Xp105

Graphite samples were obtained from the Ignalina NPP RBMK-1500 reactor, in which graphite was used as both a moderator and a reflector. The samples were collected from different reactor sites—from central and peripheral zones. Samples No. 3–5 and No. 8–10 were selected from the central zone of the reactor, while samples No. 1 and No. 2 were from the peripheral zone. Some of the samples were divided into several parts for analysis.
Prior to combustion, the mass of each graphite sample was determined using a XP105 (Mettler-Toledo, Switzerland) dual range balance. The results are listed in Table 1, organized as the sample mass by weighing. The amount of carbon in the CO₂ form that evolved during the combustion process was estimated using a thermal conductivity detector TCD from an elemental analyzer.
The experimental equipment used in this research is shown in Fig 1. It consists of both a commercial elemental analyzer, in which the graphite samples are combusted, and the mass of carbon in the sample is determined; and a semiconductor β detection system for online ¹⁴C determination, consisting of a chamber and 2 semiconductor detectors. Additionally, gas catchers and a liquid scintillation counting system were used to evaluate the accuracy of the semiconductor system.

For high-NH₄⁺ stress experiments, 5-day-old seedlings were transferred onto growth medium containing various concentrations of (NH₄)₂SO₄. Following 6 d of treatment, photographs were taken, and relative rosette size and shoot biomass were measured. To study the effect of precursors or inhibitors, the medium was supplemented with NH₄⁺ plus the indicated concentrations of ACC (Sigma), AgNO₃ (Shanghai yuanye biotechnology Co. Ltd, Shanghai, China), H₂O₂ (Shanghai yuanye biotechnology Co. Ltd), or SHAM (Shanghai yuanye biotechnology Co. Ltd). The ratio of average rosette size on NH₄⁺-stressed plates to the average rosette size on control plates was calculated as relative rosette size, according to Lei et al. (2011) . The fresh weight of each individual shoot was measured immediately after harvest using a high-precision balance (0.000001) (XP105, Mettler Toledo).