Author: Emre Akbulut

We are in the preliminary stages of analyzing different options for how to modify the Cosmic Watch v2’s configuration and code to suit our purposes in detecting gamma rays. There are some assumption based methods like using the Cosmic Watch’s master-slave configuration and deducting the difference between them as the total amount of gamma rays. However, by working with the radiation detection group we are hoping to find ways to employ more exact methods in gamma ray detection.

While waiting for parts I began reading about scintillators and SiPMs being used to detect gamma rays and muons. Muons are have an average energy level of 4 GeV at sea level [1] while gamma rays have a much lower energy range typically defined as 100 KeV to 5 MeV [2]. The way the Cosmic Watch Muon detector works is when a muon hits the scintillator it emits light, the SiPM then sees this emission of light and converts it to a voltage pulse. The resulting pulse ranges from 10-100mV, which is too small to be read by the Arduino Nano, so the signal is amplified by 20-25 through an op-amp so it can be read by the Nano as an ADC voltage value.

One interesting thing I found was how one individual created a DIY gamma ray detector with a miniature solar cell [3]. This functioned similar to the Cosmic Watch in how a pulse was created from gamma rays and then amplified to be displayed. It may be worth looking into if this method of detection could be improved to suit our purposes.

Another thing I noticed when looking through the materials we are using for the Muon detector we have is that the scintillator we have, bc408, is not meant for gamma ray detection. However, the bc412 from the same manufacturer can detect gamma rays from 100 KeV to 5 MeV [4]. We will need to meet with the radiation detection group at OSU first before considering the use of bc412 material.

[1] “Muons.” [Online]. Available: https://cosmic.lbl.gov/SKliewer/Cosmic_Rays/Muons.htm. [Accessed: 24-Jan-2019].

[2] “Radioactivity : Gamma Rays in Matter.” [Online]. Available: http://www.radioactivity.eu.com/site/pages/Gamma_Matter.htm. [Accessed: 24-Jan-2019].

[3] “Alan Yates’ Laboratory – Photodiode Gamma Ray Detector.” [Online]. Available: http://www.vk2zay.net/article/265. [Accessed: 24-Jan-2019].

[4] “BC-408, BC-412, BC-416 | Products | Saint-Gobain Crystals.” [Online]. Available: https://www.crystals.saint-gobain.com/products/bc-408-bc-412-bc-416. [Accessed: 24-Jan-2019].

March 29, 2019

Major developments have happened since the last blog post. Some questions that were answered from the previous post:

• BC412 and plastic scintillators will not offer the resolution we need for detecting gamma rays due to their low Z value. This is because the method of using gamma ray detection to get the snow water equivalency (SWE) of snow requires very high resolution detection.
• Steven Czyz, one of Dr. Farsoni’s Ph.D students informed me and Selker on the issues with an inexpensive way to detect gamma rays mentioned in the above bullet point. However, Steven’s ph.D thesis project is a full spectrum, small gamma ray detector which cost about $5,000 to build two. He said that after he finishes his ph.D project thesis that his gamma ray detectors will probably be not used; so it is possible we could use them.

Originally with our backgrounds we were expecting gamma ray detection would be inexpensive and neutron detection would require very expensive that would only emit light due to neutrons.

On March 15th, 2019 during a meeting with John we were reaching out to Eljen Technology inquiring about their neutron detectors. John explained the overview of the CRES project and asked about their green sandwich “paddle” for thermal neutrons and asked if it was possible to get any defective scintillators to help orient ourselves with neutron detection.

About two weeks later they decided to contribute an entire 6 cm by 20 cm green sandwich “paddle”, which is composed of two scintillating tiles, EJ-426, and a green wavelength shiftier EJ-280. They sourced this from a larger order in Europe and there is already a small square cut on one of the tiles to for using a SiPM with the sandwich. This contribution is worth about $200, about the same price it took to assemble the muon detector.

To my excitement about this I started looking into this green paddle configuration to see what modifications we would need to make to the current CRES electronics. First off was understanding if our SiPM for blue light would work. The color wavelength chart below for reference will help understand why the sandwich configuration is used.

EJ-426’s emission spectrum peaks around 450 nm which is on the boarder of violet and blue light. The EJ-280 takes the violet/blue light and then shifts the wavelength to green light. This sandwich has some advantages over typical light collection methods like used in the Cosmic Watch V2 Muon Detector.