US Patent 4282440 中英译文.docx

United States PatentNEUTRON ACCELERATOR TUBE HAVING IMPROVED IONIZATION SECTION具有改进的电离层的中子加速器管ABSTRACTA neutron accelerator tube having a target section, an ionization section, and a replenisher section for supplying accelerator gas to the ionization section. The ionization section is located between the target and the replenisher section and includes an ionization chamber adapted to receive accelerator gas from the replenisher section. The ionization section further includes spaced cathodes having opposed active surfaces exposed to the interior of the ionization chamber. The active surface of at least one of the cathodes is formulated of a -emitting material. An anode is located intermediate the cathodes whereby in response to an applied positive voltage, electrons are transmitted between the opposed active surfaces of the cathodes and produce the emission of secondary electrons. The active surface of the other cathode may be formulated of a -ray emitter or material having a secondary electron emission factor of at least 2. One cathode member located in the tube adjacent to the replenisher section may have a protuberant portion extending axially into the ionization chamber and formulated of a -ray emitting material. A portion of the active surface of the cathode which is recessed with respect to the protuberant portion may be formulated of a material having a secondary electron emission factor of at least 2. The other cathode spaced from the first cathode member in the direction of the target has an aperture therein along the axis of the protuberant portion. 摘要一个中子加速器管具有目标层，电离层和补充液层，其中补充剂层是用于给电离层提供加速器气体。电离层位于目标层与补充液层之间，并包括用来接收来自补充剂层的加速器气体的电离室。电离层还包括具有相对活性表面的相间隔开的阴极，其中这些活性表面是直接暴露于电离室中的内部。这些阴极中至少有一个阴极的活性表面的是由具有放射性的材料制成的。一个阳极位于阴极的中间,并提供了一个正电压,使得电子在阴极的相对的活性表面之间传输，从而产生了次级电子的发射。其他阴极的活性表面也可能是由一个射线发射器或者是由次级电子发射系数的至少是2的材料制成的。中子管里靠近补充剂层的一个阴极可能会有一个突起的部分轴向延伸进入电离室，它可能是由发射射线的放射性材料制定的。阴极的活性表面上凹嵌于相关突起处的一部分可能是次级电子发射系数至少是2的材料制定的。与第一个阴极成员在目标层方位上间隔的其他阴极，在沿突起部分主轴方向上，有一个孔径在其中。NEUTRON ACCELERATOR TUBE HAVING IMPROVED IONIZATION SECTION BACKGROUND OF THE INVENTION本发明的背景This invention relates to neutron sources and more particularly to accelerator-type neutron tube sources having improved ionization sections. 本发明涉及中子源，更具体地说，涉及具有改进的电离层的加速器式中子管的源。Accelerator-type neutron tube sources are employed in many applications. A well known application is in the radioactivity logging of wells penetrating subterranean formations. For example, in the art of neutron-neutron well logging a source of primary neutrons is employed to irradiate subterranean formations of interest. The resulting secondary radiation is measured by one or more detectors spaced axially from the source within the borehole. Such secondary irradiation may take the form of thermal neutrons, epithermal neutrons, or thermal neutron capture gamma rays. A logging tool of this type employed for porosity measurements is disclosed in U.S. Pat. No. 4,005,290 to Allen wherein the logging tool includes a neutron source and epithermal and thermal neutron detectors. 在许多应用中采用加速器型中子管源。一个众所周知的应用是在穿透地层的放射性测井中的应用。例如，在中子领域中的中子测井时，主中子的源被用在照射感兴趣的地下地层。由此产生的二次辐射是由一个或多个检测器测量的，这些检测器从井眼内的源处轴向地隔开。这样的二次辐射可能需要热中子，超热中子，热中子俘获伽玛射线的形式来实现。甲孔隙度测量时采用的这种类型的测井工具在来自艾伦的第4005290号美国专利中公开，其中日志记录的工具就包括了中子源以及超热中子和热中子探测器。