Double-source rod shielding device and assembling and disassembling method

Abstract

The invention relates to the technical field of petroleum and natural gas drilling, in particular to a double-source rod shielding device and a loading and unloading method, and the device comprises a neutron source tank, a source rod, a gamma source tank and a double-source rod; the neutron source tank and the gamma source tank are oppositely connected, communicating holes are coaxially formed in the neutron source tank and the gamma source tank, the two ends of the source rod extend into inlets of the communicating holes of the neutron source tank and the gamma source tank respectively, the double-source rod is arranged in the source rod, one end of the double-source rod is provided with a neutron source, and the other end of the double-source rod is provided with a gamma source; the end, provided with the neutron source, of the double-source rod extends into an inlet of the communicating hole of the neutron source tank in the source rod, the end, provided with the gamma source, of the double-source rod extends into an inlet of the communicating hole of the gamma source tank in the source rod, and a fishing head is arranged at the end, provided with the neutron source, of the double-source rod. A neutron source plug is arranged at the outlet of the communicating hole of the neutron source tank, and a gamma source plug is arranged at the outlet of the communicating hole of the gamma source tank; and the neutron source tank and the gamma source tank are filled with shielding materials, so that the double-source rod can be effectively shielded.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas drilling, in particular to a double-source rod shielding device and a loading and unloading method. Background Art

[0002] Chemical source neutron and lithology density instruments while drilling are widely used to measure formation porosity and density parameters. However, the instruments use chemical sources (20Ci 241Am-Be neutron source and 2Ci 137Cs gamma source), which may cause radiation contamination to the personnel who install the sources and the risk of radioactive sources falling into the well, which has gradually attracted great attention from oilfield companies, national environmental protection agencies and the government.

[0003] At present, there is no standard storage device, rapid loading and unloading chemical source tools and mature salvageable radioactive source design for chemical source logging while drilling in China, and the logging personnel are exposed to radiation for a long time.

[0004] In addition, once an instrument or radioactive source falls into a well, the salvage operation will be difficult, seriously affecting the success rate of the salvage. Summary of the invention

[0005] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a dual-source rod shielding device and a loading and unloading method to solve the technical problems in the prior art of long radiation exposure time for logging personnel during storage, loading and unloading and salvaging of radioactive sources, high difficulty and low efficiency in loading and unloading and salvaging.

[0006] The present invention is achieved through the following technical solutions:

[0007] A dual-source rod shielding device comprises a neutron source tank, a source rod, a gamma source tank and a dual-source rod; the neutron source tank and the gamma source tank are relatively connected, and the neutron source tank and the gamma source tank are coaxially provided with a connecting hole, the two ends of the source rod respectively extend into the connecting hole entrances of the neutron source tank and the gamma source tank, the dual-source rod is arranged in the source rod, one end of the dual-source rod is equipped with a neutron source, and the other end is equipped with a gamma source; the end of the dual-source rod equipped with the neutron source extends into the connecting hole entrance of the neutron source tank in the source rod, and the end of the dual-source rod equipped with the gamma source extends into the connecting hole entrance of the gamma source tank in the source rod, and a salvage head is arranged at the end of the dual-source rod equipped with the neutron source; a neutron source plug is provided at the outlet of the connecting hole of the neutron source tank, and a gamma source plug is provided at the outlet of the connecting hole of the gamma source tank; the neutron source tank and the gamma source tank are filled with shielding material.

[0008] Preferably, the dual-source rod includes a salvage head, a fastening ring, a neutron source compartment, a flexible rod and a gamma source compartment; one end of the flexible rod is threadedly connected to one end of the neutron source compartment, the other end of the neutron source compartment is connected to the salvage head through the fastening ring, and the other end of the flexible rod is threadedly connected to the gamma source compartment; the neutron source compartment contains a neutron source; the gamma source compartment contains a gamma source.

[0009] Furthermore, the material of the salvage head is beryllium copper soft metal material, and the salvage head includes a rope cap and a connecting head; the rope cap is connected to the connecting head and is arranged on the fastening ring through the connecting head, and an inverted trapezoidal groove platform is provided in an annular manner on the connecting head.

