WO2021136562A1 - Device for measuring the mixed radiation field of photons and neutrons - Google Patents

Device for measuring the mixed radiation field of photons and neutrons Download PDF

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Publication number
WO2021136562A1
WO2021136562A1 PCT/CZ2020/050091 CZ2020050091W WO2021136562A1 WO 2021136562 A1 WO2021136562 A1 WO 2021136562A1 CZ 2020050091 W CZ2020050091 W CZ 2020050091W WO 2021136562 A1 WO2021136562 A1 WO 2021136562A1
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WO
WIPO (PCT)
Prior art keywords
neutrons
radiator
photons
diode
pin diode
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PCT/CZ2020/050091
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French (fr)
Inventor
Martin KÁKONA
Iva Ambrožová
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Ústav Jaderné Fyziky Av Čr V.V.I.
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Application filed by Ústav Jaderné Fyziky Av Čr V.V.I. filed Critical Ústav Jaderné Fyziky Av Čr V.V.I.
Publication of WO2021136562A1 publication Critical patent/WO2021136562A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/20—Measuring radiation intensity with scintillation detectors
    • G01T1/2018—Scintillation-photodiode combinations
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16—Measuring radiation intensity
    • G01T1/24—Measuring radiation intensity with semiconductor detectors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T3/00—Measuring neutron radiation
    • G01T3/08—Measuring neutron radiation with semiconductor detectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof  ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/86—Types of semiconductor device ; Multistep manufacturing processes therefor controllable only by variation of the electric current supplied, or only the electric potential applied, to one or more of the electrodes carrying the current to be rectified, amplified, oscillated or switched
    • H01L29/861—Diodes
    • H01L29/868—PIN diodes

