Synthesis of plastic scintillator and applications Ildefonso León Monzón Universidad Autónoma de Sinaloa Centro de Investigación y de Estudios Avanzados

MUON BUNDLE triggered by plastic scintillator modules from ACORDE

Plastic Scintillator – how does it work ? Excitation of base plastic by radiation Foster energy transfer ( resonant dipole-dipole interaction)‏ Emit UV ~340nm Absorb UV photon Emit blue ~400nm photon Detector (PMT... )‏ Base plastic PPO (~1%)‏ Or P-Terphenyl POPOP (~.03%)‏

Why to use P-Terphenyl and POPOP? ‏ Quantum efficiency from a typical PMT is around 420 nm

Once the method was under control, next step was to try bigger volumes.

Plastic made of Polystyrene dopped with PPO (1% w/w) and POPOP(.05% w/w).

Emission of the 0,5% PPO and 0,01% POPOP solution in the mixed solvent: Nemchenok et at.

Up to now everything looks nice. How to construct the detector?

Counting cosmic rays...and coincidences!

Measuring quality Minimum Ionizing Particle: It will be carried out using cosmic muons. Light yield: Number of photons created by MIPS, and/or Radioactive sources Optical attenuation λ: exponential decay as a function of distance Time response: Measurement of fast and slow components (Luminescence and fluorescence) Aging, number of photons as a function of time.

CALIBRATION: charge per QDC channel To know the amount of charge entering by ADC channel, it is necessary to input a well know signal to each channel into the QDC. A B H QDC V965V1718

Data fitted to a linear function

Once calibration is know, next step is to measure: 1 p.e

PMT GAIN The relation of 1p.e position as a function of voltage is called GAIN of the PMT (it is recommended to equalize all PMT's at same gain in an experiment) The position of 1p.e must be as far as possible from pedestal. Its position depends of PMT design.

The calibration steps are clear. Now it is necessary to calibrate last 15 channels. Two (Bachelor) students will be enrolled. One Student from Chemistry Faculty will be working on the process of polimerization and developing a protocol for security reasons: Substances are TOXIC. Calibration almost finished (for one channel!) Next tasks...

FUTURE: The experience in the synthesis of plastic scintillator, bring us the opportunity for innovation, it is possible because we have complete control about time polymerization, dopants concentration, etc. Now we will try to work in a plastic doped with metals, such as Gadolinium, Boron, and some other lanthanide metals.

Gadolinium: Why to use Gd? It has highest cross section for absorbing neutrons. Some experiments use a concentration of 0.1% by weight of Gd (Daya Bay). But, why could be that relevant for us? After a discussion with a colleague from Chemistry Faculty, we conclude that it is possible to obtain a COMPLEX compound with Gd. And... We could increase our concentration of Gd up to a value of 3 % or even more, 10 %.

Gadolinium complex are used in Medicine: NMR The plan is to start to work with not TOXIC Compounds and obtain a COMPLEX containing Gd. Of course, this must be dissolved in our polymer with a concentration as high as possible. Of course, we need to optimize concentration and attenuation length, as well as timing resolution after Gd is loaded.

Reaction for neutron detection The gadolinium-loaded scintillator are chosen for the anti-neutrino experiment because it offers two important advantages over pure hydrocarbon-based scintillator. Firstly, a large thermal neutron capture cross- section of the isotopes 155,157Gd (61,400 and 255,000 b) Shorten the neutron capture time. And a release of a high-energy (8 MeV) gamma cascade after thermal neutron capture on Gd results in a neutron capture signal well above the radioactivity backgrounds

Advantages of using plastic scintillators High Flash point (>90 °C): Security reasons! If a high concentration is required, there is no phase separation or sedimentation. It is possible to reach concentrations up to 3%, or even more with good transparency Because it is solid, it is possible to have independent sectors in a detector. Good for mainteinance and reparation. A concentration of 3% could reduce a detector of 100 Tonne of LS, to 5.5 Tonne.

Other Applications 1) Nuclear Reactor monitoring 2) Civil Applications: Monitoring of radioactive material (terrorism) 3) Measurement of solar activity

Some applications of other dopants

Summary Synthesis method of polystyrene scintillators are under control We have a good response for detecting cosmic rays, mainly muons. There are good opportunities for innovation and look for other novel materials We have started a project research at CINVESTAV and UAS, for synthesis of materials for neutron, antineutrino and neutrino detectors And much more...

Thanks!