Thermal Neutron Activation:

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Thermal Neutron Activation

• Our Contribution To The War Against Terror

Name Viliami .T. Takau Supervisors Dr. M.N.
Thompson, Dr. R.P. Rassool
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Outline of This Talk

• Current methods of detecting explosives
• Nuclear techniques
• TNA technique leads the way
• Development of an airport explosive
  detection
• system
• Immediate future

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Current Explosive Detection Systems

• violation of civil liberties, explosives can be
  concealed in unusual configurations
• trained animals has short attention span,
  mechanical sniffers sensitive only to certain
  explosives
• non-uniqueness of the signal, human error is a
  huge factor

• manual search
• vapour detection
• X-ray imaging

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Explosive Composition(wt.) ?(14N)

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Measuring Nitrogen in Explosives Nuclear methods

• Photonuclear Reactions
• 14N ? ? ¹³N n (t 600s)
• ? ¹³C ß ? 2?

! Problems
2. Inelastic Scattering of Neutrons 14N n
? 14N n ?
14N ?
! Problems
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Measuring Nitrogen in Explosives Nuclear Methods

• 3. Thermal Neutron Activation
• 14N nthermal ? 15N
• ? 15N
  ? (10.83 MeV)

Way to Go?
NB 10.83 MeV is the highest prompt neutron
capture ?-ray found in nature
hence an excellent signature
of the presence of nitrogen.
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Q-value for Radiative Capture Reactions

• Q(n,?) m(AXz) m(1n0) m(A1Xz)
  931MeV/a.m.u
• Energy available for ?-ray emission is just the
  difference in the binding energies of the target
  and compound nuclei.
• Q-values are always positive and has a zero
  energy threshold the only energetically
  possible reactions for thermal neutrons and many
  nuclei.

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Capture Cross Section(sc) 14N
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14N
fn
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14N
n
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15N
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15N
10.8 MeV ? ray
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15N
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15N
10.8 MeV ? ray
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15N
10.8 MeV ? ray
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15N
10.8 MeV ? ray
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15N
10.8 MeV ? ray
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Development of an Airport Explosive Detection
System

• Based on the following previous work

Development and investigation of a compact
parcel bomb detector C. Everton, M.N.
Thompson, R.P. Rassool et al
Development and investigation of a total body
protein measuring system D.J.
Borovnicar, M.N. Thompson, D.B Stroud et al
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SNUPA I
Moderator
?-ray Detectors
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SNUPA I
?-ray Detectors
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Problems !!!

• Increasing the cavity size results in a drop in
  the overall flux
• Increasing the number of neutron sources will
  cause activation in the detector leads to
  pile-up effect
• ?-ray flux will decrease as a result of the above
• Plus other problems

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Modeling larger cavity


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Cross-section of Integrated Thermal Neutron Flux
(scanning region)
No. of Counts
-30
-20
-10
0
10
20
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Width of Cavity (cm)
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Immediate Future

• General Optimisation of the System
• Signal to background ratio
• Minimum amount of nitrogen detected
• Signal processing electronics
• Pile-up reduction electronic means etc.

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