Definitions

  • the invention relates to devices for measuring ionizing radiation in a mixed field consisting of neutrons and photons based on semiconductor components and a radiator.
  • radiators made of materials that have a large effective cross section for converting neutrons (e.g., 10 B, 6 Li, 3 He) to positively charged ions (e.g., protons or alpha particles) are used to convert neutrons to detectable particles (e.g., protons or alpha particles). These particles can then be detected directly by the semiconductor diode.
  • An example of such use is the method described in document DEVELOPMENT OF A PORTABLE THERMAL NEUTRON DETECTOR BASED ON A BORON RICH HETERODIODE (Tomov et al. ; 2008).
  • the above-mentioned disadvantage can be solved by a suitable geometric arrangement of several detectors in a so-called telescope. Or generally by reducing the sensitivity of the detector to photons by reducing the sensitive volume of the diode.
  • a thin PIN diode is given in patent document US 8569708 B2.
  • the first solution increases the complexity of the instrument, because it requires electronics to perform coincidence measurements.
  • the use of two or more diodes also involves doubling or multiplying the analog signal processing.
  • An example of such diode array is given in patent document US 20190243012 A1.
  • the second solution (reducing the diode thickness) assumes that another detector will be used to detect photons in the mixed field.
  • the object of the invention is to eliminate all the above-mentioned drawbacks of the prior art, so that the detector is capable of qualitatively resolving photons and neutrons while maintaining the required simplicity of the instrument.
  • the subject of the invention is a dosimeter detection unit for the detection of photons and neutrons in a mixed field.
  • the detection unit consists of a semiconductor diode and a radiator for the conversion of neutrons into positively charged ions.
  • the semiconductor diode for the construction of such detection unit is preferably a PIN diode, since use of only one is sufficient to achieve the desired effect, i.e. the function of the detector.
  • a multi-diode design is required.
  • This PIN diode is connected in the closing direction and the thickness of its depleted area is at least 100 ⁇ m. Using lower thickness of the depleted diode region does not allow efficient photon capture and the efficiency of the diode for its function in the context of the invention is insufficient. Conversely, a higher thickness improves the diode's ability to capture high-energy photons. Achieving the effect of the invention, i.e. the detection of both photons and neutrons, and their resolution, also occurs when using a PIN diode with a thickness of the depleted area of up to 30 mm.
  • a PIN diode is advantageous, because it allows the construction of a detector with a large effective area of the radiator and a large area of the diode at low dark current and low diode capacity. High dark current and large capacity degrade the applicability of conventional diodes as large-area ionizing radiation detectors.
  • a large area of the detection unit which contains a larger volume of the moderator, is also advantageous.
  • the radiator for constructing such a detection unit may be, for example, 10 B, 6 Li, or 3 He.
  • the radiator is a layer of 10 B with a thickness of 1 to 60 ⁇ m, since this material has four times bigger effective cross-section than 6 Li and, compared to 3 He, is solid at normal temperature and pressure.
  • a radiator layer of less than 1 ⁇ m the effect of the invention does not occur, since such a small volume of boron will not allow reliable particle generation.
  • the range of these particles generated in the radiator is only units of ⁇ m. For this reason, the upper limit of functionality is the 60 ⁇ m layer, which corresponds to the thinnest available 10 B film.
  • the most preferred layer thickness is 3 ⁇ m.
  • the radiator it is necessary for the radiator to be placed directly on the diode's surface. Detection of neutrons and photons in this configuration is the most efficient at the PI interface and in the immediate vicinity of the PI interface. There is usually additional 100 to 200 nm of Si and SiO 2 between the alpha-particle sensitive area and the diode surface, with the SiO 2 layer protecting the diode from atmospheric oxygen and other possible contaminants.
  • the device according to the invention achieves its effects by advantageously combining a radiator capable of generating alpha particles by capturing thermal neutrons and the properties of a PIN diode connected in the closing direction with low or zero negative bias of zero to units of volts with a large detection volume sensitive to gamma and X-ray photons which is at the same time capable of distinguishing with a high efficiency these photons from the alpha particles emitted by the radiator.
  • Both components of the mixed field, i.e. photons and neutrons simultaneously, can be measured by a detection unit equipped with a single diode.
  • the detector For use in a field of neutrons with energies higher than those characteristic for thermal neutrons, the detector must be placed in a moderator, which slows down the neutrons, and thus takes advantage of the radiator's ability to convert them.
  • FIG. 1 shows a cross-section of the mechanical assembly of the detector according to an exemplary embodiment.
  • the example describes a mixed-field detection unit on board of an airliner flying at a flight level of approximately 10 km above the ground.
  • the detection unit is made in a sandwich arrangement, which consists of a planar semiconductor PIN diode with a thickness of the depleted area of 300 ⁇ m and a radiator.
  • the radiator is a 60 ⁇ m layer of isotope 10 B deposited on a carrier PET film close to the p++ doped region of the PIN diode.
  • Such an arrangement is sensitive to thermal neutrons. The neutrons react with a radiator, which emits alpha particles due to neutron capture, which are then captured in a PIN diode.
  • the detection unit is placed in a 300 mm thick HDPE layer.
  • the invention is industrially applicable in the construction of instruments for quantitative and qualitative measurements in a mixed field of ionizing radiation, where photons and neutrons occur simultaneously. Determination of the neutron-to-photon flux ratio can be then used to determine the dose equivalent.

Abstract

Device for measuring the mixed radiation field of photons and neutrons consisting of a PIN diode and a radiator with a large effective cross-section, with the depleted area of the PIN diode having a thickness of at least 100 μm and the radiator with a large effective cross section and a layer thickness of not more than 60 μm for the conversion of neutrons to alpha particles being placed directly on the PIN diode's surface. The radiator is preferably 10B on the outside covered with a plastic foil.

