Neutron: An Atomic Particle With No Charge, Essential for Imaging - Essay Sample

Introduction

The neuron is an atomic particle that does not have any charge on it, and therefore coulomb forces of attraction do not affect it in any way. Neutron is also an essential atomic substance that can be used in imaging (Berger, 1964). Therefore it is usually used in radiography to complement X or gamma radiography. It is also believed that neutrons are attenuated by substances such as hydrogen, boron and lithium because they are light in terms of atomic numbers. Therefore they can quickly react with nuclei of an atom. The reaction of these particles is either in the form of absorption or scattering. The likelihood of absorption or scattering depends on the cross-section of the material.

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Neutron radiography is a form of imaging whereby a radiograph is produced through the use of neutrons as the primary penetration radiation. Generally, neutrons used must have an atomic number closer to zero but not more than 1. It is therefore considered as a film technique which allows for the production of neutron images.

Physics of Neutron Radiography

Neutron radiography is transmitted through the application of universal law of attenuation of radiation passing through any given matter or substance. Because various materials have varied attenuation ability, the neutron beam that passes through any content can be assumed to carry valuable information about the structure and material composition. The example can be illustrated, as shown below.

When using neutron radiography, there must be a neutron beamline which has various elements ranging from neutron source to exit of the collimator. Neutrons are produced with a very high initial energy that has MeV magnitude order. Other applications require the transmission of very high neutrons because there is a high cross-sectional thickness of the material. They, therefore, need radiographing with fast neutrons. The image resolution relies on the collimator of the beam (Berger, 1964). It usually works in the same manner as a beam, and therefore it forms the geometric properties of a beam, and sometimes it has filters to regulate energy spectrum so that there is a low content of gamma in terms of change in

The collimator is filled with air or coated with Neutron absorbing medium to ensure that there are no parallel neutrons. The most appropriate neutron beam must be nonmagnetic, must be parallel, has no contaminant radiation and must have a uniform cross-section. The inlet aperture usually must be large enough to allow a sufficient amount of Neutron to flow into but small enough to support high collimation. The divergence value, which is generally expressed in terms of Length over diameter, is also affected by the Length of the collimator (Berger, 1964). When there is a longer collimator, there is the possibility of the high resolution of the image. If the moderator continues to produce more neutrons in different directions, there is a decrease in the intensity proportionately with 1/r2, and this requires a change in either Length or diameter. To produce an excellent image resolution, the beam is expected to be transmitted through the object and recorded by a plane position sensitive detector which usually records it in a two-dimensional image. The image produced must be a projection of the real object directly on the detector plane. Within the image projected, there must be information relating to the composition and structure of the sample interior. This is due to the interaction between different neutrons with the object. In the same condition, the attenuation of the neutron beam is managed by exponential weakening as illustrated by the equation below.

Source and Detectors

Sources of Neutrons

There are three sources of neutrons, namely accelerator, radioactive and nuclear reactor. The accelerator is the most common source of Neutron, which is commonly used by most people. It requires the reaction of positive ions whereby proton or deuteron bombards different regions. The response involves 3H reacting with 4He, which bombard tritium by using deuterons, which generates high-intensity neutron source with a voltage between 150 to 400 Kv and other reactions need a slightly higher acceleration voltage.

Another source of Neutron is a radioactive source (Robertson, 2008). There are some neutrons which can only be generated from contaminated sources. These kinds of neutrons are high energy neutrons, and therefore, there is a problem of collimation and acceleration.

Finally, the nuclear reactor is another source of Neutron. In the reaction of nuclear, there is the generation of neutrons from materials such as uranium fissions. This is the primary source of high-quality neutrons where radiographers have managed to produce more neutrons. It is possible to generate more neutrons because it has high thermal neutron beam intensities, which is considered to be almost three orders. The main factors that must be considered when assessing neutron properties include gamma radiation intensities, cadmium ratio, which is used in describing thermalized Neutron in association with those from high energy producing neutrons.

Neutron Detection

Various detectors are used in neutron radiography because it is sensitive to all kinds of objects that have substances or particles that react with neutrons. All the indicators required must have the ability to measure neutron fields in two dimensions perpendicular to the direction of the beam.

