Alternatives to Geiger Mueller tubes?
There are a number of solid state/semiconductor approaches for ionizing radiation and they fall roughly into the following categories.

detectors with a conversion layer:
- XRay detectors: Image sensors with Gadox, NaI scinillators

Direct detectors:
- using Selenium, Germanium and Silicon

Indirect detectors:
- Using bolometric techniques, i.e. measuring heat increase in a material that causes a parametric shift like resistance.  VOx on bolometers, Thermopiles.  Can have issues with thermal (non-ionizing) radiation giving conflicting information.

In general though, because the work functions are higher lower energy ionizing radiation or that which has low penetration (beta) is harder to detect using these techniques.