Description

Device for measuring the mixed radiation field of photons and neutrons
The invention relates to devices for measuring ionizing radiation in a mixed field consisting of neutrons and photons based on semiconductor components and a radiator.
Currently, semiconductor diodes are used in many ionizing-radiation detectors. An example of the construction of such a detector is depicted in patent document WO 9961880 A2.
Semiconductor diodes are not able to detect neutrons directly. Therefore, radiators made of materials that have a large effective cross section for converting neutrons (e.g., 10B, 6Li, 3He) to positively charged ions (e.g., protons or alpha particles) are used to convert neutrons to detectable particles (e.g., protons or alpha particles). These particles can then be detected directly by the semiconductor diode. An example of such use is the method described in document DEVELOPMENT OF A PORTABLE THERMAL NEUTRON DETECTOR BASED ON A BORON RICH HETERODIODE (Tomov et al.; 2008). However, in places where the field of neutrons occurs, in most cases also the field of gamma photons occurs due to nuclear reactions, which are associated with the occurrence of neutrons. Since the accompanying photons are also detected by the diode, it is difficult to separate the detection of these photons from the detection of neutrons (or, more specifically, generated protons and alpha particles). Thus, with an unknown ratio of neutrons and photons in a mixed field of ionizing radiation, it is difficult to determine, for example, the spatial dose equivalent.
According to the state of the art, the above-mentioned disadvantage can be solved by a suitable geometric arrangement of several detectors in a so-called telescope. Or generally by reducing the sensitivity of the detector to photons by reducing the sensitive volume of the diode. Such an example of a thin PIN diode is given in patent document US 8569708 B2. The first solution increases the complexity of the instrument, because it requires electronics to perform coincidence measurements. The use of two or more diodes also involves doubling or multiplying the analog signal processing. An example of such diode array is given in patent document US 20190243012 A1. The second solution (reducing the diode thickness) assumes that another detector will be used to detect photons in the mixed field.
Currently, an invention describing a method for determining the type of ionizing radiation by means of a semiconductor diode and a circuit for carrying out this method is known from patent document CZ 307570. However, the present invention cannot be used directly to build a neutron detector without further development, since a detector assembled according to the technical features in the presented document is not able to detect neutrons.
The object of the invention is to eliminate all the above-mentioned drawbacks of the prior art, so that the detector is capable of qualitatively resolving photons and neutrons while maintaining the required simplicity of the instrument.
The subject of the invention is a dosimeter detection unit for the detection of photons and neutrons in a mixed field. The detection unit consists of a semiconductor diode and a radiator for the conversion of neutrons into positively charged ions.
The semiconductor diode for the construction of such detection unit is preferably a PIN diode, since use of only one is sufficient to achieve the desired effect, i.e. the function of the detector. In the case of another type of photodiode, a multi-diode design is required. This PIN diode is connected in the closing direction and the thickness of its depleted area is at least 100 μm. Using lower thickness of the depleted diode region does not allow efficient photon capture and the efficiency of the diode for its function in the context of the invention is insufficient. Conversely, a higher thickness improves the diode's ability to capture high-energy photons. Achieving the effect of the invention, i.e. the detection of both photons and neutrons, and their resolution, also occurs when using a PIN diode with a thickness of the depleted area of up to 30 mm.
The use of a PIN diode is advantageous, because it allows the construction of a detector with a large effective area of the radiator and a large area of the diode at low dark current and low diode capacity. High dark current and large capacity degrade the applicability of conventional diodes as large-area ionizing radiation detectors. In the case of using a moderator for braking neutrons before their conversion in a radiator, a large area of the detection unit, which contains a larger volume of the moderator, is also advantageous.
The radiator for constructing such a detection unit may be, for example, 10B, 6Li, or 3He. Preferably, the radiator is a layer of 10B with a thickness of 1 to 60 μm, since this material has four times bigger effective cross-section than 6Li and, compared to 3He, is solid at normal temperature and pressure. With a radiator layer of less than 1 μm, the effect of the invention does not occur, since such a small volume of boron will not allow reliable particle generation. The range of these particles generated in the radiator is only units of μm. For this reason, the upper limit of functionality is the 60 μm layer, which corresponds to the thinnest available 10B film. Theoretically, the most preferred layer thickness is 3 μm. For the same reason, it is necessary for the radiator to be placed directly on the diode's surface. Detection of neutrons and photons in this configuration is the most efficient at the PI interface and in the immediate vicinity of the PI interface. There is usually additional 100 to 200 nm of Si and SiO 2 between the alpha-particle sensitive area and the diode surface, with the SiO 2 layer protecting the diode from atmospheric oxygen and other possible contaminants.
The device according to the invention achieves its effects by advantageously combining a radiator capable of generating alpha particles by capturing thermal neutrons and the properties of a PIN diode connected in the closing direction with low or zero negative bias of zero to units of volts with a large detection volume sensitive to gamma and X-ray photons which is at the same time capable of distinguishing with a high efficiency these photons from the alpha particles emitted by the radiator. Both components of the mixed field, i.e. photons and neutrons simultaneously, can be measured by a detection unit equipped with a single diode.
By using the invention in a connection with a method for determining the type of ionizing radiation by means of a semiconductor diode, it is possible to distinguish whether the individual signals obtained from the detection unit are photons from the environment or alpha particles generated by the interaction of neutrons in the radiator.
For use in a field of neutrons with energies higher than those characteristic for thermal neutrons, the detector must be placed in a moderator, which slows down the neutrons, and thus takes advantage of the radiator's ability to convert them.
 Fig.1
shows a cross-section of the mechanical assembly of the detector according to an exemplary embodiment.
Fig.2
shows an example of the shape of the pulses for a selected amplitude, with pulses with a steeper rise and fall representing alpha particles and neutrons, respectively, and other pulses with a slower rise and fall representing photons.
 Example 1
The example describes a mixed-field detection unit on board of an airliner flying at a flight level of approximately 10 km above the ground. The detection unit is made in a sandwich arrangement, which consists of a planar semiconductor PIN diode with a thickness of the depleted area of 300 μm and a radiator. In this example, the radiator is a 60 μm layer of isotope 10B deposited on a carrier PET film close to the p++ doped region of the PIN diode. Such an arrangement is sensitive to thermal neutrons. The neutrons react with a radiator, which emits alpha particles due to neutron capture, which are then captured in a PIN diode. The detection unit is placed in a 300 mm thick HDPE layer.
The invention is industrially applicable in the construction of instruments for quantitative and qualitative measurements in a mixed field of ionizing radiation, where photons and neutrons occur simultaneously. Determination of the neutron-to-photon flux ratio can be then used to determine the dose equivalent.

