Sture Petersson

Highly sensitive silicon detectors of thermal neutrons

Planar semiconductor diodes supplemented with a layer of an appropriate neutron converter such as 6LiF can be used for thermal neutron counting or imaging. Neutrons interacting in the converter generate alphas and tritons which enter the semiconductor and are detected there. However, simple planar devices suffer from limited detection efficiency which cannot reach more than about 5%. The limit in detection efficiency can be overcome by etching a 3D microstructure of trenches, pores or columns in the detector and filling it with the neutron converter. The overall neutron detection efficiency of such structure with pores was simulated. The results indicate an increase in the detection efficiency by factor of 6 in comparison with a standard planar neutron detector. Samples with different silicon column sizes were fabricated to study the electrical properties of 3D structures. The charge collection efficiency in silicon columns from 10 mum to 800 mum wide and 80 mum high was measured. Single pad detectors with pores were also fabricated and tested for thermal neutron detection. The samples have square pores of 20 mum wide, ~60 mum deep. The pore pitch is 70 mum. 6LiF was used as the neutron converter in all cases. Pulse height spectra of the filled samples irradiated by thermal neutrons were measured. The measurement proved functionality of such detectors and its usability for thermal neutron detection.

A CMOS APS for dental X-ray imaging using scintillating sensors

In this paper we present an integrating CMOS Active Pixel Sensor (APS) circuit to be used with scintillator type X-ray sensors for intra oral dental X-ray imaging systems. Different pixel architect ...

Silicon sensors with pyramidal structures for neutron imaging

Neutron detection is a valuable tool in nuclear science research, homeland security, quality assurance in nuclear plants and medical applications. Recent developments and near future instrumentations in neutron imaging have a need for sensors with high spatial resolution, dynamic range, sensitivity and background discrimination. Silicon based neutron detectors can potentially fulfil these requirements. In this work, pad and pixel detectors with pyramidal micro-structures have been successfully fabricated that should have an improved detection efficiency when compared to conventional planar devices. Titanium di-boride (TiB2) and lithium fluoride (LiF) were deposited as the neutron converters. Excellent electrical performances were measured on both simple pad and pixel detectors. A selection of pad detectors was examined by alpha spectroscopy. Measurement with thermal neutrons from a 241Am-Be source shows an improvement in relative efficiency of up to 38% when compared to conventional planar devices.

An optimized system for measurement of radon levels in buildings by spectroscopic measurement of radon progeny

Radon gas, 222Rn, is a problem in many buildings. The radon gas is not harmful in itself, but the decay chain contains charged elements such as 218Po, and 214Po ions which have a tendency to stick to the lungs when inhaled. Alpha particles from the decay of these ions cause damages to the lungs and increase the risk of lung cancer. The recent reduction in the limits for radon levels in buildings call for new simple and efficient measurement tools [1]. The system has been optimized through modifications of the detector size, changes to the filters and the design of the chamber. These changes increase the electric field in the chamber and the detection efficiency.

An integrating CMOS APS for X-ray imaging with an in-pixel preamplifier

We present in this paper an integrating CMOS Active Pixel Sensor (APS) circuit coated with scintillator type sensors for intra-oral dental X-ray imaging systems. The photosensing element in the pix ...

Measurement of radon levels in buildings by spectroscopic measurement of radon progeny

A fast, simple and low cost system for measuring radon levels by spectroscopic measurement of radon progeny has been developed. A spectrum with energy resolution of the decays from 218Po and 214Po is provided. The fast measurement makes it possible to control ventilation to keep the radon level below the limit without excess energy loss due to over ventilation.

Silicon Detectors for Neutron Imaging

Semiconductor silicon detectors are used in many applications for detection and imaging of ionizing radiation. Detection of neutrons is also possible with these devices. However, the silicon detectors must be adapted for the thermal neutron detection and imaging. The devices must be supplemented with a material which “converts” neutrons into a radiation detectable directly in the semiconductor detector. The principle of the thermal neutron detection with semiconductor silicon detectors is explained. Advantages of such detectors are shown as well as their limitations. The way of the detector improvement using 3D detector technologies is described. The 3D detector properties were simulated; real 3D structures were fabricated and successfully tested with a beam of thermal neutrons, finally. The functionality of these devices was proved.

Development of neutron image sensor technology for AD-BANG project

A demonstrator of the portable position sensitive neutron detecting device for neutron imaging in a mixed radiation field is presented. A detector of the device is based on multilayer perpendicularly crossed strip sensors interlaced with neutron converter. A 6LiF converter producing energetic alpha particles and tritons is used. The converter permits precise determination of a position of the neutron interaction even in a radiation fields with a high gamma background. The neutron detection efficiency is increased with a 3D structured surface of the multilayer silicon strip sensor. The demonstrator is comprised of the neutron sensitive multilayer silicon strip detector, a 128 channel general purpose charge sensitive amplifier ASICs IDEAS VATAGP8 with nominal dynamic range of +/− 250 fC, a 13 bit analogue to digital conversion and an FPGA control. Basic characteristics of the amplifier like amplifier linearity probed with an external charge generator is shown. Moreover, results of experimental tests of the demonstrator with alpha, beta, gamma sources and neutrons is demonstrated. The device may be used for neutron imaging via position sensitive detection of particular neutrons on the basis of coincidence detection of neutron conversion products or on the basis of response comparison of individual strips. An effect of charge sharing between individual strips on position resolution will be elaborately discussed.