High-energy radiation damages plastics in a certain way. POM and some fluoroplastics such as PTFE are particularly sensitive.

Gamma ray bursts release extremely large amount of energy - approximately 10^52 ergs (or 10^45 joules), with the most extreme bursts releasing up to 10^54 ergs. This is the equivalent of turning a star like the Sun into pure energy (using Einstein's famous equation E=mc^2).

No. The average amount of radiation a patient is exposed to during an X-ray is extremely low and well within the acceptable recommended amount.

The naming system for gamma ray bursts is very simple: "GRB yymmdd". For exmaple, a gamma ray burst which occured on July 4, 1999 is called GRB 990704. If there is more than one gamma ray burst on the same day, the letter a, b, c, etc. are added to the name (for example, the second gamma ray burst on July 4, 1999 is called GRB 990704b).

Up until the 1990s and the launch of the Compton Gamma Ray Observatory (CGRO; see next question) there was a heated debate in the astronomical community about the source of, and distance to gamma ray bursts. One group claimed that gamma ray bursts occur in our own galaxy (the Milky Way), while others claimed that they occur in very distant galaxies.

Based on almost 30 years of observing gamma ray bursts, we now think that on average there is one gamma ray burst per day somewhere in the Universe. However, recent developments in the study of gamma ray bursts indicates that the true number of these events may be 500 times larger. This means that we only see one out of every 500 gamma ray bursts.

Gamma ray bursts are detected by satellites orbiting the Earth and travelling through the Solar system. They can only be detected from space because the Earth's atmosphere absorbs gamma rays and therefore we cannot observe them from the ground. The first gamma ray bursts were detected by the Vela satellites, which were launched in the 1960s to ensure compliance with the Nuclear Test Ban Treaty.

The study of several thousand bursts has shown that there are two main classes of gamma ray bursts: those shorter than 2 seconds, and those longer than 2 seconds. In addition, it was found that the short bursts release more of their energy in very energetic gamma rays relative to the longer bursts. Therefore the terminology that is used to describe the two classes is "short and hard" and "long and soft". All of all bursts that have been studied in detail so far are "long and soft".

In principal every gamma ray burst is followed by an afterglow. However, we do not always see these afterglows for several reasons. First, prior to 1997 and the launch of the BeppoSAX satellite (see question 15) it was impossible to find the position of gamma ray burst accurately enough to detect the afterglow. Second, even after 1997 the afterglows from some gamma ray bursts are too faint to detect from Earth.

There are many popular level and scientific articles about gamma ray bursts. For popular level discussion of gamma ray bursts try looking for articles in Scientific American. Scientific articles can be found on the astro-ph preprint server and ADS.

Gamma ray bursts (GRBs for short) are intense and short (approximately 0.1-100 seconds long) bursts of gamma-ray radiation that occur all over the sky approximately once per day at very large distances from Earth. Gamma rays are very energetic photons (E>10^5 eV), which represent the most extreme portion of the electromagnetic spectrum (ranging from radio waves at the lowest energies through visible optical light at higher energies, to gamma rays at the highest energies).

The average amount of exposure to an X-ray is very low and is well within the acceptable amount recommended.

It is now thought that the "long and soft" gamma ray burts come from the collapse of massive stars, while the "short and hard" bursts come from the merger of binary systems. This result comes from computer simulations which show that the merger of neutron star or black hole binaries occurs much faster than the collapse of the iron core of a massive star.

NIOSH arranges for experts to review your chest X-ray, and stores the film for future comparisons. If you need a copy or want more information about your chest X-ray, contact NIOSH (see enclosed resource list).

The distribution of several thousand bursts which were detected primarily by the Burst And Transient Source Experiment (BATSE) on CGRO is uniform across the sky. This means that there is no prefered direction from which we detect more gamma ray bursts. This distribution was the first indication that gamma ray bursts occur in bery distant galaxies and not in our own galaxy.

In the first years of gamma ray burst research there were more proposed sources (or progenitors) for gamma ray bursts than the actual number of gamma ray bursts detected! However, ever since it was determined that gamma ray bursts occur at very large distances (and therefore release huge amounts of energy) the list of proposed progenitors shrunk into two main classes: very massive stars, and binary (2 star) systems composed of neutron stars or black holes.