In procedures such as porosity logging, the neutron source is a continuous source usually of a chemical type. Other well known radioactive well logging techniques involve the use of pulsed neutron sources. For example, in the art of radioactive assay well logging an assay tool is lowered into the well to the level of a formation to be assayed. The assay operation is then carried out by cyclically operating a neutron source in the tool in order to irradiate the formation under investigation with repetitive bursts of fast neutrons. In one assay procedure, disclosed in U.S. Pat. No. 3,686,503 to Givens et al, delayed fission neutrons emitted by uranium within the formation may be detected by a neutron detector. Another procedure, disclosed in U.S. Pat. No. 4,180,730 to Givens et al, involves detection of prompt fission neutrons emitted from uranium in the formation. Pulsed neutron logging techniques may also be employed in procedures in which radioactive decay rates are determined. Thus, the formation under investigation is irradiated with a burst of fast neutrons and the resulting neutron population is detected during successive or overlapping time windows. For example, U.S. Pat. No. 3,800,150 to Givens discloses a pulsed neutron logging technique in which epithermal neutron decay or thermal neutron decay is measured by employing time windows for detection which partially overlap one another. 在如孔隙度测井的程序里，中子源是一个通常的化学类型的连续源。其他知名的放射性测井技术还涉及到使用脉冲中子源。例如，在放射性检测测井的领域中，测定工具下降入井而形成待测定的水平。该测定的操作是通过在工具中的中子源循环操作，然后进行测定以便于调查研究一阵重复的快中子的照射形成。在一个公开在吉文斯等人的美国专利第3686503号里的分析过程，说它可能是通过在延迟裂变中子发射的地层内铀的中子检测器检测到的。而另一个过程，则是公开在吉文斯等人的第4180730号美国专利里，它涉及从铀矿的形成发出提示裂变中子检测。脉冲中子测井技术也可用于确定放射性衰变率的过程里。因此，调查过程是在一阵快中子照射下，并且在连续或重叠的时间窗口中检测到产生的中子数量时形成的。例如，在吉文斯的第3800150号美国专利中公开了一种脉冲中子测井技术，其中，超热中子衰变或热中子衰减是通过采用部分地彼此重叠的时间窗进行检测来测量的。Neutron sources such as may be employed in radioactive logging procedures as described above may take the form of accelerator-type neutron tubes comprising a target section, a replenisher section, and an ionization section located between the target and the replenisher section. The replenisher section provides a source of accelerator gas to the ionization section where it is ionized and then accelerated to impact the target. The target is formulated of material which responds to the bombarding ions to produce neutrons. In a number of well known accelerator-type tube sources, heavy isotopes of hydrogen are employed as the accelerator gas and in the target. For example, the accelerator gas may take the form of deuterium or mixtures of deuterium and tritium and the target may include tritium molecules, deuterium molecules or mixtures of deuterium and tritium molecules. The so-called deuterium-tritium nuclear reaction is one commonly employed in an accelerator-type neutron tube to produce neutrons. In the replenisher section a filament or reservoir usually made of zirconium or titanium is electrically heated (under controlled conditions) to release deuterium gas previously adsorbed in the filament or reservoir. Zirconium and titanium have the property of adsorbing copious quantities of different gases such as hydrogen, deuterium, tritium, and other gases. These materials have the further property of releasing the hydrogen isotope gases under a controlled release condition when heated to about 300 been adsorbed. The deuterium molecules are ionized in the ionizing section by the application of a positive voltage to an anode in the ionizing section. The deuterium ions are then accelerated by a large negative voltage, e.g. -100 KV, and impact the tritium target to produce a supply of neutrons.中子源，也可能被用于如上所述的放射性测井程序中，它可以采用加速器式中子管的形式，这种形式包含目标层，补充剂层，还有位于目标与补充剂层之间的电离层。补充剂层给电离层的提供了一个加速器气体源，在电离层那里它被电离后，然后加速到影响目标。目标是由能轰击离子产生中子的反应的物质材料制成的。在一些熟知的加速器型管源，重氢的同位素被用作为加速器气体，并且用在目标部。例如，加速器气体可采取的形式有氘或氘和氚的混合物，且做目标时可能包括氚的分子，氘分子或氘和氚分子的混合物。