Here are half a dozen assessment questionnaires for PTSD and intrusive memories.  The Impact of Event Scale (IES) is a classic which has been used for many years.  Unfortunately it only measures Intrusions and Avoidance, but not Hyperarousal.  The revised IES (the IES-R) puts this omission right and is the recommended PTSD scale for the NHS Increasing Access to Psychological Therapies (IAPT) initiative.  There's a lack of data providing typical scores on the IES-R in both normal and clinical populations.  The Institute of Psychiatry booklet provides some orientation here.  The PTSD with Pain screen is a quickly administrable questionnaires of use for people suffering from chronic pain disorders.  The Intrusive Memories Assessment is a four item questionnaire that's helpful more broadly than just for PTSD sufferers.  The Posttraumatic Growth and Trauma Belief Inventories can help direct the focus of therapy and monitor progress.

IES and scoring details - this is the classic 1979 Horowitz Impact of Event Scale that has been widely used in subsequent research.  A major problem with the scale is that it assesses only Intrusions and Avoidance and does not consider Hyperarousal symptoms.