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CN-121995424-A - Thorium-based gas intrinsic measurement method and device

CN121995424ACN 121995424 ACN121995424 ACN 121995424ACN-121995424-A

Abstract

The invention provides an intrinsic measurement method and device of thorium, wherein the intrinsic measurement method comprises the following steps of recording detection time of alpha particles released by decay of 220 Rn gas to be measured and a daughter 216 Po thereof in a measurement cavity, carrying out Bayesian analysis according to the detection time, calculating 220 Rn- 216 Po true coincidence count, and calculating the thorium activity concentration according to 220 Rn count, 216 Po count and 20 Rn- 216 Po true coincidence count. The intrinsic measurement method and the device utilize the intrinsic characteristic that two alpha particles emitted by 220 Rn and 216 Po after being sequentially decayed form a coincidence signal, so that the detection efficiency is reduced.

Inventors

  • ZHAO CHAO
  • HAN GANG
  • HE LINFENG
  • Hu chongqing
  • LIU JIAYU
  • WANG JINGHANG

Assignees

  • 上海市计量测试技术研究院有限公司

Dates

Publication Date
20260508
Application Date
20260205

Claims (9)

  1. 1. A method of intrinsic measurement of thorium gas, the method comprising the steps of: Recording the detection time of alpha particles released by decay of 220 Rn gas to be detected and the daughter 216 Po thereof in the measurement chamber; performing Bayesian analysis according to the detection time, and calculating 220 Rn- 216 Po true coincidence count; The thorium activity concentration was calculated from 220 Rn count, 216 Po count, and the 20 Rn- 216 Po true coincidence count.
  2. 2. The intrinsic thorium gas measurement method according to claim 1, wherein the calculation formula of the thorium gas activity concentration is shown in formula 1: 1 (1) Wherein C is the activity concentration of 220 Rn in the measurement chamber, For the count of 220 Rn, For the count of 216 Po, For 220 Rn- 216 Po true coincidence count, V is the measurement chamber volume, T is the measurement duration, lambda is the decay constant of 216 Po, tau is the time length of coincidence window, expression To fit the decay coefficients, 216 Po is represented as the probability of decay within the fit window.
  3. 3. The method according to claim 1, characterized in that the time accuracy of the detection time is not lower than 500 ms, preferably not lower than 10 ms.
  4. 4. The intrinsic measurement method of thorium activity concentration according to claim 1, characterized in that the energy of the α -particles released by decay of 220 Rn gas and its daughter 216 Po to be measured can also be recorded in the measurement chamber.
  5. 5. The method of claim 1, wherein determining whether two alpha particles constitute coincidence signals is performed based on a comparison of a detection time difference of the two alpha particles with a coincidence window, and then accumulating probabilities of each coincidence signal being 220 Rn- 216 Po true coincidence signals according to equation 2 to obtain 220 Rn- 216 Po true coincidence counts: 2, 2 Where i denotes the i-th coincidence signal, w i denotes the i-th coincidence signal with an alpha signal time difference, Indicating the probability that the coincidence signal is 220 Rn- 216 Po true coincidence signal in the case of w i where the coincidence signal α signal time difference is.
  6. 6. The thorium-gas eigenvalue measurement method according to claim 1, characterized in that, when said bayesian analysis is performed, the probability of coincidence signal being 220 Rn- 216 Po true coincidence signal is calculated according to formula 3: 3 Wherein, the 、 Respectively representing prior probabilities that one coincidence signal is 220 Rn- 216 Po true coincidence signal and accidental coincidence signal under the condition of no posterior information; 、 The probability that the alpha signal time difference is w is respectively expressed on the premise that one coincidence signal is 220 Rn- 216 Po true coincidence signal and accidental coincidence signal.
  7. 7. The method according to claim 4, wherein when the energy of alpha particles released by decay of 220 Rn gas to be measured is recorded in the measurement chamber, it is determined whether the two alpha particles constitute coincidence signals based on not only the difference in detection time of the two alpha particles but also the energy of the two alpha particles, and 220 Rn- 216 Po true coincidence count is calculated based on the energy of the two alpha particles.
  8. 8. A device for intrinsic measurement of thorium activity, characterized in that the device for intrinsic measurement of the concentration of thorium activity is capable of operating the intrinsic measurement of thorium according to any one of claims 1-7.
  9. 9. The thorium-gas intrinsic measurement apparatus of claim 8, wherein the intrinsic measurement apparatus comprises a measurement chamber, a counting module, and a data analysis module; the counting module is used for recording the detection time of alpha particles released by decay of 220 Rn gas to be detected and also used for recording the energy of the alpha particles released by decay of 220 Rn gas to be detected; the data analysis module is used for performing Bayesian analysis and calculating the concentration of thorium activity.