Claims (3)

  1. Device for measuring a mixed radiation field of photons and neutrons consisting of a PIN diode and a radiator with a large effective cross section, characterized in that the depleted area of the PIN diode has a thickness of at least 100 μm and the radiator with a large effective cross section and a layer thickness of not more than 60 μm for the conversion of neutrons to alpha particles is placed directly on the PIN diode's surface.
  2. Device according to claim 1, characterized in that the radiator is 10B.
  3. Device according to claim 1 or 2, characterized in that the radiator is covered on the outside with a plastic foil.
PCT/CZ2020/050091 2020-01-05 2020-12-03 Device for measuring the mixed radiation field of photons and neutrons WO2021136562A1 (en)

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Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999061880A2 (en) 1998-04-24 1999-12-02 Digirad Corporation Integrated radiation detector probe
US6545281B1 (en) * 2001-07-06 2003-04-08 The United States Of America As Represented By The United States Department Of Energy Pocked surface neutron detector
WO2009117477A2 (en) * 2008-03-19 2009-09-24 The Government Of The United States Of America, As Represented By The Secretary Of The Navy Neutron detector with gamma ray isolation
US8569708B2 (en) 2009-01-30 2013-10-29 Alliance For Sustainable Energy, Llc High sensitivity, solid state neutron detector
CN107884811A (en) * 2017-11-27 2018-04-06 中核控制***工程有限公司 A kind of neutron detector based on silicon PIN
CZ307570B6 (en) 2017-10-12 2018-12-12 Ústav jaderné fyziky AV ČR, v. v. i. A method for determining the type of ionizing radiation and a connection for implementing this method
US20190243012A1 (en) 2018-02-05 2019-08-08 Rhombus Holdings Llc Physical structure for a tunable sensor system for particle detection

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999061880A2 (en) 1998-04-24 1999-12-02 Digirad Corporation Integrated radiation detector probe
US6545281B1 (en) * 2001-07-06 2003-04-08 The United States Of America As Represented By The United States Department Of Energy Pocked surface neutron detector
WO2009117477A2 (en) * 2008-03-19 2009-09-24 The Government Of The United States Of America, As Represented By The Secretary Of The Navy Neutron detector with gamma ray isolation
US8569708B2 (en) 2009-01-30 2013-10-29 Alliance For Sustainable Energy, Llc High sensitivity, solid state neutron detector
CZ307570B6 (en) 2017-10-12 2018-12-12 Ústav jaderné fyziky AV ČR, v. v. i. A method for determining the type of ionizing radiation and a connection for implementing this method
CN107884811A (en) * 2017-11-27 2018-04-06 中核控制***工程有限公司 A kind of neutron detector based on silicon PIN
US20190243012A1 (en) 2018-02-05 2019-08-08 Rhombus Holdings Llc Physical structure for a tunable sensor system for particle detection

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
TOMOV ET AL., DEVELOPMENT OF A PORTABLE THERMAL NEUTRON DETECTOR BASED ON A BORON RICH HET-ERODIODE, 2008

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