The Cosmic R A y Telescope for the Effects of Radiation
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Transcript of The Cosmic R A y Telescope for the Effects of Radiation
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The Cosmic RAy Telescope for theEffects of Radiation
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Presentation Goals
• Sources and Effects of Radiation in Space• Designing and Testing a of a
Space Craft Instrument• Initial Results and Expected Goals of this Work
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Energetic Particles in Space
SEP’s
GCR’s
•Energetic particles can be, electrons, protons and heavier ions such as oxygen, carbon, and iron.
•The particles are charged and have enough energy to break chemical bonds such as those that hold together DNA.
•Damage to DNA is a major source of medical problems due to radiation exposure.
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Solar Energetic ParticlesSEP’s
• SEP’s are mainly protons.• Some SEP’s are accelerated
during a solar flare.• Others are created as a result
interactions in the solar wind.• SEP’s come in short bursts.• Particle energies can vary
from KeV to MeV(eV stands for electron volt)
Solar Flare that accelerates charged particles to near light speeds
Flare Movie: http://sohowww.nascom.nasa.gov/gallery/Movies/flares.html
Webcam Movie: http://www.youtube.com/watch?v=vCFQZqSxWns
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Galactic Cosmic Rays (GCR’s)• Sources outside of the solar system
•Supernovas can accelerate heavy ions particles to very high energies.•GCR’s are a mix of electrons and protons along with heavier elements. •GCR’s come from many different sources and so are constantly raining in from outside the solar system.
Particle energies can vary from 10’s of MeV to GeV’s and higher
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SEP’s and GCR’s are tied to the solar cycle
• SEP events happen more frequently during solar maximum
• But…..• GCR’s are deflected more by
the Suns magnetic field during solar maximum
SEP’s
GCR’sYearly Average Sunspot Number
0
20
40
60
80
100
120
140
160
180
1970 1975 1980 1985 1990 1995
Year
Averag
e S
un
sp
ot
Nu
mb
rer
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Protection on Earth
Quebec, CanadaAug. 19, 2009
http://www.spaceweather.com/
Atmosphere Absorbs High Energy Particles
Earth’s Magnetic Field Traps Charged Particles
http://radbelts.gsfc.nasa.gov/outreach/outreach.html
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Effects of Ionizing Radiation
• Ionizing radiation can cause cell damage • The damage is particularly harmful if DNA is
broken apart• Top:
• Images of cellular nuclei that have been bombarded by ionizing radiation
• Green spots are places where DNA was split• Bottom:
• Visualization of DNA strand breaks from an x-ray and a cosmic ray
Image Credits: A. Cucinotta / NASA,JSC,SRAG
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Measuring Cosmic Rays• This ionization effect is used by
instruments to measure the particles
• Radiation ionizes atoms in our detector
• Electric field accelerates electrons into our electronics
• We measure the amount of energy deposited by each particle (LET)
Step 1: Electrons freed from atoms by incident radiation
Step 2: Electrons collected and measured. More electrons = more energy deposited
Electric Field Electric Field
CRaTER Electronics
Incident C
osmic
Ray
How much energy is deposited?•Not all the particles energy is deposited
•Low energy particles leave more energy then high energy particles
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Measuring Cosmic Rays with CRaTERDetectors
1 & 2Detector
3 & 4Detectors
5 & 6
Particles from Deep Space
TEP TEP
Particles from the Moon
Warning: The animator’s creative license has LRO pointing the wrong way. Don’t worry though…the spacecraft operators know which way to point it!
Spacecraft Animation
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PrototypeSame electronics as we would use in flight, but easy to
use (they plug into the wall!)
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Protype TestingNeed a source similar to the one we will measure, e.g. Brookhaven National Lab, where they can accelerate ions to very high energies
Image taken with Iron nuclei at Brookhaven National Lab
Shadow of CRaTER
prototype detector
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Power:Payload: 98 Watts CRaTER:
6 Watts
The Rest of LRO: 690 Watts
The Rest of LRO: 2092 lbs
Fuel: 1774 lbs
Payload: 190 lbs
CRaTER: 13 lbs
Entire Satellite: 100 Mbps :about the same as a wireless router…not bad!CRaTER: ~90 kbps (~0.1% of LRO rate!):better than dial-up connection, but not much!
But what’s the real limitation?$ Mass = Launch Costs: $
Data Rate:
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Engineering Model TestingNeed sources similar to the one we will measure in space
Radioactive SourcesCobalt-60
Source (gamma
rays)
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Engineering Model TestingParticle accelerators, e.g. Brookhaven National Lab
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Flight Model
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Flight Model Calibration
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Flight Model Environmental Testing
Make sure that instrument can survive in space environment
Thermal – Large temperature gradients in space
Vibration – Huge vibrations during launch
Acoustic – Launch causes large sound waves
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Integration with LRO
Who are those masked men??
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Testing of Entire Satellite
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Launch!
http://www.nasa.gov/mission_pages/LRO/launch/index.html
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• Originally driven by exploration goals (measure energy deposited at different depths in the human body)
• Exploration Enables Science!• High-data-rate and uniquely capable galactic
cosmic ray (GCR) and solar energetic proton (SEP) science instrument
CRaTER Science Goals
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CRaTER Sees the Moon!When spacecraft is closer to the Moon, the moon shields more cosmic rays coming from deep space
Altitude above the Moon
CRaTER Count Rates
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Periodic Table as Seen by CRaTER
•Iron Ion Beam at Brookhaven National Labs•Iron factures in material placed in front of the detectorcreating smaller ions
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Flight Data
Why we do the experiment: Because this is what is really out there!
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Two Detector Histograms
Detectors 1 & 2
Detector 3 & 4
Detectors 5 & 6
Particles from Deep Space
TEP TEP
Comparing Energy transfer to different detectors
•Particles deposit energy as they travel through material•Lower energy particles leave more energy
•Each ion species leaves its owncharacteristic plot.
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Keeping Track of CRaTERhttp://crater.bu.edu/monitor/
Time of Upload
Instrument Power Usage
Counts for Each Detector
Instrument Temperature
Dosimeter Reading
Total Counts
- no data is available when the spacecraft is out of communication
- CRaTER runs on the same power as 6 mini-Christmas lights
- 3 pairs of detectors separated by Tissue Equivalent Plastic (TEP)
- some detector counts are deemed noise by the instrument electronics.
- instrument is warmed by the Sun but cools off in the Moon’s shadow; using electric current warms circuitry
- reading of medical dosimeter on board the instrument