) using the plastic scintillation pulse height weighting integration method

The pulse height weighting integration method for measuring H'(0.07) using a plastic scintillator has been developed through Monte Carlo simulations and laboratory tests. In order to design an optimal detector configuration, the parameters of input-window thickness and plastic scintillator thickness were investigated by EGS4 for their influences on the energy response for electrons. Based on the calculated deposited spectra in the plastic scintillator for electrons with various incident energies, a weighting function W(E), folded with the deposited energy spectra, was introduced in order to obtain a flat energy response in the low energy range. A constant response within +/-3% was confirmed, by calculation, for electrons with energy >0.15 MeV. In addition, a preliminary experiment was performed using three beta sources (90Sr-90Y, 147Pm, 204Tl) and the energy response within +/-6% for beta rays with the maximum energy >0.22 MeV was obtained. Some factors causing uncertainties in the measurements are also discussed in this article.     

Excitation of Triplet and Septet Levels of MnII during Electron–Atom Collisions

The excitation of triplet and septet levels of a singly charged manganese ion during collisions of electrons with manganese atoms is investigated using the method of extended crossed beams. At the electron energy of 50 eV, 26 excitation cross sections are measured, and 11 optical excitation functions are registered in the range of electron energies from zero to 200 eV. Possible channels of excitation of the triplet and septet levels of MnII are discussed. The obtained results are compared with the data of previous experiments.     

Study of a BGO calorimeter using electron and hadron beams from 1 to 50 GeV

A calorimeter of 25 bismuth germanate (BGO) crystals equipped with silicon photodiode readout has been tested at the CERN SPS in the energy range 1–50 GeV. The response for electrons has been shown to be linear in this energy range and the rms resolution obtained ( ) is approximately 1%, for E > 4 GeV. The electron/pion separation was found to be better than 1:500 in the energy range 1–20 GeV. Data on lateral and longitudinal shower development were compared with the results of a Monte Carlo simulation using the SLAC-EGS program and found to be in good agreement.     

Influence of surface roughness on conversion electron scattering and its effect in CEMS and DCEMS analysis

The effect of surface roughness on the scattering and energy loss of internal conversion electrons has been studied by Monte Carlo simulation. The initial electron energy is 7.3 keV, corresponding to the K-conversion electrons in ⁵⁷Fe CEMS and DCEMS, or to a ⁵⁷Co source. Roughness is modelled by a surface oscillation with amplitudes and wavelengths in the range ～ 10¹–10⁴ Å. Total transmission, angular distributions, energy loss profiles and transmission into restricted energy and angular intervals (DCEMS weight functions) have been simulated, assuming Fe as scattering material. The results show that it may be possible to estimate surface roughness from the energy loss profiles measured at different angles. Conditions for the use of conventional (plane surface) weight functions in ⁵⁷Fe CEMS and DCEMS are obtained.     

Energy dependence of TLD-300 response from 6 keV up to 1250 keV

The energy dependence of the response function S(E), of CaF2:Tm (TLD-300) thermoluminescent material (3.2 x 3.2 x 0.90 mm3 ribbons) was measured from 6 keV up to 1250 keV (60Co) using 55Fe, 137Cs and 60Co gamma ray sources as well as X ray ISO reference beams. To the best knowledge of the authors the data for energies below 45 keV are reported for the first time. The S(E) function was also calculated in the energy range from 1 keV up to 20 MeV and compared with the experimental data relative to the total glow curve. The comparison shows good agreement from 1250 keV down to 40 keV. At lower energy the discrepancy increases. This is interpreted in terms of the X ray attenuation within the thickness of TLD-300. Finally, measurements point out the effects of different reading and annealing treatments on the measured function S(E).     

Photon spectrometry in thermal neutron standard field

An NE213 liquid scintillation counter (5.08 cm in diameter and 5.08 cm long) with an LiF filter was used to measure the energy distribution of photons mixed in a thermal neutron field. The response function matrix of photons in an energy range up to 10 MeV was calculated by the EGS4/PRESTA code and properly folded with a resolution function. Pulse height spectra measured with a set of reference γ-ray sources were compared to the calculated response function and agreed very well for all reference γ-ray sources. The GRAVEL and MIEKE codes from the HEPRO program were used to unfold measured pulse height spectra. Energy distributions obtained by the unfolding were applied to evaluate the effective dose equivalent of photons mixed in a thermal neutron field.     

