Passive Neutron Coincidence Timing for Plutonium-Curium Separation
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Solution Overview
Problem
Existing passive neutron measurement methods struggle to accurately estimate the mass of plutonium in the presence of curium in radioactive waste or nuclear materials, leading to significant overestimation due to curium's intense neutron emission, especially when the ratio of curium to plutonium exceeds 0.1%, and are hindered by spurious gamma contributions.
Innovation Solution
A method utilizing a nonlinear regression model with distinct time windows to differentiate neutron coincidences from 240Pu and 244Cm, employing polyvinyl-toluene (PVT) plastic scintillators to detect fast neutrons, and accounting for different neutron emission probabilities in specific time intervals to improve plutonium estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If passive neutron measurement is used to avoid technical constraints and costs of active measurement, then cost and complexity are reduced, but measurement precision deteriorates due to curium interference
Solution Approach 1:
The measurement time is segmented into distinct time windows (first time window and second time window) with different durations. The first window is optimized for detecting plutonium neutron coincidences while the second window captures curium neutron coincidences. By analyzing the ratio of coincidences from these segmented time periods, the method distinguishes plutonium signal from curium background interference, thereby maintaining measurement precision without requiring complex active measurement systems.
2Device complexity
If curium presence is not accounted for in passive measurement, then measurement process is simpler, but measurement precision deteriorates due to significant overestimation of plutonium quantity
Solution Approach 1:
The patent introduces a curium quantification mechanism that acts as an intermediary correction factor. By measuring the ratio of neutron coincidences in two different time windows, the system indirectly quantifies the curium content and uses this information to correct the plutonium mass estimation. This intermediary approach allows the simple passive measurement process to account for curium interference without adding significant complexity, thereby maintaining both process simplicity and measurement precision.
3Device complexity
If single time window measurement is used, then measurement process is simpler, but measurement precision deteriorates due to inability to differentiate plutonium and curium contributions
Solution Approach 1:
The measurement method employs dynamic time windowing where two distinct time windows are used with different durations optimized for different isotopes. The first time window is shorter and captures the prompt neutron coincidences from plutonium fission, while the second time window is longer and captures the delayed coincidences from curium spontaneous fission. This dynamic temporal separation allows the system to differentiate between plutonium and curium contributions, improving measurement precision while maintaining relatively simple measurement methodology.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method provides precise plutonium mass estimation by distinguishing between 240Pu and 244Cm contributions in different time windows, reducing estimation errors and overcoming spurious gamma interference, even in high curium content scenarios.
Implementation Method 1
employing polyvinyl-toluene (PVT) plastic scintillators to detect fast neutrons
Implementation Method 2
curium isotopes emit more neutrons by spontaneous fission than plutonium isotopes (2.72 on average versus 2.16)
Data Source
Figure 1~2
Figure 3~4a
Figure 4b
AI summary
A method for determining the quantity of plutonium in a radioactive sample in the presence of curium, comprising the steps of: - Measuring (301) a train of electrical pulses using a radiation detection system, - Determining (302), respectively in a first and a second time window, a first and a second number of coincidences of second-order pulses between the electrical pulses supplied by the detectors, - The second time window being formed by the union of the first time window and a third time window, - The first and third time windows being chosen such that the number of coincidences of second-order pulses related to plutonium is greater than that related to curium in one of the two windows between the first and third time windows and less than that related to curium in the other window,- Determine (304) the quantity of plutonium by applying a non-linear regression model taking as parameters: the total number of measured pulses, the first number of second-order pulse coincidences and the second number of second-order pulse coincidences, the model having been previously trained on a set of simulated values from a numerical model.