所谓的氘-氚核反应是一种常用的加速器式中子管产生中子的应用。在补充剂层的灯丝或储层通常是由锆或钛的电加热（在受控的条件下）以释放先前吸附在灯丝或储层中的氘气。锆和钛有吸附大量丰富的各种不同的气体性能，如：氢，氘，氚，和其他气体。这些材料有有更进一步的性能，当加热到约300个被吸附时，它们能释放可控条件下的氢同位素气体。在电离层中氘分子在一个阳极产生的正电压的作用下被电离的。然后氘离子在大的负电压下加速，如-100 KV，并影响氚靶产生的中子供应。While various techniques may be employed in ionizing the accelerator gas, one ionization technique which is suitable particularly where the neutron source is operated at a low accelerator gas pressure and in a pulsed mode is the so-called Penning method. A Penning ion source comprises spaced cathodes and an anode located intermediate the cathodes. In a cold-cathode type Penning ion source, electrons are emitted from a cathode surface by field emission when a positive voltage pulse is applied to the anode. A magnet associated with the source functions to spiral the electrons thus increasing their flight path and increasing the statistical probability that they will collide with molecules of accelerator gas supplied to the ionization chamber. In a well designed Penning ion source, some of the electrons originating at one cathode surface will impact the other cathode surface and secondary electrons are emitted which also function to increase the ionization reaction. Such ion sources are well known to those skilled in the art and are described in Flinta, J. Pulsed High-Intensity Ion Source, Part I; Pauli, R. and Flinta, J. Pulsed High-Intensity Ion Source, Part II, Nuclear Instruments 2, pp 219-236 (1958). In a hot-cathode type Penning ion source, one cathode is a heated filament and initial electrons are supplied by thermionic emission from the filament. In all other respects, cold-cathode and hot-cathode Penning ion sources are essentially the same. Hot-cathode ion sources are also well known to those skilled in the art and one such source is described in Wood, J. and Crocker, A. An Electrostatically Focused Ion Source And Its Use In A Sealed-Off D.C. Neutron Source, Nuclear Instruments And Methods 21, pp 47-48 ( 1963).虽然可以采用各种技术电离加速器气体，但是有一种电离技术是特别合适的，尤其是中子源是工作在一个低加速器气体压力和脉冲模式情况下，那就是所谓的Penning方法。一个Penning离子源包括相互间隔的阴极，位于阴极中间的阳极。Penning离子源为冷阴极型时，当一个正电压脉冲施加到阳极，电子在场作用下将从阴极表面发射出来。磁铁与源的功能相关，它使电子螺旋起来，从而增加他们的飞行路径并会增加他们和电离室提供的加速器气体分子的碰撞机率。在一个精心设计的Penning离子源里，在阴极表面产生的电子影响着其他阴极表面并且次级电子将会发射，这也可以增强电离反应。这种离子源是被那些熟练的技术人员所熟知的，并在Flinta，J. 第I部分中被描述为“脉冲高强度的离子源”；在Pauli，R.和Flinta，J第二部分，核仪器2，第219-236页（1958）中被描述为“脉冲高强度的离子源”。 在Penning离子源为热阴极型时，阴极是一根加热的灯丝，并且灯丝的热电子发射提供了初始的电子。在所有其他方面，冷阴极和热阴极Penning离子源基本上是相同的。热阴极离子源也被那些熟练的技术人员所熟知的，并在Wood，J.和克罗克，核仪器和方法21，页47-48（1963）中描述了这样的一个源：“静电聚焦离子源及其在一个密封关闭DC中子源的使用”。SUMMARY OF THE INVENTION发明概要In accordance with the present invention, there is provided an accelerator-type neutron tube having a new and improved ionization section for ionizing the accelerator gas. The ionization section is located between the target section and replenisher section of the neutron tube and comprises an ionization chamber adapted to receive accelerator gas from the replenisher section. First and second cathodes are spaced from one another and have opposed active surfaces exposed to the interior of the chamber. The active surface of at least one of the cathodes is formulated of a-ray emitting material. Anode means are located at a position intermediate of the cathodes. Beta rays are continuously emitted and some impact the opposite cathode and other surfaces thus producing secondary electrons. Therefore, there exists in the ionization chamber at all times both-rays and secondary electrons. In response to a positive voltage applied to the anode, electrons are transmitted between the opposed active surfaces of the cathodes and instantaneously produce both ions and the emission of additional secondary electrons. 