Alpha Detector Research Articles

Antihydrogen detection in ALPHA

The ALPHA project is an international collaboration, based at CERN, with the experimental goal of performing precision spectroscopic measurements on antihydrogen. As part of this endeavor, the ALPHA experiment includes a silicon tracking detector. This detector consists of a three-layer array of silicon modules surrounding the antihydrogen trapping region of the ALPHA apparatus. Using this device, the antihydrogen annihilation position can be determined with a spatial resolution of better than 5 mm. Knowledge of the annihilation distribution was a critical component in the recently successful antihydrogen trapping effort. This paper will describe the methods used to reconstruct annihilation events in the ALPHA detector. Particular attention will be given to the description of the background rejection criteria.

Measurement of 222Rn diffusion through sandy soil with solar cells photodiodes as the detector

An experimental system was developed to study the diffusion rate of radon ( 222Rn) gas through porous media as a function of soil porosity/grain size and soil water content. Columns with different grain sizes, soil water content and soil depths were used. The system used solar cells photodiodes as alpha (α) detectors. This new detector is highly efficient and low cost compared to other known detectors. Soil water content was found to be the most dominant factor affecting the 222Rn diffusion rate. A maximum diffusion rate value of (6.5 ± 0.07) × 10 −6 m 2/s was found in dry conditions. The minimum diffusion value of less than (3.9 ± 0.14) × 10 −7 m 2/s was found in 2% soil water content. The experimental results were compared with theoretical calculations done with the “GREEN equation”. Two discrepancies were observed: the time to equilibrium state in the measurements was longer compare to the calculated values and the α count rates were lower in the experiment compared with the theoretical calculations. These results can be explained by the differences in the system geometry.

Development of an alpha/beta/gamma detector for radiation monitoring

For radiation monitoring at the site of nuclear power plant accidents such as Fukushima Daiichi, radiation detectors not only for gamma photons but also for alpha and beta particles are needed because some nuclear fission products emit beta particles and gamma photons and some nuclear fuels contain plutonium that emits alpha particles. We developed a radiation detector that can simultaneously monitor alpha and beta particles and gamma photons for radiation monitoring. The detector consists of three-layered scintillators optically coupled to each other and coupled to a photomultiplier tube. The first layer, which is made of a thin plastic scintillator (decay time: 2.4 ns), detects alpha particles. The second layer, which is made of a thin Gd(2)SiO(5) (GSO) scintillator with 1.5 mol.% Ce (decay time: 35 ns), detects beta particles. The third layer made of a thin GSO scintillator with 0.4 mol.% Ce (decay time: 70 ns) detects gamma photons. By using pulse shape discrimination, the count rates of these layers can be separated. With individual irradiation of alpha and beta particles and gamma photons, the count rate of the first layer represented the alpha particles, the second layer represented the beta particles, and the third layer represented the gamma photons. Even with simultaneous irradiation of the alpha and beta particles and the gamma photons, these three types of radiation can be individually monitored using correction for the gamma detection efficiency of the second and third layers. Our developed alpha, beta, and gamma detector is simple and will be useful for radiation monitoring, especially at nuclear power plant accident sites or other applications where the simultaneous measurements of alpha and beta particles and gamma photons are required.

Gamma versus alpha sensors for Rn-222 long-term monitoring in geological environments

Abstract The behavior of alpha silicon diodes, gamma crystal scintillators and ionization chamber detectors employed for long-term radon monitoring in geological media was studied and a comparison of the efficiency and sensitivity, the capability to resolve signal to noise, background, stability, and reliability of their long-term measurements is presented. An understanding of the qualities of monitoring techniques is necessary for determining suitability to the characteristics of the individual monitoring site and what exactly they will measure: radon in an air cavity, in porous media or in water. The experimental layout was located inside the Amram Mountain research tunnel near Elat (Gulf of Aqaba), within a closed room in the tunnel core. This enabled monitoring natural temporal radon variations under fairly stable internal conditions, at a high-resolution sampling rate of once every several minutes. In an interval of several days, all the sensors responded simultaneously to the same eventual radon variations. An ionization chamber device, the AlphaGUARD designed with a long-time stable calibration factor and an inherent QA-System, was used as reference calibration of the different radon detectors. The results indicate that the higher sensitivity of 2–4 orders of magnitude exhibited by gamma sensors even with narrow dimensions (1 × 3 BGO detector) are preferred for long-term radon monitoring in comparison to the solid-state alpha detectors and ionization chambers.

