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GB2491610A - A compact neutron generator for performing security inspections - Google Patents

A compact neutron generator for performing security inspections Download PDF

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Publication number
GB2491610A
GB2491610A GB1109558.5A GB201109558A GB2491610A GB 2491610 A GB2491610 A GB 2491610A GB 201109558 A GB201109558 A GB 201109558A GB 2491610 A GB2491610 A GB 2491610A
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GB
United Kingdom
Prior art keywords
accelerator
neutron
protons
ions
electrostatic
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB1109558.5A
Other versions
GB201109558D0 (en
Inventor
Paul Beasley
Timothy John Hughes
Oliver Heid
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Siemens Corp
Original Assignee
Siemens AG
Siemens Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Siemens AG, Siemens Corp filed Critical Siemens AG
Priority to GB1109558.5A priority Critical patent/GB2491610A/en
Publication of GB201109558D0 publication Critical patent/GB201109558D0/en
Priority to PCT/GB2012/050008 priority patent/WO2012095644A1/en
Publication of GB2491610A publication Critical patent/GB2491610A/en
Withdrawn legal-status Critical Current

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Classifications

    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05HPLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H3/00Production or acceleration of neutral particle beams, e.g. molecular or atomic beams
    • H05H3/06Generating neutron beams
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05HPLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H5/00Direct voltage accelerators; Accelerators using single pulses
    • H05H5/06Multistage accelerators
    • H05H5/063Tandems

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Engineering & Computer Science (AREA)
  • Plasma & Fusion (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Particle Accelerators (AREA)

Abstract

The present invention provides methods and apparatus for producing a flux 16 of neutrons suitable for use in security related applications. Protons H+ from a proton source 12 are accelerated into a proton beam 22 within a compact (preferably having a footprint of less than 2m2) DC electrostatic accelerator 10, neutrons being released when the proton beam 22 impacts a lithium Li-7 target 14 located at the centre of the accelerator 10. Alternatively, a source of deuterium ions D+ and a beryllium Be-9 target may be used. The present invention may instead use a tandem DC electrostatic compact accelerator (30, Fig 4), in which case the source of protons comprises: a source (32) of H- ions (36); and an ion stripper arrangement (34) to convert the H- ions into a proton beam (38). The proton beam (38) is then accelerated out of the accelerator to impact an external neutron generating target (40).