Description

Thorium-based gas intrinsic measurement method and device Technical Field The invention belongs to the technical field of radioactivity measurement, and particularly relates to a method and a device for intrinsic measurement of thorium emanation. Background Thorium gas (220 Rn) is one of the isotopes of the radioactive element radon (Rn), a natural radioactive inert gas. Radon is the second largest lung cancer causative agent identified by the world health organization as being next to smoking. Radon exposure is a major source of public natural radiation dose, in which the two radioactive isotopes of radon (222 Rn and 220 Rn) and their short-lived daughter contribute more than half of the total natural radiation dose. Therefore, accurate measurement of 222 Rn and 220 Rn in air is of great importance for assessing public health risk. For the isotope 222 Rn of 220 Rn, corresponding measurement standards are established in China, so that a 222 Rn measuring instrument can trace to a unified standard, and the accuracy of a measurement result is ensured. However, for 220 Rn, no corresponding measurement standard is established in China, so that 220 Rn measuring instruments cannot trace home, the magnitude of the 220 Rn measuring instruments cannot be unified, and accuracy cannot be guaranteed. International, germany Federal physical institute (PTB) and French Huntion Libei g Lehr national laboratory (LNE-LNHB) established 220 Rn activity concentration primary measurement standards, respectively. The standard of 220 Rn primary measurement in Germany does not directly measure 220 Rn, but indirectly estimates the concentration of 220 Rn in standard 220 Rn chamber by measuring the activity and the emanation coefficient of the parent source 228 Th (i.e. the proportion of 220 Rn precipitated from the parent source by decay of 228 Th). The accuracy of the method is seriously dependent on the uniformity and stability of the gas in the standard 220 Rn chamber, so that the size and practical application of the 220 Rn chamber are limited. A set of 20 Rn measuring device is developed according to the 220 Rn primary measuring standard in France, and the detection efficiency of 220 Rn and the daughter thereof is calculated by a Monte Carlo simulation method so as to realize accurate measurement of 220 Rn activity concentration. The accuracy of the method is seriously dependent on the accuracy of the detection efficiency, and the detection efficiency is influenced by factors such as temperature, humidity, detector state and the like, so that the accuracy is poorer than that of the German 220 Rn primary measurement standard. In summary, a 220 Rn accurate measurement method which does not depend on external measurement standards and can avoid the limitations of Germany and French methods is researched, which is helpful for the development of 220 Rn measurement capability and is helpful for guaranteeing public radiation safety. Disclosure of Invention The invention provides a method and a device for intrinsic measurement of thorium, which utilize two alpha particles emitted by 220 Rn and 216 Po which decay successively to form an intrinsic characteristic which accords with a signal, so as to reduce detection efficiency; the method and the device have self-tracing property because the detection efficiency is reduced without the need of an external measurement standard scale, and simultaneously, the influence of the detection efficiency change on the measurement accuracy is avoided, and the measurement accuracy is improved. In order to achieve the above purpose, the present invention adopts the following technical scheme: One of the purposes of the invention is to provide an intrinsic measurement method of thorium activity concentration, which comprises the following steps: Recording the detection time of alpha particles released by decay of 220 Rn gas to be detected and the daughter 216 Po thereof in the measurement chamber; performing Bayesian analysis according to the detection time, and calculating 220Rn-216 Po true coincidence count; The thorium activity concentration was calculated from 220 Rn count, 216 Po count, and the 20Rn-216 Po true coincidence count. As a preferable technical scheme of the invention, the calculation formula of the thorium activity concentration is shown as formula 1: 1 (1) Wherein C is the activity concentration of 220 Rn in the measurement chamber,For the count of 220 Rn,For the count of 216 Po,For 220Rn-216 Po true coincidence count, V is the measurement chamber volume, T is the measurement duration, lambda is the decay constant of 216 Po, tau is the time length of coincidence window, expressionTo fit the decay coefficients, 216 Po is represented as the probability of decay within the fit window. As a preferred embodiment of the present invention, the time precision of the detection time is not less than 500 ms, preferably not less than 10 ms. As a preferred technical solution of the invention, the en