Possible effect of solar tides on radon signals

Large temporal variations of radon ( 222Rn) are often encountered in air in the geologic environment, at time scales from diurnal to annual. Interpretations as to the nature of these variations, unique to 222Rn, often invoke either above surface atmospheric variations, or the influence of subtle active geodynamic processes. So far the eventual geophysical drivers of the variation of 222Rn as well as its specific qualities enabling this temporal variation are not known. New insight on the temporal variation of 222Rn is gained by experimental simulation in confined air. Two short laboratory experiments, and one external experiment lasting over 3 years, were performed inside closed canisters and using natural and commercial 222Rn sources. Internal and external gamma and alpha detectors recorded variations of the radiation, up to around 20% of the equilibrium level. Radon signals of different time scale occurred with: a) periodic annual and semi-annual signals; b) non-periodic multi-day signals; c) periodic daily signals. Similar, related, inversely-related and dissimilar temporal patterns were manifested in the measured time series of the different sensors. Diurnal periodicity was dominated by the solar tide components S1, S2 and S3, exhibiting unlike relative amplitudes and different phases at the different sensors. A compound association occurs among the amplitudes and phases of the diurnal and seasonal periodicities of the daily 222Rn signal, linking the periodic phenomena to the rotation of earth around its axis and around the sun. 222Rn variation patterns in the frequency–time domain cannot be driven by the corresponding atmospheric variation patterns. These results, obtained under static and isolated conditions, are in disagreement with the expected radioactive equilibrium and its spatially uniform expression within and around the experimental volume. The external influence which drives the daily signals evolving from 222Rn inside the canister is non-atmospheric and seemed to be from a remote source and traversed a 5-cm thick lead shield. The similarities with observations on 222Rn signals from upper crustal levels imply that such an external influence, possibly as a component of solar irradiance, drives the 222Rn signals to a depth of at least 100 m. New combined prospects for the research are indicated in terms of the radioactive behavior of 222Rn in air and in terms of an above surface geophysical driver for this behavior.

Radon signals at the Roded site, Southern Israel

Abstract. Temporal variations of radon in the geological environment (upper crust) are frequent and recognized as unique in terms of the signals encountered and for the lack of substantial and generally applicable explanations. The phenomena observed at the Roded site, located in arid southern Israel, illustrate this situation. The monitoring of radon in the last 10 years or more has been carried out in massive meta-diorite of the Precambrian basement block of Roded. The measurement is conducted using an alpha detector at a resolution of 15-min, placed in a borehole at a depth of 9 m, within a PVC casing to that depth. Systematic temporal variation patterns, manifested as large relative signals are composed of sub-diurnal (SDR) radon, multi-day (MD) and annual (AR) signals. The overall variation is dominated by the intense SDR signals which occur in some days, and may vary from background levels (5 counts or less) to peak values (attaining >1000 counts) and back to background at an interval of 6 to 12 h. Intervals of up to several tens of days without significant SDR signals interchange with times of intense daily occurrences of such signals. Their occurrence indicates very fast variations of radiation from radon at the point of measurement. The peak times, within the diurnal 24-h cycle of SDR signals occur preferentially at an interval of 14–16 h (UT+2). Spectral analysis indicates: (a) A diurnal periodicity composed of a primary 24-h and a secondary 12-h periodicity, which are attributed to the solar tide constituents S1 and S2. Tidal constituents indicative for gravity tide (O1, M2) are lacking; (b) An annual periodicity. A compound relation among the diurnal and annual periodicity is indicated by: (a) Continuous Wavelet Transform (CWT) analysis shows an overall annual structure with a modulation of the S1 and S2 periodicities; (b) Moving-time-window Fourier spectral analysis showing that the amplitudes of S1 and S2 vary in an annual pattern, with relatively high values in summer. The phase of S1, S2 and S3 shows a systematic multi-year variation. It is suggested that the significant signatures of the periodic phenomena and their modulations reflect a direct link with the solar radiation tide.

A simple technique for studying the dependence of radon and thoron exhalation rate from building materials on absolute humidity

Indoor radon and thoron concentrations were dominated with their exhalation rate from building materials. Thus, the evaluation of exhalation rate with highly precise is important. This paper presented a new technique to measure the dependence radon/thoron exhalation rate, from building materials used in Japan, on absolute humidity. The measurement technique consisted of a solid state alpha detector equipped a ventilation-type chamber and humidity control system in a flow through method. The exhalation rate of dried samples (Indian red granite and Japanese gray granite) was measured at various absolute humidity levels in the range of 1–20 g cm−3. It was found that exhalation rate increased exponential with increasing of absolute humidity for both samples. Furthermore, the dependence of radon emanation coefficient on building material’s temperature was also studied using an accumulation chamber equipped with scintillation cell alpha detector. The emanation coefficient of dry sample increased proportionally with increasing the material’s temperature with a correlation factor of 0.88.

