The Radiation Assessment Detector (RAD)

Scot C. R. Rafkin, RAD Project Scientist
Southwest Research Institute, Boulder, Colorado

rafkin@boulder.swri.edu (720)240-0116

image of Mars and lander

Slide 2
Presentation Outline

• RAD Team and Organization
• RAD Instrument Overview
– Design Drivers
– Principle of Operation
– Predicted Performance
– RAD Build and Delivery Schedule
• RAD on Mars Science Laboratory
– Science Requirements Flowdown Summary 
– Investigation Background
– Science Objectives
– Measurement Requirements
• Summary

Slide 3
RAD Organization

RAD Team is in place for completing Design and Development at both SwRI and CAU/Kiel

RAD Core Team interfaces to MSL Project via the RAD Instrument Engineer (A. Sirota) and RAD Investigation Scientist (D. Brinza)

Flow chart with labels: Education and Public Outreach/D. Boice (SwRI); MSL Payload Manager (JPL); Principal Investigator/D. Hassler (SwRI); MSL/RAD Science Team/US Scienc Leads: Scot Rafkin (SwRI),
Mark Bullock (SwRI), Frank Cucinotta (JSC), European Leads: Rober Wimmer- Schewingruber (Kiel), Guenther Reitz (DLR/Cologne); Project support/SwRI Business Office D. Vera, Import/Export/ITAR D. Shaffer, 
Purchasing B. Stone, Parts Engineering J. Stack, Scheduling/Cost Control T. Case, SwRI QA B. Gupta; Project Manager/ J. Andrews (SwRI); Instrument Scientist/A. Posner (SwRI); System Engineer/M. Epperly (SwRI);
Elect. Systems/ Y. Tyler, K. Neal, R. Bokman (SwRI); Mech. System/Structure/K. Smith (SwRI); Flight Software/J. Hanley, E. Weigle (SwRI); I&T, Cal/A. Posner (SwRI), G. Reitz (DLR); MO & DA/J. Peterson (SwRI);
Sensor Head/ Rober Wimmer-Schweingruber (Kiel)

Slide 4
RAD Teaming Arrangements & Responsibilities

SwRI
PI Institution, RAD electronics, Project Management, System Engineering, Instrument I&T, Data Analysis
Large Non-Profit Research Organization (>3000 employees, >$400M 2005 revenues). 30+ years experience w/ space research and instrumentation w/ >50 space borne scientific 
instruments developed and operated. Well equipped facilities for systems I&T. 

CAU – Kiel, Germany 
Co-I Institution, RAD Sensor Head, Data Analysis
Large research university in Germany. Very experienced team of radiation/plasma detection instrumentalists w/ recent experience on STEREO, SOHO, ISS, Ulysses. Well 
equipped facilities for developing space flight instrumentation.

DLR – Cologne, Germany
RAD Instr. Calibration Lead, Data Analysis
Branch of German Aerospace Agency in 
Cologne. Experienced w/ dosimetry, Astronaut Safety, and calibration of radiation detection instrumentation.

NASA/JSC
Astronaut Safety, Data Analysis
NASA field center with oversight of manned spaceflight, oversees and implements NASA's Astronaut Safety program. Experienced w/ dosimetry and radiation data analysis.

Slide 5
Design Challenges

• Low mass, power (energy) and telemetry requirements driven by unique aspects of MSL mission
• Extreme thermal environment and rarified CO2 atomosphere unique to Mars Surface Operations
• Extremely wide energy dynamic range required to observe both electrons, protons and iron with same instrument
• Extremely wide variation in fluence of relevant species must be observed to characterize both GCR and SPE with same instrument

Slide 6
RAD Instrument Overview

diagram of RAD with labels: RAD-PMP interface cylinder, SSD A, RSH SSD telescope, SSd B & C, Csl, Netron Channel, Anti-Coincidence, RAE, RDE, RSE

• Solid state detector telescope and CsI calorimeter with active coincidence logic to identify charged particles. Separate scintillators with 
anti-coincidence logic to detect neutrons and gamma-ray.
• Zenith pointed with 65 deg. FOV, 100 mm2*sr geometric factor
• Large internal storage 16 Mbyte
• CBE Mass = 1.52 kg
• Power (obs) = 4.1 W
• Telemetry = 1 Mbit/sol

Slide 7
RAD Functional Diagram (Principle of Operation)

drawing of RAD with labels: gamma-ray (accepted), Netron (accepted) Ion (rejected), Ion (accepted), Ion (rejected) (dosimetry only), A, B, C, D, E, F

