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This paper presents the remote detection of alpha contamination in a nuclear facility. Alpha-active material in a shielded nuclear radiation containment chamber has been localized by optical means. Furthermore, sources of radiation danger have been identified in a staged crime scene setting. For this purpose, an electron-multiplying charge-coupled device camera was used to capture photons generated by alpha-induced air scintillation (radioluminescence). The detected radioluminescence was superimposed with a regular photograph to reveal the origin of the light and thereby the alpha radioactive material. The experimental results show that standoff detection of alpha contamination is a viable tool in radiation threat detection. Furthermore, the radioluminescence spectrum in the air is spectrally analyzed. Possibilities of camera-based alpha threat detection under various background lighting conditions are discussed. acceptedVersion

The light collection efficiency of plastic scintillator panels used in radiation portal monitors (RPM) declines over time. We present an efficiency calibration procedure to measure the capability of an aged panel to detect 186 keV gamma rays of highly enriched uranium (HEU). The method is based on a coincidence measurement of backscattered Cs-137 gamma rays having an energy of 184 keV. Energy calibration of the plastic panel can be obtained from the same measurement.

Cameras sensitive to ultraviolet light can be applied to detection of open alpha emitting materials. When absorbed in air, alpha particles generate radioluminescence light, which can be used for detection purposes, provided that background lighting levels are adequately low. In this study, three low-light sensitive camera technologies (CCD, EMCCD and ICCD) were utilized in a nuclear facility, and their performance in detecting alpha emitters was investigated. The results show that low read-out noise is essential for the detection of radioluminescence, as it allows short exposure times to be used. The ICCD was found to perform slightly better than the EMCCD in the field, while both cameras enable the detection of MBqlevel alpha activities in 100 s in the test configuration. Overall, the cameras and techniques used in this study are shown to be effective in detecting alpha emitters in a standard glovebox. This technology can be applied in the field of nuclear security, safety and safeguards, when remote detection of alpha emitters is required., JRC.E.7-Nuclear Safeguards and Forensics

A Peltier-cooled silicon drift detector was successfully applied for conversion electron spectrometry. The energy resolution of the detector for 45 keV electrons was 0.50 keV (FWHM). The approximate thickness of the dead layer was determined to be 140 ± 20 nm Si equivalent. The relative efficiency of the detector was verified to be approximately constant in the energy range of 17–75 keV. This is concordant with the high transparency of the thin dead layer and the sufficient thickness of the detector (450 μm) to stop the electrons. The detector is suitable for use in plutonium analysis of chemically prepared samples. Moreover, it was demonstrated that conversion electron spectrometry is better than alpha spectrometry in preserving its capability to determine the 240Pu/239Pu isotopic ratio as a function of sample thickness. The investigated measurement technique can be considered a promising new tool in safeguards, complementary to existing methods.

In May 2010, air sampling stations in South Korea, Japan and the Russian Federation detected different unstable xenon isotopes and their progenies attached to aerosol particles. The origin of these fission products remains unclear. Previous studies have suggested that a possible reason for these observations is a nuclear test performed in North Korea in May 2010. In the present paper, preliminary spectra recorded at 2 h intervals at the particulate sampling station in Okinawa, Japan are analysed with rigorous mathematical methods. Based on the activity ratios of the 140Xe progenies 140Ba and 140La in a sudden release scenario, the analysis provides an estimate of 12 May 16:00 (UTC) for the release date of the nuclear debris in the form of 140Xe. The 95 % uncertainty limits for the release date are 11 May 9:00–13 May 13:00 (UTC). The result is very sensitive to the coincidence correction factor of the measurement setup and a larger uncertainty interval cannot be excluded. A continuous release scenario could also explain the data, possibly referring to a leak in a running nuclear reactor either on shore or in a vessel. No studies were made on the attribution of the observations to a release site. However, our conclusion is that fresh nuclear debris has been detected in East Asia, and further studies are required in an international forum to reanalyse the data. Of particular importance for the time-zero analysis is the a posteriori calibration of the Okinawa station with a 140Ba sample to resolve the uncertainty related to the coincidence correction and other factors.

A fluorescence-based alpha-gamma coincidence spectrometry approach has been developed for the analysis of alpha-emitting radionuclides. The thermalization of alpha particles in air produces UV light, which in turn can be detected over long distances. The simultaneous detection of UV and gamma photons allows detailed gamma analyses of a single spot of interest even in highly active surroundings. Alpha particles can also be detected indirectly from samples inside sealed plastic bags, which minimizes the risk of cross-contamination. The position-sensitive alpha-UV-gamma coincidence technique reveals the presence of alpha emitters and identifies the nuclides ten times faster than conventional gamma spectrometry.

Scientific Reports 6: Article number: 2153210.1038/srep21532; published online: February122016; updated: April222016 The HTML version of this Article contained a typographical error in the volume number ‘6’, which was incorrectly given as ‘5’. This has now been corrected. In addition, there were typographical errors in the Abstract. “Radon decay is directly measured by observing the secondary radiolumines cence light that alpha particles excite in air,” now reads: “Radon decay is directly measured by observing the secondary radioluminescence light that alpha particles excite in air,” “The presented technique paves the way for optical approaches in rapid radon detec tion,” now reads: “The presented technique paves the way for optical approaches in rapid radon detection,” These errors have now been corrected in the PDF and HTML versions of the Article.

With conventional methods, samples containing alpha-particle-emitting nuclides are difficult to detect and characterize from distances greater than a few centimetres. One promising technique is to observe alpha particles indirectly by utilizing alpha-induced ultraviolet (UV) photons. While absorbing in air, the energy of alpha particles is transferred to atmospheric molecules, leading to their ionization and excitation. In this work, UV photons generated in the relaxation of nitrogen molecules were used to trigger a gamma-ray spectrometer. This UV approach allows the focusing of gamma-ray measurements on a certain point containing alpha emitters. The present paper demonstrates that the new measurement principle works and has the potential to be developed for both in-field and laboratory applications.

