Gamma-Ray Spectroscopy for 237Np Using a Transition-Edge Sensor with a Thick-Trilayer Membrane.

Gamma-ray transition edge sensors (TESs) are intensively studied not only to measure isotopic composition of nuclear materials but to monitor transuranic radionuclides inside the human body. We have recently proposed a thick-trilayer membrane as an alternative to silicon-nitride (Si x N y ) single-layer ones. It consists of silicon dioxide (SiO 2 ), Si x N y , and SiO 2 layers. Their total thickness is 6.9 μ m and exhibits almost the same thermal conductance as conventional Si x N y ones with 1- μ m thickness. The thick-trilayer membrane is expected to have better mechanical strength against implementing heavy-bulk absorbers. In this paper, the gamma-ray TES with the thick-trilayer membrane is used to carry out the spectroscopy for the nuclear radiation source. Neptunium-237 and its decay product Protactinium-233 emit 86.5 and 86.6-keV lines, respectively, and they are clearly resolved by four pixels with the full-width-half-maximum (FWHM) resolution of ( 43.7 ± 0.9 ) eV. Furthermore, their intensity ratio agrees with the radioactive equilibrium between the two nuclides. Our experimental results predict that a vast array of pixel formats will reduce the statistical uncertainty in less measuring time. [ABSTRACT FROM AUTHOR]