Description

I
APPARATUS FOR PERFORMING SECURITY INSPECTIONS
COMPR1SING APPARATUS FOR PRODUCiNG A NEUTRON FLUX The present inventhn relates to apparatus and methods for performing security inspections of articles. For example, various processes and applications for scanning materials for explosives and nuclear materials as described for example in patent publications US2009/0225922A1, US2009!01 14834A1, US2009/0271068A1, US2007/0295911A1, US 5,278,418, US 5,124,554.
Conventional sources of neutron flux for use in such applications include a) isotope sources based on nuclear reactions e.g. Californium-252 b) neutron tubes using Deuterium or Tritium c) nuclear reactors d) accelerator generated sources.
However, each of these conventional sources suffers from significant drawbacks.
For example,
a) Californium-252 is extremely active and requires a large amount of radiation shielding which makes its use and transport very difficult. (as discussed in U5200910225922A1) b) Neutron tubes are very compact but have limited lifetime unless continually refilled. They also contain Tritium, which makes it very difficult for unrestricted application, although it is used in down hole well logging (as described in US 7,139,349, US 6,922455) c) Nuclear reactors generate large quantities of neutrons with wide range of energies. For applications in the security area, the neutrons from the reactor would have to be moderated. However, these facilities are large and it is not practical to direct freight/luggage to/from such facilities.
d) Accelerator based sources are conventionally least favourable because of their cost and complexity (e.g. requirement for long Radio Frequency Quadrupoles as described in US2006/0140326A1).
The present invention accordingly addresses the problem of providing a compact particle accelerator for use in the generation of neutrons for security inspection.
Examples of security inspection which may benefit from the present invention include: for luggage, cargo containers, vehicles, mine detection. A security inspection system with a small footprint would enable the detection of explosive and fissile materials. in general, for such applications, neutrons with energy ranging from Thermal-8MeV are required.
The present invention accordingly proposes alternative methods and apparatus for producing a neutron flux for use in security applications, which methods and apparatus do not require the use of large and expensive particie accelerators, or any of the other equipment described at (a) to (c) above.
The present invention accordingly proposes methods and apparatus as defined in the appended claims.
The above, and further, objects, characteristics and advantages of the present invention will become more apparent from consideration of the following description of certain embodiments thereof, together with the accompanying drawings, wherein: Fig. I schematically illustrates a DC accelerator useful in a method according to a first embodiment of the invention; Fig. 2 schematically illustrates apparatus for producing a neutron flux according to the first embodiment of the present invention; and Fig. 3 schematically illustrates a tandem DC accelerator useful in a method according to a second embodiment of the invention; and Fig. 4 schematically illustrates apparatus for producing a neutron flux according to the second embodiment of the present invention.
The present invention provides methods and apparatus for producing a neutron flux using a DC electrostatic accelerator.
In order to enable the technique to be utilised in non-specialist environments, that is other than the conventional reactors or large accelerators, a much smaller compact energy efficient system is provided. This can be achieved according to the present invention by using a compact electrostatic accelerator with having a footprint less than 2m2.
For the generation of neutrons for security related applications, typically a 10MeV -mA proton or deuterium beam can be accelerated into a neutron generator material such as Li, Be, C etc. Here the proton spallation generates a high flux of neutrons in this energy spectrum.
According to the present invention, a compact DC electrostatic acc&erator is used.
W ions are accelerated to the centre of the accelerator where they hit a neutron generator such as the proton spallation targets described above. The subsequent neutron flux, unaffected by the electrostatic field, exits the accelerator for use as required.
Such a system would have the benefit of possible mobile deployment, or relatively easy incorporation into existing sites.
The attached appendix, which forms part of the present description, describes compact high-voltage DC electrostatic accelerators which may be employed in the methods of the present invention, and may form part of the apparatus according to the present invention. As described, high voltage accelerators may be provided as tandem accelerators or conventional linear accelerators. The appendix corresponds to pages 711 -713 of the Proceedings of the Vt International Particle Accelerator Conference; held in Kyoto Japan on 23-28 May 2010 www.ipac10.org.
In a conventional linear accelerator, a target is placed in the centre of the accelerator and charged particles are directed towards that target. The charged particles interact with the target.
Fig. 1 shows such a conventional linear accelerator. A target 100 is positioned in a central region 101 of the accelerator. The accelerator itself is made up of concentric shells 102, split at an "equator" 103 such that each shall is made up of two half-shells, separated by a gap. A path 104 is provided, parallel to the "equator" and leading in a straight line to the target from outside of the accelerator. A beam 105 of charged particles may be directed along the path 104 to the target 100. Each shell is charged to a high voltage as compared to its outwardly neighbouring shell, and the description in the appendix recites one possible arrangement for achieving this. ln the described example, thirty concentric shells are used, charged up by a 100kVff, kHz AC inverter. This provides a voltage of 5MV at the centre, and a voltage gradient of 5MV1(3OxlSmm) = 11.1 1kV/mm. By charging the shells with a voltage of polarity opposite to that of the charged particles, the beam 105 of charged particles is accelerated towards the centre of the accelerator. The beam 105 of particles hits target 100 and undergoes the required reaction.
In a tandem accelerator, such as shown in Fig. 3 a particle converter is placed in the centre of the accelerator and charged particles are directed towards that particle converter. This shares features common with those of the accelerator in Fig. 1, sharing common reference numerals. The charged particles interact with the particle converter, and emerge as a different type of charged particle, in the same trajectory as the original charged particle. Assuming that the different type of particle has the opposite charge as compared to the original particle, it will be accelerated out of the accelerator, while the original particle is accelerated into the accelerator.
A particle converter 200 is positioned in the central region 101 of the accelerator.
