- Dose and dose rate meter
- Silicon Gamma Radiation Detector with gamma ray energy correction
- Dose rate[uSv/h] and Dose[uSv] display
- uSv/h value is 60 seconds moving average.
- [cps] and [cpm] display
- cpm value is 60 seconds moving average.
- Gamma energy[KeV] display
- Setting Beep ON/OFF
- Setting LED ON/OFF
- Setting ALARM ON/OFF
- Setting alarm level
- Setting uSv/h calibration
- Battery voltage
- Reset dose [uSv]
- 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.
Requirement for photodiode
- Shading window with aluminum foil
- PIN structure for low dark current
- Wide active area for high sensitibity,10x10=100[mm2]
PIN photodiode candidates
Silicon Sensor has changed the company name as First Sensor.(2011-07-15)
model number active area[mm2] manufacturer note PS100-7-CER-PIN 100 First Sensor clear glass window PS100-6-THD 100 First Sensor epoxy potting PS100-5-THD 100 First Sensor silicone potting PS100-2-THD 100 First Sensor quartz glass window S3590-08 100 Hamamatsu Photonics low available, high cost S3590-18 100 Hamamatsu Photonics low available, high cost S6775 26.4 Hamamatsu Photonics available, low cost AXUV100 100 IRD not available AXUV100GX 100 IRD not available SMP2000G-MV 100 Semelab dia. window
- Counting the pulse
- The circuit is subject to modification.
- Charge Amplifier changes a small charge to voltage.
- C1 is arrangeable between 1pF to 5pF.
- Smaller C1 comes to a high pulse.
- Bigger C1 reduces noise.
- Differentiator Amplifier changes voltage to a pulse.
Value Quantity Parts Note 2p 1 C1 Ceramic conductor 1000p 1 C2 Ceramic conductor 10u 2 C3,C4 Chemical conductor 10M 1 R2 Registor 1/4W 1M 1 R4 Registor 1/4W 75K 1 R5 Registor 1/4W 47K 1 R6 Registor 1/4W 10K 2 R1,R3 Registor 1/4W LMC662 1 U1 CMOS OpeAmp PD 1 PD PIN photodiode to detect radiation
Here is the PS100-7-CER.
- I got a PIN photodiode sample.
- The shield box is required. There is noisy and too sensitive.
- Gamma ray seem to be detected as a pulse. Similar to a pulse detected by GM counter.
- The pulse has 200-500[mV] and 50[us].
And this is a prototype(30 x 40mm, 1mA at Vdd=5V).
Noise and the pulse.
The pulse voltage range are 200-500[mV] and length are 50[us].
Enhanced shield to be stable.
This is a Gamma Ray Counter. Counting with PIC.
Silicon Gamma Radiation Detector v.s. Geiger Counter
The gamma sensitibity is around 332cpm/(uSv/h).
LND712 PS100-7-CER S6775 detected radiation alpha, beta, gamma gamma gamma background 18[cpm]=0.150[uSv/h] 6.5[cpm] 0[cpm] uranium glass 70[cpm]=0.583[uSv/h] 178[cpm] 12[cpm]
Small current and voltage
Cosmic gamma ray
- For example, Cs-137(662KeV) produces 662KeV/3.65eV=181K electrons in ideal case not real case.
- 1 electron has 1.6E-19 coulombs
- Total charge is 181Kx1.6E-19=28.96E-15 coulombs.
- Charge amplifier formula V=Q/C, V=28.96E-15/2E-12=14.48mV where C=2pF
- Cosmic gamma ray has strong energy.
- And you will see big detected pulse, sometimes.
- This is not a noise.
Power supply separation
- Guard ring is required in amplifier input for leark current.
- PCB laminate with glass epoxy FR-4 is required.
- Between analog circuit and digital circuit to avoid internal noise.
LMC662 NJU7032 LMC6482 OPA2353 AD8616 AD8656 AD822 Gain bandwidth 1.4MHz 1.5MHz 1.5MHz 44MHz 24MHz 28MHz 1.8MHz Slew rate 1.1V/us 3.5V/us 1.5V/us 22V/us 12V/us 8.5V/us 3V/us Input voltage noise 22nV/ăHz - 37nV/ăHz 22nV/ăHz 8nV/ăHz 2.7nV/ăHz 25nV/ăHz Power supply 5-15V 3-16V 3-15V 2.7-5.5V 2.7-5.5V 2.7-5.5V 3-36V Input offset voltage }1mV(type) }10mV(max) }0.11mV(type) }3mV(type) }23uV(type) }44uV(type) }0.5mV(type) Input offset voltage drift }1.3uV/C - }1uV/C }5uV/C }1.5uV/C }0.4uV/C }2uV/C Input bias current }0.002pA(type) }1pA(type) }0.02pA(type) }0.5pA(type) }0.2pA(type) }1pA(type) }2pA(type) Input offset current }0.001pA(type) }1pA(type) }0.01pA(type) }0.5pA(type) }0.1pA(type) }10pA(max) }2pA(type)
Requirement for amplifier
- Wide gain bandwidth
- High slew rate
- Low input bias current
- Analyzing pulse hight statistics, we can indentify the kind of radiation source.