The Number and Reaction Multiplicities of GCR Nuclei and Delta-rays

Passing through a Cell Nucleus on a Mars Mission

 Xiaodong Hu1, Premkumar Saganti2, Francis A. Cucinotta3,

1U.S.R.A., Houston TX, 2Lockheed Martin, Houston TX and 3NASA Lyndon

Johnson Space Center Houston TX, 77058.

Fig. 1. Results of calculations of the integral number of particle tracks per cell per Year from GCR exposures in free space at solar minimum as a function of ion chargeBehind 5 g/cm2 Aluminum using cell areas of 100 um2 , the upper curve is with Delta-rays and lower curve is without Delta-rays.

Charge, Z

0 5 10 15 20 25 30

Pa

rtic

le T

rack

s p

er

Cel

l pe

r ye

ar

10-5

10-4

10-3

10-2

10-1

100

101

102

103

Multiplicities of GCR Reaction Events

• Nuclear reactions produced by GCR as they traverse tissue are quite frequent.

• Reaction lead to high-multiplicity events with a large number of ions produced in a small volume (<1 cm)

• The reaction products are distributed between– Target like (highly ionizing from tissue constituents)– Projectile like including projectile fragment and like particles – Intermediate rapidity fragments

• For Biological damage, the highly ionizing target fragments are most important and can lead to a high doses in small volumes (>1 Gy)

• The Quantum multiple scattering model of nuclear fragmentation (QMSFRG) is used to model multiplicities and combined with the HZETRN code to project the number and types of high-multiplicity events in tissue from GCR.

La + La Collision showing high multiplicity event

Energy, MeV/u

10 100 1000 10000

Pro

babi

lity

of R

eact

ion

/ cm

of t

issu

e

0.01

0.1

1

Proton

NeutronHelium

OxygenSilicon

Iron

Fig. 2a. The probability of a nuclear reaction per cm of tissue traversed versus energy

for several ions prominent in the GCR.

Charge, Z

0 8 16 24GC

R F

Lu

x o

r N

o. I

nte

ract

ion

s cm

-1 ye

ar-1

102

103

104

105

106

107

108

Fluence

Reactions

Fig. 2b. Comparisons of the elemental fluence of GCR ions near solar minimum to the number of nuclear interactions that occur per cm of tissue traversed by each charge GCR group. Calculations are made behind 5 cm of tissue.

Oxygen Target Fragmentation

nprotons

0 2 4 6 8 10

Fra

ctio

n of

Eve

nts

0.1

0.2

0.3

0.4

0.5

Proton ProjectilesCarbon ProjectilesIron Projectiles