The acc&erator itself is made up of concentric shells 102, spilt at an equator" 103 such that each shell is made up of two half-shells, separated by a gap. A first path 104 is provided, parallel to the equator" and leading in a straight line to the particle converter from outside of the accelerator. A second path 204 is provided, in ilne with the first path 104 and leading in a straight line from the particle converter to outside of the accelerator.
A beam 105 of charged particles may be directed along the path 104 to the particle converter 200. Each shell is charged to a high voltage as compared to its outwardly neighbouring shell, and the description in the appendix recites one possible arrangement for achieving this. In the described example, thirty concentric shells are used, charged up by a lOOkVen, 100 kHz AC inverter. This provides a voltage of 5MV at the centre, and a voltage gradient of 5MV/(30x 15mm) = 11.11kV/mm. By charging the shells with a voltage of polarity opposite to that of the charged particles, the beam of charged particles is accelerated towards the centre of the accelerator.
When the charged particles hit the particle converter, they are converted into different particles, with an opposite charge. For example, H-ions may hit a particle converter being an ion stripper arrangement, conventional in itself, and be converted to H ions, protons.
The oppositely-charged particles are then repelled from the centre of the accelerator, accelerating out along path 204. A target 210 is positioned outside of the accelerator. The opposely-charged particles leave the accelerator and hit target 210. The beam 105 of particles hits target 100 and causes emission of other particles.
With a tandem accelerator, the particles are accelerated both into the accelerator and back out again. The potential difference (voltage) between the outermost shell and the innermost shell need therefore only be half of the required acceleration voltage, while in the case of the linear accelerator of Fig. 1, the potential difference (voltage) between the outermost shell and the innermost shell should equal the required acceleration voltage.
The present invention may be applied both to conventional linear accelerators and tandem accelerators. Various different targets may be used, as will be described in more detail in the following examples.
According to a first example of the first embodiment of the invention, a neutron flux may be produced using a compact neutron generator.
According to this embodiment of the invention, and as schematically represented in Fig. 2, a conventional linear DC electrostatic accelerator 10, similar to that described with reference to Fig. 1, is provided with a beam 22 of protons (H4 ions) from a proton source 12. ln the centre of the DC electrostatic accelerator is a target of neutron source material 14, such as a thin Lithium Li-7 target, which produces neutrons 16 from the (p,n) reaction Li-7(p,n)Be-8 or similar.
The Li-? reaction is particularly advantageous because it is a transition reaction which, at around 1.885MeV, produces a collimated neutron beam 16. Depending on their required energy the collimated neutron beam 16 can be directed at a moderator 18 to produce an epithermal neutron spectrum. An epithermal neutron is a neutron that has energy greater than that of a thermal neutron, but not as large as for fast neutrons, so having a modest requirement for shielding. Alternatively, by controlling the voltage applied to the accelerator 10, epithermal neutrons of about 2.3MeV may be generated directly.
The epithermal neutrons, generated directly or emerging from moderator 18 may then be employed as required in a selected security application.
In an example DC electrostatic accelerator, the protons (Ht ions) are accelerated to the centre of the accelerator, at which point they cross the centre into the shell structure of the accelerator on the opposite side, which has a decelerating field.
The incident proton beam 22 loses a portion of its energy as it passes through neutron-source material 14. As the resulting proton beam 24 exits the target, it is gradually slowed as it passes through the accelerator 10 and is collected in the structure of the DC electrostatic accelerator, acting as a collector assembly. ln this way, the energy of the beam is recovered.
In a second example of the first embodiment of the invention, similar to the first example, the proton source 12 is replaced with a source of deuterium ions 2W (Dt).
The neutrons are generated as a result of accelerated particles of deuterium 2W (Dt) hitting a target 14 of beryllium Be-b in a Be-10(d,n)C-1 I reaction to produce carbon- 11 and a free neutron.
The free neutron may then be employed as required in a selected security application.
According to a second embodiment of the invention, alternative apparatus and methods are provided for producing a neutron flux using a tandem compact neutron generator.
Fig. 4 schematically represents an example of apparatus according to the second embodiment of the present invention, using a tandem DC electrostatic accelerator.
According to a first example of this second embodiment of the invention, a tandem DC electrostatic compact accelerator 30, similar to that described with reference to Fig. 3, is provided with a source 32 of R ions, and produces a beam 36 of ft ions directed towards the centre of the accelerator. In the centre of the tandem DC electrostatic accelerator 30 is an ion stripper arrangement 34 (such as a carbon stripper foil which is conventional in itself), which converts ft ions to H ions (protons) by removal of two electrons from each ion. The resulting Ht beam 38 is incident upon a target material 40 which produces a neutron flux 42 in reaction to the incident protons. For example, the material 40 may be a proton spallation target such as Li, Be, C. This Li-7(pn)Be-7 reaction is particularly advantageous because it is a transition reaction which, at around 1.885MeV, produces a collimated neutron beam 42. The coflimated neutron beam 42 may be directed at an optiona' moderator (not shown in the drawing, but could be a simple water vessel or wax block) to produce a neutron spectrum of appropriate energy profile. The resultant neutron flux may be employed as required in a selected security application.
Accordingly, the present invention provides methods an apparatus for the production of neutron flux which is suitable for use as required in a selected security application.
Such apparatus has the advantages of being compact with a small footprint and requiring modest amount of power, mainly for the ion source and vacuum pumps.
The apparatus would aso have a very simple user friendly interface for non-expert operation. All these features would enable easy siting and running in the vicinity of regular inspection areas such as airports or ports. Furthermore, the system could be made portable using a simple electrical generator.
The appended annex contains detailed descriptions of certain types of DC electrostatic acc&erator, which are considered suitable for use in the present invention.
Numerous variations and modifications to the present invention will be apparent to those skiUed in the art, and the scope of the invention is as defined in the appended claims. For example, while certain arrangements have been described for producing neutrons from a proton beam, any suitable known or later-devised combination of particles or target material may be employed in the present invention.

