In contrast to X-rays, neutrons are able to

Medicinsk Neutron Vetenskap 

B. Neutron Radiografi

B. Neutron Radiografi

In contrast to X-rays, neutrons are able to

penetrate heavy metals such as lead or uranium.

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Neutron radiation has other advantages: g

it is the method of choice for delicate organic materials and for water.

Neutron imaging represents a valuable g g p

complement and alternative to conventional X- ray technology. y gy

Thanks to this method, researchers are able to ,

produce images of the insides of objects where

other methods fail.

Comparison of crossections of  elements with various o pa so o c ossec o s o e e e s a ous

atomic number for X‐rays (yellow) and neutrons (blue)

The two images on the left are radiographs of the  reinforced concrete sample photographed on the  right. The blue and green images are tomograms.

right. The blue and green images are tomograms.

The principle of the radiography system: a surface detector fixed behind the sample records the

detector fixed behind the sample records the

radiation emitted by the source, thus revealing the weakening effect within the sample.

weakening effect within the sample.

Neutron source :

High energy protons hit a target of heavy metal (Mercury Lead/Bismut Wolfram) metal (Mercury, Lead/Bismut, Wolfram) splitting the nuclei into nuclear fragments (Spallation), protons, gamma radiation and (Spallation), protons, gamma radiation and neutrons w

hich are moderated.

decelerated in the moderator

Neutron yield from a lead target as a  function of proton energy

function of proton energy. 

Neutron yield is almost proportional  to proton energy at up to 12 GeV to proton energy at up to 12 GeV. 

Here the symbols show experimental results wheres the lines show the results, wheres the lines show the  results of various calculations.

Neutron energy spectrum from Neutron energy spectrum from mercury and PbBi alloy targets.

Graphic representation of the neutron radiographic beam

Internal view of Neutron  te a e o eut o Radiographic beam

(shielding partially (shielding partially removed).

The detector The detector

arrangement is shown at  th f t

the front

Although neutron images can be created on X-ray film by using a converter, digital methods have been increasingly used in recent years The advantages of digital methods are used in recent years. The advantages of digital methods are obvious: the image data can be saved, copied, transferred

CCD camera with scintillator

h i d d h i i

The image produced on the neutron-sensitive

scintillator is captured by a light-sensitive, cooled camera and stored digitally Variable lens systems camera and stored digitally. Variable lens systems are used to generate differing fields of vision

(between 4 and 40cm). This setup is used mainly

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for tomography.

Intensified CCD with scintillator

A series image amplifi er can be used to achieve g p

a significantly higher light yield. By setting very

narrow time windows, this system can be used to , y

investigate rapidly repetitive processes.

Film methods

Neutron images can be produced with X-ray and trace

i fil h d d l i

corrosion films. However, the exposure and developing times are very long.

An early thermal neutron radiograph of a human chest was limited by multiple scattering and poor detector spatial resolution

th-neutrons

X-rays 20 keV X-rays 20 keV

C i f t i d ith th l t (t ) d 20 kV X (b tt ) Th

adenocarcinoma liposarcoma, leiomyoma

Comparison of tumors imaged with thermal neutrons (top) and 20‐kV X‐rays (bottom). The  contrast in the neutron radiographs is more pronounced because of higher hydrogen 

concentrations in tumorous tissue

X-rays 42 kV thermal neutrons

Radiographs of a rat paw and tail using

(A) thermal neutrons and (B) 42-kV X-rays.

Gd O in oil was used as the contrast agent Gd₂O₃ in oil was used as the contrast agent

Epithermal neutrons X-rays 42 kV

Radiographs of a rat head using (A) epithermal (i.e., 0.5 to 2 eV) neutrons and (B) 42‐kV X‐rays. 

Th t h i i ibl i (A) i di t d b th Alth h I O d

The rat nasopharynx is visible in (A), as indicated by the arrow. Although In₂O₃ was used as a  contrast agent, the epithermal neutron flux was not sufficient to demonstrate its contrast capabilities [

Natural bone Natural bone

X‐ray 42 kV neutrons

X ray 42 kV neutrons

Images of natural bone made by

40-keV X-ray radiography (left) and neutron radiographs (right)

Approximate location of the thin porcine lung specimen imaged using thermal neutrons.

Only the lung airways are O y t e u g a ays a e illustrated

In a recent study, the anatomical changes in corn kernels affected by Aspergillus flavus fungus were analyzed quantitatively by T.E. Cleveland et al., J.

Cereal Sci 1 (2008) using neutron tomography Cereal Sci. 1 (2008). using neutron tomography.

They demonstrated the effectiveness of neutron radiography in identifying the degradation of the radiography in identifying the degradation of the

biological tissues compared with tissues in uninfected control kernels. Resistant kernels showed no sign of anatomical change.

This interesting research shows the sensitivity of This interesting research shows the sensitivity of neutron radiography to the effects of diseases on biological tissues. The most recent and promising biological tissues. The most recent and promising studies by. B. Schillinger et al., 2011 are illustrated by tomography of a rat lung.

Multimodal images of the same specimen of porcine lung tissue

Neutron computed tomography of rat lungs

2 d 30 V ^{8 2}

Neutrons (energy between 2 and 30 meV; flux at target: 10⁸ neutrons s⁻¹ cm⁻²) enter  a 16 m long evacuated aluminium flight tube through a collimator (typically 20 mm 

diameter), delivering a quasi‐parallel beam without intrinsic image magnification. A beam 

d h l b f l ll

diameter at the sample position is 40 × 40 cm, but for lung measurements typically 4 × 4  cm beam diameters were used. 

6Li( )³H

After penetrating the sample, neutrons are detected by a nuclear reaction (⁶Li(n,α)³H⁾ 

in a LiF+ZnS(Ag,Cu) scintillation screen. This reaction is highly exothermic with a  kinetic energy of 4.7 MeV. Resolution is limited to about 100 μm on a standard screen  (thickness: 200 μm) and to about 30 μm (thickness: 50 μm) on specially thinned screens,  which were used here. A high‐resolution cooled CCD camera (Andor DW436, 2048 × 2048 pixel, 16 bit) records the resulting image.p , ) g g

Neutron images of SPGO (small particulate gadolinium oxide) - doped liver tissue. A: original liver specimen; B: colorenhanced image of A; C: distribution of the SPGO nanoparticles created using simple thresholding

Neutron imaging of living human subjects

till k b i di l i l

still provokes obvious radiological concerns.

However, its potential for applications such as clinical research, small-animal imaging, , g g, and forensic science needs to be

investigated further investigated further.

The high sensitivity of neutrons to The high sensitivity of neutrons to

hydrogen atoms should be of benefit for

forensic applications, where quantification

of water changes in dead tissues is highly g g y

important.

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