Neutron Scattering

Table 2 .1 :
Comparison of X-rays and neutrons
X-rays are transversal
electromagnetic waves
neutrons are particle waves
Mass Mpho, = 0 ni, = 1 .6749286(10) - 10-27kg
Charge 0 0
Spin 1 1/z
Magnetic Moment 0 fi,, _ - 1.91304275(45),uN
Typical Energy 10keV 25meV
Wave length  x = c% =1.24Â
,i h
" - 2Em )
1/2
=1 .8Â
Velocity speed of light
2Elv2
u - =
n
-C m n
2200 5/sec
2 .3 Neutron production
Neutrons are generated by nuclear reactions . For the investigation ofmatter a large luminosity
that means a high flux of neutrons 0 ofthe requested energy range is essential . Such fluxes at
prescrit cari only be obtained through nuclear fission or spallation . Both are schematically
displayed in Fig .2 .5 .
In nuclear fission a thermal neutron is absorbed by an 235U nucleus . The thereby highly
excited nucleus fissions into a number of smaller nuclei of middle heavy elements and in
addition into 2-5 (on average 2 .5) highly energetic fast fission neutrons . Typical energies are
in the rage of several MeV. In order to undertain a nuclear chain reaction, on the average 1 .5
moderated neutrons are necessaiy . At a balance a research reactor delivers about 1 neutron per
fission event .
The most powerful research reactor worldwide, the IIFR at the Institute Laue Langevin in
Grenoble, produces a neutron flux of