依照本发明,提供了一个拥有新的和改进的电离层加速器类型中子管来电离加速器气体。电离层位于中子管目标层和补充剂层之间，并有一个电离室用来接收来自补充剂层的加速器气体。第一个和第二个阴极相互间隔，并有着暴露在电离室内却极性相反的活性表面。阴极中至少有一个的活性表面是由的具有射线的放射性材料制定的。阳极位于阴极位置的中间。射线不断发射并且其中一些影响着相对的阴极和其他表面，从而产生次级电子。因此，在电离室在一直同时存在着射线和次级电子。在加到阳极一个正电压作用下，电子在极性相对的活性表面之间传输从而瞬间产生离子和次级电子的发射附加。In a further embodiment of the invention, the active surface of a first cathode member located adjacent to the replenisher section of the tube has a protuberant member extending axially into the ionized chamber which is formulated of a -ray emitting material. A second cathode member spaced from the first cathode member in the direction of the target has an aperture therein along the axis of the protuberant portion. The second cathode member has a surface exposed to the interior of the ionization chamber which is formulated of a material having a secondary electron emission factor of at least 2. An anode member extends peripherally around the interior of the ionization chamber at a position intermediate the first and second cathode members. 进一步具体化本发明，中子管里靠近补充剂层的第一个阴极有一个突起的部分轴向延伸进入的电离室，并且是由能发射射线的放射性材料制定的。与第一个阴极在目标层方位上相间隔的第二个阴极，在沿突起部分主轴方向上，有一个孔径在其中。第二个阴极有一个表面暴露在电离室内，并且这表面是由一种次级电子发射系数至少是2的材料制定的。阳极在电离室内部的周围延伸，位于第一和第二阴极中间的一个位置。BRIEF DESCRIPTION OF THE DRAWINGS 附图说明FIG. 1 is a schematic illustration of a well logging system embodying the present invention,FIG. 2 is a sectional view of the ionization section portion of an accelerator-type neutron tube constructed in accordance with the present invention. AndFIG. 3 is a view partly in section of an alternative cathode element suitable for use in this invention.图1是体现本发明的一个测井系统的示意图图2是根据本发明构成的加速器式中子管的电离层的剖视图。图3是这项发明适用的可替代阴极元素的部分视图。DESCRIPTION OF SPECIFIC EMBODIMENTS 具体实施方式 Turning now to FIG. 1, the invention will be described with respect to a preferred application in a radioactive well logging system and particularly one in which the neutron source is operated in a pulsed mode. The well logging system comprises a logging tool 3 which is suspended from a cable 4 within a well 5 traversing a subterranean formation of an interest indicated by reference numeral 6. The well bore may be lined or unlined with casing but will normally be filled with a fluid such as drilling mud, oil or water. Signals from the logging tool are transmitted uphole via suitable conductors in the cable 4 to an uphole analysis and control circuit 8. Circuit 8 operates on the downhole measurements and applies one or more output functions to a recorder 9. In addition, Circuit 8 transmits certain control functions to the logging tool via conductors in cable 4. As the logging tool is moved through the hole, a depth recording means, such as measuring sheave 10, produces a depth signal which is applied to recorder 9, thus correlating the downhole measurements with the depths at which they are taken.现在看着图1。如图1所示，本发明将通过相对于放射性测井系统的优选应用，特别是在其中的中子源在脉冲模式下操作下测定来叙述。测井系统包括一个由电缆4控制暂停的测井仪3，其中电缆4是在井5里的，并且井5贯穿了表示权益标号6的地下岩层内的。井孔可能被线性或非线性的包围住，但通常会被钻井泥浆，油或水等流体填充。来自测井仪的信号通过电缆4中合适的导体进行井上分析和控制电路8来传输。电路8操作着井下的测量，并提供了一个或多个输出功能给记录器9。此外，电路8通过电缆4中的导体发送了一定的控制功能给测井工具。由于测井仪是移动通过孔的，深度的记录的方法比如测量滑轮10，则产生一个深度的信号，该信号被施加到记录器9，从而关联到他们要测量的井下测量的深度。The logging tool 3 comprises a pulsed neutron source 12, a downhole power supply 14 for the source, and a radiation detector 15, which responds to primary or secondary radiation in the formation in response to the output of the pulsed neutron source. For example, the detector 15 may be a gamma ray detector, a thermal neutron detector or an epithermal neutron detector. While only one detector is shown, it will be recognized that such logging tools may comprise a plurality of detectors responsive to similar or dissimilar radiation.