[0010] Furthermore, the diameter of the connecting end of the rope cap is larger than the diameter of the connecting end of the connector, and a concave platform is formed at the connection.

[0011] Furthermore, the material of the end of the source rod close to the gamma source is tungsten alloy.

[0012] Furthermore, the material of the neutron source plug is boron-containing polyethylene; the material of the gamma source plug is lead.

[0013] Furthermore, the shielding material filled in the neutron source tank and the gamma source tank is boron-containing polyethylene.

[0014] Furthermore, a connecting piece is provided on the neutron source tank, and a connecting buckle is provided on the gamma source tank, and the neutron source tank is connected to the connecting buckle of the gamma source tank via the connecting piece.

[0015] A method for assembling and disassembling a dual-source rod shielding device, based on the dual-source rod shielding device described above, comprises the following steps:

[0016] Open the connection device between the neutron source tank and the gamma source tank, open the gate of the gamma source tank, and slowly lift the neutron source tank out of the gamma source tank with a pneumatic winch;

[0017] After the neutron source tank is removed from the gamma source tank, the neutron source tank is slowly inserted into the water hole of the instrument, and it is confirmed whether it is safe and reliable, and the neutron source plug on the upper end of the neutron source tank is removed; the well crew uses a pneumatic winch to lift the assembled source loading tool to the drilling platform, and after lifting it to the drilling platform, the protective cap of the source loading tool is removed and lifted to the top of the upper body;

[0018] Grasp the dual source rods in the source tank with the source loading tool, and lift the source loading tool with both hands to confirm that the source loading tool holds the dual source rods firmly; open the source rod locking device, open the neutron source tank gate, and use the pneumatic winch to slowly lower the source loading tool with the dual source rods to the inside of the instrument, and confirm whether it reaches the inside of the instrument according to the scale mark of the source loading tool; use the rotation tool to turn the source loading tool clockwise to confirm whether the source is installed in place according to the scale mark of the source loading tool, and tighten the source rod and the instrument;

[0019] Use a special key to disconnect the source loading tool from the dual source rod. The operator carries the source loading tool and checks whether it is disconnected from the dual source rod. After confirming that the source loading tool is disconnected from the dual source rod, use a pneumatic winch to lift the source loading tool out of the instrument. After installing the source loading tool cap, the source loading tool can be lifted off the drilling platform.

[0020] The well crew used a pneumatic winch to lift the neutron source tank out from inside the instrument and insert it into the gamma source tank.

[0021] Furthermore, the neutron source tank and the neutron source plug are made of boron-containing polyethylene.

[0022] Compared with the prior art, the present invention has the following beneficial technical effects:

[0023] The present invention provides a dual-source rod shielding device, which places the dual-source rod in the source rod, and the two ends of the source rod are respectively extended into the connecting hole entrances of the neutron source tank and the gamma source tank, and the neutron source tank and the gamma source tank are filled with shielding materials, so that the dual-source rod can be effectively shielded, and the exposure time of logging personnel can be minimized. A salvaging head is arranged at the end of the dual-source rod equipped with a neutron source, and the salvaging effect can be directly achieved through the salvaging head without the need to load and unload the dual-source rod again, thereby improving work efficiency.

[0024] Furthermore, the material of the salvage head is beryllium copper soft metal material, and the salvage head includes a rope cap and a connecting head; the rope cap is connected to the connecting head and is arranged on the fastening ring through the connecting head, and an inverted trapezoidal groove platform is provided in a ring on the connecting head to facilitate the removal of the rope cap.

[0025] Furthermore, the diameter of the connecting end of the rope cap is larger than the diameter of the connecting end of the connector, and a recessed platform is formed at the connection to ensure that the rope cap does not come loose during the salvaging process.

[0026] Furthermore, the end of the source rod close to the gamma source is made of tungsten alloy to form a double-layer shielding structure, which effectively improves the shielding efficiency of the dual source rods.

