Patent GB-1411792-A (GB)
Title: Crystal body with an optical surface produced by seeded non- epitaxial growth
IPC: G01T1/164
Filed: 1972-08-31
Abstract: 1411792 Treating crystals; joining glass to crystals KEWANEE OIL CO 31 Aug 1972 [2 Sept 1971] 40350/72 Headings C1A and C1M [Also in Divisions B1 and C4] A process for controllably disfiguring a surface of an optical body of inorganic crystalline material (e.g. a seintillator crystal) so as to increase the light diffusion comprises contacting with a finely divided solid crystal nidus agent or mixture of agents of particle size - 80 to + 325 Tyler Standard screen mesh in the presence of a transferable moiety capable of generating non- epitaxial growth on the crystal surface in a substantially uniform yet random manner irrespective of the microscopic orientation of the base crystal, and removing the transferable moiety to prevent further non-epitaxial growth. The diffuse surface improves resolution. Detailed examples, dimensions and pretreatments are included. It is immaterial whether or not the nidus agent is a seintillator. For a base crystal which forms a hydrate with water, a nidus agent may have water of crystallization as the transferable moiety associated with it. e.g. CaSO 4 .- H 2 O; MgSO 4 .7H 2 O; BaI 2 .2H 2 O; NaBr.2H 2 O. For LiF or CsI base, boron fluoride with potassium fluoroborate may be the nidus agent, or LiI.3H 2 O may be used with LiI and NaI.2H 2 O with NaI. Nidus agents with transferable moisture may also include aluminium oxide, silica, magnesium oxide or fluoride, or calcium carbonate. The examples include plaster of Paris nidus agent; potassium fluoroborate with boron fluoride ethyl ether as moiety; potassium fluoroborate powders with metaboric acid and hydrochloric acid vapour; and also boron fluoride gas as moiety, further details of particular combinations being given. The moiety may be gaseous or liquid. Carbon black and inorganic pigments may be seeds for non-white surfaces, and also finely divided hydrate forms of the base, macroporous and microporous alkali metal silicates and alkaline earth metal silicates (e.g. molecular sieves) which may have associated water, sulphur dioxide, ammonia or boron fluoride as growth forming moieties. Detailed examples include methods of applying the agents to bases, including by a fluidized stream, e.g. a T1: NaI crystal is bonded to a glass window by a polymerized transparent coupling fluid, encapsulated in a heavy metal support flange with an Al back covered with white reflector paint or an alumina reflector powder, and coupled to a complex light pipe with phototubes. The crystal is included in an Angercamera. Roughening and polishing treatments are applied to specified crystal surfaces. References are made to charged particle, α, #, γ sensitive scintillators, and inorganic crystals, e.g. NaI : Tl, CsI : Tl or Na, KI : Tl as used for camera plates and spectrometers, LiI : Eu; KBr; BaF 2 ; CaF 2 ; CaF 2  : Eu; SrF 2 ; MgF 2 . Excitation may be by γ rad. from Cs<SP>137</SP> or Tc<SP>99</SP>. Medical applications employing phototubes and pulse height analysers are instanced. Other applications include creation of uniform light intensity in sensing scintillations; display of a real image as when focusing, comparison of flux density of opposing beams; acceptance of wide angle beams, reduction of ghosts by treatment of prism ends and edges of lenses or beam splitting elements 626.