Properties Of Radiation Detectors Research Articles

Neutron detection using boron gallium nitride semiconductor material

In this study, we developed a new neutron-detection device using a boron gallium nitride (BGaN) semiconductor in which the B atom acts as a neutron converter. BGaN and gallium nitride (GaN) samples were grown by metal organic vapor phase epitaxy, and their radiation detection properties were evaluated. GaN exhibited good sensitivity to α-rays but poor sensitivity to γ-rays. Moreover, we confirmed that electrons were generated in the depletion layer under neutron irradiation. This resulted in a neutron-detection signal after α-rays were generated by the capture of neutrons by the B atoms. These results prove that BGaN is useful as a neutron-detecting semiconductor material.

The role of activator concentration and precipitate formation on optical and dosimetric properties of KCl:Eu2+ storage phosphor detectors

The activator ion (Eu(2+) in KCl:Eu(2+)) plays an important role in the photostimulated luminescence (PSL) mechanism of storage phosphor radiation detectors. In order to design an accurate, effective, and robust detector, it is important to understand how the activator ion concentration affects the structure and, consequently, radiation detection properties of KCl:Eu(2+). Potassium chloride pellets were fabricated with various amounts of europium dopant (0.01-5.0 mol.% Eu(2+)). Clinical radiation doses were given with a 6 MV linear accelerator. Radiation doses larger than 100 Gy were given with a (137)Cs irradiator. Dose response curves, radiation hardness, and temporal signal stability were measured using a laboratory PSL readout system. The crystal structure of the material was studied using x ray diffraction and luminescence spectroscopy. The most intense PSL signal was from samples with 1.0 mol.% Eu. However, samples with concentrations higher than 0.05 mol.% Eu exhibited significant degradation in PSL intensity for cumulated doses larger than 3000 Gy. Structural and luminescence spectroscopy showed clear evidence of precipitate phases within the KCl lattice, especially for high activator concentrations. Analysis of PL emission spectra showed that interactions between Eu-Vc dipoles and Eu-Vc trimers could explain trends in PSL sensitivity and radiation hardness observations. The concentration of the activator ion (Eu(2+)) significantly affects radiation detection properties of the storage phosphor KCl:Eu(2+). An activator concentration between 0.01 and 0.05 mol.% Eu in KCl:Eu(2+) storage phosphor detectors is recommended for linear dose response, good PSL sensitivity, predictable temporal stability, and high reusability for megavoltage radiation detection.

Lanthanum halide nanoparticle scintillators for nuclear radiation detection

Nanoparticles with sizes <10 nm were fabricated and characterized for their nanocomposite radiation detector properties. This work investigated the properties of several nanostructured radiation scintillators, in order to determine the viability of using scintillators employing nanostructured lanthanum trifluoride. Preliminary results of this investigation are consistent with the idea that these materials have an intrinsic response to nuclear radiation that may be correlated to the energy of the incident radiation.

Fabrication and Characterization of MOVPE-Grown CdTe-on-Si Heterojunction Diode-Type Gamma-Ray Detectors

We report on the growth of very thick (>260 μm) high-crystalline-quality single-crystal CdTe epitaxial films on (211) Si substrates in a metalorganic vapor-phase epitaxy reactor, and the development of gamma ray detectors and their radiation detection properties. Films were grown with a high growth rate varying from 40 μm/h to 70 μm/h. A heterojunction diode was fabricated by growing a 90-μm-thick CdTe layer on an n+-Si substrate, which exhibited good rectifying behavior and had a low reverse bias leakage current of 0.18 μA/cm2 at 100 V bias. The diode clearly demonstrated its gamma radiation detection capability by resolving energy peaks from the 241Am radioisotope during room-temperature measurements. By cooling the diode detector to −30°C, the leakage current could be reduced by three orders of magnitude from the room-temperature value. At this operating condition dramatic improvements in the pulse height spectrum were observed.

A synthetic diamond probe for low-energy X-ray dose measurements

The desirable physical properties of diamond have made the mineral a choice material in radiation measurements. Diamond detectors are currently used extensively in high-energy physics. Their use for low-energy beams such as, for example, in mammography X-ray beams however, has not been fully investigated. This paper describes a diamond probe which has been constructed for the evaluation, as the radiation sensing material, of polycrystalline synthetic diamonds produced by chemical vapour deposition (CVD). The specimens were fabricated in wafer form and so the exposure orientation geometry of the diamond wafers, to give optimum absorption of the incident X-ray beam, was also investigated both experimentally and theoretically. The samples were characterized to obtain information regarding the elemental impurity levels, especially nitrogen, and consequently to establish the material quality. Nitrogen impurities and concentration levels in the diamond lattice have been shown to have a profound effect on the radiation detection properties of diamond. The probe described has the diamond surfaces metallized with titanium, platinum and gold to provide ohmic contacts. The probe was connected independently to both Wellhöfer Dosimetrie (model CU 500) and PTW Unidos E commercial electrometers. In all of the measurements, the incident radiation beam was normal to the edge of the diamond wafer to optimize absorption of the X-ray beam after establishing that this orientation was the optimum geometry. The results of the study are presented in both tabular and graphical forms.

