More than 80 years have passed since the first calculations of electron-nucleus bremsstrahlung cross sections were published by Sommerfeld, for non-relativistic electrons, and, independently, by ...Sauter, Bethe and Heitler, and Racah, for relativistic electrons. The Bethe-Heitler expression, that is based on the first Born approximation and includes the screening of the Coulomb field of the nucleus by the atomic electrons, has proven to work well at moderately high energies where the Landau-Pomeranchuk-Migdal effect is negligible. We review the current theoretical and experimental status with a highlight on electrons with kinetic energies between 1 and 10 MeV. The choice is motivated by the peculiar difficulties present in this energy region, where it is necessary to treat simultaneously the interaction with the Coulomb field beyond the first Born approximation and the effect of screening. A fully numerical approach within the S-matrix formalism has proven to be extremely difficult above a few MeV, because the number of partial waves needed for an accurate evaluation is prohibitively large. Here we focus on analytic results, including the more complex ones employing the Furry-Sommerfeld-Maue wave functions and taking into account the next-to-leading order, and discuss the advantages and limitations in light of the best available data. The influence of multiple scattering in the target is investigated under the actual experimental conditions. A comparison with the widely used cross section tabulations by Seltzer and Berger is also presented.
Bremsstrahlung spectra below 250 MeV have been measured colliding 500 MeV–electrons with Cu, Ag, and Au targets. The experimental intensity ratios relative to Cu are well described by an accurate ...analytical high-energy theory, which accounts both for Coulomb distortion and screening. This represents the first experimental verification of the discovery by Bethe-Maximon that leading-order quantum mechanical calculations, equivalent to quasiclassical approximations, become exact at high energies and small angles. It also shows that radiative QED effects play a minor role in the covered part of the spectral distribution within the accuracy (1.6%) of the present measurements.
Thunderstorms emit terrestrial gamma-ray flashes with photon energies of up to tens of MeV and electron-positron beams that are created by photons with energies above 1.022 MeV. These photons are ...produced through the bremsstrahlung process when energetic electrons collide with air molecules. However, presently used cross sections for bremsstrahlung treat only the interaction of the electrons with the nuclei of molecules while we here include their interaction with shell electrons. We simulate the production of energetic photons by a negative stepped lightning leader, and we find that electron-electron bremsstrahlung contributes significantly, although the direct photon emission is less than from electron-nucleus bremsstrahlung. However, electron-electron bremsstrahlung also ejects shell electrons and therefore feeds the electron population above 1 MeV significantly. We find that it hence dominates the photon spectrum of the stepped lightning leader at 10 MeV.
A quantitative understanding of bremsstrahlung by electrons in the screened field of atomic nuclei has been developed by several researchers over the last 80 years. However, some ranges of the ...possible parameters can still not be covered with good accuracy. Dirac partial-wave calculations are the best method developed to date, while analytic calculations are the only viable solution at high impinging electron energies. Recent progresses on both fronts will be discussed. In particular, state of the art partial wave results, including screening, allowed to test the Olsen–Maximon–Wergeland additivity rule discovered by analytic means. Closed expressions for the next-to-leading order corrections to the Furry–Sommerfeld–Maue wave functions are known. One next-to-next-to-leading order term is typically included in this type of approach. The effect of this extra term on the angular dependence of the double differential cross sections for photon emission by 2.5 MeV electrons is compared in detail with partial wave calculations which are exact at all orders.
•Dirac partial-wave results are used as reference.•The screening correction to nuclear bremsstrahlung is investigated.•The Furry-Sommerfeld-Maue wave functions are employed.•Analytic higher order corrections are studied.
Tissue-equivalent gases (TEGs), often made of a hydrocarbon, nitrogen, and carbon dioxide, have been employed in microdosimetry for decades. However, data on the first Townsend ionization coefficient ...(α) in such mixtures are scarce, regardless of the chosen hydrocarbon. In this context, measurements of α in a methane-based tissue-equivalent gas (CH4 – 64.4%, CO2 – 32.4%, and N2 – 3.2%) were performed in a uniform field configuration for density-normalized electric fields (E/N) up to 290Td. The setup adopted in our previous works was improved for operating at low pressures. The modifications introduced in the apparatus and the experimental technique were validated by comparing our results of the first Townsend ionization coefficient in nitrogen, carbon dioxide, and methane with those from the literature and Magboltz simulations. The behavior of α in the methane-based TEG was consistent with that observed for pure methane. All the experimental results are included in tabular form in the Supplementary material.
Commercial PIN photodiodes, repurposed as particle detectors, have received a lot of attention along the past decades because they can offer a low-cost solution suitable for several applications. The ...BPX-65 photodiode has been chosen because of its interesting features for measuring electrons in a harsh radiation environment close to the beam of an accelerator. Its electrical characterisation and its application to photon spectrometry have been presented in the companion paper I. Here, its response function (RF) to electrons is investigated using the beam from an electron accelerator with a small energy spread. The empirical expressions for the RF available in the literature have been improved, simplified, and combined to obtain a final form with 7 free parameters: 4 non-linear and 3 linear. A special fitting procedure, which takes advantage of the presence of the linear parameters, is described. The behaviour of these parameters with beam energy and bias is investigated to uncover the physical origin of the three components included in the proposed RF. The interpretation of the features of the spectra is confirmed by Monte Carlo simulations carried out employing the general-purpose PENELOPE/penEasy package. To take into account the charge-collection properties of the device, a simple model has been implemented and is compared to data. It has then been possible to estimate the thickness of the partially dead layer from the experiment.
