DESCANT

DESCANT (the Deuterated Scintillator Array for Neutron Tagging) is a neutron detector custom-designed to provide neutron data in conjunction with the TIGRESS and GRIFFIN gamma ray spectroscopy analysis of nuclear structure. 

Many of the neutron-rich exotic nuclei explored with TIGRESS and GRIFFIN emit, in addition to gamma rays, radiation in the form of neutrons. The neutrons detected by DESCANT carry critical information about the structure of exotic nuclei. For example, with neutron-rich lithium-11 (¹¹Li), the angle-of-emission data collected by DESCANT provides insight into the structure of ¹¹Li‘s very weakly bound halo neutrons, those at the extreme outer edge of the nucleus. 

Similarly, neutron emission probability is critical for understanding element formation in exploding stars, as well as in having applications in nuclear engineering and advanced fuel-cycle reactor design. 

TRIUMF collaborator Dr. Paul Garrett, a professor of experimental physics at the University of Guelph, conceived of DESCANT and led its design and fabrication.  

From a distance, DESCANT looks like an impressive, large red, white, and blue shield, with a green and blue trim, mounted behind TIGRESS or GRIFFIN. 

The concave array consists of 70 individual neutron detector boxes, each 15 cm thick, and precisely shaped so they assemble with only the width of a $20 bill between them. DESCANT is positioned 50 cm from the TIGRESS or GRIFFIN target.

Each detector is filled with about two liters of the scintillator material deuterated benzene. This is a form of benzene in which each of the molecule’s six hydrogen atoms is replaced by deuterium, a hydrogen isotope with an additional neutron. When a deuterium nucleis is struck by an incoming neutron, the benzene absorbs its energy and scintillates – it re-emits the absorbed energy as visible light, which is detected by photomultiplier tubes.

The benzene scintillator material has several advantages, including enabling TRIUMF scientists to distinguish between neutrons and gamma rays interacting with the scintillator material. The distinctive behaviour of neutron-deuterium scattering also enables the determination of the neutron energy spectrum, or the range of energies the neutrons possess. In addition, DESCANT detects neutrons’ angle of incidence and time-of-flight.

DESCANT’s distinctive colouration is a consequence of the “20-dollar-bill” separation between elements. This simply cannot be accomplished with a single detector shape.  The central detectors have three distinct shapes, and the outer rim has two mirror-image shapes. The manufacturer offered to colour the inner detectors by shape in red, white and blue, and the outer detectors green and yellow. This also aids in correct assembly of DESCANT.