Half-life effective

For any nucHde that decays only by this electron capture process, if one were to produce an atom in which all of the electrons were removed, the effective X would become infinite. An interesting example of this involves the decay of Mn in interstellar space. For its normal electron cloud, Mn decays with a half-life of 312 d and this decay is by electron capture over 99.99% of the time. The remaining decays are less than 0.0000006% by j3 -decay and a possible branch of less than 0.0003% by /5 -decay. In interstellar space some Mn atoms have all of their electrons stripped off so they can only decay by these particle emissions, and therefore their effective half-life is greater than 3 x 10 yr. 

Calculations for determining system makeup rates and chemical treating effective half life are presented in the section on Cooling Tower design. 

Effective half-life Average neutron energy Neutron emission rate Decay heat... 

The biological half-life of a radioisotope is the time required for the body to excrete half of the radioisotope. The effective half-life is the time required for the amount of a radioisotope in the body to be reduced to half its original amount, as a result of both the decay of the radioisotope and its excretion. Sulfur-35 (tu2 = 87.4 d) is used in cancer research. The biological half-life of sulfur-35 in the human body is 90. d. What is the effective half-life of sulfur-35 ... 

Barium-140 (tl/2 = 12.8 d) released in the fire at the Chernobyl nuclear plant has been found in some agricultural products in the region. The biological half-life of barium-140 in the human body is 65 d. What is the effective half-life (see Exercise 17.55) of barium-140 ... 

Caribou in northern Quebec contained up to 1129 Bq 137Cs/kg muscle FW in 1986/87, but only 10 to 15% of this amount originated from Chernobyl the remainder is attributed to fallout from earlier atmospheric nuclear tests (Crete et al. 1990). The maximum concentration of 137Cs in meat of caribou (Rangifer tarandus granti) from the Alaskan Porcupine herd after the Chernobyl accident did not exceed 232 Bq/kg FW, and this is substantially below the recommended level of 2260 Bq 137Cs/kg FW (Allaye-Chan et al. 1990). Radiocesium transfer in an Alaskan lichen-reindeer-wolf (Canis lupus) food chain has been estimated. If reindeer forage contained 100 Bq/kg DW in lichens and 5 Bq/kg DW in vascular plants, the maximum winter concentrations — at an effective half-life of 8.2 years in lichens and 2.0 years in vascular plants — were estimated at 20 Bq/kg FW in reindeer-caribou skeletal muscle and 24 Bq/kg FW in wolf muscle (Holleman et al. 1990). 

Under such conditions the time required for a radioactive element to be halved as a result of the combined action of radioactive decay and biological elimination is the effective half-life T eff = (T biol X... 

VII.a.2.2. Treatment. Treatment of established vitamin D deficiency requires much larger doses of vitamin D, such as calciferol tablets of 1 mg (40,000 units) daily. Newer but more expensive preparations such as alfa-calcidol and calcitriol are very effective, and are particularly valuable in patients with renal failure who are unable to hydroxylate calciferol. Patients treated with pharmacological doses of vitamin D preparations must be monitored by checking serum calcium at regular intervals because of the risk of inducing hypercalcaemia. This should always be suspected if patients develop thirst, nausea or vomiting. The newer hydroxylated preparations have a shorter effective half-life, and therefore problems of overdosage are quicker to resolve once identified. 

Local anesthetics are frequently coadministered with vasoconstrictor molecules such as epinephrine. Normally, they are applied or injected locally and then taken up by local blood vessels into the systemic circulation, ultimately leading to their metabolic breakdown. The co-administration of a vasoconstrictor decreases the systemic absorption of the local anesthetic, thereby increasing its effective half-life in the area of administration and decreasing the probability of systemic toxicity (i.e., cardiac toxicity) secondary to systemic distribution. 

Pharmacokinetics In patients receiving the Zevalin therapeutic regimen, the mean effective half-life of Y-90 activity in blood was 30 hours. 

At long times, the ratio of daughter to parent activity becomes constant, and both species disappear with the effective half-life of the parent. The classic examples of this decay equilibrium are the decay of 140Ba (ti/2 = 12.8 d) to 140La (ti/2 = 40 h) or the equilibrium between 222Rn Of/2 = 3.8 d) and its short-lived decay products. 

Schlenker RA. 1986. Comparison of intake and committed dose equivalent permitted by radiation protection systems based on annual dose equivalent and committed dose equivalent for a nuclide of intermediate effective half-life. Health Phys 51 207-213. 

Iodine is lost from herbage by the same processes which cause field loss of Sr, 137Cs and other nuclides (Section 2.13). There is also the possibility of revolatilisation of iodine. If XG is the rate constant of field loss (fraction of iodine per unit area of ground lost from vegetation per second) and X1 the rate constant of radioactive decay, the combined apparent or effective loss rate is XE = XG + Xt. The effective half-life is Te = 0.693/A . The use of the term half-life implies that field loss is exponential and TE invariant with time, which is not always true. 

From day 6 onwards, the slope of the curve corresponds to the effective half-life of 131I on herbage, namely 5 d. Assuming that this continues indefinitely, the area under curve A in Fig. 3.6 is 1.4 m2 d l-1. This is equivalent to the transfer factor km, defined by equation (2.12). Values of Fm for 131I and 137Cs are about the same, but the radioactive decay of 131I reduces km compared with that for137Cs (Table 2.19). Also shown in Fig. 3.6 are values of C/ as deduced from measurements near... 

The sulfone and its conjugates are the major products excreted in urine, and account for 27.6 + 2.8% of the administered dose. Sulindac and its glucuronide accounted for 20.2 + 0o2% of the dose excreted in the urine. Mean renal clearance of sulindac and its sulfone metabolite was 45.1 + 16.2 and 33.2 + 12.2 ml/min respectively(16). The effective half-life for accumulation is about 7 hours for sulindac(17). The long half-life is due to extensive enterohepatic recirculation(18). 

Pharmacokinetic data were available for 97 patients. The tasidotin plasma concentrations declined rapidly, and were less than 1% of maximal concentrations within about 8 h after dosing (Fig. 13.2). With such a short effective half-life, accumulation with daily tasidotin administration was not likely - once-daily multiple doses resemble a series of single doses. Concentrations appeared to decline in a biphasic manner (Fig. 13.2). The presence of a third, gamma phase was observed in some patients, but was not consistently detected, and for this reason the effective half-life was calculated instead of the terminal elimination phase half-life. 

In a clinical setting, the effective half-life of a radionuclide depends on two processes. First is the physical half-life. But we can naturally excrete foreign substances, so there is also a biological half-life. For example, the physical half life of "Tcm is about 6.0 hr, and the biological half life is 24 hr. So, how long does it... 

Again, we have a common term (In 2), and we can divide it out, so the effective half-life is given by ... 

So, what is the effective half-life of "Tcm If we substitute the known values into the above equation,... 

Taking the inverse of 0.208 hr-1, we find the effective half life is 4.80 hr. 

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