## 3 The High-Rate Sealed MRPC
### X-ray Test  
To examine the current behavior of the prototype at high rate, a Spellman XRB80N100 X-ray source with Tungsten as the target material was placed on the top of the counter. The operating HV and current of the source is no higher than 50 kV and 1 mA. Accordingly, the X-ray and secondary charged particles have lower energy than to even penetrate a detector. Hence, only the sealed prototype on the top will get the proper high rate. The X-rays cover a large area to realize full irradiation to the prototype. In the test, the counting rate was recorded by a TDC, and the current of the counter was monitored by the HV power source in the precision of 10 nA. In the cosmic background, they are both very low, as described previously. The gas flow to the sealed prototype is 30 mL/min during the X-ray test, which indicates that the gas exchange of the whole gas volume can be realized in several minutes in order to protect the detector.  
The counting rate of the detector has a positive correlation with the operating current, as shown in Figure 8. The misalignment to strict linearity is possibly due to the increase in energy of the incident particles when magnifying the HV of the X-ray tube, as more gas gaps will be penetrated and more avalanches will develop, which lead to a higher current at high-rate situations. In general, the sealed prototype has a normal response to the incident flux. The prototype was then tested in a continuous run that lasts for 9 h. Figure 9 shows the current behavior since the X-ray was on. The prototype was first laminated for more than 6 h, with the X-ray source operated in 42 kV/0.3 mA. The counting rate was kept at 3.4 kHz/cm\({}^{2}\); simultaneously, the current of the counter was stable around 5 \(\mu\)A. For 6 h, there was no sign of rising on the MRPC current, and the fluctuation was ranged within 20 nA. Afterward, the flux was reinforced or intermitted several times to check the current response, with the details in Figure 8. It can be found that the current was quite stable at three rate stages (<10 nA/7.08 \(\mu\)A\(-\)<0.14% measurement precision at 4.3 kHz/cm\({}^{2}\), and 15 nA/8.58 \(\mu\)A \(-\)0.2% at 5 kHz/cm\({}^{2}\)) and responded with high sensitivity in the changes of X-ray flux. Moreover, it should be mentioned that the current-rate correlation agrees well with that in Figure 8. In Figure 10, when the X-ray was shut down, the current of the sealed prototype dropped to the dark current level of 30 nA in less than a half minute. It should be mentioned that the same decay patterns were performed in all the three shutdown actions in Figure 9. An enlarged decay process can be seen in Figure 10a. In comparison, the  
Figure 7: Performances of the high-rate sealed prototype working in different flow rates.  
current relaxation procedure of the SoLID MRPC in Figure 10b took hours after exposed in high rate, which may indicate the existence of pollutant accumulation, and the ful recovery to the dark current level took about a day. The X-ray test has offered the potential prospect of the sealed MRPC to deal with mass pollutant production at a high rate.  
Figure 8: The relation of the counting rate with respect to the operating current of the detector. The error bars are contained within the size of the symbol.  
Figure 10: The current decay comparison since the X-ray was shut down. (**a**) The high-rate sealed MRPC; (**b**) the SoLID prototype.  
Figure 9: The current of the high-rate sealed prototype under full-area X-ray irradiation. The current at the early 6 h remains unchanged as well.