Sakari Ihantola

Determination of 239Pu/240Pu isotopic ratio by high-resolution alpha-particle spectrometry using the ADAM program

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 (239)Pu and (240)Pu. 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 (239)Pu/(240)Pu activity ratios from alpha spectrometry agreed, within the stated uncertainties, with the reference values. Number of counts in the (239,240)Pu peak group must be larger than 100 to obtain reliable values when using semiconductor detector of energy resolution FWHM=10.6 keV.

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.

Determination of 235 U, 239 Pu, 240 Pu, and 241 Am in a nuclear bomb particle using a position-sensitive α-γ coincidence technique

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.

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.

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.