Could you tell me if gallium scans detect chronic infections?

Yes: Gallium scans can detect both acute and chronic infections.

Yes: Gallium scans are very good for detecting chronic infections or any chronic inflammatory process, often better than acute infections. Some infections they can be used to identify are pcp pneumonia or osteomyelitis of the spine. They are not very good for intra-abdominal infections or inflammation since the normal clearance of gallium through the gut may cause false positive result.