cate experiments and several forms of dose-response curves were postulated to
fit the data.
KBE values around 10 were found, with a range of estimates be-
tween 8.6 and 15.0, according to the assumptions made.
The data were thought
to be inadequate to establish whether or not the RBE depended on the level of
daily exposure.
197.
The RBE of thermal column radiation, composed of thermal neutrons and
hard gamma rays, was tested against 250 kVp x rays in experiments by Storer and
Sanders
[S17] performed on Swiss white mice.
Since the neutron and the x ray
data could be fitted by a common linear non-threshold regression of per cent
life-shortening versus dose, the RBE had a value of unity.
Storer et al.
{S18]
exposed CF1
In another series,
female mice to neutrons or to mixtures of neu-
trons and gamma rays from an atomic weapon.
neutrons was calculated to be 2.6 + 0.9.
The relative effectiveness of the
In both series the RBE values for
life-shortening were in close agreement with those obtained for the production
of acute effects.
198,
In experiments by Vogel, Frigerio and Jordan [V1] CF1 female mice were
exposed to daily doses of fission neutrons or gamma-rays at dose-rates of about
4.4 and 13 rad/min, respectively.
Groups of animals were given 13 brief ex-
posures, each corresponding to 2.2 - 70 rad/day of neutrons and 6.5 - 208 rad/
day of gamma rays.
The neutron RBE was not increased over the figure of 2.8
previously obtained for acute single doses.
Other experiments performed with
13 brief exposures of the two radiations given at 1 rad/min indicated an RBE
for median survival time of 2-3, in fairly good analogy with the figure of
2.8 for the DS 9/30 after single exposures.
199.
Curtis, Tilley and Crowley [C19] reviewed the literature data on life-
shortening by acute or chronic irradiation of mice with x rays or neutrons.
They concluded that acute gamma doses could be up to 4 times as effective as
chronic doses, while for neutrons equal efficiencies by acute and chronic exposures were the most common finding.
Accordingly, the neutron RBE of about 2
for life-shortening by acute doses might increase to about 8 for chronic treatments.
Chromosome damage in the liver of animals was shown to behave similarly
and these data were thought to provide some cellular basis for the differential
action of low- and high-LET radiations.
The data on chromosomes were also in-
terpreted to support indirectly the hypothesis that mutations in somatic cells
might be at the origin of natural and radiation-induced aging.