[0027] The present invention also provides a loading and unloading method for a dual-source rod shielding device, which comprises the following steps: opening a connecting device between a neutron source tank and a gamma source tank, opening a gate of the gamma source tank, slowly lifting the neutron source tank out of the gamma source tank by a pneumatic winch, and after the neutron source tank is removed from the gamma source tank, slowly inserting the neutron source tank into a water hole of an instrument, thereby ensuring that a shielding effect is played during the loading and unloading process; grasping the dual-source rod in the source tank by a source loading tool and lifting the source loading tool with both hands, using a special key to disengage the source loading tool from the dual-source rod, and an operator carrying the source loading tool by hand to check whether the source loading tool is disengaged from the dual-source rod; after confirming that the source loading tool is disengaged from the dual-source rod, using a pneumatic winch to lift the source loading tool out of the instrument, and effectively loading and unloading the dual-source rod by the source loading tool, thereby ensuring the working efficiency and shielding function of the dual-source rod during the loading and unloading process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the overall structure of the double-source rod shielding device in the present invention;

[0029] Figure 2 Schematic diagram of the dual-source rod structure in the present invention;

[0030] Figure 3 It is a schematic diagram of the structure of the fishing head in the present invention;

[0031] Figure 4 It is a schematic diagram of the simulated position of the dose equivalent rate around the source tank in the present invention;

[0032] Figure 5 It is a schematic diagram of the dual source rod loading and unloading process in the present invention.

[0033] In the figure: 1-neutron source tank; 2-source rod; 3-gamma source tank; 4-dual source rod; 5-boron-containing polyethylene; 6-neutron source plug; 7-first connecting piece; 8-lead; 9-second connecting buckle; 10-gamma source plug; 11-salvage head; 12-fastening ring; 13-neutron source; 14-neutron source chamber; 15-flexible rod; 16-gamma source chamber; 17-gamma source; 18-tungsten alloy; 111-rope cap; 112-connector; 113-recessed platform; 114-inverted trapezoidal groove platform. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0035] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0036] The purpose of the present invention is to provide a dual-source rod shielding device and a loading and unloading method to solve the technical problems in the prior art of long radiation exposure time for logging personnel and high difficulty and low efficiency in loading and unloading and salvaging during the storage, loading and unloading and salvaging of radioactive sources.

[0037] See also Figure 1In one embodiment of the present invention, a dual-source rod shielding device is provided, comprising a neutron source tank 1, a source rod 2, a gamma source tank 3 and a dual-source rod 4; the neutron source tank 1 and the gamma source tank 3 are relatively connected, and the neutron source tank 1 and the gamma source tank 3 are coaxially provided with a connecting hole, the two ends of the source rod 2 are respectively extended into the connecting hole entrances of the neutron source tank 1 and the gamma source tank 3, the dual-source rod 4 is arranged in the source rod 2, one end of the dual-source rod 4 is equipped with a neutron source 13, and the other end is equipped with a gamma source 17; the dual-source One end of the rod 4 equipped with a neutron source 13 extends into the entrance of the connecting hole of the neutron source tank 1 in the source rod 2, and one end of the dual-source rod 4 equipped with a gamma source 17 extends into the entrance of the connecting hole of the gamma source tank 3 in the source rod 2. A salvage head 11 is provided at the end of the dual-source rod 4 equipped with the neutron source 13; a neutron source plug 6 is provided at the outlet of the connecting hole of the neutron source tank 1, and a gamma source plug 10 is provided at the outlet of the connecting hole of the gamma source tank 3; the neutron source tank 1 and the gamma source tank 3 are filled with shielding material.

[0038] Specifically, according to Figure 2 As shown, the dual-source rod 4 includes a salvage head 11, a fastening ring 12, a neutron source compartment 14, a flexible rod 15 and a gamma source compartment 16; one end of the flexible rod 15 is threadedly connected to one end of the neutron source compartment 14, the other end of the neutron source compartment 14 is connected to the salvage head 11 through the fastening ring 12, and the other end of the flexible rod 15 is threadedly connected to the gamma source compartment 16; the neutron source compartment 14 contains a neutron source 13; the gamma source compartment 16 contains a gamma source 17.