Organic Semiconductors for Detection of Ionizing Radiation

AbstractOrganic semiconductors are increasingly common in electronics and sensors, and are now under investigation for a novel type of radiation sensors at Sandia National Laboratories. This class of materials can offer wide band gaps, high resistivities, low dielectric constants, and high dielectric strengths, suggesting they may be suitable for solid-state particle counting detectors. A range of solution cast materials have been evaluated for this application, primarily in the family of poly(p-phenylene vinylene)s, or PPVs. The high ratio of hydrogen to carbon offers neutron sensitivity, while the low Z material provides some natural gamma discrimination. Compared to existing detectors, these materials could potentially offer large-scale radiation detection at a substantially reduced cost.While PPVs hold promise for radiation detection, the mechanical and electrical properties must be optimized and the processing effects understood. Polymers can offer significantly simplified processing compared to the more common crystals used in solid state detection, which can be size limited and fragile. However, organic semiconductors are very sensitive to processing conditions, and mobility can be affected by orders of magnitude by processing variables, without altering any chemistry. Additives can also have dramatic effects on both electrical and mechanical properties. We report on nanoparticle additives that cause an increase in photoresponse of approximately three orders of magnitude as compared to a polymer film without additives. We separately show an order of magnitude increase in photoresponse by exposing the polymer/fullerene composite to sub-bandgap light.Future work will analyze the feasibility of single particle detection and various geometries for optimization. Additional processing variables will also be investigated for further improvement of mobility and reduction of trap density.

Influence of irradiation by 24 GeV protons on the properties of 4H–SiC radiation detectors

We had investigated the effects of the irradiation by 24 GeV protons with the doses from 10 13 cm − 2 up to 10 16 cm − 2 on the properties of radiation detectors fabricated as Schottky diodes on 4H–SiC. Numbers and activities of radionuclides and isotopes produced after the irradiation were analysed. Activities of 7Be and 22Na were found to be proportional to the irradiation dose and ranged from 1.3 up to 890 Bq and from 1.9 up to 950 Bq, respectively. The total amount of formed stable isotopes was from 1.2 × 10 11 cm − 2 up to 5.9 × 10 13 cm − 2 . 390 days after the irradiation the number of radiated electrons with different energies ranged from 1.0 up to 600 per second, respectively. The contact properties were investigated by means of the current–voltage analysis. At lower irradiation doses a slight decrease of the effective potential barrier height from about 0.74 eV down to < 0.7 eV took place. The reverse current of the diodes grew by up to one order of magnitude. At the doses above 3 × 10 15 cm − 2 opposite changes were observed. Irradiation by up to 1 × 10 16 protons/cm − 2 , resulted in the increase of the potential barrier height up to ∼ 0.85 eV, followed by the drop of the reverse current by up to two orders of magnitude. The observed effects were explained by the appearance of the disordered material structure because of the high-energy particle bombardment.

Radiation Detection Properties of 4H-SiC Schottky Diodes Irradiated Up to$10^16$n/cm$^2$by 1 MeV Neutrons

We report the results of an experimental study on the radiation hardness of 4H-SiC diodes used as alpha-particle detectors with 1 MeV neutrons up to a fluence of 8times1015 n/cm2. As the irradiation level approaches the range 1015 n/cm2 , the material behaves as intrinsic due to a very high compensation effect and the diodes are still able to detect with a reasonable good Charge Collection Efficiency (CCE=80%). For fluences >1015 n/cm2 CCE decreases monotonically to ap20% at the highest fluence. Heavily irradiated SiC diodes have been studied by means of Photo Induced Current Transient Spectroscopy (PICTS) technique in order to characterize the electronic levels associated with the irradiation-induced defects. The dominant features of the PICTS spectra occur between 400-700 K; in this temperature range the deep levels associated with the induced defects play the main role in degradation of the CCE. Enthalpy, capture cross-section and concentration of such deep levels were calculated and we found that two deep levels (Et=1.18 eV and Et=1.50 eV) are responsible for the decrease in CCE. They have been associated to an elementary defect involving a carbon vacancy and to a defect complex involving a carbon and a silicon vacancy, respectively

Epitaxial silicon carbide charge particle detectors

The radiation detection properties of Schottky detectors made on epitaxial layers of 4H silicon carbide were evaluated. Exposure to 5.48 MeV alpha particles from a 241 Am source in vacuum led to robust signals from the detectors. The collection of the charge carriers was found to increase linearly with the square root of the applied reverse bias.

