Determination of the Branching Ratio of CH3OH + OH Reaction on Water Ice Surface at 10 K

The CH _3 O and CH _2 OH radicals can be important precursors of complex organic molecules (COMs) in interstellar dust. The COMs presumably originating from these radicals were abundantly found in various astronomical objects. Because each radical leads to different types of COMs, determining the abundance ratio of CH _3 O to CH _2 OH is crucial for a better understanding of the chemical evolution into various COMs. Recent work suggested that the reaction between CH _3 OH and OH on ice dust plays an important role in forming CH _3 O and CH _2 OH radicals. However, quantitative details on the abundance of these radicals have not been presented to date. Herein, we experimentally determined the branching ratio (CH _3 O/CH _2 OH) resulting from the CH _3 OH + OH reaction on the water ice surface at 10 K to be 4.3 ± 0.6. Furthermore, the CH _3 O product in the reaction would participate in subsequent diffusive reactions even at a temperature as low as 10 K. This fact should provide critical information for COMs formation models in cold molecular clouds

Gated Silicon Drift Detector Fabricated from a Low-Cost Silicon Wafer

Inexpensive high-resolution silicon (Si) X-ray detectors are required for on-site surveys of traces of hazardous elements in food and soil by measuring the energies and counts of X-ray fluorescence photons radially emitted from these elements. Gated silicon drift detectors (GSDDs) are much cheaper to fabricate than commercial silicon drift detectors (SDDs). However, previous GSDDs were fabricated from $10$-k$\Omega \cdot$cm Si wafers, which are more expensive than $2$-k$\Omega \cdot$cm Si wafers used in commercial SDDs. To fabricate cheaper portable X-ray fluorescence instruments, we investigate GSDDs formed from $2$-k$\Omega \cdot$cm Si wafers. The thicknesses of commercial SDDs are up to $0.5$ mm, which can detect photons with energies up to $27$ keV, whereas we describe GSDDs that can detect photons with energies of up to $35$ keV. We simulate the electric potential distributions in GSDDs with Si thicknesses of $0.5$ and $1$ mm at a single high reverse bias. GSDDs with one gate pattern using any resistivity Si wafer can work well for changing the reverse bias that is inversely proportional to the resistivity of the Si wafer