The time-over-threshold (TOT) technique is being used widely due to itsimplications in developing the multi-channel readouts, mainly when fast signal processing is required. Using the TOT technique, as a measure of energy loss instead of charge integration methods, significantly reduces the signal readout costs by combining the time and energy information. Therefore, this approach can potentially be utilized in J-PET tomograph which is built from plastic scintillators characterized by fast light signals. The drawback in adopting this technique lies in the non-linear correlation between input energy loss and TOT of the signal. The main motivation behind this work is to develop the relationship between TOT and energy loss and validate it by the J-PET tomograph setup. The experiment was performed using a 22Na beta emitter source placed in the center of the J-PET tomograph. This isotope produces photons of two different energies: 511 keV photons from the positron annihilation (direct annihilation or through the formation of a para-positronium atom or pick-off process of ortho-positronium atoms) and a 1275 keV prompt photon. This allows the study of the correlation between TOT values and energy loss for energy ranges up to 1000 keV. Since the photon interacts predominantly via Compton scattering inside the plastic scintillator, there is no direct information of the energy deposition. However, using the J-PET geometry, one can measure the scattering angle of the interacting photon. Since the 22Na source emits photons of two different energies, it is necessary to know unambiguously the energy of incident photons and their corresponding scattering angles in order to estimate energy deposition. In summary, this work presents a dedicated algorithm developed to tag photons of different energies and studying their scattering angles to calculate the energy deposition by the interacting photons. A new method was elaborated to measure the energy loss by photons interacting with plastic scintillators used in the J-PET tomograph. We find the relationship between the energy loss and TOT is non-linear and can be described by the functions TOT = A0 + A1 * ln(E dep + A2) + A3 * (ln(E dep + A2))2 and TOT = A0 - A1 * A2$^{E_{dep}}\phantom {\dot {i}\!}$. In addition, we also introduced a theoretical model to calculate the TOT as a function of energy loss in plastic scintillators. A relationship between TOT and energy loss by photons interacting inside the plastic scintillators used in J-PET scanner is established for a deposited energy range of 100–1000 keV.

中文翻译：

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估算J-PET扫描仪中使用的塑料闪烁体中超过阈值的时间与光子能量损失之间的关系。

阈值时间（TOT）技术由于其在开发多通道读数中的含义而被广泛使用，主要是在需要快速信号处理时。使用TOT技术代替电荷积分方法作为能量损失的一种度量，通过组合时间和能量信息，可以显着降低信号读取成本。因此，该方法可潜在地用于由塑料闪烁体构建的J-PET断层扫描仪中，该闪烁体具有快速的光信号特征。采用该技术的缺点在于输入能量损耗与信号的TOT之间存在非线性关系。这项工作的主要动机是发展TOT与能量损失之间的关系，并通过J-PET断层扫描仪进行验证。使用放置在J-PET断层扫描仪中心的22Naβ发射源进行了实验。该同位素产生两种不同能量的光子：来自正电子an灭（直接an灭或通过形成对正电子原子或正正电子原子的拾取过程）的511 keV光子和1275 keV的即时光子。这样就可以研究TOT值与高达1000 keV能量范围的能量损失之间的相关性。由于光子主要通过塑料闪烁体内部的康普顿散射相互作用，因此没有直接的能量沉积信息。但是，使用J-PET几何形状，可以测量相互作用的光子的散射角。由于22Na光源发射两种不同能量的光子，有必要明确地了解入射光子的能量及其相应的散射角，以便估算能量沉积。总之，这项工作提出了一种专用算法，用于标记不同能量的光子并研究它们的散射角，以计算相互作用的光子的能量沉积。阐述了一种新方法来测量光子与J-PET断层扫描仪中使用的塑料闪烁体相互作用的能量损失。我们发现能量损失和TOT之间的关系是非线性的，可以通过函数TOT = A0 + A1 * ln（E dep + A2）+ A3 *（ln（E dep + A2））2和TOT =来描述。 A0-A1 * A2 $ ^ {E_ {dep}} \ phantom {\ dot {i} \！} $。此外，我们还引入了理论模型来计算TOT作为塑料闪烁体中能量损失的函数。