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When comparing the dose rate readings of the meters the deviation often comes from that the response time of the instruments differs.
The 451P requires about 2s exposure to get reproducible readings on dose rates of about 20mR/h, and even longer times if the dose rate is lower, which is probably the reason why the results got closer to the higher dose rates you had.
451P response time specs:
451P response time specs The 452 will capture a x10 step increase in dose rate in about 2s, and if the dose rate increase is higher it will be faster. This is a probable cause why you see a higher reading on the 452 than on the 451P, hence the 451P has a higher risk of under-estimating the dose rate on these short pulses.
452 response time specs:
452 response time specs Please also note, that although the 452 is much faster, it updates the displayed dose and dose rate value every second so looking at the dose rate or peak dose rate on the display may under-estimate also the displayed dose rate you see on the 452. The best approach for short pulses would be to capture the accumulated/integrated dose and then calculate the peak by using the known exposure time of the machine. That approach should give readings of 451P and 452 closer to each other and is not dependent on the response time of the instruments. If you do this approach and find that the calculated values are similar to the displayed dose rate values, you have verified that the meter is fast enough for this setup and you don’t need to do this manual calculation next time.
Finally, another reason why there still might be differences and that 452 may show higher readings than 451P is that the low energy response is better with the 452 than 451P, capturing more low-energy photons, but this effect will not give the 2-3 times higher rates that you have seen.
If you’d like to learn more about the 452 technology, please enjoy this white paper.
Looking for a new meter? Check out the RaySafe 452 Radiation Survey Meter.