Experimental Apparatus

Sample Preparation

Students will first load their MnO sample in the Centre for Crystal Growth in ABB 435.  The powder sample will be loaded into an aluminum sample can.  The Centre for Crystal Growth has an array of infrastructure for materials preparation and handling. The chemicals you will be handling are inert and not dangerous, but you should be following appropriate lab protocols all the time.  Please follow the instructions of Dr. Qiang Chen and do not touch anything in the laboratory unnecessarily.

It is an interesting observation that scientists often use Aluminium as the material of choice for their sample holders. Using the active periodic table at https://www.ncnr.nist.gov/resources/n-lengths/ and the fact that the visibility of different atoms to neutrons is described in terms of a scattering cross section (scatt xs) in this active periodic table, can you guess at why Aluminium is used in this way?  You will have to use this periodic table, and compare the scatt xs between Aluminum and other common machinable metals, like Iron.

Closed Cycle Refrigerator

At Beamport 6 of the McMaster Nuclear Reactor, the students will assist Dr. Bo Yuan or Dr. Gaulin in loading the filled sample can into a closed cycle refrigerator (CCR).  The CCR uses cycles of compressing and expanding hydrogen gas to control the temperature of the sample between ~ 5 K and 800 K.  You will take measurements between ~ 5 K and 300 K.  Note that this refrigerator is made from aluminium for all parts of it which would be exposed to a neutron beam.  It turns out that aluminium is an ideal material to use if you think your apparatus is going to be blasted by neutrons because it is not easily activated (i.e. turned into an unstable isotope).

The MAD neutron diffractometer

The McMaster Alignment Diffractometer (MAD) neutron diffractometer is situated on Beamport 6 of the McMaster Nuclear Reactor.  A schematic diagram of this instrument is illustrated in Fig. 3.  This instrument uses a silicon monochromator crystal to select out a single de Broglie-wavelength neutron beam from the reactor and deliver it to the sample. The monochromator has a value of 3.12 Angstrom.

The C2 linear position sensitive neutron detector

Neutrons diffracted by the MnO sample will be detected in the horizontal plane by a position sensitive neutron detector, C2.  Because neutrons have no electric charge, they don’t interact via the electromagnetic force, which limits us to interactions via the strong nuclear force.  C2 uses the neutron-absorbing boron in BF₃ gas to detect the neutrons.  The ¹⁰B absorbs a neutron and becomes ⁷Li³⁺ and ⁴He²⁺ (an alpha particle).  The alpha particle is then detected via ionization. C2 has 800 detector wires arranged over 80 degrees, resulting in an angular resolution of 0.1 degrees in scattering angle.