Rigaku AFX-90L-Rh | Sealed X-Ray Tube with Rh Anode

Description

Key Technical Specifications

• Anode Material: Rhodium (Rh)
• Maximum Power: 900 W
• Maximum Voltage: 60 kV
• Maximum Current: 15 mA
• Focal Spot Size: Typically 0.05 mm x 10 mm (Line focus)
• Insulation: Ceramic / Oil (Side window configuration)
• Cooling Method: Water Cooled (Requires external chiller)
• Filament: Tungsten
• Window Material: Beryllium (Be)
• Application: Wavelength Dispersive XRF (WDXRF)

Product Introduction

Replacing an X-ray tube is the most nerve-wracking part of maintaining a spectrometer. The Rigaku AFX-90L-Rh is a workhorse sealed tube commonly found in Rigaku’s wavelength-dispersive XRF systems. Unlike generic tubes, this specific model utilizes a Rhodium (Rh) anode. Rh is the “Swiss Army knife” of anode materials because its characteristic K-lines are high enough to excite heavy elements efficiently, while its Bremsstrahlung (continuum) background is strong enough to excite lighter elements.From a field perspective, the 900W power rating is the sweet spot for high-throughput labs. It provides enough photon flux to get good counting statistics in short measurement times without requiring a massive, industrial-sized chiller. I’ve pulled these out of ZSX Primus units that ran for 40,000+ hours. As long as the water quality was maintained and the warm-up cycles were respected, the vacuum integrity usually holds up remarkably well.

Quality SOP & Tech Pitfalls (The Reality Check)

The Lab Report (SOP):
Before this tube leaves the bench, we run a strict protocol. We start with a Visual Inspection of the Beryllium window (looking for oxidation or physical dents) and the ceramic insulators. We then perform a Cold Resistance Check on the filament using a Fluke 87V to ensure it hasn’t burned out during transit. Finally, we verify the vacuum integrity indicator (if equipped) and seal it in a double-layer anti-static, shock-absorbing crate.The Engineer’s Warning (Pitfalls):
Here is the brutal truth: Water quality kills these tubes faster than age. I have seen the AFX-90L series fail in under six months because the lab used tap water instead of deionized water. The copper anode leaches into the water, creating a conductive path that arcs right through the ceramic insulator. Also, never touch the Beryllium window with bare fingers. The oils from your skin can carbonize under heat, creating a permanent shadow on your spectrum that no amount of calibration can fix.

Installation & Configuration Guide

Swapping an X-ray tube isn’t like changing a lightbulb; treat it like bomb disposal.

1. Pre-Installation & Safety:
   • ⚠️ LOTO (Lockout/Tagout): Cut main power to the XRF. Wait at least 15 minutes for the high-voltage capacitors to discharge. Verify with a multimeter.
   • Coolant Drain: Disconnect cooling lines and catch the water. If the old water is green or cloudy, your heat exchanger is compromised.
2. Removal:
   • Unscrew the high-voltage (HV) cable. Note the orientation.
   • Unbolt the tube from the goniometer or housing. Support the weight of the tube with your hand while removing the last bolt so it doesn’t drop.
3. Installation:
   • Clean the Interface: Wipe the mating surface with isopropyl alcohol. Any dust here ruins the vacuum seal.
   • Seat the Tube: Gently slide the AFX-90L-Rh into place. Do not force it. Torque the bolts to the OEM spec (usually finger-tight plus a quarter turn, but check the manual).
   • Reconnect HV & Water: Ensure the HV cable clicks into place. Reconnect water lines (Inlet/Outlet).
4. Power-On & Aging:
   • Turn on the water chiller first. Verify flow.
   • Aging Protocol: Do not crank it to 60kV immediately. Start at 20kV / 5mA for 30 minutes. Slowly ramp up voltage and current over 2-3 hours. This outgasses the tube and prevents thermal shock to the anode.

Compatible Replacement Models

• ✅ Drop-in Replacement: Rigaku AFX-90L-Rh (Current Revision)
  • This is the direct OEM part. It fits the existing housing, HV cable, and cooling block without modification.
• ⚠️ Hardware Mod Required: Rigaku AFX-100L-Rh
  • While electrically similar, the 100L series often has a different physical footprint and cooling block interface. Using this would require machining adapters or replacing the entire X-ray generator housing. Not recommended for a quick swap.
• ❌ Incompatible: Rigaku AFX-90L-Cr (Chromium Anode)
  • Physically identical, but the anode material is different. You cannot use a Cr tube for general-purpose analysis intended for a Rh tube; your calibration curves will be useless.

Frequently Asked Questions (FAQ)

• Can I run this tube at full power (900W) right away?
  Absolutely not. If you skip the aging process, you risk cracking the anode due to thermal stress. You need to “train” the tube by slowly ramping up the voltage over a few hours.
• My old tube is arcing. Is it definitely the tube?
  90% of the time, yes. But check your high-voltage cable and the oil in the housing first. If the oil is dark or the cable insulation is cracked, you’ll just blow the new tube immediately.
• How do I know if the Beryllium window is broken?
  If the window is breached, you will likely hear a “pop” or hiss, and the vacuum interlock will trip immediately. Sometimes, you might see a milky white oxidation spot on the window surface.
• Does this come with the oil?
  Usually, the tube is shipped dry. You need to fill the housing with the specific X-ray transparent oil specified in your Rigaku maintenance manual.
• What is the shelf life of a new tube?
  If kept in a dry environment, it can sit for years. However, if it’s been sitting in a humid warehouse for 5+ years, the filament might be degraded. It’s always best to put a “fresh” tube into service rather than one that has been boxed for a decade.