Monte Carlo simulations of the Galileo energetic particle detector

Monte Carlo radiation transport studies have been performed for the Galileo spacecraft energetic particle detector (EPD) in order to study its response to energetic electrons and protons. Three-dimensional Monte Carlo radiation transport codes, MCNP version 4B (for electrons) and MCNPX version 2.2.3 (for protons), were used throughout the study. The results are presented in the form of “geometric factors” for the high-energy channels studied in this paper: B1, DC2, and DC3 for electrons and B0, DC0, and DC1 for protons. The geometric factor is the energy-dependent detector response function that relates the incident particle fluxes to instrument count rates. The trend of actual data measured by the EPD was successfully reproduced using the geometric factors obtained in this study.     

Thermoelectric power and AC electrical properties of PAN-based carbon fiber composites

The thermoelectric power and AC electrical properties of conductive polymer composites made of polycarbonate filled with randomly distributed PAN-based carbon fibers of different concentration: 0, 5, 10, 18, and 30 wt% were studied. The thermoelectric power was measured as a function of temperature in the frequency range from 200 kHz to 12 MHz. It was found that the observed Seebeck coefficient and thermoelectric activation energy depend on temperature, frequency and fiber concentration. The Seebeck coefficient calculated using the electrical transport theory of semiconductors decreases with both increasing temperature and carbon fiber content. The thermoelectric power results revealed that the composites function electrically as semiconductors. Dielectric constants and AC conductivity were calculated from impedance and phase angle measurements. It was found that both increase with increasing temperature. The activation energy and relaxation time decrease with increasing temperature measured and applied frequency. The thermoelectric power results indicated that electrical conduction in bulk composites is produced from a combination of transport processes involving: electrons, holes, ions and charged impurity motion in addition to protonic migration.     

Monte Carlo simulation of beta radiation response function for semiconductor Si detector

This paper describes the modeling of the Passivated Implanted Planar Silicon (PIPS) detector for the beta particles response function simulations with the MCNP-5 code. The simulated and measured energy response functions were compared and a good agreement was found in the entire range of energies. The verified model of a PIPS detector was applied in a non-destructive method that determines the activity of beta emitters in the sample with a known geometry and atomic number densities. The procedure for the identification of beta emitters in the samples was also described. Finally, the application of the proposed method for the determination of ¹³⁷Cs and ⁹⁰Sr activity in water samples taken from the RA reactor spent fuel storage pools and from the paper filter taken from an air monitor operated during repackaging of spent fuel elements, was presented.     

Estimation of response functions of moderating type neutron detectors by the time-of-flight method combined with a large lead pile

The energy dependent response functions of moderating type neutron detectors having cylindrical polyethylene moderators of 1, 3, 6 and 10 cm thicknesses were determined using the time-of-flight (TOF) technique. By combining the 35 MeV electron linear accelerator with a large lead pile of about 150 t, a pulsed neutron field which is rich in intermediate neutrons was formed and its spectrum at the standard measuring point for the TOF experiment was measured by a Li glass scintillator. In this kind of TOF, the neutron time delay in the polyethylene moderator due to multiple collisions with hydrogen was evaluated by the time dependent neutron transport Monte Carlo code, and compiled to the time response matrix. By using the neutron spectrum at the standard measuring point and the time response matrix, the energy dependent response functions of the moderating type neutron detectors were determined from the measured time spectra for the first time in a considerably wide energy range from a few eV to about 50 keV. The experimental response functions showed good agreement with the calculated results.     

Performance of a BGO calorimeter with photodiode readout and with photomultiplier readout at energies up to 10 GeV

Bismuth germanate (BGO) calorimeter arrays, consisting of up to 12 elements of 30 × 30 × 200 mm³ have been tested at the CERN PS with pions and electrons of up to 10 GeV/c momentum, and at SIN with pions, electrons and protons up to 450 MeV/c. Both photomultiplier (PM) and photodiode (PD) readouts were used. Accurate calibration in the 100 MeV energy range was achieved with stopping protons, stopping pions and minimum ionizing pions. With 212 MeV electrons and PM readout, a time resolution of the BGO signal of 640 ps fwhm has been measured. The energy resolution for electrons above 1 GeV (PD readout) was found to be roughly constant at σ/E ～ 1%. This is consistent with a negligible intrinsic resolution for BGO at these energies, after taking into account shower leakage and PD noise. For electrons of 92 and 200 MeV, we obtained (PM readout) energy resolutions close to the theoretical limit given by photon statistics and shower leakage. The electron/hadron separation was better than 1:500 over the energy range of 0.5 to 10 GeV, and improved to better than 1:1000 after a simple pattern cut. The energy deposition of the e.m. showers, both laterally and longitudinally (rear leakage), was found to be in agreement at the 0.1% level with Monte Carlo calculations using the SLAC-EGS program.     

