You will be presented with the full text of a science research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
fragmentation reactions induced by protons and light nuclei of energies around 1 gev / nucleon and below on light target nuclei are involved in different applications , like cosmic - ray - induced single event upsets ( seu s ) , radiation protection , and cancer therapy with proton and ion beams , among others .
it is impossible to measure all nuclear data needed for such applications ; therefore , monte carlo transport codes are usually used to simulate impacts associated with fragmentation reactions .
it is important that available transport codes simulate such reactions as well as possible .
the los alamos monte carlo transport code mcnp6 @xcite uses by default the latest version of the cascade - exciton model ( cem ) as incorporated in its event generator cem03.03 to simulate fragmentation of light nuclei at intermediate energies for reactions induced by nucleons , pions , and photons , and the los alamos version of the quark - gluon string model ( laqgsm ) as implemented in the code laqgsm03.03 ( see @xcite and references therein ) to simulate fragmentation reactions induced by nuclei and by particles at energies above @xmath1 gev , up to about 1 tev / nucleon .
generally , both cem and laqgsm assume that nuclear reactions occur in three stages .
the first stage is the intranuclear cascade ( inc ) , completely different in cem and laqgsm , in which primary particles can be re - scattered and produce secondary particles several times prior to absorption by , or escape from the nucleus .
when the cascade stage of a reaction is complete , cem and laqgsm use the coalescence model to  create " high - energy d , t , @xmath2he , and @xmath0he via final - state interactions among emitted cascade nucleons , already outside of the target .
the subsequent relaxation of the nuclear excitation is treated in terms of an improved version of the modified exciton model of preequilibrium decay followed by the equilibrium evaporation / fission stage of the reaction .
but if the residual nuclei after the inc have atomic numbers with @xmath3 , cem and laqgsm use the fermi breakup model to calculate their further disintegration instead of using the preequilibrium and evaporation / fission models . thus , for targets with @xmath3 , reactions are assumed to occur only in two stages .
the `` standard '' version of cem and laqgsm account for possible multiple emission of only n , p , d , t , @xmath2he , and @xmath0he during the preequilibrium stage of reactions ( see ref .
their latest , `` f '' , version ( see refs .
@xcite ) considers a possibility of preequilibrium emission of light fragments ( lf ) heavier than @xmath0he , up to @xmath4 mg .
it also simulates coalescence of lf heavier than @xmath0he , up to @xmath5 , in cem03.03f ( see @xcite ) , and up to @xmath6 , in laqgsm03.03f ( see @xcite ) .    in recent years , mcnp6 , with its cem and laqgsm event generators , has been extensively validated and verified ( v&v ) against a large variety of nuclear reactions on both thin and thick targets ( see , e.g. refs .
@xcite - @xcite and references therein ) . in ref .
@xcite , it was tested specifically on fragmentation of light nuclei at intermediate energies . here
, we present a few results from our recent work @xcite and investigate further the performance of mcnp6 , cem , and laqgsm in simulating fragmentation reactions at intermediate energies and discuss possible ways of further improving these codes .
figs . 1 , 2 , 3 , and 5 show examples of fragmentation reactions on light nuclei simulated by our codes . figs .
6 and 4 shows examples for medium targets , @xmath7ca and @xmath8ag .
many more similar results , their discussion , and useful details can be found in refs .
@xcite - @xcite and references therein .
to 50 mm c from p + @xmath9o calculated with cem03.03 using the `` standard '' version of the fermi breakup model ( @xmath10 ) and with cut - off values for @xmath11 of 16 and 14 , as well as with mcnp6 using cem03.03 ( @xmath10 ) compared with experimental data , as indicated .
experimental data are from the t16 lib compilation @xcite ( see details in @xcite ) . ,
title="fig:",width=226 ]      to 50 mm li spectra at 20 , 45 , 60 , 90 , and 110 degrees by machner et al .
@xcite ( symbols ) with calculations by the unmodified cem03.03 ( dashed histograms ) and results by cem03.03.f ( solid histograms ) , as indicated ( see more details in @xcite ) .