Radon signals in the Gavnunim intrusion, Makhtesh Ramon, Israel

SUMMARY High time resolution monitoring of radon, using alpha detectors is carried out in a massive and jointed syenite located in arid southern Israel. Monitoring, at a resolution of 15-min, is conducted in two boreholes at depths of 1.2 and 85–90 m, resulting in more then 10-yr long time-series. Systematic temporal variation patterns, manifesting large relative signals are composed primarily of annual (AR), multiday (MD), daily (DR) and subdaily (SDR) radon signals. Prominent periodic diurnal variation underlies the DR and probably also the SDR signals. Diurnal (S1; 24-hr) and semidiurnal (S2; 12-hr) constituents characterize the DR signal at 1.2 m, while diurnal constituents typical for gravity related periodicities (M2, O1) are absent. The amplitudes of the S1 and S2 constituents, calculated for consecutive 512-hr-long time intervals, exhibit a similar covarying annual pattern. The periodic DR signal is absent at 85 m depth. The peak time of SDR signals, occurring at this depth in some days, exhibits a 24- and 12-hr periodicity. Time offsets of hours are observed between time-series of the measured signal from the two levels. The lag, investigated for the decomposed MD signal, using consecutive 20-d-long time intervals, shows that the signal at depth systematically lags by around 9 hr the signal at the shallow level. Discrepancy of the patterns of the temporal variation in the time domain, and also in the frequency and time-frequency domains of the diurnal periodic components, indicates that atmospheric influence on the radon signal is insignificant even at a depth of 1.2 m. Combining this conclusion with the compound interrelations occurring among the different radon signals suggests that other geophysical processes are driving the radon variation in the subsurface geogas. It is suggested that the significant S1 and S2 signatures, and their modulations, are imposed on the radon system by means of a direct link with solar radiation tide.

PANDA—A novel instrument for non-destructive sample analysis

An instrument known as PANDA (Particles And Non-Destructive Analysis) for non-destructive sample analysis has been designed and built at the Finnish Radiation and Nuclear Safety Authority (STUK). In PANDA the measurement techniques and instruments designed for the basic research are applied to the analysis of environmental samples. PANDA has two vacuum chambers, one for loading samples and the other for measurements. In the measurement chamber there are two individual measurement positions. Currently the first one hosts an HPGe gamma detector and a position-sensitive alpha detector. The second measurement position is intended for precise characterization of found particles. PANDA's data are recorded in event mode and events are timestamped. In the present article the technical design of PANDA is presented in detail. In addition, its performance using depleted uranium particles and an air filter is demonstrated.

Characterization of an Associated Particle Neutron Generator With ZnO:Ga Alpha-Detector and Active Focusing

A deuterium-tritium (DT) associated particle neutron generator (APNG) with active focusing has been operated using an alpha particle detector made of a ZnO:Ga phosphor with decay time of approximately 1 ns. The APNG is capable of producing 109 neutrons per second. The DT beam spot diameter was adjusted and measured from 7 mm to 2.1 mm with the possibility of achieving 1 mm subject to the removal of a safety interlock protecting the APNG tritiated target. In addition, the alpha detector was found to have a detection efficiency of 88% and sub-nanosecond time resolution (<0.7 ns) using a Burle 8850 bialkali photocathode. Lastly, the neutron beam was obstructed using various amounts of lead shielding to study the generator's imaging contrast capability for neutron radiography. The APNG provides high-rate capability and a large solid angle with acceptance of 8%.

Development of a RF-Driven Neutron Generator for Associated Particle Imaging

We present recent work in the development of a compact, radio frequency (RF) D-T neutron generator with a maximum neutron yield of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> n/s for the application of associated particle imaging (API) used in explosive and contraband detection. API makes use of alpha particles produced in conjunction with 14 MeV neutrons in the D-T reaction to locate the neutron interaction and reduce background noise. To achieve high spatial resolution in API, a beam diameter of les1 mm on target is desired. For portable neutron generators used in API, the ion source and target cannot be water-cooled and the power deposited on the target must be low. By increasing the atomic ion fraction, the ion beam can be used more efficiently to generate neutrons, resulting in a lower beam power requirement and an increased lifetime of the alpha detector inside the acceleration column. The RF ion source produces very high atomic ion fractions (> 90%) compared to traditional Penning ion sources that produce less than 10% of atomic ions. Experimental measurements of the ion source plasma parameters including ion current density, atomic ion fraction, ignition and operating pressures, will be presented along with a discussion on the ion optics and engineering challenges.

