The recent progress of hydrogen analysis in solid in our group is introduced. Two topics are picked up here: (1) the effort and achievement of high sensitivity HERDA (high-resolution elastic recoil detection analysis) and (2) the development of NRA (nuclear reaction analysis) with 1H(15N, )12C in the ambient condition.
At first we installed HERDA system at the beam line of 1 MV Tandetron in UTTAC (Univ. of Tsukuba, Tandem Accelerator Complex) under the instruction by K. Kimura [1,2]. In this most conventional HERDA system, a MCP (micro channel plate) is used as the PSD (position sensitive detector). In this case, the dark current in the MCP is crucial to make the detection limit of hydrogen worse. In the second type of HERDA system, we introduced the double MCP and coincidence detection to remove the dark current as noises. While this system was originally developed to observe the dilute B (boron) by the group of Kimura [3], we successfully improved the detection limit also of hydrogen. As the third version of HERDA, we tried to use PIPS (passivated implanted planer silicon-detector) by Canberra and also 16 channels strip PIPS as PSD. A 16 channels preamplifier set [4] and dToT (dynamic time over threshold) system suitable to the strip PIPS are also tested [5]. The most remarkable point in usage of the PIPS as PSD is that it can distinguish the stray particles (or particles non-interesting) from the signals as well as the dark current noise (see fig. 1). The current status of the detection limit of hydrogen in our system is 7.98×1019 at./cm3 with the data acquisition time of 149 s.
NRA by means of ~6.4 MeV 15N is commonly used for the hydrogen observation. We applied the good characteristics of NRA, high energy and simple setup, to the in-situ observation of hydrogen uptake into the multi-layer hydrogen storage target [6]. The focused 15N beam was extracted to the target cell via the SiN membrane [7], which was filled by H2 gas with various pressures: 10, 50, 100 and 500 Pa. The hydrogen depth profiles were taken by sweeping the 15N beam energy at four different gas pressures. The results directly supported the previous report [6], which indirectly implied that the Mg layer near the substrate is hydrogenated at first and then the Mg layer near the surface absorbs the hydrogen. Our results successfully determined the absolute hydrogen quantity in each layer.

References
[1] K. Kimura, et al., Appl. Phys. Lett., 78 (2001) 1679.
[2] D. Sekiba et al., NIMB, 401 (2017) 29.
[3] H. Hashimoto et al., NIMB 273 (2012) 241.
[4] Y. Hosono et al., NIMA, 361 (1995) 554.
[5] T. Orita et al., NIMA, 775 (2015) 154.
[6] A. Baldi et al., Phys. Rev. Lett., 102 (2009) 226102.
[7] H. Yonemura et al., NIMB, 269 (2011) 632.