, title="fig:",width=226 ]          however , mcnp6 is not yet ready to predict well heavy fragments from reactions with heavier nuclei , with mass numbers @xmath12 .
such nuclear targets are considered too light to fission in conventional codes .
similarly , the fragments are too light to be produced as spallation residues and too heavy to be produced via standard evaporation and/or preequilibrium models , or via coalescence .    to 50 mm
ne + @xmath13ne with calculations by laqgs03.03 using its `` standard '' version of the coalescence model ( @xmath14 gev / c for t and @xmath2he ; dotted lines ) and with modified values of @xmath15 labeled in legend as `` coal1 '' ( dashed lines ) and `` coal2 '' ( solid lines ) , as indicated in legend and discussed in detail in ref .
, title="fig:",width=226 ]      to 50 mm li at an angle of 60@xmath16 from the reaction 480 mev p + @xmath8ag , with results by standard cem03.03 ( dot - dashed line ) from cem03.03f without coalescence expansion ( solid line ) and cem03.03f with coalescence expansion ( dashed line ) ( see details in @xcite ) . ,
title="fig:",width=245 ]        in our case , this means separately merging cem and laqgsm with gemini .
actually , we already have done so more than a decade ago , producing the `` g '' versions of cem and laqgsm we had at that time ( see , _ e.g. _ , ref . @xcite and references therein ) .    another way to address
this problem is to implement in cem and laqgsm the statistical multifragmentation model ( smm ) by botvina _
thus , we would consider multifragmentation as a mode competitive to evaporation of particles and light fragments , when the excitation energy @xmath17 of a compound nucleus produced after the preequilibrium stage of a reaction is above a certain value , @xmath18 , e.g. , @xmath19 mev , as we did in the  s " versions of cem03.01 and laqgsm03.01 ( see , e.g. , ref . @xcite and references therein ) .
as of today , neither the `` s '' nor the `` g '' versions of cem and laqgsm have been implemented in mcnp6 .
we plan to incorporate them in our event generators used by mcnp6 after we tune several parameters in smm    to 55 mm he spectra ( at 35@xmath16 ) from 1.2/1.9/2.5 gev p + @xmath20c measured by m. fidelus of the pisa collaboration @xcite ( symbols ) with calculations by mcnp6 using cem03.03 ( see details in @xcite ) .
, title="fig:",width=226 ]          this study was carried out under the auspices of the national nuclear security administration of the u.s .
department of energy at los alamos national laboratory under contract no .
de - ac52 - 06na25396 .
this work is supported in part ( for l.m.k ) by the m. hildred                      s. g. mashnik , _ validation and verification of mcnp6 against high - energy experimental data and calculations by other codes .
primers i to iv _ , lanl reports la - ur-11 - 05129 , la - ur-11 - 05627 , la - ur-13 - 26944 , la - ur-14 - 27018
los alamos ( 2011 , 2013 , and 2014 ) ; https://mcnp.lanl.gov/.      s. g. mashnik _
_ in _ proc .
sare-4 , knoxville , tn , september 13 - 16 , 1998 _
( ornl , 1999 , pp .
151 - 162 ) ; arxiv : nucl - th/9812071 ; our t-16 library `` t-16 lib '' is updated permanently when new experimental data became available to us .
j. p. bondorf , a. s. botvina _
et al . _ ,
phys . rep .
* 257 * ( 1995 ) 133 .
s. g. mashnik _
cem03.s1 , cem03.g1 , laqgsm03.s1 , and laqgsm03.g1 versions of cem03.01 and laqgsm03.01 event - generators _ , lanl report la - ur-06 - 1944 , los alamos ( 2006 ) ; + e - print : nucl / th-0603046 .
fragmentation reactions induced on light and medium nuclei by protons and light nuclei of energies around 1 gev / nucleon and below are studied with the los alamos transport code mcnp6 and with its cem03.03 and laqgsm03.03 event generators . 
 cem and laqgsm assume that intermediate - energy fragmentation reactions on light nuclei occur generally in two stages . 
 the first stage is the intranuclear cascade ( inc ) , followed by the second , fermi breakup disintegration of light excited residual nuclei produced after the inc . 
 cem and laqgsm account also for coalescence of light fragments ( complex particles ) up to @xmath0he from energetic nucleons emitted during inc . 
 we investigate the validity and performance of mcnp6 , cem , and laqgsm in simulating fragmentation reactions at intermediate energies and discuss possible ways of further improving these codes .