The first step in the detection of afterglows is always the detection of a new gamma ray burst by a satellite such as the IPN, BeppoSAX, and HETE-II (see qeustion 4). The information from the satellite is quickly sent down to Earth and is distributed to gamma ray burst astronomers by email, pagers, and cellular phones. When astronomers get the information, they observe the part of the sky where the gamma ray burst occured, and look for an object which fades quickly.

The twinkling of radio waves from afterglows (see question 23) has shown that afterglows start very small (about the size of the Earth's orbit around the Sun), and then expand and become larger than the Solar system.

Licensed medical professionals trained to actually administer the radiation treatments prescribed by the doctor. Therapists are responsible for accurately positioning the patient daily and operating the treatment machines. The training programs are very different. Radiation therapists complete a 4 year program of classroom study and clinical training. Subjects include physics, anatomy, radiation biology, and oncology.

The HEASARC's XANADU package supports spectral, temporal and spatial analysis of high-energy data and has been developed to be quite portable. You can use this immediately on the high-level products in the HEASARC archive. The FTOOLS provide more discrete analysis tools including mission-specific analysis pipelines. These two packages were recently merged into the HEAsoft package.

While the adult thyroid gland is much less sensitive to radiation, it too may be affected, especially during radiation therapy for head and neck cancers. Hypothyroidism, thyroid nodules and thyroid cancer all can occur after radiation exposure in adults.

AMI and x-ray are complementary techniques that are both frequently found in the same laboratories. They have important differences with regards to what they reveal in a sample. X-rays can be used to see inside a sample based upon material density differences. Dense materials are more opaque to x-radiation and penetration is more limited through metals compared with ceramics or polymers.

In addition to providing an indication of whether or not you have pneumoconiosis, the X-ray examination may also reveal evidence of other medical disorders. Heart problems and certain other diseases such as tuberculosis and lung cancer may be detected through a chest X-ray. The law requires that NIOSH report the results of your examination to the U.S. Department of Labor, Mine Safety and Health Administration (MSHA).

The maximum x-ray energy you need is determined by your sample. Thinner, low-density materials (e.g. plastics) require less x-ray energy than, for example, metals or very thick parts. You also want to make sure that your source has sufficient power to provide enough x-ray flux to give you a useful image signal-to-noise ratio. a rule of thumb, materials such as plastic or circuit boards are typically imaged at 50-70 kVp (kVp = peak x-ray energy; i.e. your source voltage setting).

If TB disease is present, it is probably in the lungs. If your skin test is positive, you will be asked to get a chest x-ray on the day of your skin test reading. A chest x-ray takes a picture of the lungs and shows the doctor if there are any signs there of TB. View an abnormal X-ray the State TB Program, your waiting time for the x-ray will depend on the number of people ahead of you.

X-ray imaging itself is painless. If you are having a non-invasive procedure, the only discomfort should be lying flat on a hard table or a cold feeling if your skin comes in contact with some of the equipment. Some movements may be uncomfortable to you if you have a fracture or other problems like arthritis that limit your ability to move. Please tell the technologist and he or she will help make you as comfortable as possible.

The physician who schedules your test should give you instructions to follow prior to your x-ray if any are needed. A brief overview of the examination and preparation needed may be seen by clicking on the exams listed on the diagnostic home page.

Astronomers now think that the iron cores of some very massive stars (at least 30 times more massive than the Sun) can collapse into black holes several million years after they form. The energy released in the formation of the black hole emerges out of the collapsed star in the form of a gamma ray burst. Gamma ray burst astronomers call this the "collapsar" model. Other names are "hypernova" or "failed supernova" models.

It is known that most stars in the Universe reside in multiple systems of 2 (binary), 3 and even 4 stars. Some of the binary systems have two stars more massive than about ten times the mass of the Sun, and eventually after these stars die they leave behind neutron stars or black holes. Over time the two objects in the system spiral in toward each other and eventually they merge into a single black hole.

Traditional X-ray radiation affects everything in its path, so doctors often limit the radiation dose to minimize damage to critical organs. X-rays also continue to pass through the body after reaching the tumor, affecting the healthy cells beyond it. Proton radiation therapy achieves greater precision while providing a lower dose of radiation to healthy tissues. This advantage allows higher doses to be delivered to the tumor with a lower risk of hurting healthy cells.