X-ray Spectrum Reconstruction by Diamond Detectors with Linear Response to Dose Rate

The absorbers method is here applied by interposing filters of variable thickness between the X-ray source and a detector so to attenuate the radiation intensity by using the attenuation coefficient as a selective photon energy operator. The analysis of the signal provided by a polycrystalline diamond thin film detector exposed to the energy-selectively-attenuated X-ray beam was used for the reconstruction of the radiation spectrum. The 50 μm thick diamond detector achieves conditions of linear response to the dose rate of the incident radiation (linearity coefficient of 0.997 ± 0.003) for a bias voltage ≥90 V, corresponding to an electric field ≥1.8 × 104 V/cm. Once the absorbers method is applied, only the detector signal linearity to dose rate allows reconstructing the source X-ray bremsstrahlung spectrum with sufficiently high accuracy.

Effect of Coulomb Focusing on the Electron–Atom Bremsstrahlung Cross Section for Tungsten and Iron in Nonthermal Lorentzian Plasmas

The Coulomb focusing effect on the electron–atom bremsstrahlung spectrum is investigated in nonthermal Lorentzian plasmas. The universal expression of the cross section of nonrelativistic electron–atom bremsstrahlung process is obtained by the solution of the Thomas-Fermi equation with the effective atomic charge. The effective Coulomb focusing for the electron–atom bremsstrahlung cross section near the threshold domain is also investigated by adopting the modified Elwert-Sommerfeld factor with the mean effective charge for the bremsstrahlung process. In addition, the bremsstrahlung emission rates are obtained by considering encounters between nonthermal electrons and atoms such as Fe and W atoms. We found that the bremsstrahlung emission rates for nonthermal electron–atoms are lower than those for thermal plasmas. Various nonthermal effects on the bremsstrahlung emission rates in Lorentzian plasmas are also discussed.

X-ray: An Effective Photon

Following years of discussion and debate regarding the economics of X-ray radiation for sterilization of healthcare products, the benefits of the technology are now being realized. X-ray, like gamma radiation, is a process whereby energic photons penetrate to sterilize medical devices. Compared to gamma, photons in the bremsstrahlung spectrum from X-ray radiation allow for improved dose uniformity ratio, higher dose rates, and shorter process time, which provide additional opportunities for sterilization process enhancement. Such improvements may be realized in a number of ways: 1) economic, where more products may be processed on a carrier; 2) improved dose range fit; and/or 3) wider material compatibility. Despite noted benefits, X-ray sterilization has not yet been widely accepted and currently accounts for less than 5% of the contract sterilization market. This article brings X-ray sterilization into focus by sharing knowledge and experience gained over the past 10 years at the STERIS Däniken site, with an aim to identify opportunities for future medical device sterilization.

CROSS-SECTIONS FOR PHOTONUCLEAR REACTIONS 93Nb(γ,n)92mNb AND 93Nb(γ,n)92tNb IN THE END-POINT BREMSSTRAHLUNG ENERGIES 36...91 MeV

The flux-weighted averaged over the energy range of bremsstrahlung spectrum from reaction threshold up to the maximum energy of γ-ray cross-sections <σ(E)> of the 93Nb(γ,n)92mNb and 93Nb(γ,n)92tNb photonuclear reactions were determined by the gamma-activation method within the end-point bremsstrahlung energies Еmax = 36…91 MeV. Activation of 93Nb targets has been done by a bremsstrahlung flux using an electron beam at the linear accelerator LUE-40 at RDC "Accelerator" NSC KIPT. The γ-ray spectra of irradiated targets were registered using the HPGe detector with an energy resolution of 1.8 keV for the 1332 keV line 60Co. To control the bremsstrahlung flux we used natMo witness-targets and a reaction cross-section of 100Mo(γ,n)99Mo. Obtained experimental cross-sections <σ(E)> of the studied reactions are in good agreement with the theoretical values calculated within TALYS 1.9 code and the results of other authors. The averaged cross-sections <σ(E)> of the 93Nb(γ,n)92mNb and 93Nb(γ,n)92tNb reactions in the energy range 35...45 MeV and > 70 MeV were obtained for the first time.

Перспективы использования рентгеновских трубок с автоэмиссионным катодом и "прострельным" анодом в диапазоне мягкого рентгеновского излучения

The use of field emission cathodes in the design of x-ray tubes requires the placement of a cathode assembly with a small distance from the anode, complicating the output of radiation. Most acute this problem occurs when generating a relatively soft spectrum with wavelengths of 1-10 nm: in this case, the accelerating voltage does not exceed several kilovolts, and the inter-electrode distance composes several hundred micrometers. In this work, we experimentally demonstrated the applicability of beryllium-based submicron films as “shot-through” anodes for generating the Be K line ( = 11.4 nm) and the associated bremsstrahlung spectrum. In particular, the characteristic radiation of a tube with a field emission blade cathode and a Be film anode was recorded within the scheme of a grazing incidence grating spectrometer. The characteristics of beryllium films necessary for the development of X-ray tubes of this type with a higher output power are determined.

Isomer ratios for products of photonuclear reactions on Rh

Over the past several years various preequilibrium models for nuclear reaction mechanisms description were developed. Diversified detailed experimental data in the medium excitation energy region for nuclei are needed for reasonable selection among these theoretical models. Lack of experimental data in this energy region does essentially limit the possibilities for analysis and comparison of different preequilibrium theoretical models. For photonuclear reactions this energy range covers 30-100 MeV. Experimental measurements and estimations of isomer ratios for products of photonuclear reactions with multiple particle escape on antimony were performed using bremsstrahlung spectrum as projectile with end-point energies 74,9 and 85,7 MeV. Method of the induced activity measurement was applied. For acquisition of gamma spectra we used HPGe spectrometer with 20% relative efficiency. Linear accelerator of electrons LU-40 was a source of bremsstrahlung. Energy resolution of electron beam was about 1% and a mean electron current varied within (3.8 - 5.3)μA.

The Ratio between Absorbed Dose, Kerma and Ionization Kerma for Small-size Fields

Purpose: Research of the relationships between spatial distributions in water of the main dosimetric values, namely the absorbed dose, kerma and ionization kerma, for small-size fields with a circular cross section created by divergent beams of bremsstrahlung spectrum with a maximum energy of 6 MeV. Material and methods: Using the Monte-Carlo method with the codes EGSnrc and MCNP4C2, calculations were carried out for these distributions in a water phantom for beam radii on the phantom surface from 0.1 to 3.0 cm and for depths up to 40 cm. The ratio at depths up to 5 cm, where there is a so-called build-up area, is studied in particular detail. Results: The results of calculations show that the ratio of ionization kerma to kerma for such beams at depths up to 40 cm is practically constant and equal to 0.9930 ± 0.0005. The ratio of the absorbed dose to the ionization kerma, in contrast to conventional square beams with a cross-sectional area  20 cm2, is much less than unity at radii of 1 cm at all the depths considered. Conclusion: The data obtained show that the relationship between absorbed dose, kerma and ionization kerma for photon fields produced by beams of small cross sections is very different from that for traditional beams. This circumstance should be taken into account when conducting dosimetry of small fields.