Lead tungstate

Structural formula
General
Surname	Lead tungstate
other names	Lead (II) tungstate
Molecular formula	PbWO 4
External identifiers / databases
EC number	231-849-7
ECHA InfoCard	100,028,954
PubChem	24464
Wikidata	Q883696
properties
Molar mass	455.04 g mol −1
Physical state	firmly
density	8.28 g cm −3 ; 8.46 g cm −3 (raspit);
Melting point	1123 ° C
solubility	almost insoluble in water
safety instructions
H and P phrases	H: 302-332-360-373-410
	P: 201-273-308 + 313-501
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Lead tungstate ( PWO ) is a crystalline compound made of tungsten , lead and oxygen . Lead tungstate is used as a very radiation-resistant scintillator in calorimeters in particle physics .

Occurrence

Lead tungstate occurs naturally as the mineral stolzite and raspite .

Extraction and presentation

The crystals are produced from a stoichiometric melt of PbO and WO ₃ using both the Czochralski method and the Bridgman-Stockbarger method .

{\ displaystyle \ mathrm {PbO + WO_ {3} \ \ longrightarrow {} \ PbWO_ {4}}}

properties

Lead tungstate has a melting temperature of 1123 ° C, a density of 8.28 g / cm ³ and is not hygroscopic. The spectral maximum of the scintillation light is 430 nm, there the refractive index is 2.17. The radiation length is 0.89 cm. 80% of the scintillation light is emitted within 25 ns. The scintillation light output of lead tungstate is low and is only 5% of bismuth germanate or 0.6% of sodium iodide . Furthermore, the light output is strongly dependent on the temperature. At around 400 ° C, Raspit turns into Stolzite.

use

At the Large Hadron Collider at CERN , lead tungstate is used in the CMS and ALICE detectors, and use is also planned in the PANDA detector at the FAIR accelerator center .

ECAL of the Compact Muon Solenoid

The electronic calorimeter ECAL of the Compact Muon Solenoid consists of a tube of 61,200 crystals and two end elements of 7,324 crystals each. The crystals have the dimensions of 24 × 24 × 230 mm in the radial area and 30 × 30 × 220 mm at the end pieces. The expected radiation dose over the course of 10 years of operation is 4000 Gy and 2 · 10 ¹³ neutrons / cm ² for the radial area ; 50 times the dose is expected at the end pieces. Due to the high radiation dose, a fluctuation in transmittivity of around 5% is expected in the CMS. To correct the fluctuations, the CMS is equipped with a system with which laser light is coupled into the individual crystals via glass fibers for calibration purposes.

ALICE-PHOS detector

Crystals measuring 22 × 22 × 180 mm are used in the PHOS calorimeter of the ALICE detector. The crystals are doped with about 100 ppm yttrium oxide . To increase the light yield, the lead tungstate calorimeters in the ALICE detector are cooled to −25 ° C. After ten years of operation, a radiation dose of 1 Gy and a neutron dose of 2 · 10 ¹⁰ neutrons / cm ^{2 are} expected.

PANDA EMC detector

In the electromagnetic calorimeter (EMC) of the PANDA detector, 16,000 lead tungstate crystals measuring around 21 × 28 × 200 mm and weighing around one kilogram are used. The operating temperature of the EMC is −25 ° C.

Web links

CERNCourier: Use in the CMS (English)

Individual evidence

↑ ^a ^b ^c ^d ^e Florian Feldbauer: Studies on the radiation hardness of lead tungstate crystals, master's thesis. Ruhr-Universität Bochum , 2009, accessed on November 12, 2018 (German).
↑ ^a ^b ^c Dale L. Perry, Sidney L. Phillips; Handbook of Inorganic Compounds; ISBN 978-0849386718 .
↑ ^a ^b data sheet lead tungstate from Sigma-Aldrich , accessed on March 13, 2011 ( PDF ).
↑ ^a ^b M. Ippolitova et al .: Lead tungstate crystals for the ALICE / CERN experiment . In: Nuclear Instruments and Methods in Physics Research A . 537, No. 1-2, 2005, pp. 353-356. doi : 10.1016 / j.nima.2004.08.042 .
↑ Baoguo Han, Xiqi Feng, Guangin Hu, Yanxing Zhang, Zhiwen Yin: Annealing effects and radiation damage mechanisms of PbWO ₄ single crystals . In: J. Appl. Phys. . 86, No. 7, 1999, pp. 3571-3578. doi : 10.1063 / 1.371260 .
↑ ^a ^b Q. Ingram1: The Lead tungstates Electromagnetic Calorimeter of CMS. (PDF; 165 kB) March 16, 2006, archived from the original on October 7, 2006 ; accessed on April 2, 2010 (English).

[Feldbauer-1] Florian Feldbauer: Studies on the radiation hardness of lead tungstate crystals, master's thesis. Ruhr-Universität Bochum , 2009, accessed on November 12, 2018 (German).

[hb-2] Dale L. Perry, Sidney L. Phillips; Handbook of Inorganic Compounds; ISBN 978-0849386718 .

[Sigma-3] ta sheet lead tungstate from Sigma-Aldrich , accessed on March 13, 2011 ( PDF ).

[Ippolitova-4] M. Ippolitova et al .: Lead tungstate crystals for the ALICE / CERN experiment . In: Nuclear Instruments and Methods in Physics Research A . 537, No. 1-2, 2005, pp. 353-356. doi : 10.1016 / j.nima.2004.08.042 .

[Baoguo-5] Baoguo Han, Xiqi Feng, Guangin Hu, Yanxing Zhang, Zhiwen Yin: Annealing effects and radiation damage mechanisms of PbWO ₄ single crystals . In: J. Appl. Phys. . 86, No. 7, 1999, pp. 3571-3578. doi : 10.1063 / 1.371260 .

[Ingram1-6] Q. Ingram1: The Lead tungstates Electromagnetic Calorimeter of CMS. (PDF; 165 kB) March 16, 2006, archived from the original on October 7, 2006 ; accessed on April 2, 2010 (English).