Development of a silicon carbide radiation detector

The radiation detection properties of semiconductor detectors made of 4H silicon carbide were evaluated. Both Schottky and p-n junction devices were tested. Exposure to alpha particles from a /sup 238/Pu source led to robust signals from the detectors. The resolution of the Schottky SiC detector was 5.8% (FWHM) at an energy of 294 keV, while that of the p-n junction was 6.6% (FWHM) at 260 keV. No effect of temperature in the range of 22 to 89/spl deg/C was observed on the characteristics of the /sup 238/Pu alpha-induced signal from the SiC detector. In addition, testing in a gamma field of 10,000 rad-Si h/sup -1/ showed that the alpha-induced signal was separable from the gamma signal.

Radiation detector properties of CdTe0.9Se0.1:Cl crystals grown under microgravity in a rotating magnetic field

The influence of growth conditions on radiation detector performance was studied by examining Cd(Te,Se):Cl crystals. They were grown by the travelling heater method under microgravity conditions during the PHOTON 8 mission. An additional forced convection was produced by a rotating magnetic field (400 Hz) of 2 mT. The influence on crystal quality was analyzed by several characterization methods such as time dependent charge measurement, photo-induced current transient spectroscopy and admittance spectroscopy. The charge collection efficiency of detectors was increased from 10% without magnetic field up to 66% by the influence of the rotating magnetic field. The improved detector performance is explained by the increased resistivity and a reduced number of deep levels.

Radiation ionization energy in a-Si:H.

The radiation ionization energy ${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{p}}$, which is the mean energy expended per electron-hole pair generated in a given material by an ionizing radiation, is one of the most important parameters governing the properties of radiation detectors based on this material. Since the advent of semiconductor detectors in the 1950s, a great deal of experimental and theoretical work has been done to determine values of ${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{p}}$ for various crystalline semiconductors. After some review of the theoretical models proposed for crystalline semiconductors, we present a detailed study for an amorphous semiconductor. A microscopic Monte Carlo calculation, taking into account the actual density of states, was performed in a-Si:H to study the energy sharing between ionization and phonon production during hot carrier thermalization. This simulation yields values from 4.3 to 5.0 eV for ${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{p}}$ for reasonable values of the phonon emission mean free path ${\ensuremath{\lambda}}_{\mathit{r}}$ in a-Si:H. This result is in agreement with experimental results of about 4.4 eV and are comparable to 3.63 eV in crystalline silicon, despite the larger 1.7- eV gap. \textcopyright{} 1996 The American Physical Society.

The effects of nitrogen impurity on the radiation detection properties of synthetic diamond

Abstract This contribution examines the influence of nitrogen impurity on the radiation detecting properties of synthetic diamonds. The relatively low sensitivity of the commonly available synthetic diamonds, when used as dosimeters/detectors, is attributed to the presence of nitrogen. A systematic decrease of the nitrogen level shows an increase in the radiation detection sensitivity of these crystals, and below the 25–50 ppm level the increase is even steeper. Experimental evidence strongly suggests that the nitrogen, which is generally accepted to appear in synthetic diamond in dispersed paramagnetic form, not only acts as a radiationless recombination centre for charge carriers (with an estimated hole capture cross section of ≈10−12 cm2), but also affects the amount of traps formed in the synthesis of diamonds. This dual role of nitrogen which is suggested by the accumulated data is found to be consistent with a two-state model that is composed of a trapping and a recombination centre.

Vertical unseeded vapor growth of large CdTe crystals

Single crystals of CdTe were grown by the vertical, unseeded vapor growth technique. The faceted, high quality crystals showed higher purity than the ∼6N source materials. The growth rate was found to be strongly dependent on the excess Te present in the growth charge. A maximum growth rate of about 2 g/day was observed at about 0.001–0.02 mol% excess Te at charge preparation. X-ray analysis and metallography of the crystals and mechano-chemical polished slices revealed high quality monocrystallinity. The crystals showed high resistivity (⩾ 10 8 ω cm) and did have nuclear radiation detection properties.