Legend
A Solid State Detector (SSD) A
B SSD B
C SSD C
D Cesium Iodide (CsI)
E Neutron Channel (Bicron 430M scintillating plastic)
F Anti-coincidence Shield

Slide 8
RAD Functional Block Diagram

Main labels: RAD Senor Head; RAD Analog Electronics; RAD Digital Electronics; RAD Sleep Electronics. 
Slide 9
RAD Energy Coverage

table of Energy Coverage with rows for p,He; ions (Li-O); ions (mg-Fe); netrons; gamma-rays; electrons; positrons with corresponding energy (MeV) indicated 

Slide 10
RAD Species Identification 
uses dE/dx vs E Method

graph of Stopping Charged Particle dE/Dx (SSD-A) and geomery factor versus total energy deposit. labels: E(AC) < 1.5 MeV, E(SSD-S) > 30 keV, E(SSD-B) > 30kdV, 
E(SSD-B) > 0.05*E(SSD-A), Cut = 0.1*[E(SSD-A)+E(SSD-B)], E(SSD-A) > CUT, if E(SSD-C > CUT Then E(SSD-B) > CUT, if E(Csl) > 0.5 MeV then E(SSD-C > CUT, E(SSD-AC) < CUT

slide 11
Data Matrix Bins

"Bohm Plot" with lable E(SSD-A)*E(total[MeV^2], E(total)/E(SSD-A), Fe, Ca, Si Be, Li He, e

Slide 12
Predicted Performance (Signal-to-Noise)

		GCR S/N 	GCR S/N		GCR S/N 	SPE S/N 	SPE S/N 	SPE S/N 
		(required)	(current best	Margin 		(required)	(current best 	Margin
				estimate)					estimate)

neutrons	10		>10^2		10		10		>10^3		100

protons		20		1.3x10^3	65		20		1.1x10^3	55

He (Z = 2)	10		2.0x102		20		10		56		5.6

3 <= Z <= 11	10		56		5.6

Z >= 12		10		20		2

Assume: GCR integration tome = 6months (25% duty cycle) (requirement)

SPE integration time - 1 hour (25% duty cycle) (requirement)

Slide 13
NASA Space Radiation Laboratory (NSRL) at Brookhaven

image of assembly line
image of assembly line


Representative beams available at NSRL, along with energy ranges and maximum intensities.

A RAD Technology Demonstration (TDM) has already been tested at the Brookhaven National Laboratory (BNL) Heavy Ion Accelerator Facility.

Results of characterization indicate that MSL/RAD will function as designed/modeled


Slide 14
Photo-Diode Tests 

Pulse Height Histogram over Nuclear Charge Number
Gaussian Fits for Element Peaks

graph of 1 GeV.n Fe spallatioon products with labels: Counts, Nucl. Charge Number, F, Ne, Na, Mg, Al, Si, P, S, Cl, Ar, K, Ca, Sc, Ti, V, Cr, Mn, Fe

Slide 15
Photo-Diode Elemental Resolution

RAD Photo-Diode Elemental Resolution is Sufficient for Element Separation up to Fe

graph for Elemental Resolution for Spallation Peak Mg (Z=12): Z/delta Z=14 with labels: Fe elemental resolution, counts, Nucl. Charge Number, Mg (Z=12), Z/delta Z = 14.0

Elemental Resolution for Primary Beam Fe (Z=26): Z/deltaZ=41.9 with labels: Fe elemental resolution, counts, Nucl. Charge Number, Fe (Z=26), Z/delta Z = 41.9

Slide 16
RAD Hardware Development Plan

Flow diagram labels: SwRI|CAU/DLR|JPL; EM RAD to JPL for Flight Ops Bench ;Oval: EM3 REB Refurbished
Oval: EM3 REB, Integrate w/ Appropriate RSH Simulator; Verify I/F & Functionality; Deliver to JPL;
Oval: EM2 REB; Integrate w/ EM RSH and use to Support EM RSH Tests; EM RSH -Functional/Performance Tests@ CAU and DLR;
Oval: EM1 REB; Integrate w/ Appropriate RSH Simulator; Early I/F Tests @ JPL; Stays at SwRI to Support System Development & FSW
Oval: FM1 REB; FM1 RSH; Integrate & Test RSH/REB to create FM RAD; Cal FM RAD; Deliver to JPL
Oval: EM2 REB; FMS RSH; Integrate EM2-RSH & Conduct Perf/Func. Tests; Extended FMS Cal