[0039] Among them, according to Figure 3 As shown, the material of the salvage head 11 is beryllium copper soft metal material, and the salvage head 11 includes a rope cap 111 and a connector 112; the rope cap 111 is connected to the connector 112 and is arranged on the fastening ring 12 through the connector 112, and an inverted trapezoidal groove platform 114 is annularly provided on the connector 112.

[0040] The diameter of the connecting end of the rope cap 111 is larger than the diameter of the connecting end of the connecting head 112, and a concave platform 113 is formed at the connecting portion.

[0041] In the present invention, if the chemical source falls into the well, the chemical source can be salvaged using the salvage head device of the double source rod. The salvage head includes a conical rope cap 111 and a cylindrical connector 112 which are connected to each other as one body. The salvage head is designed with beryllium copper soft metal material to ensure that the radioactive source can be smoothly fastened and pulled up when the rope cap 111 is deformed; the rope cap 1 is provided with an annular recessed platform 113 to ensure that the rope cap will not be disengaged during the salvage process; in addition, the connector 112 is symmetrically provided with two inverted trapezoidal recessed platforms 114, and the design of the inverted trapezoidal recessed platforms 114 can facilitate the removal of the rope cap.

[0042] Specifically, the end of the source rod 2 close to the gamma source 17 is made of tungsten alloy 18, the neutron source plug 6 is made of boron-containing polyethylene 5; the gamma source plug 10 is made of lead 8, and the shielding material filled in the neutron source tank 1 and the gamma source tank 3 is boron-containing polyethylene 5.

[0043] In the present invention, a connector 7 is provided on the neutron source tank 1 , and a connector buckle 9 is provided on the gamma source tank 3 . The neutron source tank 1 is connected to the connector buckle 9 of the gamma source tank 3 via the connector 7 .

[0044] The neutron source tank 1 and the gamma source tank 3 in the present invention are intended to safely transport the Am-Be neutron source and the Cs-137 gamma source, and to shield the radiation generated by the radioactive source to the greatest extent, thereby avoiding the generation of doses exceeding the safety standard for the staff. The source tank is mainly shielded by boron-containing polyethylene and an additional lead plate. In order to accurately describe the dose situation around the source tank, a simulation analysis of the dose equivalent rate around the source tank was carried out, and the results were compared with the national standards.

[0045] The ambient dose equivalent rate H*(d) refers to the dose equivalent produced by the extended directional field at the measurement point at a depth d on the radius of the inverse extended directional field in the ICRU sphere (a sphere with a diameter of 30 cm made of tissue equivalent material with a density of 1 g·cm. The material composition (by mass percentage is 76.2% oxygen, 11.1% carbon, 10.1% hydrogen, and 2.61% nitrogen). For strong penetrating radiation, d=10mm is recommended, and H*(d) is recorded as H*(10). For weak penetrating radiation, d=0.07mm is recommended. For neutron radiation field, d=10mm is selected, and for gamma radiation field, d=0.07mm is selected. At present, the ambient dose equivalent rate has become a commonly used evaluation indicator in radiation protection standards.

[0046] Common methods for dose simulation assessment include using a human body model to simulate dose deposition, converting flux to dose through a flux-dose conversion multiplier, etc. ICRP-74 recommends the ICRU sphere human body model as a dose assessment model. Therefore, the ICRU sphere was first used to simulate the ambient dose equivalent rate at different distances. The simulated positions are as follows: Figure 4 The summary results of the simulation are shown in Table 1, where the distance is the straight-line distance between the ICRU sphere surface and the source tank surface, and the unit of the result is μSv / h.

[0047]

[0048]

[0049] Table 1 Ambient dose equivalent rate of ICRU spherical model at 5cm, 50cm and 100cm from the source tank surface

[0050] According to the standards specified in "Radiation Protection Requirements for Oil and Gas Field Well Logging" (GBZ 118-2020), the ambient dose equivalent rate at 5 cm from the surface of the source tank should be less than the control value shown in Table 2.

[0051]

[0052] Table 2 Control value of ambient dose equivalent rate at 5 cm from the surface when the radioactive source tank for logging is loaded with source

[0053] The radiation sources used include an Am-Be neutron source with an activity of 20Ci and a Cs-137 gamma source with an activity of 2Ci. According to the ambient dose equivalent rate control values ​​corresponding to the activities, it can be seen that the source tank is fully in compliance with the standards.

