- Under development
- Gamma ray energey analyzer with PIN photodiode (PS100-7-CER-PIN)
- Released X100-7 with black window.
- A.K.A. Energey spectrum of ionizing radiation.
- Analyzing pulse hight statistics, we can indentify the kind of radiation source.
- For example, Cs-137 emits gamma ray with 0.662 MeV.
- When we detect 0.662 MeV, we can indentify as Cs-137
- Si detector has high energy resolution.
- MCA:Multi Channel Anaylzer
- This is a detector module.
- Silicon Gamma Radiation Detector without GM tube
- Gamma-ray or X-ray detector with PIN photodiode
- When a Gamma-ray hits a depletion region on the PIN photodiode, it produces a small charge.
- As known as Photoelectric effect or Compton effect.
- The signal is generated as a pulse with amplifer.
- Electron pair creation is needed 1.022MeV at least.
- E value of Si is 3.65eV. When Si atom gets 3.65eV, Si puts out an electron.
- Energy equation of electromagnetic wave
- h:Planck constant
- c:speed of light
- Visible light have between 400nm to 800nm wavelength. Gamma ray have under 10pm wavelength.
- Mainly Photoelectric effect under 60KeV, mainly Compton effect upper 60KeV
- Mainly Electron pair creation upper 6MeV
- Gamma energy of radionuclide have between 5keV to 4MeV. So rare electron pair creation without cosmic rays. Cosmic ray have strong energy.
- The lower energy come to high detection probability, the higher energy come to low detection probability.
- The detection probability on 10keV is 100%, but 1% between 100KeV to 1MeV
- Pulse Shaping process
- Typical pulse width is 1us.
- Time factor is RC.
- Gamma-ray produces a small charge
- Charge amplifier converts a small charge to DC voltage.
- Diffrentiator amplifier converts DC voltage to a pulse with Pole Zero Cancellation.
- Integrator amplifier converts a pluse to gauss pulse instead of cusp pulse and separates it from noise. Cusp pulse is ideal for Integrator amplifier.
- Base Line Restorer.
- Multi Channel Analyzer counts pulse hight.
- Typical AD convertion resolution is 12 bits(4096 steps).
- Making histogram of pulse hight as a gamma spectrum.
- Consideration of AD convertion speed.
- 1us pulse is required 0.1us(10MHz) sampling rate.
- Time factor is important.
- The simulation with LTspice to design the circuit.
- To find best C1 capacity
- Example 1pF, 2pF and 5pF
- To check the lineality between input charge and output peak voltage.
- Real pulse
- Detected pulse on left area, as oscilloscope
- Energy level on right area, as spectrum
- It seems to characteristic spectrum of uranium.
- figure on PC
- It takes long time. At least, 1000 counts needed.
- 1000/10cpm=10 minutes where 10cpm.
- Back ground figure
- KCL figure
- 0.0117% of K is radioactive K40.
- 10.7% of K40 emits 1.46MeV gamma ray.
- So 0.0117% x 10.7% = 0.0012519%, too little
- KCL - Back ground figure
- To find the peaks
- Cs soil figure
- Cs - Back ground figure
- To find the peaks
- There are many peaks.
- Cs134 has some gamma energy rays. Not only 605KeV but also 796KeV.
Beta 1.31MeV(89.3%) Gamma 1.46MeV(10.7%)
Beta 88.6KeV(27.3%),415KeV(2.51%),658KeV(70.2%) Gamma 563KeV(8.4%),569KeV(15.4%),605KeV(97.6%),796KeV(85.5%),802KeV(8.7%),1.345MeV(3.0%)
Beta 1.176MeV(5.6%),514KeV(94.4%) Gamma 662KeV(85.1%),32.1KeV(5.8%),36.5KeV(1.3%)
Beta 546KeV(100%) Gamma -
- You can see a Gauss wave.
- Test case
- X axis:define energy[eV]
- Y axis:calibrate radiation rate
- Use the radionuclide known gamma ray energy. Ra-226
- 89% of K40 emit beta ray and 11% of K40 emit gamma ray.
- Efficency of silicon and window
- Photoelectric effect, Compton effect, Electron pair creation
- Efficency of X100-7
- Approximate expression
- Omiting 10KeV below
- Normalizing energy efficency