Slide 17
RAD Summary Schedule
(From P3e to MS Project)

ID	WBS	Task Name				% Complete	Duration
1	1.0	Management and Science			22%		729 days
2		Milestones				0%		586 days
3		IPDR					100%		0 days
4		ICDR					0%		0 days
5		IPER					0%		0 days
6		EM Funded Schedule Reserve		0%		33 days
7		FM Funded Schedule Reserve		0%		41 days
8		Key Deliverables			0%		252 days
9		EM RAD to JPL				0%		0 days
10		FM RAD to JPL				0%		0 days
11	2.0	Systems Engineering			22%		729 days
12	3.0	RAD Instrument Development		29%		587 days
13		EM RAD Analog Electronics (RAE)		55%		260 days
14		FM RAD Analog Electronics (RAE)		0%		95 days
15		EM RAD Digital Electronics (RDE)	62%		257 days
16		FM RAD Digital Electronics (RDE)	0%		93 days
17		RAD Mechanical Package (RMP)		35%		462 days
18		EM RAD Sleep Electronics (RSE)		53%		279 days
19		FM RAD Sleep Electronics (RSE)		0%		98 days	
20		RAD Flight Software (FSW)		30%		531 days
21		GSE & Test Software			8%		285 days
22		RAD Sensor Head (RSH)			27%		587 days
23		RAD Rover Window (RRW) Assembly		9%		412 days
24	3.2	RAD I&T					0%		397 days
25		EM#1 I&T				0%		77 days
26		EM#2 I&T				0%		46 days
27		EM#3 I&T				0%		157 days
28		Early I/F Test at JPL			0%		5 days
29		FM REB I&T				0%		70 days
30		FM I&T					0%		87 days
31	4.0	Post-Delivery Support			0%		591 days
32		EM Post Delivery Support		0%		406 days
33		FM Post Delivery Support		0%		330 days
34	5.0	Education / Public Outreach (E / PO)	0%		0 days
35	6.0	Mission Operations & Data Analysis 	15%		1088 days
36		Phase B/C/D Operations 			15%		1088 days
37	7.0	Science Data Processing 		0%		0 days

Slide 18
RAD on MSL

Slide 19
Characterizing the Radiation Environment on the Surface of Mars

MSL AO Science Investigation D (Sect. 2.0):

“Characterize the broad-spectrum of the surface radiation environment, including galactic cosmic radiation, solar proton events, and secondary neutrons”. 

image of mars surface with labels: Solar Energetic Particles, Galactic Cosmic Ray (Protons and HZE), Atmospheric Absorption & Molecular Dissociation, 
Secondary Particle Production (atomosphere), Secondary Particle Production (regolith), DNA Damage & Mutagenesis, C14 Production & Other Nuclear Reactions

Slide 20
MSL RAD Accommodation / Field of View
design of RAD 
desing of rover

FOV ~ 65 deg. (full angle)
Geometric factor ~ 100 mm^2 * sr

Slide 21
RAD Science Requirements Flowdown Summary

• RAD Level 1 Science Requirements determine RAD Level 2 Measurement Requirements
• RAD Level 2 Measurement Requirements determin RAD Performance Requirements
• Simulations are used to 
– Translate measurement requirements to instrument requirements
– Track/verify instrument performance

Slide 22
RAD Level 1 Science Objectives

• 1) Characterize the energetic particle spectrum incident at the surface of Mars, including direct and indirect radiation created in the atmosphere and regolith.
• 2) Determine the radiation dose rate and equivalent dose for humans on the Martian surface.
• 3) Determine the radiation hazard and mutagenic influences to life, past and present, at and beneath the Martian surface.
• 4) Determine the chemical and isotopic effects of energetic particle radiation on the Martian ssurface and atmosphere.

Slide 23
RAD Level 1 Science Objective

Objective 1: Characterize the energetic particle spectrum incident at the surface of Mars, including direct and indirect radiation created in the atmosphere and regolith.