Silicon PIN (p-type-intrinsic-n-type) photodiodes are well suited as particle detectors. Here the interest is on a low-cost solution by repurposing a commercial device meant to be used as a light ...sensor. The intended application is to measure the energy spectra of electrons scattered by thin metallic foils covering small angles close to the beam of the accelerator. The main requirements for a suitable device are: 1) a low-cost solution to allow frequent replacements; 2) a small size to avoid as much as possible an unused area that contributes with unnecessary capacitance; 3) a good energy resolution; and 4) an easy repurposing as a charged-particle detector. The photodiode type BPX 65 manufactured by Osram® fulfils well these requirements. Four samples of these commercial devices have been electrically characterised with respect to reverse current and depleted-region capacitance. At the selected working point of 18 V, comfortably below the maximum rating of 20 V recommended by the manufacturer for continuous operation, the total thickness of the depleted and intrinsic regions is estimated to be (60±3) μm. For the four samples considered, the measured reverse currents for a reverse bias of 18 V are around 0.1 nA, well below the typical value specified by the manufacturer (1 nA). To evaluate the performance of the device as a detector, energy spectra have been acquired for γ-rays with energies from 10 to 140 keV using 241Am, 133Ba, and 57Co radioactive sources. The resolution of the BPX 65 encountered with the γ-rays emitted by 241Am at 59.5-keV is ≈2.5 keV (FWHM - Full Width at Half Maximum), which is close to the value obtained with a pulser, showing that its main limitation is the electronic chain employed in the setup. The response function to monoenergetic electrons in the same energy range is studied in the companion paper.
•A commercial PIN photodiode type BPX 65 has been repurposed as a particle detector.•An electrical characterisation of the device has been done.•The thickness of the depleted and intrinsic regions has been determined.•Spectra from radioactive sources have been acquired and analysed.•The energy resolution is 2.5 keV (FWHM) dominated by electronic noise.
The results of an experimental feasibility study of a position sensitive thermal neutron detector based on a resistive plate chamber (RPC) are presented. The detector prototype features a thin-gap ...(0.35 mm) hybrid RPC with an aluminium cathode and a float glass anode. The cathode is lined with a 2 μm thick 10B4C neutron converter enriched in 10B. A detection efficiency of 6.2% is measured at the neutron beam (λ=2.5 Å) for normal incidence. A spatial resolution better than 0.5 mm FWHM is demonstrated.
The dosimetric response of silicon diodes produced with distinct engineering technologies, Magnetic Czochralski (MCz), and standard Float Zone (Fz), has been investigated, aiming at their use for ...online dosimeters in gamma radiation processing applications. The p
+
-n-n
+
junction diodes, 300 µm thick with an active area of 25 mm
2
, are operated as online radiation dosimeters in the short-circuit current mode. In this case, the key dosimetric quantity is the dose rate, which is correlated with the output current from the diode subjected to radiation. Thus, the dose is obtained offline by the integration of the corresponding current signal. The irradiations are performed with an industrial Gammacell
60
Co facility at 2.3–2.44 kGy/h covering doses up to 275 kGy. Under continuous irradiation, both diodes delivered current signals whose intensities decreased with accumulated doses. Mitigation of this decay has been accomplished by pre-irradiating the devices to 700 kGy. Polynomial functions best represent the dose responses for either pristine or preirradiated diodes. The relevant dosimetric parameters as response stability, charge sensitivity, and repeatability of current signals (<5%) reveal the better performance of the MCz diode. It is important to note that the whole dataset fully complies with the international standard protocols for routine dosimeters in radiation processing dosimetry. Regarding radiation damage, which in unbiased diodes manifests primarily in the decay of current sensitivity, the results also showed greater tolerance of the MCz diode. Based on these studies, large availability, and better cost-effectiveness, it is possible to endorse the potential use of MCz devices as online routine dosimeters in radiation processing applications. However, the data reproducibility with the accumulated dose, the dose lifespan, and the effect of the irradiation conditions (e.g., temperature, relative humidity, and dose fractionating) remain to be investigated. Works in this direction are currently in progress.
When an ultrarelativistic electron traverses two closely spaced foils, a radiation spectrum ‘resonance’ appears, arising from the photon formation length extending from one foil, across the gap and ...into the second foil. Several theoretical approaches yield quite different answers to the spectral location of this ‘resonance’, and we have therefore in the CERN NA63 collaboration addressed the question experimentally with a 178 GeV electron beam. The experimental technique used – where a variable gap separates two thin gold foils – allows for a direct measurement of a length that is closely related to the distance over which the photon formation takes place. These are the first measurements to observe the gap dependence of the energy of the ‘resonance’ in the radiation spectrum from a structured target on a truly macroscopic scale up to 0.5 mm. The results are compared with the theory of Baier and Katkov, with both the modified and unmodified theories of Blankenbecler as well as with a naïve, straightforward expectation. Surprisingly, the experiment shows a clear preference for the two latter, comparatively unsophisticated, approaches.
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