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Abstract: A solid state heterojunction diode based on a micrometer thick n-Mg2B14 on p-type Si substrates, deposited by laser ablation, was demonstrated as thermal neutron detector. The neutron signal from a thermal neutron source with 105 ns−1 cm−2 from a spallation beam and moderated Cf-252 source producing 5 thermal n/s was registered at reverse bias of 20V and 10μs shaping time, with the diode detector cooled to temperature ranging to liquid nitrogen boiling point to reduce thermally induced leakage currents. The results were consistent with simulated neutron capture efficiencies considering material imperfections. Simulations also showed detector performance and enhancement of the efficiency with increasing boride thickness and using enriched boron. For a 10μm enriched in B-10 Mg2B14 detector, efficiencies in excess of 30% may be possible, with a high gamma–neutron discrimination level. [Copyright &y& Elsevier]

Abstract: Complementary metal-oxide-semiconductors (CMOS) active pixel sensors (APS) have been introduced recently in many scientific applications. This work reports on the performance (in terms of signal and noise transfer) of an X-ray detector that uses a novel CMOS APS which was developed for medical X-ray imaging applications. For a full evaluation of the detector''s performance, electro-optical and X-ray characterizations were carried out. The former included measuring read noise, full well capacity and dynamic range. The latter, which included measuring X-ray sensitivity, presampling modulation transfer function (pMTF), noise power spectrum (NPS) and the resulting detective quantum efficiency (DQE), was assessed under three beam qualities (28kV, 50kV (RQA3) and 70kV (RQA5) using W/Al) all in accordance with the IEC standard. The detector features an in-pixel option for switching the full well capacity between two distinct modes, high full well (HFW) and low full well (LFW). Two structured CsI:Tl scintillators of different thickness (a “thin” one for high resolution and a thicker one for high light efficiency) were optically coupled to the sensor array to optimize the performance of the system for different medical applications. The electro-optical performance evaluation of the sensor results in relatively high read noise (∼360 e−), high full well capacity (∼1.5×106 e−) and wide dynamic range (∼73dB) under HFW mode operation. When the LFW mode is used, the read noise is lower (∼165) at the expense of a reduced full well capacity (∼0.5×106 e−) and dynamic range (∼69dB). The maximum DQE values at low frequencies (i.e. 0.5lp/mm) are high for both HFW (0.69 for 28kV, 0.71 for 50kV and 0.75 for 70kV) and LFW (0.69 for 28kV and 0.7 for 50kV) modes. The X-ray performance of the studied detector compares well to that of other mammography and general radiography systems, obtained under similar experimental conditions. This demonstrates the suitability of the detector for both mammography and general radiography, with the use of appropriate scintillators. The high DQE values obtained under low mammographic exposures (up to 0.65 for 22.3μGy) matches the demand for high detectability in imaging of the dense breast. [Copyright &y& Elsevier]

Abstract: Energy dispersive X-ray diffraction is proposed as a suitable non-destructive method to rapidly identify illicit drugs in parcels. A preliminary data set of 7 illicit drug samples and a possible cutting agent has been collected with a range of count times using a tungsten target X-ray source, a high resolution HpGe detector and a variable geometry diffraction cell. These results have been used to calibrate and train multivariate analysis software to predict the drug content in previously unseen spectra. [Copyright &y& Elsevier]