2 Components of Primary Radiation:

• Galactic Cosmic Rays (GCR) 
• Solar Energetic Particles (SEP)

Slide 24
Galactic Cosmic Rays

• GCR flux varies with solar cycle and is more enriched in heavy nuclei at solar maximum than predicted by models. 
• Physics-based models agree better than semi-empirical models but both can be improved (Mewaldt, 2004).

graph image described: Figure F01-1. Ground-based neutron monitor observations (black) provide a proxy for GCR flux. (Sunspot number is in red). GCRs are modulated by solar 
activity with 15-30% reduction at solar maximum. Labels: Kile NM countrate, Year, Ave. sun spot number

graph of GCR Intensity Ratio (Solar-Max/Solar-Min) with labels: Ratio at 200 MeV/nucleon, Nuclear Charge (Z), ACE/CRIS (H&He from IMP-8), JPL/Caltech Model (Davis et al. 2001), CREME

Slide 25
Composition Changes in Solar Energetic Particle Events

Solar Energetic Particle Event (SPE) from Oct/Nov 2003. Shown are GOES proton fluxes and ACE/SWEPAM solar wind data superposed on SOHO/EIT images.

• Energetic particle spectra SOHO/COSTEP of 3 particle species (electrons, protons, helium) show changes over several days (Posner et al., 2004).
• Quality factors (Q) for each type of radiation are shown on left.

Slide 26
RAD Time Resolution Required is Derived from Need to Characterize/Resolve the Onset of a Solar Particle Event (SPE)

graph of Cycle 22 SPEs

Slide 27
RAD Energy Range Required is Derived from Modeled SEP and GCR Energy Spectra at Mars

graphs for Input (Space Spectra for SEP and GCR
graphs for Output Surface Fluxes for SEP and GCR

*From David Brain et al., VSE Workshop, Wintergreen, VA, 2005 (using SIREST model)

Slide 28
Science Objective 1 Measurement Requirements

			GCR				SEP

Particle Species	0 <= Z <= 26			0 <= Z <= 2		
			Electrons			Electrons

Energy Range		
a)(0 <= Z <= 1)		a) 10 – 100 MeV/n		a) 10 – 100 MeV/n
b)(2 <= Z <= 11)	b) 20 – 100 MeV/n		b) 20 – 100 MeV/n	
c)(12 <= Z <= 26)	c) 30 – 200 MeV/n
d) electrons		d) 2 – 20 MeV			d) 2 – 20 MeV

Energy Resolution	< 30%				< 30%

Time Resolution /	6 months (sufficient to		1 hr (sufficient to
Sample Interval		resolve seasonal changes	resolve onset of SPE and 
			in Mars atmosphere)		changes in time profile)

Slide 29
RAD Level 1 Science Objective

Objective 2: Determine the radiation dose rate and equivalent dose for humans on the Martian surface.

Slide 30
Determining the Radiation Dose Rate for Humans on Mars

GCRs produce near-constant background flux of radiation, modulated by the solar cycle. 

Composed mostly of H+ and He2+, but heavy ions contribute disproportionately to the Dose Equivalent due their high quality factor, Q. (Wilson et al. 1997)

pie charts of GCR Abundance (200 MeV/n) with labels: He Z >2, and H (TA004354) and Relative Contribution to Dose Equivalent with labels: Fe-Fragments, Fe, Others, H, He CNO, Ne-S

Slide 31
Astronaut Safety Requires Monitoring Certain Particle Species

Table A1-2: Requirements for Complete Characterization of Radiation Environment. Full characterization requires measuring ALL of these relevant species.

Particle	Quality  	Relevance
Species		Factor (Q)	(Biological Importance and Need for Measurement)

Protons		1-7		Largest flux, large contributor to total dose (>90% of GCR, > 98% of SEP)
He (alphas)	2-30		Large flux, high Q at low energies thus large contributor to equivalent dose
C, N, O		5-30		High Q with large probability of reaction in body tissue, significant contributor to equivalent dose, relevance to carbon provenance, carbon cycle from 14C/12C ratio
Fe		6-30		High Q factor with largest probability of reaction in bocy tissue, large contributor to equivalent and effective dose, primary astronaut safety concern
Neutrons	3-10		High Q factor, relevant near regolith and within tenuous atmospheres, high probability of reaction in tissue at 10-100 MeV, highly penetratin, high astronaut safety concern
gamma-rays	1		Solar flar indicator, relevant to Mars geology: saline gamma-line (40K) detection
Electrons	1		SEP precursor, highly penetrating, large fluence during SEP events (even with Q=1, large fluence contributes to large equivalent dose)
Positrons	1		GCR cascade by-product, required for radiation transport model validation

Slide 32
Dosimetry

graph T. Doke et al. | Radiation Measurements 33 (2001) 373-387 with lables Diff. Flux [/cm^2 sr sec keV/΅ m\, LET [keV/΅ m-water], STS-84 RRDM-III GCR, STS-84 DOSTEL GCR

LET distribution for GCR particles observed on board STS-84. 