Measurement of the Activity Per Unit Mass with Hand-Held Alpha and Beta Detectors

This paper describes how to use hand-held alpha and beta detectors to measure volume or mass contamination (Bq g-1) instead of the usual surface activity (Bq cm-2). As a proof of principle, measurements with a hand-held detector of the specific activity of K in potassium chloride yielded the expected result. Field measurements agree well with the results from analytical laboratories.

Development of ZnO:Ga as an ultra-fast scintillator

We report on several methods for synthesizing the ultra-fast scintillator ZnO(Ga), and measurements of the resulting products. This material has characteristics that make it an excellent alpha detector for tagging the time and direction of individual neutrons produced by t–d and d–d neutron generators (associated particle imaging). The intensity and decay time are strongly dependent on the method used for dopant incorporation. We compare samples made by diffusion of Ga metal to samples made by solid-state reaction between ZnO and Ga 2O 3 followed by reduction in hydrogen. The latter is much more successful and has a pure, strong near-band-edge fluorescence and an ultra-fast decay time of the X-ray-excited luminescence. The luminescence increases dramatically as the temperature is reduced to 10 K. We also present results of an alternate low-temperature synthesis that produces luminescent particles with a more uniform size distribution. We examine possible mechanisms for the bright near-band-edge scintillation and favor the explanation that it is due to the recombination of Ga 3+ donor electrons with ionization holes trapped on H + ion acceptors.

Development of Alpha Detector Module based on Large Area PIN Photodiode

Two alpha detectors based on scintillator coated PIN PD were manufactured and investigated for 3.5 MeV alpha particles. ZnO(Ga) and CsI(Tl) scintillators were coated on the large area of 1 cm × 1 cm PIN type photodiode, respectively. After connecting them with a charge sensitive preamplifier, system noise, signal output, and signal speed were measured and analyzed. Although the system noise after scintillator coating was increased, especially large in ZnO(Ga) coating, alpha detection was possible for both detectors. The output signal was relatively large in the CsI(Tl) coated detector compared with the ZnO(Ga) coated detector. In detection time test, the ZnO(Ga) coated detector showed the performance of about 3 times faster than the CsI(Tl) coated detector.

Development of the In-situ Monitoring System for Pipe Internal Contamination Measurement in the Decommissioning Site

The in-situ monitoring system of pipe internal (IMSPI) was developed for transporting a variety of survey tools into pipes. Tools available for use with the system include alpha, beta and gamma-ray detectors and video cameras. In the IMSPI, phoswich detector for simultaneous measurement of alpha- and beta-particles and CdTe detector for gamma-rays were used. The phoswich detector composed with ZnS(Ag) and plastic dual scintillator was manufactured, which could be applicable in the contamination monitoring systems. The IMSPI used a helical gear and automatic controller to transport radiation detectors and video cameras into pipes. And the membrane inserted into a pipe to transfer the characterization tools through the piping, providing a clean conduit through which the detectors and camera could travel.

Detectors for alpha particles and X-rays operating in ambient air in pulse counting mode or/and with gas amplification

Ionization chambers working in ambient air in currentdetection mode are attractive due to their simplicity and low cost andare widely used in several applications such as smoke detection,dosimetry, therapeutic beam monitoring and so on. The aim of this workwas to investigate if gaseous detectors can operate in ambient air inpulse counting mode as well as with gas amplification whichpotentially offers the highest possible sensitivity in applicationslike alpha particle detection or high energy X-ray photon or electrondetection.To investigate the feasibility of this method two types of open- endgaseous detectors were build and successfully tested. The first onewas a single wire or multiwire cylindrical geometry detector operatingin pulse mode at a gas gain of one (pulse ionization chamber). Thisdetector was readout by a custom made wide -band charge sensitiveamplifier able to deal with slow induced signals generated by slowmotion of negative and positive ions. The multiwire detector was ableto detect alpha particles with an efficiency close to 22%. The secondtype of an alpha detector was an innovative GEM-like detector withresistive electrodes operating in air in avalanche mode at high gasgains (up to 104). This detector can also operate in a cascadedmode or being combined with other detectors, for example withMICROMEGAS. This detector was readout by a conventional charge-sensitive amplifier and was able to detect alpha particles with 100%efficiency. This detector could also detect X-ray photons or fastelectrons. A detailed comparison between these two detectors is givenas well as a comparison with commercially available alphadetectors. The main advantages of gaseous detectors operating in airin a pulse detection mode are their simplicity, low cost and highsensitivity. One of the possible applications of these new detectorsis alpha particle background monitors which, due to their low cost canfind wide application not only in houses, but in public areas:airports, railway station and so on.

