Im applying for jobs in the NHS i wondered how long does it take for your criminal record to be clear ? Is thi?

Is this CRB the same as a police check ? As i work in a juniors school at the moment which i have done for 6 years and was checked ? If you have bee arrested,cautioned or had to go to court but was thrown out as there wasent enough evidence will this still be on my file for any employer to check ?