测井仪3包括一个脉冲中子源12，井下源的电源14，和辐射检测器15，其中辐射检测器15是在响应响应脉冲中子源的输出形成时感应主要和次要辐射的。例如，检测器15可以是射线检测器，一个热中子探测器或超热中子探测器。虽然只有一个检测器被示出，但应当认识到，这样的测井工具可包括多个相似或不同的辐射的检测器响应。The pulsed neutron source is an accelerator-type neutron tube comprising a replenisher section 16, an ionization section 18, and a target section 19. Replenisher section 16 may comprise replenisher element 16a which releases deuterium gas in response to an applied DC or AC voltage from power supply 14. Target section 19 comprises a tritium target 19a. The target section will also typically include an extraction-focusing electrode assembly and a negative high voltage supply (not shown) which functions to direct ions from the ionization section 18 to the target 19a while suppressing the counter current flow of secondary electrons produced by ion impact on the target. The ionization section 18 includes anode means 18a and cathode means 18b and 18c.脉冲中子源是一种加速器式中子管，它包括补充剂层16，电离层18，以及目标层19。补充剂层16可包括在电源14提供直流或交流电压时产生响应而发出氘气的补充剂元件16a。目标层19包括一个氚靶19a。目标层通常还主要包括提取聚焦电极的组件和负极的高压电源（图中未示出），其中负极的高压电源功能是导向从电离层18的目标19a的离子，同时抑制离子冲击在目标上产生的次级电子的逆流。电离层18包括阳极装置18a，阴极装置18b和18c的。The neutron source 12 may be operated in a continuous or in a pulsed mode. In either mode of operation, deuterium gas released upon the application of power to the replenisher element 16 enters the ionization section 18 where the gas molecules are ionized by a positive (with respect to cathodes 18b and 18c) ionization voltage applied across anode 18 and cathodes 18b and 18c. The deuterium ions formed in the ionization section are then accelerated toward the target 19a by a negative voltage applied to the target section. For example, a positive voltage or voltage pulse with an amplitude from a few hundred volts to a few kilovolts may be applied to anode member 18a and a -100 kilovolt voltage applied to target section 19.中子源12可以在连续或脉冲模式下工作。在任一这两种模式的操作中，在提供了电源给补充剂元件16后释放出的氘气进入电离层18，在电离层18，气体分子被一个正极（相对于图18b和18c的阴极）的电离电压所电离，其中这正的电离电压加在阳极18和阴极18b和18c上。然后形成电离层的氘离子在被加到目标层的一负电压作用下加速朝目标19a移动。例如，振幅从几百伏到数千伏的正电压或电压脉冲可被加到阳极构件18a并且-100千伏的电压加到目标层19。The Penning ionization section of the accelerator-type neutron tube may be of the cold cathode or of the hot cathode type. In the cold cathode source, the primary electrons are produced by field emission when a positive voltage pulse is applied to the anode. In the hot cathode type of source, electrons are initially produced by thermionic emission from an electrically heated filament. The cold cathode source suffers the disadvantage, which is of particular significance when the neutron source is operating in a pulsed mode, of having a time lag before the electron flux reaches a sufficient value for optimum ionization of the accelerator gas. Thus, upon applying a positive voltage pulse to the anode there normally is a period from about 3-10 microseconds in which the electron flux builds up to an equilibrium value. The hot cathode source, because electrons are instantly available from thermionic emission, does not suffer this disadvantage. However, the hot cathode source requires an additional high voltage power supply which is particularly significant in the case of downhole logging tools where the power requirements must be met by transmission from the surface.加速器式中子管的Penning电离层的可能是“冷阴极”或“热阴极”型。当是冷阴极源时，一个正电压脉冲被加到阳极，产生了场的发射，从而产生初始电子。当是热阴极型源时，电子最初是从电加热的灯丝导致的热电子发射而产生的。冷阴