[0054] according to Figure 5 As shown, the present invention also provides a method for loading and unloading a dual-source rod shielding device, based on the dual-source rod shielding device described above, comprising the following process:

[0055] Open the connection device between the neutron source tank 1 and the gamma source tank 3, open the gate of the gamma source tank 3, and slowly lift the neutron source tank 1 out of the gamma source tank 3 with a pneumatic winch;

[0056] After the neutron source tank 1 is removed from the gamma source tank 3, the neutron source tank 1 is slowly inserted into the water hole of the instrument, and it is confirmed whether it is safe and reliable, and the neutron source plug 6 on the upper end of the neutron source tank 1 is removed; the well crew uses a pneumatic winch to lift the assembled source loading tool to the drilling platform, and after lifting it to the drilling platform, the protective cap of the source loading tool is removed and lifted to the top of the upper body;

[0057] Grasp the dual source rod 4 in the source tank with the source loading tool, and lift the source loading tool with both hands to confirm that the source loading tool holds the dual source rod 4 firmly; open the source rod locking device, open the gate of the neutron source tank 1, and use the pneumatic winch to slowly lower the source loading tool with the dual source rod 4 to the inside of the instrument, and confirm whether it reaches the inside of the instrument according to the scale mark of the source loading tool; use the rotation tool to turn the source loading tool clockwise to rotate it, and confirm whether the source is installed in place according to the scale mark of the source loading tool, and the source rod 2 needs to be tightened with the instrument;

[0058] Use a special key to disengage the source loading tool from the dual source rod 4. The operator carries the source loading tool and checks whether it is disengaged from the dual source rod 4. After confirming that the source loading tool is disengaged from the dual source rod 4, use a pneumatic winch to lift the source loading tool out of the instrument. After installing the source loading tool cap, the source loading tool can be lifted off the drilling platform.

[0059] The well crew uses a pneumatic winch to lift the neutron source tank 1 out from inside the instrument and insert it into the gamma source tank 3.

[0060] The present invention also provides a method for fishing out the chemical source through a fishing head device of a double-source rod when the chemical source falls into a well.

[0061] In summary, the present invention provides a dual-source rod shielding device, which places the dual-source rod in the source rod, and the two ends of the source rod are respectively extended into the connecting hole entrances of the neutron source tank and the gamma source tank, and the neutron source tank and the gamma source tank are filled with shielding materials, which can effectively shield the dual-source rod and minimize the exposure time of logging personnel. A salvaging head is arranged at the end of the dual-source rod where the neutron source is installed. The salvaging head does not need to be used to load and unload the dual-source rod again, and the salvaging effect can be directly achieved, thereby improving work efficiency.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A dual-source rod shielding device, characterized in that: The invention comprises a neutron source tank (1), a source rod (2), a gamma source tank (3) and a dual source rod (4); the neutron source tank (1) and the gamma source tank (3) are connected relative to each other, and the neutron source tank (1) and the gamma source tank (3) are coaxially provided with a connecting hole, the two ends of the source rod (2) respectively extend into the connecting hole entrances of the neutron source tank (1) and the gamma source tank (3), the dual source rod (4) is arranged in the source rod (2), one end of the dual source rod (4) is equipped with a neutron source (13), and the other end is equipped with a gamma source (17); the neutron source (13) is installed in the dual source rod (4). ) is inserted into the entrance of the connecting hole of the neutron source tank (1) in the source rod (2), and one end of the dual source rod (4) equipped with a gamma source (17) is inserted into the entrance of the connecting hole of the gamma source tank (3) in the source rod (2). A salvaging head (11) is arranged at the end of the dual source rod (4) equipped with a neutron source (13); a neutron source plug (6) is arranged at the outlet of the connecting hole of the neutron source tank (1), and a gamma source plug (10) is arranged at the outlet of the connecting hole of the gamma source tank (3); and shielding material is filled in the neutron source tank (1) and the gamma source tank (3).