RAD required LET measurement range is derived from need to measure relevant range of GCR particles contribute to total Dose and Equivalent Dose.

Slide 33
RAD Level 1 Science Objective

Objective 3: Determine the radiation hazard and mutagenic influences to life, past and present, at and beneath the Martian surface.

Slide 34
Radiation and Mutagenic Hazards to Life

• By determining the flux and measuring the variations (diurnal, seasonal, solar cycle), RAD will allow calculations of the depth in rock or soil for 
which there is a lethal dose of radiation for biological organisms. 

• It would then be possible to learn how deep life would have to be to provide sufficient natural shielding. 

• These depths can be compared to calculations of diffusion depths of strong oxidizers which destroy organisms near the surface…and then judge whether 
radiation or oxidizing chemistry will determine the minimum depth to drill to look for extant life on Mars. 

• Following validation and improvement of current transport codes, these calculations can be made for past higher pressure or warmer climate scenarios.

Slide 35
Science Objective 2 & 3 Measurement Requirements
	
			GCR				SEP

Particle Species	0 <= Z <= 26			0 <= Z <= 2

Energy Range		LET: 0.3 – 1000 keV/΅m		LET: 0.3 – 1000 keV/΅m

Energy Resolution	< 30%				< 30%

Time Resolution /	6 months (sufficient to		1 day (sufficient to 
Sample Interval		resolve seasonal changes	resolve SPE)
			in Mars atmosphere)

Slide 36
RAD Level 1 Science Objective

Objective 4: Determine the chemical and isotopic effects of energetic particle radiation on the Martian surface and atmosphere.

---Not discussed here…but happy to discuss off-line!

Slide 37
RAD Level 2 Measurement Requirements

RAD shall measure:
• Req. 1: neutral particles (neutrons and gamma-rays) with energies up to 100 MeV.
• Req. 2: dose and LET spectra in the range of 1 to 1000 KeV/΅m.
• Req. 3: energetic particles with an energy resolution sufficient to distinguish between major particle species (i.e. electrons, ions), low Z 
ions (i.e. p, He, Li), medium Z ions (i.e. C, N, O ions), and high Z ions (i.e. heavier nuclei up to Fe).
• Req. 4: energetic particles with (one hour) observing cadence sufficient identify the onset of solar particle events (SPEs), and resolve the time profiles associated with such events
• Req. 5: energetic ions with energies in the range of 10 to 100 MeV/n for p, He; 20 to 100 MeV/n for Li-Na (Z = 3-11); and 30 to 200 MeV/n for Mg-Fe (Z = 12-26).

Slide 38
RAD Science Data:
Classification

Count Rates (L0):

Combinations of trigger signals in detectors determine the pre-defined nominal science channels. For each channel, the count rates per accumulation interval are recorded and transmitted 
to the ground.

Pulse-Height Analyzed (PHA) Data (L0):

For each nominal channel, pulse height workds (i.e. energy losses) are recorded. The number of pulse heights per event depends on coincidence depth (1-5). Due to limited telemetry, 
not all PHA data can be transmitted to the ground. PHA therefore requires a prioritization scheme.

Histograms (L0/2):

Histograms are a compressed form of science data that require on-board processing. One of the benefits is spectra for particle species with good 
statistics.

Slide 39
Summary

• RAD will characterize the radiation environment on the surface of Mars for both GCR and large SPEs, measuring all relevant energetic particle species, including secondary neutrons 
created both in the atmosphere and the regolith. 
• RAD is an important element of the Mars Science Laboratory investigation to explore and quantitatively assess a potential habitat for life and the processes that influence habitability. 
• RAD meets or exceeds all Science Requirements with substantial margin.
• RAD provides monitoring of:
– Charge particle fluence Z=1 to 26
– Absorbed dose
– Dose Equivalent (time-resolved LET)
– Neutron fluence 1-100 MeV(10-100 MeV with RTG)
• RAD is undergoing build
– Engineering model in beam by winter of 2007
– Flight build in 2008
– Flight in 2009
• RAD is suitable for LEO, Lunar, and interplanetary measurements as is or with little modification, and with advantageous non-recurring cost base.