Druck-Materie 20b.qxd - JUWEL - Forschungszentrum Jülich

of radicals, that is, before a burp. Otherwise, saturated concentration of radicals would sharply
depend on irradiation temperature as Tact>>Teff,act , which was not actually observed.
For analyzing experimental data, we applied Eq. #1 without the second order term. Assuming
primarily that radical production rate is time independent, we have for an amount of stored
energy (SE) in the course of irradiation:
Qse(t) = 1/ K1(T) ⋅(1- exp (-t/τ)) = Q∞ ⋅ (1- exp (-t/τ)) (2),
where τ =(RK1) -1 is a “saturation time”.
Table 3. Estimated values of an energy released in a burp, solid methane samples
N 0 of ex- 2.14 2 3b 5 7 11 13 14 17
periment
Q, J/g 80 ∼50 ∼50 ∼45 for 25.5K
**)
120-180 45-50 for 26 K
**)
38 ∼60 ∼50
N 0 of ex- 18 19 21 22 23 23 47 48
periment
Q, J/g 72-100 95-100 46-56 33-37 ∼65 *) (25.5K) ∼100 *) (18K) ∼100 ∼70
Notes: *)- For segments of big sizes the Q-value is space-dependent
Basing on a host of experimental data on Qse (t), see in Table 3 and Fig. 4, and on Eq. 2,
Q∞ , R (we assume that R now represents «energy storing rate», J/g/h, which proportional to
radical production rate), and τ-value were deduced. Saturated stored energy, Q∞, can be estimated
with an appropriate precision only for temperature range 21-26K. Its temperature dependence
can be described with a linear equation with an error about ± 10%:
Then we have received
Q∞, J/g ≈ 13⋅(30 - Tirr) (2a).
R ≈ (13 ± 1) J/g/hour,
which is equivalent to a maximal rate of energy accumulation in solid methane (1.6 ± 0.2) %
of an absorbed dose. The τ-value can be described, naturally, also with a linear function is
within 20% accuracy:
τ, hours ≈ 1.0 (30 - Tirr) (2b).
Approximation of Q∞ and τ-values in the Arrhenius form is worse than in linear one; in this
case, Teff, act varies with temperature from 100 K at 26 K down to 70 K at T