1. Matthew Rose - Emission Spectra of Bicron Scintillators
Objectives
Measurements of Scintillator emission spectra using Laser and spectrometer, potentially for use in Super-NEMO calorimeter
Repeat using X-ray
Comparison - can Laser be used to approximate ionizing radiation of b decay?
Comparison to spectra given by the manufacturers
Effect on Energy Resolution
Reasons for differences?
I have been studying the emission spectra of three scintillators potentially for use in Super-NEMO
Used a 337nm laser to produce scintillations
Comparing these spectra with those produced using x-ray
Comparison with manufacturer’s spectra
Effect on energy resolution
Reasons???
7/28/2019
Matthew Rose - Emission Spectra of Bicron Scintillators

2. Matthew Rose - Emission Spectra of Bicron Scintillators
Acquiring Spectra
BC-404, BC-408 and BC-412 studied
Laser! Scintillator! Spectrometer ! Laptop
USB2000 miniature spectrometer used, with OOIBase32 spectrometer software
Spectra processed using ROOT
Three bicron scintillators used, chosen due to high light output
Set up like so, laptop displays real-time spectra and saves data
For analysis using root
7/28/2019
Matthew Rose - Emission Spectra of Bicron Scintillators

3. Matthew Rose - Emission Spectra of Bicron Scintillators
Laser Spectra
Uneven spectra observed
Unexpected peaks
Could be due to Laser effect
Otherwise results very consistent
Repeat using X-ray to check similarity
Spiky spectra observed
Unexpected peaks, especially in 412
Not attributed to background (see 412 pink line)
Due to laser?
Results otherwise very consistent - 5 spectra are plotted on each one, only tiny differences
Perhaps using an X-ray set to produce scintillations would remove these problems…
7/28/2019
Matthew Rose - Emission Spectra of Bicron Scintillators

4. Matthew Rose - Emission Spectra of Bicron Scintillators
X-ray vs. Laser
Upon comparison however, the two spectra are very similar -
the peaks are in the same place and the spikiness remains
The ‘tail’ observed here only occurs when using the laser,
however it would not be picked up by a PMT, as shown later
Can therefore use the laser to approximate ionizing radiation, i.e. B decays
Laser and X-ray spectra look similar
Tail above 550 nm is removed by Q.E. of PMT
Can use Laser to approximate ionizing radiation
7/28/2019
Matthew Rose - Emission Spectra of Bicron Scintillators

5. Comparison with Bicron Spectra
Can now compare measured spectra with those provided by Bicron
Clearly different, extra peaks are observed
Direct Comparison necessary
Having chosen to use laser spectra, can now compare these with provided Bicron spectra
When measured spectra were rebinned to 10nm, the same as the bicron spectra, the spiky shape disappeared.
The spectra clearly do not match, need to examine them more directly
7/28/2019
Matthew Rose - Emission Spectra of Bicron Scintillators

6. Matthew Rose - Emission Spectra of Bicron Scintillators
Closer Inspection
Peak wavelength is close to that expected
Extra peaks observed
Spectra seem to be stretched towards higher wavelengths
Much light is lost when Q.E. of PMT is taken into account
Upon closer inspection, the peaks can be seen to be within a few nanometres of those expected
however there are other, unexpected peaks in the spectra, especially with BC-412
Some of these seem to corespond to minor peaks in the bicron spectra, but amplified and shifted to longer wavelengths
This would cause much more of the light produced to be lost when the quantum efficiency of the PMT is taken into account, reducing the number of photoelectrons produced
7/28/2019
Matthew Rose - Emission Spectra of Bicron Scintillators

7. Q.E. and Energy Resolution
Extra peaks mean that less light is being converted within the PMT, worsening the obtainable energy resolution
Integral / Npe
And as the energy resolution is proportional to the inverse square root of the number of photoelectrons, this would also worsen the energy resolution
This figure shows the emission spectrum of BC-412 before and after multiplying by the QE, where the integral is proportional to the number of photoelectrons produced in the PMT
7/28/2019
Matthew Rose - Emission Spectra of Bicron Scintillators

8. Matthew Rose - Emission Spectra of Bicron Scintillators
Analysis
Bicron data using thin samples of Scintillator
5x5x2 cm3 blocks used, possibly light is absorbed and reemitted at longer wavelengths as it passes through the scintillator
Extra peaks due to this, as well as spread of the spectra
Only used Hamamatsu, Q.E. > 25% between 300 and 500 nm
Could minimise effect on energy resolution using green-extended PMTs (peak Q.E. between 400 and 600 nm)
These differences in spectra could be due to the thickness of the scintillators for which the bicron data is provided
The measured spectra were taken for 5x5x2 blocks, comparable to the geometry planned for use in Super-NEMO
Within the scintillator short, UV wavelength light is absorbed and reemitted at longer, visible wavelengths. Within a thicker piece of scintillator this wavelength shifting could occur multiple times, stretching the spectra towards longer wavelengths and reducing the relative height of the peaks at shorter wavelengths
Have only taken energy resolutions using Hamamatsu high QE PMT, with a peak QE between 300&500nm
As seen before, very little light is emitted below 400nm, so using a PMT which has the peak QE between 400 and 600 nm would hopefully minimise the effects of the geometry, and thus improve the achievaable energy resolution.
7/28/2019
Matthew Rose - Emission Spectra of Bicron Scintillators