Measurements of the response functions of a large size NE213 organic liquid scintillator for neutrons up to 800 MeV

The response functions of 25.4 cm (length) x 25.4 cm (diameter) NE213 organic liquid scintillator have been measured for neutrons in the energy range from 20 to 800 MeV at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) and at the Research Center for Nuclear Physics (RCNP) of Osaka University. At HIMAC, white (continuous) energy spectrum neutrons were produced by the 400 MeV per nucleon carbon ion bombardment on a thick graphite target, whose energy spectrum has already been measured by Kurosawa et al., [Nucl. Sci. Eng. 132, 30 (1999)] and the response functions of the time-of-flight-gated monoenergetic neutrons in a wide energy range from 20 to 800 MeV were simultaneously measured. At RCNP, the quasi-monoenergetic neutrons were produced via 7Li(p,n)7Be reaction by 250 MeV proton beam bombardment on a thin 7Li target, and the TOF-gated 245 MeV peak neutrons were measured. The absolute peak neutron yield was obtained by the measurement of 478 keV gamma rays from the 7Be nuclei produced in a Li target. The measured results show that the response functions for monoenergetic neutrons < 250 MeV have a recoil proton plateau and an edge around the maximum light output, which increases with increasing incident neutron energy, on the other hand > 250 MeV, the plateau and the edge become unclear because the proton range becomes longer than the detector size and the escaping protons increase. It can be found that the efficiency of the 24.5 cm (diameter) x 25.4 cm (length) NE213 for the 250 MeV neutrons is -10 times larger than the 12.7 cm (length) x 12.7 cm (diameter) NE213, which is widely used as a neutron spectrometer.     

A model for energy loss and straggling of slow ions in electron gas with intraband exchange

Influence of ferro-paramagnetic phase transition on the electronic energy loss and the straggling of ions in the electron gas subjected to magnetic ordering is reported. The linear response (LR) theory was used in application to low velocity ions. The medium was described by the Lindhard dielectric function ε(k,ω). The magnetic interactions were included in the model by means of the Stoner treatment of itinerant electrons. The intraband exchange interaction was shown to shift the energy levels, change degeneracy, shift the Fermi level and thus contribute to the change of electron gas stopping characteristics. Results of the calculations were critically compared to change of stopping at the Curie temperature measured for Ni and Gd foils in transmission experiments.     

Characterization of liquid scintillation detectors

Five scintillation detectors of different scintillator size and type were characterized. The pulse height scale was calibrated in terms of electron light output units using photon sources. The response functions for time-of-flight (TOF)-selected monoenergetic neutrons were experimentally determined and also simulated with the NRESP code over a wide energy range. A comparison of the measured and calculated response functions allows individual characteristics of the detectors to be determined and the response matrix to be reliably derived. Various applications are discussed.     

Surface excitation parameter for electrons crossing the AlN surface

Fast electrons crossing a solid surface induce surface excitations. The total probability of such excitations for electrons moving outside the solid, i.e. in vacuum, is characterized by the surface excitation parameter (SEP). In the present work, the SEP was calculated for either incident or escaping electrons with normal or glancing crossing angles over the surface of aluminum nitride (AlN), a wide-band-gap semiconductor. These calculations were performed based on the dielectric response theory using the sum-rule-constrained extended Drude dielectric function with parameters obtained from a fit of this function to experimental optical data and electron energy-loss data. Dependences of the SEP on electron energy and crossing angle were analyzed. A simple formula was proposed for the fitting of SEP as a function of electron energy and crossing angle.     

Electron detection with a dual-readout calorimeter

Electromagnetic shower development in a copper-based fiber calorimeter is studied by simultaneously measuring the scintillation light and the Cherenkov light generated in this process. We report on the energy resolution, the signal linearity and the dependence of the response function on the impact point and the angle of incidence.The electrons range in energy from 8 to 200 GeV. Differences observed between the results from the two types of signals are presented and interpreted.