Pmt Calculator

by

Photomultiplier Tube (PMT) Gain & Sensitivity Calculator

Total count of multiplication steps.
Average electrons emitted per impact.
In μA/lm (Microamperes per lumen).
Coefficient for voltage/gain slope.

Calculated Performance Metrics

Current Gain (μ):

Anode Luminous Sensitivity (Sa): A/lm

Multiplication Factor: (log10)

function calculatePMTPhysics() { var n = parseFloat(document.getElementById('dynodeStages').value); var delta = parseFloat(document.getElementById('emissionRatio').value); var sk = parseFloat(document.getElementById('cathodeSensitivity').value); var alpha = parseFloat(document.getElementById('supplyVoltage').value); if (isNaN(n) || isNaN(delta) || isNaN(sk)) { alert("Please fill in all primary fields with valid numbers."); return; } // Formula for Gain: G = delta^n var gain = Math.pow(delta, n); // Formula for Anode Sensitivity: Sa = Gain * Cathode Sensitivity // sk is in uA/lm, so result will be converted to A/lm var sa = (gain * sk) / 1000000; var logGain = Math.log10(gain); document.getElementById('resGain').innerText = gain.toLocaleString(undefined, {maximumFractionDigits: 0}); document.getElementById('resSensitivity').innerText = sa.toLocaleString(undefined, {maximumFractionDigits: 2}); document.getElementById('resFactor').innerText = logGain.toFixed(2); document.getElementById('pmt-results').style.display = 'block'; }

Understanding Photomultiplier Tube (PMT) Logic

In the field of photonics and high-energy physics, a PMT (Photomultiplier Tube) is a vacuum tube that converts light into an electrical signal. Unlike a standard photodiode, the PMT features an internal multiplication mechanism that can amplify a single photon into a detectable pulse of millions of electrons.

The Physics of Gain Calculation

The core logic of a PMT relies on the Secondary Emission Ratio (δ). When a primary electron hits a dynode, it releases multiple secondary electrons. The total gain (μ) is determined by the number of stages (n) using the power law formula:

Gain (μ) = δn

Sensitivity Metrics

While the gain tells us how much the signal is amplified, Cathode Sensitivity (Sk) tells us how efficiently the initial light is converted into the first batch of electrons. This is usually measured in microamperes per lumen (μA/lm) or milliamperes per watt (mA/W). The resulting Anode Luminous Sensitivity (Sa) is the final output strength of the device.

Example Calculation

If you have a PMT with the following specifications:

  • Number of Stages (n): 10
  • Secondary Emission Ratio (δ): 4.0
  • Cathode Sensitivity (Sk): 60 μA/lm

The gain would be 410, which equals 1,048,576. The final Anode Sensitivity would be 1,048,576 × 60 μA/lm = 62.91 A/lm. This massive amplification allows PMTs to be used in medical imaging (PET scans), nuclear research, and astronomy.

Key Factors Affecting PMT Performance

  • Voltage Distribution: The emission ratio (δ) is highly dependent on the voltage between dynodes. Even small fluctuations in high-voltage supply can lead to significant changes in total gain.
  • Quantum Efficiency: This represents the probability that an incident photon will actually release a photoelectron from the cathode.
  • Dark Current: This is the background noise or "leakage" current that flows even when no light is entering the PMT.

Leave a Comment