A photographic detector is one of the indicators used in neutron radiography. It uses a traditional X-ray film and the converter screens to capture the image. It is the responsibility of the screen to convert neutron image in such a way that it can be identified easily by the X-ray film. This kind of detector ensures that the neutron image is transformed into alpha, beta or gamma radiation, which makes it more detectable photographically as compared to other models which have not been changed into the picture. The two materials used must have some features that allow it to convert neutron images into different forms. They must be potentially radioactive and must be prompt emission materials for them to be used as materials for detectors. The possible examples of these materials include lithium, boron, gadolinium and cadmium, although they cannot quickly become radioactive but can produce radiation once they absorb neutrons.

Other essential detectors in neutron radiography are scintillator which is usually used in converting neutrons into photon signals that can easily be seen or detected by charged devices such as CCD system such as lithium. The neutrons are absorbed by a high cross section neutron absorbing materials in the scintillation screen. The light produced from the screen is reflected in the camera by a mirror so that the camera is not located in the direction of the neutron beam. This is because the radiation of neutrons can easily damage the chip to create a focus on CCD chip by the lens.

It is more appropriate to use this detector because it has excellent linearity and has high sensitivity which makes it produce real-time images

Advantages of Neutron Radiography

Neutron radiography matches with X and gamma radiography in many instances. X and gamma radiation are mostly applied in imaging materials with very high atomic numbers such as lead. On the contrary, neutron radiography is usually used in imaging materials with deficient nuclear numbers such as plastics and rubbers in a matrix of a very high atomic number material like lead. For that matter, neutron radiography works best in documents that have meagre atomic numbers thus work best in detecting materials that have deficient nuclear numbers. Neutron radiography is mainly used in detecting explosives stored in metallic containers aimed at providing military services. For that reason, it works best in detonating explosives. Neutron radiography is also used in differentiating materials with the same atomic numbers or materials that have different isotopes. The quality of neutron radiography is the ability to scatter or absorb neutrons since this property is essential in removing neutrons from the imaging beam and this is the feature of this radiographic method to work more efficiently than X and Gamma radiography (Polach, 2008). Neutron distribution from the beam can only be achieved through the use of low atomic number materials such as carbon. Neutron absorption is a feature associated with the atomic nucleus structure but not the role of the nuclear number. This quality, therefore, allows neutron radiography to distinguish metallic materials from non-metallic materials such as iron.

Neutron radiography is also capable of separating isotopes, and this quality ensures that it can image one isotope from other isotopes of the same element. This ability makes neutron radiography more applicable in nuclear fuels radiography when imaging fissionable U-235 instead of U-238, which is dominant in uranium. Furthermore, isotopes like Cd-113 commonly applied in reactor control rods can also undergo imaging in the presence of other elements. Nuclear fuel radiography is also considered as one of the benefits that neutron radiography provides to the users. It allows users to image extremely radioactive materials which have not been radiographed by any other scientists. Radiation generated by irradiated nuclear fuel exposes radiographic film when using X or Gamma radiography. This does not happen in neutron radiography, which works by passing electrons through a specimen to generate a radioactive image on the metal converter foils (Robertson, 2008). The dangerous converter screen which has been exposed is separated from a high radiation area and located in a film loaded cassette.

Limitation of Neutron Radiography

In the use of neutron radiography, there is a need for radiation safety precaution as it exposes people to high risk of radiation hazard which all the users must know. Radiographers, therefore, must receive formal training on safety precautions which X and gamma radiographers have not gone through to eliminate such risks (Tharwat Alaa Eldin, 2011). To overcome this challenge, it is essential to establish another serious radiation safety program beyond the one used by X and gamma radiography.

Since the primary sources of neutrons include accelerator, radioactive and reactors, it is therefore costly to use neutron radiography as compared to X rays or gamma radiography. This especially correct when there is a need for significant sources of neutrons.

There are no neutrons which can be transported by any means (Polach, 2008). This cannot be collected from any source. There are neutrons which are low flux, and for that matter, they produce neutrons, which slow down the whole process which only supports the production of moderate image resolution (Burca et al., 2018). There are some processes which require the use of transportable isotopes alongside with electronic imaging systems that enhance the condition of the image resolution.

Currently, there is little functional neutron radiography in the world, and also there are few people who have the experience on how to use neutron radiography and therefore, its use is not easy. For it to work well, there is a need to train much personnel and ensure that they work closely with each other to support one another on how to use this method.

Main Application

There are various applications of neutron radiography. It is usually used for nondestructive tests of different materials. It is also applicable in different research areas, especially industries, but when the researcher has faced some challenges when using X-rays and other conventional methods (Polach, 2008). Although it works so well, the user cannot be sure of receiving positive results all the times, mainly when a failure has been observed when X rays a...