Due to terrorist use of explosive devices, intense interest has been directed towards the development of techniques and instrumentation to detect explosives. A number of analytical techniques are currently under investigation for bulk explosive detection. Several methods have been successfully commercialized including x-rays, neutrons, electromagnetic imaging and gamma- rays that see widespread field use. A key limitation of all currently utilized field techniques is that they require close proximity or physical interaction with the object being analyzed. The ideal bulk explosive detection technique would be able to detect bulk amounts of explosives from a distance to ensure personnel safety. Neutron interrogation has been proved to be the only currently viable techniques that can be utilized to sense bulk amounts of explosives at standoff distances. This review compares currently used explosive detection techniques with recently developed standoff methods. We emphasize the development of Neutron interrogation for standoff explosive detection.






Standoff bomb detection technique is a non-destructive inspection process to determine whether a container contains explosive materials. This is commonly used at airports, ports and for border control.


Initiated explosives have already killed thousands of people and injured several tens of thousands. Infrastructural facilities, like railway stations, airports, undergrounded railways; water supply, etc. are preferred targets involving up to thousands of people. New forms of bomb attacks are more sophisticated, more dangerous, using remote control of Improvised Explosive Devices (IED) initiation by mobile phones permits terrorists to initiate a bomb immediately. Therefore, standoff bomb detection techniques with a reliable detection efficiency used in broad range of IEDs have an important role in the society and world at large (Woodfin, 2007).

These techniques have aided immensely in the saving of life and properties and have prevented chaos in our society.

Improvised explosives devices (IEDs) and homemade explosives (HMEs) have become the primary threat jeopardizing the safety of civilian and military personnel. HMEs are significant threats because the materials used to construct them are easily obtained (Wilson, 2006).

The detonation of a single nuclear bomb or “war head” would cause a local disaster on a scale that few people in the world have seen and survived.

1.1.1 BOMB

The term bomb is defined as an explosive weapon that uses the exothermic reaction of an explosive material to provide an extremely sudden and violet release of energy. It inflicts damage principally through ground and atmosphere transmitted mechanical stress, the impact and penetration of pressure-driven projectiles, pressure damage and explosion generated effects (Jimmie, 2009).

There is a current need to improve security screening methods for bomb detection. For example, in airports, it is important to detect the presence of hidden bomb in luggage, to detect explosive residues on people’s hands, and to detect bomb on the aircraft itself. Explosive detection is also needed to monitor vehicle surfaces at security checkpoints, for screening individual people, and for screening mail.


The adverse effect of nuclear bomb can be averted by some detective techniques and these techniques obviously must sense trace explosive residues that are left by people handling bomb. Improvised Explosive Devices (IEDs) detection techniques can be divided into two groups:

  • Bulk detection techniques, and
  • Trace detection of techniques.

In bulk detection, a macroscopic mass of explosive material is detected directly, usually by viewing images made by X-ray scanners or similar equipment.

Bulk detection techniques include ˗ X-ray and gamma ray systems, neutron methods, electromagnetic systems.

In trace detection, the explosive is detected by chemical identification of microscopic residues of the explosive compound. These residues can be applied in either or both of two forms: vapor and particulate.

Vapor detection refers to gas-phase molecules emitted by a solid or liquid explosive. The concentration of explosives in the air is related to the vapor pressure of the explosive material and to other factors, such as the duration of the presence explosive material in the given location, its packing, temperature, air circulation in the location, etc.

In particulate detection microscopic particles of solid explosive material adhering to the surface (i.e., by direct contact with the explosive, or indirectly, by its contact with someone’s hands in handling the explosives).

The trace detective techniques includes electronic and chemical, optical and biosensors. (Kanu et al 2008).

Approaching a suspicious object such as a suspected IED is extremely undesirable from a safety standpoint. It is therefore highly desirable to develop current and reliable techniques to determine the composition of a bomb from a safe distance in order to keep personnel, properties and instrumentation from harm.


Neutron interrogation has appeared to be the most currently viable standoff detection methods. It involves the use of specially designed machines. These machines bombard the suspect explosives with neutrons and read the gamma radiation decay signatures to determine the chemical composition of sample.

Explosives materials all have similar ratios of carbon, hydrogen, nitrogen and oxygen which the machine is able to detect (Will, 2006).

Neutron interrogation has the potential of serving as a useful technique for detecting shielded fissionable material. The technique has been well-developed for nuclear safeguards measurements for assaying waste drums and stored materials but also has a role to play beyond application for these well-constrained problems. Recent innovations in the design and engineering of small, compact-accelerator electronic neutron generators now make it feasible to consider deploying portable active neutron interrogation systems for field use (Chichester et al 2007).


Many of these bomb detection techniques are limited either by fundamental physical constraints (e.g resolution limits for microwave imaging) or by the circumstances of a particular scenario (e.g background explosive residue in embattled locations such as Iraq).However, neutron interrogation technique have been considered and proven to be the best detective technique because it allows the analysis of materials without the opening of storage containers easily and also it produces results through its various kind of methods such as Thermal Neutron Activation (TNA), Fast Neutron Analysis (FNA), Pulsed Fast Neutron Analysis (PFNA), Pulsed Fast Thermal Neutron Analysis (PFTNA) and Nuclear Resonance Absorption (NRA)  but its cost is highly effective and the speed rate of attaining results is slow.  Hence, it became imperative for this study to be reviewed in order to have a reliable detection efficiency used in broad range of IEDs.


The aim of this study is to research the importance, efficiency and reliability of neutron interrogation as a detective technique.

In order to achieve this aim, specific objectives are needed to be attained.


Objectives include:

  • To research and review the neutron interrogation detection method.
  • To explore the applications of nuclear physics technology in national and homeland defense.
  • To determine the effects, limitations, merits and applications of neutron interrogation detection method over other method.

Additional effort and wider input from the basic nuclear physics research community are needed in order to benefit the nation and its homeland security needs.



1.5           SCOPE OF THE STUDY

Intense interest has been directed towards the development of techniques and instrumentation to detect explosives due to terrorist use of explosive devices.

A number of analytical techniques are currently under investigation for trace and bulk explosive detection. Several methods have been successfully commercialized including neutron interrogation technique.

A key limitation of all currently utilized field techniques is that they require close proximity or physical interaction with the object being analyzed. For neutron interrogation technique, there are two noteworthy drawbacks to its use, even though the technique is essentially non-destructive. These drawbacks include:

  • An irradiated sample that will remain radioactive for many years after the initial analysis that requires handling and disposal protocols for low-level to medium –level  radioactive material.
  • As the number of suitable activation nuclear reactors is declining with a lack of irradiation facilities, the technique has declined in popularity and become more expensive (Glascock, 1996).


This work is divided into five (5) chapters;

The general introduction involves the background of the study, the scope of the study, its limitations, together with the significance of the study. The general introduction gives an overview of the work in general.

The Literature work review includes previous works done by scholars and researchers in relation to this project work.

The methodology of the data gathering/collection of this work is solely by research, the analysis of the work is also by research. The knowledge of neutron physics is required in order to achieve concrete information and data concerning this work.

Results and discussion, which is the fourth chapter in this work shows mainly the results obtained from the research. The project work ends with summary, conclusion and recommendation.


Though this work seems to review neutron interrogation technique, but it goes further than this. It involved a critical and close study of this technique with the view of making strong personal suggestions discovered to security agencies. These suggestions if taken seriously could lead to further investigations to better this technique for the enhancement of national and homeland defense in security, reduction of terrorism and infrastructural facilities e.t.c.