Claims (18)

  1. CLAIMS1. Apparatus for performing security inspections comprising -apparatus for producing a neutron flux (16; 42), the apparatus for producing a neutron flux comprising: -a source of protons (12; 32, 34); -a DC electrostatic accelerator (10; 30) to accelerate the protons from the source of protons into a proton beam (22; 38); and -a neutron generator target material (14; 40) which releases a flux of neutrons (16; 42) in response to an incident beam of protons (22; 38).
  2. 2. Apparatus according to claim I wherein the neutron generator target material comprises lithium Li-7.
  3. 3. Apparatus according to any preceding claim, further comprising a moderator (18) to reduce the energy of neutrons in the neutron beam.
  4. 4. Apparatus according to claim 3, wherein the neutron generator target material (14) is at the centre of the DC electrostatic accelerator.
  5. 5. Apparatus according to any preceding claim, wherein the DC electrostatic accelerator is a DC electrostatic compact accelerator (30).
  6. 6. Apparatus according to any preceding claim, further comprising a collector assembly in the DC electrostatic accelerator (10), arranged to catch and recycle proton beam energy.
  7. 7. Apparatus according to claim 1, wherein the DC electrostatic accelerator is a tandem DC &ectrostatic compact accelerator.
  8. 8. Apparatus according to claim 7, wherein the source of protons comprises: -a source (32) of R ions and -an ion stripper arrangement (34) at the centre of the accelerator, such that V ions from the V ion source accelerate into the accelerator (30) and impact upon the ion stripper arrangement (34) arranged to convert the V ion beam (36) to a proton beam (38).
  9. 9. A method for performing securay inspections comprising the steps of -producing a neutron flux; and -applying the neutron flux to an article to be inspected, the step of producing a neutron flux itself comprising the sub-steps of: -generating protons (12; 32, 34); -accelerating the protons into a DC electrostatic accelerator (10; 30) to form a proton beam (22; 38); and -applying the proton beam to a neutron generator target material (14; 40) which releases a beam of neutrons (16; 42) in response to the incident beam of protons (22; 38).
  10. 10. A method according to claim 9, further comprising the sub-step of reducing the energy of neutrons in the neutron beam by passing the beam of neutrons through a moderator (18).
  11. 11. A method according to any of claims 9-10 wherein the sub-step of generating protons itself comprises the steps of: -generating H ions -accelerating the H-ions into the accelerator to form a beam of Ft ions; -stripping electrons from the E ion beam (36) to generate a proton beam (38).
  12. 12. A method according to any of claims 11-15 further comprising the sub-step of catching and recycling proton beam energy by collecting protons in a collector assembly in the DC electrostatic accelerator.
  13. 13. Apparatus for performing security inspections comprising -apparatus for producing a neutron flux (16; 42), the apparatus for producing a neutron flux comprising: -a source of deuterium ions Dt; -a DC electrostatic accelerator (10; 30) to accelerate the deuterium ions from the source of deuterium ions into a beam of deuterium ions; and -a neutron generator target material (14) which releases a flux of neutrons (16) in response to an incident beam of deuterium ions.
  14. 14. Apparatus according to claim 13 wherein the neutron generator target material comprises Beryllium Be-lU.
  15. 15. Apparatus according to any of claims 13-14, further comprising a moderator (18) to reduce the energy of neutrons in the flux of neutrons.
  16. 16. Apparatus according to any of claims 13-15, wherein the neutron generator target material (14) is at the centre of the DC electrostatic accelerator.
  17. 17. Apparatus according to any of claims 13-16, wherein the DC electrostatic accelerator is a DC electrostatic compact accelerator (30).
  18. 18. Apparatus for performing boron neutron capture therapy! comprising apparatus for generating a neutron flux according to any of claims 1-6 or 13-17.
GB1109558.5A 2011-01-12 2011-06-08 A compact neutron generator for performing security inspections Withdrawn GB2491610A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB1109558.5A GB2491610A (en) 2011-06-08 2011-06-08 A compact neutron generator for performing security inspections
PCT/GB2012/050008 WO2012095644A1 (en) 2011-01-12 2012-01-05 A compact, low energy neutron source

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB1109558.5A GB2491610A (en) 2011-06-08 2011-06-08 A compact neutron generator for performing security inspections

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GB201109558D0 GB201109558D0 (en) 2011-07-20
GB2491610A true GB2491610A (en) 2012-12-12

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5135704A (en) * 1990-03-02 1992-08-04 Science Research Laboratory, Inc. Radiation source utilizing a unique accelerator and apparatus for the use thereof
US5818054A (en) * 1996-04-30 1998-10-06 Radio Programmes Corp. Substance detection device using monoenergetic neutrons
US20100033115A1 (en) * 2008-08-11 2010-02-11 Cleland Marshall R High-current dc proton accelerator

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5135704A (en) * 1990-03-02 1992-08-04 Science Research Laboratory, Inc. Radiation source utilizing a unique accelerator and apparatus for the use thereof
US5818054A (en) * 1996-04-30 1998-10-06 Radio Programmes Corp. Substance detection device using monoenergetic neutrons
US20100033115A1 (en) * 2008-08-11 2010-02-11 Cleland Marshall R High-current dc proton accelerator

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