If I understand the question correctly, then they are much the same. The only difference I can think of is possibly the methodology with which you assess the risk. Task analysis, or 'Job Hazard Analysis' as you refer to it, looks at a specific task and the hazards associated with that task,which could be equipment, tools and environment. Alternatively you can isolate a specific hazard ie working with electricity, and conduct a risk assessment based purely on that hazard. This method is more inclined towards generic RAs as opposed to task based RAs. Task based RAs tend to be more thorough and economical as they look at the whole task and all the hazards inherent in the task. Not all hazards are necessarily recorded, only the significant ones. It is possible to do a cross reference matrix so that reoccurring hazards are not duplicated in other tasks or for a different set of workers. Whatever the outcome, a risk assessment will always be just that. How you achieve it or indeed regardless of what you name it - it is still a risk assessment. I dare say others will put their views on the question and a massive debate will erupt about the semantics of risk - LOL.