The PANDA (Particles And Non-Destructive Analysis) device is a measuring system developed for non-destructive analysis of samples for safety, security and safeguards. It consists of two complementary measurement positions. The position sensitive alpha–gamma coincidence setup of PANDA has been updated with a pile-up rejection circuit. This article demonstrates, using a 241 Am source, that this circuit can be used to identify gamma-ray sum peaks in the spectra. The second measurement position reported here hosts a 10-mm 2 windowless silicon drift detector that detects electrons and X-rays with a very good energy resolution. An experimental value of 0.30 keV for full width at half maximum was obtained at 17.7 keV energy (Np X-rays). Conversion electron spectrometry, for example, provides an independent, complementary means to study actinides whose low energy transitions are often highly converted.

The correct handling of statistical uncertainties is crucial especially when unfolding alpha spectra that contain a low number of counts or overlapping peaks from different nuclides. For this purpose, we have developed a new spectrum analysis software package called ADAM, which performs a full covariance calculus for alpha-particle emitting radionuclides. By analyzing a large number of simulated and measured spectra, the program was proved to give unbiased peak areas and statistically correct uncertainty limits. This applies regardless of the peak areas and the number of unknown parameters during the fitting. In addition, ADAM performs reliable deconvolution for multiplets, which opens the way for the determination of isotope ratios, such as 239 Pu/ 240 Pu.

High-resolution alpha spectrometry was applied for the activity determination of 10 reference sources containing different amounts of 238Pu, 239Pu, 240Pu and 242Pu. They were analyzed as blind sources using a novel spectrum analysis tool ADAM. The information needed in the spectrum unfolding was taken only from the spectrum under investigation, and no tracers were applied. Therefore, a Monte Carlo program AASI was used to compute geometrical detection efficiency of the measurement setup. All reported activities corresponded to those of the reference sources within expanded uncertainty. The developed tools can be used for the activity determination in nondestructive alpha spectrometry or when the radionuclide composition does not change during the sample processing.

Thin Mylar foils are often used to protect detectors from contamination. However, these foils can be electrostatically charged, possibly leading to their contamination with airborne radon progenies. In the present work, the collection and behaviour of radon progenies on Mylar foils was investigated in detail using alpha spectrometry. The radon progenies collection rate of a small Mylar foil (3 cm 2 ) is equivalent to an air sampler with a flow rate of approximately 0.1 m 3 /h. It was demonstrated that such contamination may jeopardise the validity of the entire analysis if not interpreted correctly.

A novel analysis program to unfold alpha-particle energy spectra was introduced, demonstrated and validated using radiochemically processed test sources, which contained different amounts of 239Pu and 240Pu. A high-resolution alpha spectrometer was used for data acquisition. The software known as ADAM unfolds the spectra using nuclide-specific decay data as a constraint. The peaks can have different shapes and the software can also cope with the coincidences between alpha particles and electrons/photons. In the present paper, the 239Pu/240Pu activity ratios from alpha spectrometry agreed, within the stated uncertainties, with the reference values. Number of counts in the 239,240Pu peak group must be larger than 100 to obtain reliable values when using semiconductor detector of energy resolution FWHM=10.6 keV.

A nuclear bomb particle containing 1.6 ng of Pu was investigated nondestructively with a position-sensitive α detector and a broad-energy HPGe γ-ray detector. An event-mode data acquisition system was used to record the data. α-γ coincidence counting was shown to be well suited to nondestructive isotope ratio determination. Because of the very small background, the 51.6 keV γ rays of (239)Pu and the 45.2 keV γ rays of (240)Pu were identified, which enabled isotopic ratio calculations. In the present work, the (239)Pu/((239)Pu+(240)Pu) atom ratio was determined to be 0.950 ± 0.010. The uncertainties were much smaller than in the previous more conventional nondestructive studies on this particle. Obtained results are also in good agreement with the data from the destructive mass spectrometric studies obtained previously by other investigators.

Alpha particles can be detected by measuring the radioluminescence light which they induce when absorbed in air. The light is emitted in the near ultraviolet region by nitrogen molecules excited by secondary electrons. The accurate knowledge of the radioluminescence yield is of utmost importance for novel radiation detection applications utilizing this secondary effect. Here, the radioluminescence yield of an alpha particle is investigated as a function of energy loss in air for the first time. Also, the total radioluminescence yield of the particle is measured with a carefully calibrated Pu emitter used in the experiments. The obtained results consistently indicate that alpha particles generate 19±3 photons per one MeV of energy released in air at normal pressure (temperature 22°C, relative humidity 43%) and the dependence is found to be linear in the studied energy range from 0.3 MeV to 5.1 MeV. The determined radioluminescence yield is higher than previously reported for alpha particles and similar to the radioluminescence yield of electrons at comparable energies. This strengthens the evidence that the luminescence induced by charged particles is mostly proportional to the energy loss in the media and not very sensitive to the type of primary particle.

In this work, an electron-multiplying camera is introduced for the first time for rapid alpha imaging in a glovebox. To demonstrate the technique, fuel pellets containing uranium and plutonium isotopes were measured at the Institute for Transuranium Elements, Karlsruhe. Further development of the EMCCD imaging system can evolve to a viable tool for security and safety officials around the world. The method has potential to be used in crime scene investigation if illicit use of alpha active materials is suspected. Other applications lie in the field of nuclear industry and especially in decommissioning of old facilities.