Analysis of Nuclear Material by Alpha Spectroscopy with a Transition-Edge Microcalorimeter

We present measurements from a cryogenic microcalorimeter designed to detect alpha particles. The enhanced resolution of microcalorimeter alpha detectors will provide new capabilities for actinide analysis. We demonstrate a spectral resolution of 2.4 keV full width at half maximum (FWHM) for 5.3 MeV alpha particles from a 210Po source. In addition, we present an alpha spectrum from 209Po showing the first direct measurement of decay into the 205Pb ground state. Finally, measurements of 100 keV gamma-rays from a Gd source show an ultimate alpha particle resolution of 159 eV to be achievable which may provide an avenue for investigating ion energy loss mechanisms in bulk materials.

COHN analysis: Body composition measurements based on the associated particle imaging and prompt-gamma neutron activation analysis techniques

The measurement of the body’s carbon (C), oxygen (O), hydrogen (H), and nitrogen (N) content can be used to calculate the relative amounts of fat, protein, and water. A system based on prompt-gamma neutron activation analysis (PGNAA), coupled with the associated particle imaging (API) technique, is being developed for this purpose. A compact D,T neutron generator (~10 7 n/s output) with an internal alpha-particle detector is used. The counting system consists of 6 shielded bismuth germanate (BGO) detectors (10.2 cmu10.2 cmu10.2 cm) operated with fast-timing electronics to detect only gamma-rays within a 100 ns time window following a trigger pulse generated by the alpha detector. The body can be scanned from the shoulders to the knees within about 30 min, with the equivalent whole-body dose <0.4 mSv. The cumulative gamma-ray spectra in the 2 MeV to 8 MeV region is collected and analyzed for multiple peaks attributed to body C,O,H, and N. Measurement precision for each element, based on tissue-equivalent phantoms, are in the 2–5% range, which are sufficient for population studies in adults. Further improvements are needed to extend the measurements to pediatric clinical research studies.

Semi-continuous measurement of the unattached radon decay products size distributions from 0.5 to 5 nm by an array of annular diffusion channels

A new diffusion battery was designed to make precise measurements of the indoor activity size distribution of short-lived 222Rn decay products in the size range of 0.5–5 nm. It relies on the selection of particles by five annular diffusion channels (ADCs) and on the use of a non-linear inversion method, EVE, for the reconstruction of the particle size distributions. The ADC geometry proved to allow a better selection of the particles size compared to the wire screen and the implementation of an alpha detector set in front of the sampling filter for semi-continuous activity measurements. EVE algorithm was chosen in order to take into account the uncertainties of the measurement in the deconvolution process. The diffusion battery was tested in a radon chamber, and results showed a good reproducibility of the measurements. The degree of confidence on the obtained size distributions is then discussed. Results show that the relative uncertainty on the penetration data has to be less than 10% in order to obtain a reliable size distribution.

Silicon carbide for UV, alpha, beta and X-ray detectors: Results and perspectives

Silicon carbide (SiC) is one of the candidates for the next generation semiconductor materials. Due to the wide bandgap (4H-SiC 3.2 eV), high critical breakdown voltage, high saturated drift velocity, high thermal conductivity, the detector fabricated with SiC has very low dark current, significantly high operating temperature and for UV sensors, insensitivity to visible/IR backgrounds compared to conventional Si detectors. In this paper, recent results on UV, alpha, beta and X-ray 4H-SiC detectors will be presented. High-energy resolution and full charge collection efficiency (CCE) have successfully been demonstrated before irradiation. After irradiation, the alpha and beta detectors continue to be operative, with a high CCE until fluences of the order of some 10 14 n/cm 2. The results for UV detectors show that the 4H-SiC photodetectors are capable of operating as solar-blind UV detector. SiC pixel detectors show leakage currents of a few femptoamperes at room temperature, which means a noise contribution of less than 1 e − r.m.s. High performance for X-ray can be achieved with SiC detectors even above room temperature without using any cooling system.