153AVP — Eleven-Stage Photomultiplier Tube
An 11-stage photomultiplier tube featuring a flat, semi-transparent caesium-antimony photocathode, designed for head-on incident radiation and optimized for applications such as gamma-ray spectrometry.
Overview
The 153AVP is an 11-stage photomultiplier tube designed for detection and measurement of low-level light signals, particularly in scintillation counting and gamma-ray spectrometry. It features a flat, semi-transparent caesium-antimony (SbCs) photocathode with a minimum useful diameter of 44 mm. The multiplier system consists of 11 dynode stages utilizing silver-magnesium-oxygen-caesium (AgMgOCs) secondary-emitting material. The tube is housed in a glass envelope with a 14-pin diheptal base.
Construction and Physical Dimensions
The 153AVP is constructed with a head-on, flat-surface photocathode. The internal multiplier structure contains 11 dynode stages.
Dimensions and Mounting
- Maximum Diameter: 57 mm
- Seated Length: 129 ± 5 mm
- Overall Length: 148 ± 5 mm
- Base Type: 14-pin diheptal (compatible with socket type No. B8 700 40)
Magnetic Shielding
Due to the sensitivity of the electron trajectories within the multiplier system to external magnetic fields, magnetic shielding is highly recommended. A mu-metal screening cylinder (type No. 56128) can be utilized with the following dimensions:
- Length: 90 ± 1 mm
- Diameter: 57 +1/-0 mm
Photocathode and Multiplier Characteristics
The tube's photocathode and multiplier system are characterized by specific spectral, luminous, and capacitive properties.
Photocathode Properties
- Cathode Material: Caesium-antimony (SbCs)
- Minimum Useful Diameter: 44 mm
- Wavelength of Maximum Response: 4200 ± 300 Å (primarily in the visible spectrum)
- Luminous Sensitivity: Average of 70 µA/lm, with a minimum limit of 50 µA/lm (measured using a tungsten ribbon lamp at a color temperature of 2850 °K)
- Radiant Sensitivity: Average of 55 mA/W at the peak wavelength of 4200 Å
- Dark Current: 10^-15 A/cm² at room temperature
Multiplier System Capacitances
- Anode to Final Dynode (S11): 3 pF
- Anode to All Other Electrodes: 5 pF
- Dynode Material: Silver-magnesium-oxygen-caesium (AgMgOCs)
Typical and Operating Characteristics
Under typical operating conditions with a total supply voltage of 1800 V, the 153AVP exhibits high gain and low noise:
- Anode Sensitivity: Average of 4500 A/lm, with a minimum of 100 A/lm
- Anode Dark Current: Maximum of 0.05 µA when operated at an anode sensitivity of 60 A/lm
- Linearity: The relationship between the anode-pulse amplitude and the input-light flux is linear up to 30 mA.
- Energy Resolution: The tube is tested with a 1.5" x 1" NaI (sodium iodide) crystal to guarantee an energy resolution of less than 9% (with a typical average of 8.5%) for the 0.661-MeV caesium-137 line.
Voltage Divider and Decoupling
The operating voltage is distributed across the electrodes using a resistive voltage divider. The recommended distribution relies on a stage voltage unit (Vs):
- Cathode to Accelerating Electrode: 2 to 4 Vs
- Accelerating Electrode to First Dynode (S1): 1 Vs
- Between Consecutive Dynodes (Sn to Sn+1): 1 Vs
- Final Dynode (S11) to Anode: 1 Vs
To maintain voltage stability during high-amplitude pulses, decoupling capacitors are connected across the final stages:
- C1 (S9 to S10): 220 pF
- C2 (S10 to S11): 470 pF
- C3 (S11 to Anode): 1000 pF
The total supply voltage (Vb) is typically 13 to 15 times Vs.
Limiting Values
The following absolute maximum and minimum ratings must be maintained to prevent damage and ensure stable operation:
Note: When calculating the actual anode voltage, the voltage drop across the load resistance (RL) must be subtracted from the supply voltage.
Operational Considerations
Stability and Divider Current
To achieve an operating stability of approximately 1%, the current flowing through the voltage-divider bridge must be approximately 100 times greater than the current through the heaviest loaded stage of the tube. For moderate radiation intensities, a practical bridge current value is approximately 0.5 mA.
Spectrometry Optimization
For optimal performance in gamma-ray spectrometry, the voltage between the cathode and the first dynode should be set to 4 times the stage voltage (Vs), provided that the maximum limit of 500 V is not exceeded. The tube operates most favorably at a high tension of 1200 V.
Exposure to Light
If the photomultiplier is exposed to full daylight prior to installation, it will temporarily exhibit an increased dark current. The dark current will return to its normal specified value after several hours of operation in darkness under voltage.
Technical Summary
The 153AVP is an 11-stage, head-on photomultiplier tube featuring a 44 mm flat caesium-antimony photocathode and silver-magnesium-oxygen-caesium dynodes. It is optimized for high-resolution applications such as gamma-ray spectrometry, offering a guaranteed energy resolution of under 9% for the 0.661-MeV caesium line. Operating with a maximum supply voltage of 1800 V, it provides an average anode sensitivity of 4500 A/lm and maintains pulse linearity up to 30 mA. Proper implementation requires magnetic shielding with a mu-metal cylinder and careful design of the voltage divider network to ensure stability and protect the tube from exceeding its maximum ratings.
