Technical background
Scintillation crystal can be made detector, in fields such as high energy physics, nuclear physics, image nuclear medicine diagnostic (XCT, PET), geological prospecting, astronomical Space Physics and safety inspection great application prospect is arranged.Along with the develop rapidly of nuclear science technology and other correlation technique, its Application Areas is constantly being widened.The different application field has also proposed more higher requirements to inorganic scintillator.Scintillation crystals such as traditional NaI (Tl), BGO can't satisfy the particular requirement of new Application Areas.
People are exploring the novel good scintillation crystal that is applicable to the different application field.These novel scintillation crystals may be on over-all properties and production cost, and are bigger with traditional scintillation crystal gaps such as existing sophisticated NaI (Ti), BGO.But people wish that they can have special performance and purposes in some aspects, satisfy the particular requirement in different application field.To these new crystalline basic demands be exactly: physical and chemical performance is stable, high-density, fast decay of luminescence, high-luminous-efficiency, high irradiation hardness and low cost.Except that should having the good characteristics of luminescence and stability, also need certain size and optical homogeneity as outstanding scintillation crystal.
At present the development trend of scintillation crystal is to be the center around performances such as high output, fast-response, high-density, carries out the exploratory development of novel scintillation crystal.By ionic replacement, improve some deficiency of existing scintillation crystal, improve its scintillation properties, reduce its growth difficulty.Optimize crystal growth technique, carry out engineered growth research, reduce the growth cost.Mutual relationship between research crystalline defective and its scintillation properties.By reducing the various defectives in the crystal, improve the crystalline optical homogeneity, improve its scintillation properties.Explore the research of the novel scintillation crystal of new crystal substrate.
Ce
3+The allowed transition of ion 5d → 4f energy level can produce the fast decay fluorescence of tens nanoseconds.Realizing scintillation properties by mixing the Ce ion, is novel scintillation crystal exploratory development focus.People obtain many novel scintillation crystals, such as Ce: LSO, Ce: LuAP, Ce: GSO, Ce: YSO, Ce: YAP by mix the Ce ion in crystal substrates such as silicate, aluminate, phosphoric acid salt at present.They have high light output, characteristics such as fast decay, and as the flash detection material, to improving time, the spatial resolution of detector, miniaturization and multifunction are significant.Obtained very big success although mix at present the research of Ce high temperature scintillation crystal, also there are many problems in they, cost an arm and a leg etc. such as self-absorption phenomenon, fusing point height, growth difficulty, high pure raw material, have restricted their application greatly.
At home and abroad there is no the relevant report of mixing cerium vanadates crystal at present.
Embodiment
Embodiment one: solid phase raw material synthetic method synthesis material
Suppose that the synthetic Ce concentration of mixing is 2% Ce
0.02: Y
0.98VO
4Crystal raw material is promptly chosen x=0.02, according to reaction formula:
According to 0.02: 0.98: 1 mol ratio, take by weighing purity respectively and be 99.99% Ce
2O
3, Y
2O
3And V
2O
5Raw material 6.6 grams, 221.3 grams, 191.9 grams are all poured these three kinds of raw materials into agate and are rolled in the alms bowl, mix, and are pressed into sheet; The platinum crucible of packing into then is placed in the retort furnace, and 1200 ℃ of following sintering 12 hours, took out the cooling back, just becomes Ce
0.02: Y
0.98VO
4Polycrystal raw material.
Embodiment two: liquid phase feed synthetic method synthesis material
Suppose that the synthetic Ce concentration of mixing is 2% Ce
0.02: Re
0.98VO
4Crystal raw material is promptly chosen x=0.02, according to reaction formula:
According to 0.02: 0.98: 1 mol ratio, take by weighing purity respectively and be 99.99% Ce
2O
3, Y
2O
3And NH
4VO
3Raw material 6.6 grams, 221.3 grams, 116.9 grams.Then with Ce
2O
3, Y
2O
3Dissolve simultaneously in the dilute acid soln, ammonium meta-vanadate is dissolved in the dilute ammonia solution.Two kinds of solution are slowly added in the big plastic tank simultaneously.In this process, do not stop to stir, solution is mixed, react completely; According to the pH value of mixing solutions, add an amount of weak ammonia or dilute acid soln simultaneously, the acidity control that guarantees mixing solutions is at 6.8~7.2.Then middle reaction is generated Ce
0.02: Y
0.98VO
4Precipitation behind centrifugal, oven dry, ball milling, compressing tablet, sintering, just becomes Ce
0.02: Y
0.98VO
4Polycrystal raw material.
Embodiment three: crystal growth
Adopt homemade DJL-400 type pulling method monocrystal growing furnace, 25KW thyristor medium frequency induction power supply heating, double platinum rhodium (Pt/Rh30-Pt/Rh10) thermopair, Britain Continental Europe 818 type thermoswitchs, temperature-controlled precision reach ± and 0.1 ℃.
Typical crystal growth parameter is:
The technical parameter of table 1 Czochralski grown vanadate crystal
Seed orientation | <001〉or<100 axially |
Growth atmosphere and pressure | N
2+0.5~2%O
2,50KPa
|
The rate of pulling | 1.5~2.5mm/h |
Slewing rate | 5~10rpm |
Annealing rate | 15~25K/h(>1200℃), 30~50K/h(<1200℃) |
The segregation coefficient of Ce in crystal | 0.6~0.8 |
Preparation work before step 1 crystal growth
The clean that comprises burner hearth is changed material, seed crystal centering and give in the stove and charge into protective atmosphere.
Step 2 seeding, receipts neck and shouldering
Seed crystal is drawn nearly liquid level, stablize for some time (about 10min) after, carry out seeding.After lifting one hour, attemperation makes crystal gradually toward radially growing up (shouldering).
The control of step 3 diameter
When the crystal shouldering when the set diameter (routine 40mm), adopt in right amount and heat up, increase with the continuation of control crystal diameter.Like this, the crystalline growth interface can little by little exceed liquid level 1~2mm, and control diameter is finished.
Step 4 isodiametric growth of crystal
Must be in the process of growth according to growing state, attemperation, control crystalline isodiametric growth.
Step 5 is received the footpath process
Long when crystal to predetermined length, in the time of need stopping growing, keep pulling rate constant, use instead big temperature rise rate (as 3~40 ℃/h) continue to lift after, the crystal afterbody becomes planar interface or dimpling face, will soon break away from liquid level, stops subsequently lifting, and changes annealing stage over to.
Step 6 furnace annealing
In high-temperature zone (1750~1200 ℃), we adopt the cooling rate of 10~20 ℃/h.Below 1200 ℃, generally adopt 30~40 ℃/h cooling rate.
Step 7 stove is annealed outward
Crystal is contained in Al
2O
3In the corundum crucible, put into retort furnace, high temperature, long term annealing under air atmosphere.Usually with 10-50 ℃ speed intensification or cooling, constant temperature is 12 hours in the time of 1200 ℃.