MainPage:Nuclear:KaonDetector:AerogelCharacteristics

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Optical properties - Transmittance

In order to starting measuring the light absorption properties of aerogel, a spectrometer was used for the measurement of the transmittance of some tiles (figure 1).

IMPORTANT: this method measures only the transmittance. It cannot distinguish between scattered and absorbed light. As in the Kaon Aerogel Detector the scattered light is still considerable to be collected by one of the PMTs, it is necessary to disentangle these parts. Discussion on this disentangling is showed below.

The spectrometer consists of a monochromatic beam of light (1 nm resolution) that is chopped in two different paths: reference and beam (figure 2). One aerogel tile is placed on the beam path (figure 3), so the spectrometer measures the light intensity difference between the beam and reference path, giving the transmittance of the analyzed sample.

Experimental setup for aerogel transmittance characterization

1) Equipment "Perkin/Elmer Lambda 750 Spectrometer" used for the analysis.

2) Inside the spectrometer where the monochromatic light beam is chopped in two: reference and beam. The sample to be analyzed is placed in the beam position.

3) Aerogel tile placed in the beam position for transmittance analysis.

Refractive index measurement

In order to evaluate the quality of the aerogel tiles we bought for the Kaon Aerogel Detector, an experimental setup was prepared. A few sample of tiles were randomly selected and analyzed.

Refractive index results

Refractive index of some randomly selected aerogel tiles with nominal index of 1.030 and 1.020.

Refractive index tiles with nominal index of 1.015.

This method consists of a laser sheet, part of it passing through the analyzed aerogel tile and the other part passing out of it. The beam that goes inside the tile get refracted. A reference paper is placed after the tile to mark both the direct and refracted beams. The deviation of the laser is them possible to be measured (using image analysis) for the calculation of the refractive index that causes such deflection.

Example of aerogel refractive index analysis

1) Experimental setup for the measurement of the aerogel refractive index. A laser sheet is refracted by the tile and hit a target paper. The deviation of the laser can be measured for the calculation of the refractive index.	2) Part of the laser sheet pass through the aerogel tile, being deflected by its refractive index. The other part pass on the top of the tile, going direct to the reference paper target.	3) Picture of the reference paper with the direct (top) and refracted (bottom) laser beam. Two lines are selected for the pixel intensity analysis, looking for the peaks identification.
4) Calibration process example: a MatLAB code identifies the grid lines of the target paper.	5) Knowing the grid size of the previous image, the relation pixel to millimeter can be calibrated along the desired line.	6) After the calibration of the two lines (directed and refracted beams), the peaks position can be fitted for the analysis of the refracted beam deflection due to the aerogel.

Kaon Aerogel Detector prototype - Aerogel light yield comparison

In order to compare the different aerogel (refractive index) we will use in the Kaon Aerogel Detector, a set of cosmic rays data was acquired with the CUA's prototype. Details of the prototype can be found in the Prototype page.

To evaluate the relative light yield of the aerogel tiles with refractive indexes 1.030 and 1.015, the setup was run with the same configuration twice (just exchanging the aerogel).

The setup configuration was kept as follows:

• Cosmic ray configuration (two triggering PMTs with scintillator on the top and bottom of the prototype)
• 08 aerogel tiles
• Mylar covering the internal walls of the prototype
• High voltage of -1.80 kV on the PMT
• Blast PMT for all runs (model XP4500/B s/n 09650, with calibration from run 481)

Aerogel comparison under cosmic ray test - Aerogel Prototype

08 tiles of aerogel 1.030. Blast PMT model XP4500/B s/n 09650.

08 tiles of aerogel 1.015. Blast PMT model XP4500/B s/n 09650.

Summary of the aerogel evaluation - Aerogel Prototype

Aerogel relative light yield evaluation using CUA Aerogel Detector prototype. 08 tiles of aerogel with Blast (XP4500/B) PMT.

To see a similar test done for the analysis of the different PMTs options for the Kaon Aerogel Detector, click here.