Cadmium telluride matrix gamma camera.

An experimental gamma camera that has significant performance has been designed, constructed, and tested. The new camera has a matrix of cadmium telluride semiconductors as the detecting medium. The detectors are located within the collimating holes (rather than behind them). Coincident outputs from each row and column are used to digitally identify the individual detector in which the energy deposition occurred. Direct digital localization of detected events and the attenuation of scatter radiation between matrix elements by the collimator septa that separate detectors, contribute to reasonable resolution and imaging time. The superior radiation detection characteristics of cadmium telluride (in comparison to sodium iodide) could provide superior discrimination against scattered radiation that contributes only spurious information to the image. Detector reliability and uniformity limit the camera's performance; however, the availability of large numbers of small cadmium telluride detectors that have uniform radiation detection properties would make a clinical camera viable.

State-of-the-art of crystal growth and nuclear spectroscopic evaluation of mercuric iodide radiation detectors

The procedure of preparing starting materials of HgI 2 pre-treated with iodine and crystal growth from the vapor phase using the temperature oscillation method, TOM, in both a horizontal and vertical furnace is reviewed. The nuclear radiation detector properties of two of the best representative crystals grown in a horizontal furnace from iodized material and in a vertical furnace from non-iodized material are shown and discussed. The smallest full width half-maximum, fwhm, so far detected with a 10×8×0.5 mm 3 mercuric iodide detector is 4.5 keV for the 662 keV photopeak of 137Cs.

Optical Attitude Sensors: A review

After recalling some definitions relative to the attitude reference systems, the paper summarizes the two main desion baselines : the reference sources radiation characteristics, and the radiation detector properties. The review of the various types of optical attitude sensors starts with a tentative classification, and then the principle and operation mode of the most important types are described, with emphasis on static Earth sensors in order to show the type of difficulties encountered in design and manufacture. Functional testing problems are briefly discussed. Après avoir rappelé Quelques définitions relatives aux systèmes de référence d'attitude l'exposé résume les deux problèmes de base de la conception des senseurs : propriétés de rayonnement des références astronomioues et caractéristioues des capteurs de rayonnement. Aprés une tentative de classification des senseurs d'attitude, on décrit le principe et le mode de fonctionnement des principaux types, en insistant sur le senseur d'horizon statique pour montrer les difficultés rencontrées dans la conception et la fabrication. Enfin, on discute brièvement le problème des tests fonctionnels.

An investigation of the properties of vacuum-ultraviolet radiation detectors

At the Institute of Physics and Astronomy of the Academy of Sciences of the Estonian S.S.R. there is a laboratory for the research on the properties of detectors for vacuum ultraviolet radiation. The laboratory has also the necessary measuring equipment, including a beam double vacuum monochromator for the wavelengths 1000–2700 Å with a balancing-out system of registration attached to it. The last-named device automatically eliminates effects on the results of measurement caused by the distribution of energy in the spectrum of the light source as well as by absorption in the apparatus.Earlier the absolute efficiency of detectors was determined by means of a thermocouple but at present it is calculated from the data obtained from the photoionisation cross sections of gases.The present report throws light on some results of the investigation of the properties of radiation detectors under different operating conditions.

Factors of Merit for Radiation Detectors*

In Part I, the need for a suitably defined factor of merit for comparing the sensitivity of different radiation detectors is explained (Section 1). Both the advantages and the very important limitations of such a factor of merit are discussed.In Section 2, separate factors of merit for Type I and Type II detectors are defined. The factor of merit for Type I detectors is defined as the ratio of the noise equivalent power given by the fundamental limit defined in Paper I to the noise equivalent power actually measured in the reference condition. The factor of merit for Type II detectors is similarly defined in terms of the actual noise equivalent power in the reference condition and the empirically determined minimum value for the noise equivalent power proposed by R. J. Havens. Section 3 contains a brief discussion of the significance of the factor of merit for the special case of the bolometer.In Part II, the noise equivalent power in the reference condition, and the factor of merit is determined for about fifty thermocouples and bolometers. The results are presented in Tables I and II, and in Figs. 1 and 2. A description of each detector is given in Section 5, along with a statement of any special calculations which were necessary.All of the results presented are based on measurements made by other persons; no measurements were performed by the writer. The sources of information are described in Section 3.An Appendix is provided whose purpose is to call attention to the wide variety of possibilities in the specification of the relevant properties of radiation detectors, and thereby to encourage precision in the statement of these properties in the future periodical literature.