Johan Sand

Stand-Off Radioluminescence Mapping of Alpha Emitters Under Bright Lighting

Remote detection of alpha emitters is achieved by measuring the secondary radioluminescence light (air fluorescence) that is induced by alpha particles when absorbed in air. A telescope was used to collect the radioluminescence photons to a photomultiplier tube, which is operated in the photon counting mode. Careful matching of photocathode response and filter pass-band allows the sensing of a faint radioluminescence emission in a brightly illuminated environment, which is essential for operative use. A minimum detectable alpha activity of 4 kBq was reached at 1 m distance in 10 s time, when ultraviolet-free lighting is present, and 800 kBq under bright fluorescent lighting. These sensitivities are realized using an ultra-bialkali and cesium-telluride photocathodes in the aforementioned environments respectively. The presented approach is a robust and affordable solution to remotely detect and localize moderate alpha activities in a field environment, providing a means for automated alpha contamination mapping. Moreover, it is shown that a signal increase of more than two orders of magnitude (150–420) can be achieved in deep ultraviolet (close to 260 nm), if nitrogen or argon purge are used to enhance the detection.

Radioluminescence yield of alpha particles in air

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.

Fluorescence-Assisted Gamma Spectrometry for Surface Contamination Analysis

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.

Transversely Excited Multipass Photoacoustic Cell Using Electromechanical Film as Microphone

A novel multipass photoacoustic cell with five stacked electromechanical films as a microphone has been constructed, tested and characterized. The photoacoustic cell is an open rectangular structure with two steel plates facing each other. The longitudinal acoustic resonances are excited transversely in an optical multipass configuration. A detection limit of 22 ppb (10−9) was achieved for flowing NO2 in N2 at normal pressure by using the maximum of 70 laser beams between the resonator plates. The corresponding minimum detectable absorption and the normalized noise-equivalent absorption coefficients were 2.2 × 10−7 cm−1 and 3.2 × 10−9 cm−1WHz−1/2, respectively.

Electromechanical film as a photoacoustic transducer

An electromechanical film, EMFi, is utilized as a transducer in a photoacoustic (PA) gas sensor. The film is a sensitive acoustic transducer, it is easily formable, and it exhibits a wide frequency response regardless of its large surface area. As a demonstration of its capabilities, the EMFi-based PA detector is used to measure NO(2) with pulsed excitation at 436 and 473 nm. The minimum detectable absorption coefficient is extrapolated to be 5.10(-7) cm(-1). Improvements for EMFi-based PA detector are discussed.

Dynamic enhancement of radioluminescence in solar blind spectral region

Alpha emitting radiation sources are typically hard to detect due to the short range of alpha particles in air (4cm). A remote detection of alpha radiation in air is possible by imaging the ionization-induced fluorescence (radioluminescence) of air molecules [1]. The alpha-induced ultraviolet light is mainly emitted by molecular nitrogen as fluorescent light with wavelengths in the regime of 297–405 nm. The main benefit of this method is the long range of UV-photons in air, which allows for remote detection of alpha emitting radiation sources. However, in many applications background lighting caused by sunlight with a spectrum reaching down to ∼300 nm makes the fluorescence signal difficult to isolate [2]. Under environmental conditions radioluminescence in wavelength regimes <300 nm (the solar blind spectral region) by molecules other than N2 is not detectable.

Optical detection of radon decay in air.

An optical radon detection method is presented. Radon decay is directly measured by observing the secondary radiolumines cence light that alpha particles excite in air, and the selectivity of coincident photon detection is further enhanced with online pulse-shape analysis. The sensitivity of a demonstration device was 6.5 cps/Bq/l and the minimum detectable concentration was 12 Bq/m3 with a 1 h integration time. The presented technique paves the way for optical approaches in rapid radon detec tion, and it can be applied beyond radon to the analysis of any alpha-active sample which can be placed in the measurement chamber.

EMCCD imaging of strongly ionizing radioactive materials for safety and security

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.

Erratum: Optical detection of radon decay in air.

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.

Optical signal enhancement in supercontinuum generation

We show in this contribution that there is a surprising beneficial application of the noise amplification capability. Launching a pulse train with a weak sinusoidal amplitude modulation into the microstructure fiber, we observe up to 30-fold optical signal amplification of this modulation after the fiber.