2. A dual-source rod shielding device according to claim 1, characterized in that: The dual-source rod (4) comprises a fishing head (11), a fastening ring (12), a neutron source compartment (14), a flexible rod (15) and a gamma source compartment (16); one end of the flexible rod (15) is threadedly connected to one end of the neutron source compartment (14), the other end of the neutron source compartment (14) is connected to the fishing head (11) through the fastening ring (12), and the other end of the flexible rod (15) is threadedly connected to the gamma source compartment (16); the neutron source compartment (14) contains a neutron source (13); and the gamma source compartment (16) contains a gamma source (17).

3. A dual-source rod shielding device according to claim 2, characterized in that: The fishing head (11) is made of beryllium copper soft metal material. The fishing head (11) comprises a rope cap (111) and a connecting head (112). The rope cap (111) is connected to the connecting head (112) and is arranged on the fastening ring (12) through the connecting head (112). The connecting head (112) is provided with an inverted trapezoidal groove platform (114) in an annular shape.

4. A dual-source rod shielding device according to claim 3, characterized in that: The diameter of the connecting end of the rope cap (111) is greater than the diameter of the connecting end of the connecting head (112), and a concave platform (113) is formed at the connecting position.

5. A dual-source rod shielding device according to claim 1, characterized in that: The material of one end of the source rod (2) close to the gamma source (17) is tungsten alloy (18).

6. A dual-source rod shielding device according to claim 1, characterized in that: The material of the neutron source plug (6) is boron-containing polyethylene (5); the material of the gamma source plug (10) is lead (8).

7. A dual-source rod shielding device according to claim 1, characterized in that: The shielding material filled in the neutron source tank (1) and the gamma source tank (3) is boron-containing polyethylene (5).

8. A dual-source rod shielding device according to claim 1, characterized in that: The neutron source tank (1) is provided with a connecting piece (7), the gamma source tank (3) is provided with a connecting buckle (9), and the neutron source tank (1) is connected to the connecting buckle (9) of the gamma source tank (3) via the connecting piece (7).

9. A method for loading and unloading a dual-source rod shielding device, based on the dual-source rod shielding device according to any one of claims 1 to 8, characterized in that: The process includes the following: Opening the connection device between the neutron source tank (1) and the gamma source tank (3), opening the gate of the gamma source tank (3), and slowly lifting the neutron source tank (1) out of the gamma source tank (3) using a pneumatic winch; After the neutron source tank (1) is removed from the gamma source tank (3), the neutron source tank (1) is slowly inserted into the water hole of the instrument, and it is confirmed whether it is safe and reliable, and the neutron source plug (6) at the upper end of the neutron source tank (1) is removed; the well crew uses a pneumatic winch to lift the assembled source loading tool to the drilling platform, and after lifting it to the drilling platform, the protective cap of the source loading tool is removed and lifted to the top of the upper body; Grasp the dual source rod (4) in the source tank with the source loading tool, and lift the source loading tool with both hands to confirm that the source loading tool holds the dual source rod (4) firmly; open the source rod locking device, open the gate of the neutron source tank (1), and use a pneumatic winch to slowly lower the source loading tool with the dual source rod (4) to the inside of the instrument, and confirm whether it reaches the inside of the instrument according to the scale mark of the source loading tool; use the rotation tool to turn the source loading tool clockwise to confirm whether the source is installed in place according to the scale mark of the source loading tool, and tighten the source rod (2) to the instrument; Use a special key to disengage the source loading tool from the dual source rod (4). The operator carries the source loading tool and checks whether the source loading tool is disengaged from the dual source rod (4). After confirming that the source loading tool is disengaged from the dual source rod (4), use a pneumatic winch to lift the source loading tool out of the instrument. After installing the source loading tool protective cap, the source loading tool can be lifted off the drilling platform. The well crew uses a pneumatic winch to lift the neutron source tank (1) out of the instrument and insert it into the gamma source tank (3).

10. A method for assembling and disassembling a dual-source rod shielding device according to claim 9, characterized in that: The material of the neutron source tank (1) and the neutron source plug (6) is boron-containing polyethylene (5).

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